the quote above out of the wright up on turbos sounds like its saying that the turbine is able to spin up easer do to the constant ex pressure not changing {much} and the ambient pressure at altitude dropping {more than the ex. pressure did} causes the turbine to spin faster/ easer {less pressure at the EX outlet allows for easer/faster flow thru the pipe} in return that spins the compressor faster/ easer creating a larger volume to be compressed and forcing more air psi in the engine hence creating barley any engine power loss as we rise in altitude?? I think this is what it is trying to say?? not poss.. but in no means am I implying that the turbo is spinning faster but not working harder....well it is cutting thru thinner air that reduces resistance??? $HiT that's a hard subject by its self ... what it easiest lifting 100pounds 10 times or 200pounds 5 times- each of u lifted 1000pounds witch one worked less...well JJ....MH.... u to seem to be a lot more educated than me by far on the sub. soooo I'm going to leave that to u two and get my opinion from that!!! we all learn from someone and put what we learn to work. I'm learning hear so keep it up lol thanks JJ - MH {o and MH I already read that octane thread...till it said pay money if u want to read more u cheap a$$ lol cant even see my post u moved rolf appreciate all your work on the sight to keep it where it goes}
EBC's, ELEVATION AND TURBO SLEDS.... A GOOD TECHNICAL DISCUSSION.
- Thread starter mountainhorse
- Start date
It's not really about MAP you guys. It's about lbs/min. That's what makes power and keeps it consistent at higher elevation. Read and understand some compressor and turbine maps and some turbo charging literature. There's a boat load of information online if you look.
J
JJ_0909
ACCOUNT CLOSED
or CFM. And I agree. MAP is an idication of this however.
I don't like maps with CFM because it's volumetric which can have really variable density. Lbs/min is mass flow and it's mass that's needed for combustion and hence power.
If you take a look at a compressor map and pick a constant mass flow rate. Then look at the difference between a low pressure ratio and a higher pressure ratio(this would be theoretical values of a low and high elevation state while running an EBC system). What you will see is higher shaft speeds. Aka wastegate held shut longer and longer time to peak power.
These EBC's typically do not keep MAP consistent, they actually increase MAP as elevation rises in order to offset the loss of density from increased air temperature associated with higher boost levels.
...
Happy Thanksgiving
Fixed it for ya there buddy... Now all members, even the cheap a$$ ones. can read the whole thing... 3 parts now.
http://www.snowest.com/forum/showthread.php?t=220800
http://www.snowest.com/forum/showthread.php?t=420642
http://www.snowest.com/forum/showthread.php?t=420643
Fixed it for ya there buddy... Now all members, even the cheap a$$ ones. can read the whole thing... 3 parts now.
http://www.snowest.com/forum/showthread.php?t=220800
http://www.snowest.com/forum/showthread.php?t=420642
http://www.snowest.com/forum/showthread.php?t=420643
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yea I seen that thanks lots MH!! now if u would just keep hashing it out with JJ.... this dumb dog might could learned sumtin 
! still wondering about the wright up JJ posted it made mention about how the turbo will spool up more just from the lack of atmospheric pressure and gain boost ,,well I think that's what it said???
! still wondering about the wright up JJ posted it made mention about how the turbo will spool up more just from the lack of atmospheric pressure and gain boost ,,well I think that's what it said???
J
JJ_0909
ACCOUNT CLOSED
I think a lot of this is getting lost in definitions...
"more spool up" I'm reading as "making more boost".
EG, if atmospheric pressure is 10psi compared to sea level 14.x psi and you have your sled setup to run 5psi.
If you are using a mechanical setup (no ECB) iit effectively works as a "pressure differential regulator" in that it'll always add 5psi back into the system, regardless of atmospheric pressure (difference between charge tube and atomsphere will always be "atmosphere + 5". So at sea level this means you have a MAP of 19-20ish whereas at 11,000 feet you'll be closer to 15. (14.7+5=19.7 - sea level pressure; 10+5=15 - 11,000 feet). Though output will be very different (and so will your clutching and fueling requirements), the turbo will react very similary, in that the way it "builds boost" and how much lag there is won't change too much (but it'll still change...in fact, your charge temps will even go up despite the net drop in power...but lets leave that out for now).
Now if you are running an electronic boost controller with a MAP sensor, the turbo's wastegate is controlled far differently. At "5psi" you are going to see a MAP pressure of 19-20 at all elevations (assuming the turbo can keep up, which again, it should be able to)
So lets walk through this scenerio...
At sea level, everything is the same. Literally nothing changes.
At 11,000 feet, the turbo has to compensate for the 5ish psi loss in air density. It does this by "working harder", "spinning faster", "compressing more air". At 11,000 feet the turbo has to put double the psi back into the manifold to arrive at the same output (10+10=20). In this case the turbo will have to "spool up" more to arrive at the same output. There will be more heat (charge temps rise), more lag (takes longer to compress more air). And yes, the turbo is compressing more air as the system can't just rely on ambient atmosphere (no compression) for its baseline air density. Depending on how much more heat it is making, your output will drop. As your air density went down. (hotter air makes less power). This may be a moot point as we are running in snow and 10psi is still relatively low amounts of boost compared to 4 stroke car world....but yeah, your charge temps are still going UP.
As tdbaugha mentioned, going to a lbs/min or any sort of true density/flow calculation is going to be more accurate as it takes into account the variable of rate. Never thought about CFM vs lbs/min but he's right. Density is going to be more important than volume, though CFM still is an indicator of this, its not as precise i suppose.
For this example, go get a crappy $50 Harbor Freight compressor. Then go get a $2,000 gas powered compressor. Set both to 80psi and try to blow your backyard sprinkler system out. Both were set to the same psi, so what happened? In this case, its all about flow. One is akin to a kitchen faucet the other a fire hose. Pressures being the same, one is doing a lot more work than the other.
How much air you can get into a motor is what we are trying to alter. More air = more power. This is why the whole idea that thinner air somehow makes it "easier" on the compressor wheel is so wrong. For that, I again turn to my snow analogy (heavy snow is easier to compact than light powdery snow...and in this case, we want the heaviest snow possible)
Again, I'm just an enthusiast. Not a real pro. YMMV.
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Moderator note:
It is difficult when someone presents info that is contrary to our own, no matter what the topic... so Kudos to all for keeping this discussion civil and level headed without getting feelings hurt.
Here is my OPINON... my 2¢
This is where a lot of people get caught up..
Air density is measured in units like lbs/cubic-foot or kg/cubic-meter.. a given MASS per unit of VOLUME.
PSI is FORCE per unit of AREA.
Even though we use 'lbs' in both terms... they do not refer to the same thing.
Confusing sometimes I know.
For example... in constant conditions (temp/humidty/composition) at 10,000 ft. you would need to have approximately 1.4 cubic feet of air to get the same mass of 1 cubic foot of air at sea level. EG: 14 cubic feet of air at 10k-feet will weigh the same as 10 cubic feet of air at sea level.
Humidity and pollutants add even more dimensionality to this and more complexity to the calculations.... but for our purposes here...we can leave this out of the discussion.
Compressing "more air", as used above, is a tricky phrase because you are talking only volume... and it leaves out the density of the air itself.
Density is key in evaluating how things are working in a turbo system. The turbo is changing the density of the air from the inlet to the outlet side of the compressor... and will spin up or down to vary delivered volume, CF, to provide as consistent of air density, lbs/CF, in the charge tract as possible... as directed by the fuel/boost management system.
EBC systems being the topic of this thread.
This is where lbs/min really comes in handy to wrap your mind around this... as tdbaugha points out.... and where keeping consistent MAP's ties into this.
Lastly, if you re-read my posts above... I talk about the the turbo not needing to work harder in less dense air... not that it needs to work less... I just want to make that clear.
BTW... CF = Cubic Foot
.
It is difficult when someone presents info that is contrary to our own, no matter what the topic... so Kudos to all for keeping this discussion civil and level headed without getting feelings hurt.
Here is my OPINON... my 2¢
This is where a lot of people get caught up..
Air density is measured in units like lbs/cubic-foot or kg/cubic-meter.. a given MASS per unit of VOLUME.
PSI is FORCE per unit of AREA.
Even though we use 'lbs' in both terms... they do not refer to the same thing.
Confusing sometimes I know.
For example... in constant conditions (temp/humidty/composition) at 10,000 ft. you would need to have approximately 1.4 cubic feet of air to get the same mass of 1 cubic foot of air at sea level. EG: 14 cubic feet of air at 10k-feet will weigh the same as 10 cubic feet of air at sea level.
Humidity and pollutants add even more dimensionality to this and more complexity to the calculations.... but for our purposes here...we can leave this out of the discussion.
Compressing "more air", as used above, is a tricky phrase because you are talking only volume... and it leaves out the density of the air itself.
Density is key in evaluating how things are working in a turbo system. The turbo is changing the density of the air from the inlet to the outlet side of the compressor... and will spin up or down to vary delivered volume, CF, to provide as consistent of air density, lbs/CF, in the charge tract as possible... as directed by the fuel/boost management system.
EBC systems being the topic of this thread.
This is where lbs/min really comes in handy to wrap your mind around this... as tdbaugha points out.... and where keeping consistent MAP's ties into this.
Lastly, if you re-read my posts above... I talk about the the turbo not needing to work harder in less dense air... not that it needs to work less... I just want to make that clear.
BTW... CF = Cubic Foot
.
Great conversation...
I will start out by saying again, this is my OPINION... IMO... My 2¢...
JJ and I actually agree more than you may think. The compressor IS moving more air volume, CF, at altitude…but the additional info needed to complement that statement is that this 'volume' at altitude, has less mass per unit volume.
In the USA, compressor maps are done in Lbs/min as tdbaugha points out... Lbs/min is a better designation when designing a system... CFM will not tell you what you need to know unless you also simultaneously calculate the pressure of that given volume... and if you want to add more dimensionality, temperature.
CFM does not take into account density of the air.
Lbs/min does however.
CFM does not indicate the latent oxygen content. A turbo's purpose is to make more Oxygen available to the engine so you can burn more fuel and make more power…or keep it constant at increased elevations.
How 'hard' a turbo has to 'work'... watts... is related to the density of the air it is moving per given unit of time, lbs/min.
This is where both JJ and I are 'splitting hairs' in definitions.
If the turbo intakes less dense air at higher elevations...it is doing less work per revolution...it is moving less mass per revolution. You have to take more "scoops of air" with the blades on a turbo to move the same lbs/min.
To get a given MAP pressure at a given engine RPM, you are still moving the same lbs/min into the engine… though you need to do it with a higher shaft RPM at higher elevations…. No more ‘work’ is being done… except for minute frictional loss.
You are sucking in more volume (CFM), but less dense air, into the inlet side turbo at higher elevations to maintain density/pressure on the charge side of the turbo... compared to lower elevations, but NOT moving more lbs/min.
JJ... I'm a bit curious about the snowball example
... my understanding is that a snowballs ability to be formed is based on moisture content not on compressibility. Dry 'powdery' snow is less cohesive...not less compressible... 'powdery snow' is more compressible for given volume of snow.
Fill two of the same 5 gal buckets to the brim ... one with 'powdery' snow and one with 'wet' snow... the 'powdery' one will compress to a greater extent and with less effort when tamped-down compared to the 'wet' snow. As far as effort required to compress that snow... the 'powdery snow' will require less effort to compress, say, to 90% of its original volume than the 'wet' snow to compress to 90% of its original volume. If you were to hold them upside down... one would most likely come out powder snow... the other, probably a slug of "coastal cement".
The net difference (increase)in work, due to minute frictional loss in the bearing, exists FOR SURE... but the level of "hair splitting" seems to go up at the same time... begging the question: How much difference is there and how does this apply to the system and objectives?
How much do very recent advancements in turbo design, and in particular, compressor wheel developments play a role in this? Lower inertia wheels, higher efficiency wheels with higher leaving velocities, different trim spec less slip, better vane shapes/thicknesss due to better QC in materials, cut-back vane use/count etc etc… all play a big role in how fast a turbo will build pressure… with the goal of minimizing lag over the range of intended use and design specs.
If you are trying to build a sled turbo system that will run well at sea level, and at 14k feet and with low boost and high boost by “simply changing settings”… I believe you will be disappointed. I don’t think you’ll be optimal across that entire range. The phrase that comes to mind is “Jack of all trades, master of none”
By “Optimal” I’m referring to that common-sense kind of feeling when the rider is on a turbo sled that is easy to operate, requires little or no adjustment from the rider and delivers the kind of quick transient throttle response and decent power levels that we sledders really like.
With as relatively few turbo kits out there... it is hard for makers to get just the right turbo because of costs involved..but it IS getting easier... custom ordered CNC wheels and Gamma-ti turbines avail on main stream units... more possibilities.
As far as heating the air... that too is related to flow rate, lbs/min in our discussion here.
As elevation rises, ambient temp generally drops. Heat gain may be minimized by this drop in temp, enough to offset heat gain in compression is the question.
The air is heated due to friction. That friction is related to the mass-flow (lbs/min in our discussion here.) The more dense the air is you are trying to compress, the more friction you will have at a given CFM... more air molecules rubbing against the surface of the blades and housing.
There is also 'slip' in any centrifugal compressor... and that slip WILL account for some heat gain in the charge side... How much slip is partly related to the pressure ratio. More slip, more induced heat. At a higher pressure-ratio, more slip occurs and you will build more heat... How much slip? This changes exponentially in relation to outlet pressure changes. Compressor wheel advancements in recent times also play a large roll in minimizing this.
Spool time is longer as pointed out by tdbaugha at higher elevations... but that is relative to the system design to a large degree... and I believe this can be made almost imperceivable with the right design, equipment and control systems.
I've ridden some very well designed turbo kits in sleds at higher altitudes. Any decrease in throttle response (lag) was not that noticeable, if at all at altitude... this system had a Fast Response Ext Waste gate, EBC with TMAP and a turbo that was sized properly for the type of MAP pressures it was intended to provide over a range of altitudes the owner rides in... (which was 4k-10k feet in these instances) The fuel system was also well tuned to interact with the boost control in real time.
I'm a fan of recirc type BOV's when we are talking Wot/Chop/Wot/cho.... throttle cycling that we do on our sleds.
If a given turbo in a sled system is operating within its intended design parameters... and the turbo itself is well matched.... things run very well, and the operator is able to control the sled easily as it is not "peaky" or "laggy".
In addition to compressor design… lag time and transitional throttle response under load are also due in large part to proper sizing of the turbo, target elevations of intended use, what type of turbo/bearing, what type of lube, supplemental injection sizing/location [if any], clutch engagement rpm and having the turbo loaded up at the same time the engine is... and... HUGELY, how well the control system programmer took the time and on hill testing to dial in the system before the customer gets his kit.
Smaller and/or light compressor wheels, with less inertia and better vane design really do make a difference here.
A small wheel can accelerate and decel at a rate that can make it really not noticeable by all but the most perceptive rider. When you are already spinning at 130,000... how much faster do you need to spin to compensate for the change in altitude?... even with the BRAP BRAP style of modern tree riders.
And yes, OF COURSE, a given turbo will build MAP faster with a denser intake air supply that comes with lower elevation... your pressure ratio is lower and the time to recover MAP is faster.
In many of the conversations posted on the forums here... you quite often hear someone say... "I'm running my [so and so's] kit at xxLbs of boost and mine does [this or that]" To which someone will invariably ask, in a following post..."At what elevation are you running xxLbs ?"
If you talk in PSIa, which is what MAP is read in, this more of a consistent way to look at it IMO. You no longer need to ask "at what altitude".
Temperature feeds into this as well, which I mention above... and if you are operating your system, for the most part, as intended at lower boost levels this is less of a concern/adjustment than those looking for higher target maps.
Temperature does play a role as mentioned abolve. How much of a MAP reading difference change there is on a system running low boost levels from absorbed compression heat however seems to be the question.
On the well thought out "6-lb" systems that I've read data logs for ... there really wasn't a noticeable difference in charge temps or MAP at elevations with an EBC holding to a target low-boost level. Up the pressure and there seems to be a point where things change faster... and things like intercoolers can play a big roll.
Intercoolers have plusses and minuses Besides cost… they add more restriction and complexity to any given system.
Yes they are just plain required when you crank up your pressures.
AND...
In some of the low-boost systems that are out there… we’ve seen that sleds can run very well without one.
Most 'EBC"s are running TMAP sensors... not just MAP sensors... TMAP also reading temp. Mechanical automatic boost controllers that I've seen do not have the ability to adjust boost for charge temps, other than fuel, ... and thus.. still need to be 'tweaked' by the rider to the desired MAP if temps climb too much (warm weather or higher MAP levels).
IMO, EBC's have better resolution in automatically optimizing, without operator input, fuel/and MAP pressure levels when compared to mechanical systems.... and this is more apparent when you are talking higher MAP targets.
At, say "6 lbs" (20.7 PSIa MAP) at 12,000 feet, I really have not noticed much diff in charge temps on a well designed system than that same system at 6000 feet. I have seen big jumps in charge temps when small turbos were asked do too much, (∆-elevation or high MAP) and were well down the road to failing. High boost, high pressure-ratio systems... yes, I've seen big changes in charge temps. So I guess we will also need to talk pressure-ratio in this discussion as it gets deeper.
Higher shaft speeds does not necessarily mean higher heat on the charge side... If you are spinning the compressor against lower density air, you will have, for our intents and purposes here, the same amount of friction for a given lb/min spec, although a true adiabatic exchange is not possible.
In the WRX example above, it would have to be "turning down boost", most likely, if you got into a situation of over-spool, where the shaft speed exceeds the designed max operational RPM of the turbocharger in use.
You've hit the choke-line in the compressor map where you can get destructive compressor operation if you have exceeded the center section bearings ability to handle the RPM needed and you "fry" a bearing or crash wheels. The compressor has exceeded it's ability deal with the pressure ratio demanded.
While at the Pikes Peak race a few years back... I talked to some of the racers in the Time-Attack production-class over dinner ... The guys with the stock STI's did not have issues of pulling boost... The modified WRX's often did however... they simply needed to keep the dreaded over-spool at bay or charge temps under control when they pushed the turbochargers/intercoolers beyond their limits and pulling boost was a way to control that.
In most of those situations, the turbo was not sized properly, pushed beyond its limits for that size, or did not have enough charge cooling... and operated outside of its design parameters. (thats what racers do, right? )
Regardless, the turbo system was pushed past it's abilities... and failure would quickly come, as jj points out, if not dialed back to the shaft speeds the system was designed for. Better charge cooling, and thus lower shaft speeds from denser air, can help to extend the 'envelope' but at a certain point it is still going to come apart. This happens often when running a turbo on the ragged-edge.
This is something that 90% of turbo sled owners will not have to worry about... though… There are not that many riders, as a percentage of total turbo sled owners, running high or extreme boost. And racers or chute climbers are not as put off by poor throttle response or lag as a say your average all-mountain rider.
In the early days of sled turbocharging when 'kits' were first being produced for the masses... which is not very long ago. The turbos were generally off the shelf automotive units not tailored to the application. There were similar situations where people would "crank it up" and exceed the turbos ability to spin that fast (overspool), leading to wheels disintegrating into shrapnel from failure by exceeding the Turbos capabilities, which can also lead to the wheels 'crashing' into the housings. (Whichever came first).
We've come a long way from those days.
Turbo and wheel selections can play a HUGE role in how well a turbo works... and it is still true that you will get different throttle response from a system that is running on the edge of its envelope of design.
How fast a wastegate responds also plays a roll in throttle response. IMO, the faster response… the better.... but at what cost and what result is realized by the operator needs to be taken into account too.
In these "NEW" turbo kits for sleds that have evolved so much so fast... that run so well... The largest contributing factor, IMO, to this "great running turbo sled" is that you are finding less expensive 'off the shelf' systems that have honed down the environment of elevation, fuel, and boost levels to a target... and not asking one system/kit to be the "swiss army knife" of turbos where you expect stellar performance (power and character) with wildly varying boost levels, elevations and fuels.
'EBC', or especially mechanical auto-boost-control, systems seem to operate more seamlessly when you are asking it make a more reasonable 180-190 hp at elevation (adding 60-70 hp over your NA buddies). and not expecting optimal throttle response at 8000 ft differences in elevation at both extremes. But simply throwing an EBC on a poorly designed system is not likely to produce the result that the owner may be looking for.
Another big factor that contributes to throttle response.
Matching turbo and engine load.. and bringing them up more evenly together...by design and through great clutching... pays huge dividends in how good throttle response is over the range of conditions and demands of the rider. This is why some people have different clutch setups for different altitudes and riding conditions...even with a good turbo kit...Though for most, one clutch setup is the best balance of performance and convenience.
This is where customer satisfaction and ease of use are truly possible... a well designed system that is marketed well/honestly... that is designed to run best where the rider runs the most and delivers consistent performance levels.
IMO...the less you push an engine/turbo to the edge of its capabilities... the better it will run in terms of smooth, reliable performance.
Fuel properties play a roll too... and are elaborated in the other thread mentioned above.
Also, at this point... I really wish that I would have set the condition in the first post of talking about turbo kits in sleds that we are seeing today for the masses...Lower boost kits... There are a WHOLE LOT of different considerations that you have to deal with on high-boost sleds... say a sled exceeding 20-PSIa MAP at any elevation.... and one that needs to run at more moderate pressures below that. These more 'moderate levels' seem to be very acceptable to those that want a truly "pull the rope and go", no-adjust system...less fuss... more riding...more reliability.
...........These are what I like to call the "USER FRIENDLY" turbo kits.
I'm all for people that want to "crank it up" when they want more power... but I would just not expect the effort of ownership to be the same as a fixed boost low pressure system.
Now, I'm sure that there are some true "turbo-heads" out there that can tweak/tune their system on the fly with effortless ease... and will run awesome at all levels...Those are a rare breed indeed and I'm impressed by you all, sincerely.
The rest of us can benefit from a well implemented EBC or other well functioning auto altitude fuel/timing/boost controller.
Whew !!
Again, Great conversation... keep it rolling!!
.
I will start out by saying again, this is my OPINION... IMO... My 2¢...
JJ and I actually agree more than you may think. The compressor IS moving more air volume, CF, at altitude…but the additional info needed to complement that statement is that this 'volume' at altitude, has less mass per unit volume.
In the USA, compressor maps are done in Lbs/min as tdbaugha points out... Lbs/min is a better designation when designing a system... CFM will not tell you what you need to know unless you also simultaneously calculate the pressure of that given volume... and if you want to add more dimensionality, temperature.
CFM does not take into account density of the air.
Lbs/min does however.
CFM does not indicate the latent oxygen content. A turbo's purpose is to make more Oxygen available to the engine so you can burn more fuel and make more power…or keep it constant at increased elevations.
How 'hard' a turbo has to 'work'... watts... is related to the density of the air it is moving per given unit of time, lbs/min.
This is where both JJ and I are 'splitting hairs' in definitions.
If the turbo intakes less dense air at higher elevations...it is doing less work per revolution...it is moving less mass per revolution. You have to take more "scoops of air" with the blades on a turbo to move the same lbs/min.
To get a given MAP pressure at a given engine RPM, you are still moving the same lbs/min into the engine… though you need to do it with a higher shaft RPM at higher elevations…. No more ‘work’ is being done… except for minute frictional loss.
You are sucking in more volume (CFM), but less dense air, into the inlet side turbo at higher elevations to maintain density/pressure on the charge side of the turbo... compared to lower elevations, but NOT moving more lbs/min.
JJ... I'm a bit curious about the snowball example
... my understanding is that a snowballs ability to be formed is based on moisture content not on compressibility. Dry 'powdery' snow is less cohesive...not less compressible... 'powdery snow' is more compressible for given volume of snow.Fill two of the same 5 gal buckets to the brim ... one with 'powdery' snow and one with 'wet' snow... the 'powdery' one will compress to a greater extent and with less effort when tamped-down compared to the 'wet' snow. As far as effort required to compress that snow... the 'powdery snow' will require less effort to compress, say, to 90% of its original volume than the 'wet' snow to compress to 90% of its original volume. If you were to hold them upside down... one would most likely come out powder snow... the other, probably a slug of "coastal cement".
Mass and volume are two units used to measure objects. Mass is the amount of matter an object contains, while volume is how much space it takes.
This balance illustrates the difference between mass and volume.
The two sets of objects have equal mass, but the yellow balls take up
more volume than the blue balls.
http://chemistry.about.com/
The net difference (increase)in work, due to minute frictional loss in the bearing, exists FOR SURE... but the level of "hair splitting" seems to go up at the same time... begging the question: How much difference is there and how does this apply to the system and objectives?
How much do very recent advancements in turbo design, and in particular, compressor wheel developments play a role in this? Lower inertia wheels, higher efficiency wheels with higher leaving velocities, different trim spec less slip, better vane shapes/thicknesss due to better QC in materials, cut-back vane use/count etc etc… all play a big role in how fast a turbo will build pressure… with the goal of minimizing lag over the range of intended use and design specs.
If you are trying to build a sled turbo system that will run well at sea level, and at 14k feet and with low boost and high boost by “simply changing settings”… I believe you will be disappointed. I don’t think you’ll be optimal across that entire range. The phrase that comes to mind is “Jack of all trades, master of none”
By “Optimal” I’m referring to that common-sense kind of feeling when the rider is on a turbo sled that is easy to operate, requires little or no adjustment from the rider and delivers the kind of quick transient throttle response and decent power levels that we sledders really like.
With as relatively few turbo kits out there... it is hard for makers to get just the right turbo because of costs involved..but it IS getting easier... custom ordered CNC wheels and Gamma-ti turbines avail on main stream units... more possibilities.
As far as heating the air... that too is related to flow rate, lbs/min in our discussion here.
As elevation rises, ambient temp generally drops. Heat gain may be minimized by this drop in temp, enough to offset heat gain in compression is the question.
The air is heated due to friction. That friction is related to the mass-flow (lbs/min in our discussion here.) The more dense the air is you are trying to compress, the more friction you will have at a given CFM... more air molecules rubbing against the surface of the blades and housing.
There is also 'slip' in any centrifugal compressor... and that slip WILL account for some heat gain in the charge side... How much slip is partly related to the pressure ratio. More slip, more induced heat. At a higher pressure-ratio, more slip occurs and you will build more heat... How much slip? This changes exponentially in relation to outlet pressure changes. Compressor wheel advancements in recent times also play a large roll in minimizing this.
Spool time is longer as pointed out by tdbaugha at higher elevations... but that is relative to the system design to a large degree... and I believe this can be made almost imperceivable with the right design, equipment and control systems.
I've ridden some very well designed turbo kits in sleds at higher altitudes. Any decrease in throttle response (lag) was not that noticeable, if at all at altitude... this system had a Fast Response Ext Waste gate, EBC with TMAP and a turbo that was sized properly for the type of MAP pressures it was intended to provide over a range of altitudes the owner rides in... (which was 4k-10k feet in these instances) The fuel system was also well tuned to interact with the boost control in real time.
I'm a fan of recirc type BOV's when we are talking Wot/Chop/Wot/cho.... throttle cycling that we do on our sleds.
If a given turbo in a sled system is operating within its intended design parameters... and the turbo itself is well matched.... things run very well, and the operator is able to control the sled easily as it is not "peaky" or "laggy".
In addition to compressor design… lag time and transitional throttle response under load are also due in large part to proper sizing of the turbo, target elevations of intended use, what type of turbo/bearing, what type of lube, supplemental injection sizing/location [if any], clutch engagement rpm and having the turbo loaded up at the same time the engine is... and... HUGELY, how well the control system programmer took the time and on hill testing to dial in the system before the customer gets his kit.
Smaller and/or light compressor wheels, with less inertia and better vane design really do make a difference here.
A small wheel can accelerate and decel at a rate that can make it really not noticeable by all but the most perceptive rider. When you are already spinning at 130,000... how much faster do you need to spin to compensate for the change in altitude?... even with the BRAP BRAP style of modern tree riders.
And yes, OF COURSE, a given turbo will build MAP faster with a denser intake air supply that comes with lower elevation... your pressure ratio is lower and the time to recover MAP is faster.
In many of the conversations posted on the forums here... you quite often hear someone say... "I'm running my [so and so's] kit at xxLbs of boost and mine does [this or that]" To which someone will invariably ask, in a following post..."At what elevation are you running xxLbs ?"
If you talk in PSIa, which is what MAP is read in, this more of a consistent way to look at it IMO. You no longer need to ask "at what altitude".
Temperature feeds into this as well, which I mention above... and if you are operating your system, for the most part, as intended at lower boost levels this is less of a concern/adjustment than those looking for higher target maps.
Temperature does play a role as mentioned abolve. How much of a MAP reading difference change there is on a system running low boost levels from absorbed compression heat however seems to be the question.
On the well thought out "6-lb" systems that I've read data logs for ... there really wasn't a noticeable difference in charge temps or MAP at elevations with an EBC holding to a target low-boost level. Up the pressure and there seems to be a point where things change faster... and things like intercoolers can play a big roll.
Intercoolers have plusses and minuses Besides cost… they add more restriction and complexity to any given system.
Yes they are just plain required when you crank up your pressures.
AND...
In some of the low-boost systems that are out there… we’ve seen that sleds can run very well without one.
Most 'EBC"s are running TMAP sensors... not just MAP sensors... TMAP also reading temp. Mechanical automatic boost controllers that I've seen do not have the ability to adjust boost for charge temps, other than fuel, ... and thus.. still need to be 'tweaked' by the rider to the desired MAP if temps climb too much (warm weather or higher MAP levels).
IMO, EBC's have better resolution in automatically optimizing, without operator input, fuel/and MAP pressure levels when compared to mechanical systems.... and this is more apparent when you are talking higher MAP targets.
At, say "6 lbs" (20.7 PSIa MAP) at 12,000 feet, I really have not noticed much diff in charge temps on a well designed system than that same system at 6000 feet. I have seen big jumps in charge temps when small turbos were asked do too much, (∆-elevation or high MAP) and were well down the road to failing. High boost, high pressure-ratio systems... yes, I've seen big changes in charge temps. So I guess we will also need to talk pressure-ratio in this discussion as it gets deeper.
Higher shaft speeds does not necessarily mean higher heat on the charge side... If you are spinning the compressor against lower density air, you will have, for our intents and purposes here, the same amount of friction for a given lb/min spec, although a true adiabatic exchange is not possible.
In the WRX example above, it would have to be "turning down boost", most likely, if you got into a situation of over-spool, where the shaft speed exceeds the designed max operational RPM of the turbocharger in use.
You've hit the choke-line in the compressor map where you can get destructive compressor operation if you have exceeded the center section bearings ability to handle the RPM needed and you "fry" a bearing or crash wheels. The compressor has exceeded it's ability deal with the pressure ratio demanded.
While at the Pikes Peak race a few years back... I talked to some of the racers in the Time-Attack production-class over dinner ... The guys with the stock STI's did not have issues of pulling boost... The modified WRX's often did however... they simply needed to keep the dreaded over-spool at bay or charge temps under control when they pushed the turbochargers/intercoolers beyond their limits and pulling boost was a way to control that.
In most of those situations, the turbo was not sized properly, pushed beyond its limits for that size, or did not have enough charge cooling... and operated outside of its design parameters. (thats what racers do, right? )
Regardless, the turbo system was pushed past it's abilities... and failure would quickly come, as jj points out, if not dialed back to the shaft speeds the system was designed for. Better charge cooling, and thus lower shaft speeds from denser air, can help to extend the 'envelope' but at a certain point it is still going to come apart. This happens often when running a turbo on the ragged-edge.
This is something that 90% of turbo sled owners will not have to worry about... though… There are not that many riders, as a percentage of total turbo sled owners, running high or extreme boost. And racers or chute climbers are not as put off by poor throttle response or lag as a say your average all-mountain rider.
In the early days of sled turbocharging when 'kits' were first being produced for the masses... which is not very long ago. The turbos were generally off the shelf automotive units not tailored to the application. There were similar situations where people would "crank it up" and exceed the turbos ability to spin that fast (overspool), leading to wheels disintegrating into shrapnel from failure by exceeding the Turbos capabilities, which can also lead to the wheels 'crashing' into the housings. (Whichever came first).
We've come a long way from those days.
Turbo and wheel selections can play a HUGE role in how well a turbo works... and it is still true that you will get different throttle response from a system that is running on the edge of its envelope of design.
How fast a wastegate responds also plays a roll in throttle response. IMO, the faster response… the better.... but at what cost and what result is realized by the operator needs to be taken into account too.
In these "NEW" turbo kits for sleds that have evolved so much so fast... that run so well... The largest contributing factor, IMO, to this "great running turbo sled" is that you are finding less expensive 'off the shelf' systems that have honed down the environment of elevation, fuel, and boost levels to a target... and not asking one system/kit to be the "swiss army knife" of turbos where you expect stellar performance (power and character) with wildly varying boost levels, elevations and fuels.
'EBC', or especially mechanical auto-boost-control, systems seem to operate more seamlessly when you are asking it make a more reasonable 180-190 hp at elevation (adding 60-70 hp over your NA buddies
). and not expecting optimal throttle response at 8000 ft differences in elevation at both extremes. But simply throwing an EBC on a poorly designed system is not likely to produce the result that the owner may be looking for. Another big factor that contributes to throttle response.
Matching turbo and engine load.. and bringing them up more evenly together...by design and through great clutching... pays huge dividends in how good throttle response is over the range of conditions and demands of the rider. This is why some people have different clutch setups for different altitudes and riding conditions...even with a good turbo kit...Though for most, one clutch setup is the best balance of performance and convenience.
This is where customer satisfaction and ease of use are truly possible... a well designed system that is marketed well/honestly... that is designed to run best where the rider runs the most and delivers consistent performance levels.
IMO...the less you push an engine/turbo to the edge of its capabilities... the better it will run in terms of smooth, reliable performance.
Fuel properties play a roll too... and are elaborated in the other thread mentioned above.
Also, at this point... I really wish that I would have set the condition in the first post of talking about turbo kits in sleds that we are seeing today for the masses...Lower boost kits... There are a WHOLE LOT of different considerations that you have to deal with on high-boost sleds... say a sled exceeding 20-PSIa MAP at any elevation.... and one that needs to run at more moderate pressures below that. These more 'moderate levels' seem to be very acceptable to those that want a truly "pull the rope and go", no-adjust system...less fuss... more riding...more reliability.
...........These are what I like to call the "USER FRIENDLY" turbo kits.
I'm all for people that want to "crank it up" when they want more power... but I would just not expect the effort of ownership to be the same as a fixed boost low pressure system.
Now, I'm sure that there are some true "turbo-heads" out there that can tweak/tune their system on the fly with effortless ease... and will run awesome at all levels...Those are a rare breed indeed and I'm impressed by you all, sincerely.
The rest of us can benefit from a well implemented EBC or other well functioning auto altitude fuel/timing/boost controller.
Whew !!
Again, Great conversation... keep it rolling!!
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is their any downfalls to a EBC vs mechanical? I've ben looking at silber don't think they offer one (not pos) is that a part that can be added or is it fully integrated in to the system?
I'm with JJ on this one , as you go up in elevation your turbo is making more boost.
You need to seperate the turbo itself , and the whole system.
The chart I made shows it black and white. Less atmosphere pressure more turbo pressure.
yes absolute pressure has remained the same , to turn around and say your "turbo" is not making more boost is false.
If you say the "system" or the "turbo kit" is not producing more boost , ok I can go with that.
Personally not a fan of recirc valves , your heating the air , re introducing it .. Then heating it again... Heating twice , no good.
Now some will say "it's minor" but go tree riding , your throwing shots of double heated air at your motor.
One topic that needs to be addressed is that boost is just a restriction. People are getting caught up in "pump gas" 10psi bla bla...
6psi can make more power than 10psi of boost.
You need to seperate the turbo itself , and the whole system.
The chart I made shows it black and white. Less atmosphere pressure more turbo pressure.
yes absolute pressure has remained the same , to turn around and say your "turbo" is not making more boost is false.
If you say the "system" or the "turbo kit" is not producing more boost , ok I can go with that.
Personally not a fan of recirc valves , your heating the air , re introducing it .. Then heating it again... Heating twice , no good.
Now some will say "it's minor" but go tree riding , your throwing shots of double heated air at your motor.
One topic that needs to be addressed is that boost is just a restriction. People are getting caught up in "pump gas" 10psi bla bla...
6psi can make more power than 10psi of boost.
If "boost" is defined as "differential pressure"... sure... I can live with that.
Seems like were on the same page anyway.
One thing that "Boost" (PSIg) does not take into account is any intake pressure depression from any restriction due to the plumbing or pow covered intakes. Pressure at the inlet of the compressor can often be less than ambient, sometimes by enough to throw things off. This is where lots of intake area makes sense.
Not sure what you are saying here though??
Seems like were on the same page anyway.
One thing that "Boost" (PSIg) does not take into account is any intake pressure depression from any restriction due to the plumbing or pow covered intakes. Pressure at the inlet of the compressor can often be less than ambient, sometimes by enough to throw things off. This is where lots of intake area makes sense.
Not sure what you are saying here though??
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Have a look at this link wong...
http://www.speedhunters.com/2014/09/turbosmart-answers-boost-control-questions/
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Dont want to sway the topic , so delete if needed.
A lot of people are looking for a pump gas turbo, which is fine.
Lets say the advertising is 8# boost , 5000 ft pump gas. With ignition control becoming more available you are able to get away with this.
I find this can be misleading to people who are thinking there 8# of boost (with timing pulled) , is the same as 8# on oem timing.
Your getting less cylinder pressure on the same boost.
You could run 15# on pump gas if you wanted to...
Thats what im trying to say is boost to boost is not always apples to apples.
At the end of the day it takes cylinder pressure to make power , dosent matter how it gets there turbo, supercharger, high compression , timing, NOS etc...
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J
JJ_0909
ACCOUNT CLOSED
Eh, see your point but timing and compression are obviously different things. And no, you could not pull enough timing to run 15 pounds on pump gas. Period.
J
jim
Well-known member
P*V = n * R * T
So, you have 5 variables...so, no, it's not simple. And that formula is for static gas...if you start moving things, like with turbos, you need thermodynamics and lots of math.
Variables are Pressure, Volume, amount of gas, gas constant and temperature.
But the formula is pretty straight forward in that an increase in pressure requires an increase in volume and the turbo works more.
Interesting thread.
So, you have 5 variables...so, no, it's not simple. And that formula is for static gas...if you start moving things, like with turbos, you need thermodynamics and lots of math.
Variables are Pressure, Volume, amount of gas, gas constant and temperature.
But the formula is pretty straight forward in that an increase in pressure requires an increase in volume and the turbo works more.
Interesting thread.
Since these sleds are running TMAP and alpha-n tuning (No MAF), is there any reason to run a recirculating BOV?
From what I understand a MAP based tune would not require BOV recirc, but the MTNTK kit has a recirculating style BOV into reed cage.
From what I understand a MAP based tune would not require BOV recirc, but the MTNTK kit has a recirculating style BOV into reed cage.
More to ponder
Good questions.
The MTNTK Turbo, a Borg-Warner EFR turbo does feature a recirc valve... but it vents back into the compressor housing. It is not really a traditional BOV that recirculates boost back to the intake side of the compressor though a hose. Think of it more as a built-in BOV for our purposes that vents directly back into the compressor... it also helps in recovery of boost quickly after chopping the throttle.
Since B-W made the EFR turbos for the aftermarket specifically.... they also produced a great technical manual that is written in fairly plain english... worth a read if you want to learn about it... or even turbos in general.
http://www.turbos.borgwarner.com/files/pdf/efr_turbo_technical_brief.pdf
As pointed out above, you are re-introducing already warmed air back into the compressor... the degree to which that matters depends on overall design and desired boost levels... IMO, at low boost levels that won't matter much... and at higher boost levels, most sleds are running an intercooler which will normalize things. The amount of time that charge is reintroduced back to the inlet... from chopping the throttle, is a low duration event...the question is, Will this affect the system beyond the designs ability to give great performance and reliability.
The EFR turbine is one of the lightest, if not the lightest in the industry... about half the weight of an inconel turbine... which makes the rotating assembly light... rolling on ceramic ball bearings.... this assembly will spool up or down super quick... something that technical riders will appreciate... ability to chop the throttle, and go WOT.... and have the turbo respond to that demand as quickly as possible. The Recirc on an EFR is easily disabled should someone choose a more traditional BOV.
Here is a good Q&A from the Link I posted for Wong above.
http://www.speedhunters.com/2014/09/turbosmart-answers-boost-control-questions/
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Good questions.
The MTNTK Turbo, a Borg-Warner EFR turbo does feature a recirc valve... but it vents back into the compressor housing. It is not really a traditional BOV that recirculates boost back to the intake side of the compressor though a hose. Think of it more as a built-in BOV for our purposes that vents directly back into the compressor... it also helps in recovery of boost quickly after chopping the throttle.
Since B-W made the EFR turbos for the aftermarket specifically.... they also produced a great technical manual that is written in fairly plain english... worth a read if you want to learn about it... or even turbos in general.
http://www.turbos.borgwarner.com/files/pdf/efr_turbo_technical_brief.pdf
As pointed out above, you are re-introducing already warmed air back into the compressor... the degree to which that matters depends on overall design and desired boost levels... IMO, at low boost levels that won't matter much... and at higher boost levels, most sleds are running an intercooler which will normalize things. The amount of time that charge is reintroduced back to the inlet... from chopping the throttle, is a low duration event...the question is, Will this affect the system beyond the designs ability to give great performance and reliability.
The EFR turbine is one of the lightest, if not the lightest in the industry... about half the weight of an inconel turbine... which makes the rotating assembly light... rolling on ceramic ball bearings.... this assembly will spool up or down super quick... something that technical riders will appreciate... ability to chop the throttle, and go WOT.... and have the turbo respond to that demand as quickly as possible. The Recirc on an EFR is easily disabled should someone choose a more traditional BOV.
Here is a good Q&A from the Link I posted for Wong above.
http://www.speedhunters.com/2014/09/turbosmart-answers-boost-control-questions/
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Wow thanks for the link. I had no idea that's how it was working. I guess I was just seeing the vacuum line being connected to the reed cage then...
I just want to say before my criticism comes across as negative, the the MTNTK kit is on another level from any other kit out there. The Intercooler/tunnel cooler setup is sweet and no other kit is utilizing the EFR turbo. They'd all rather use junk non ball bearing 1990s Garrett tech and no BOV at all.
That being said, I'd love to optimize the EFR setup. The WG and BOV are areas that could be improved to make the absolute most responsive kit possible.
After seeing this video posted in another thread
<iframe width="400" height="225" src="https://www.youtube.com/embed/ScqT0jj9ZnA?rel=0" frameborder="0" allowfullscreen></iframe>
I noticed a lot of compressor surge (way less than the no BOV boondockers setup). I would love to see a Synapse DV setup with the EFR BOV blocked off to see if that fixes the issue. And improves on/off throttle boost response at all.
As far as the WG side of things, you're definitely leaving something on the table for mid range power and boost with the spring wastegate actuator. Once the spring begins to compress the wastegate flap will start to open, well before target boost pressure is reached. This would be bleeding exhaust energy away from the turbine wheel, slowing down the rate at which the turbo is building boost. Ideal setup would be a MAP based EBC with a 4 port boost control solenoid, paired with a dual port wastegate actuator with a light spring. This would allow you to build boost as quickly as possible and when desired boost pressure is hit (some threshold below target boost where it does not cause boost spike) open the wastegate as soon as possible.
I have been looking at integrating a setup like this on the MTNTK kit, but I've read the turbosmart dual port WG doesn't work properly. Also, I do not see many car setups utilizing 4 port boost control solenoids, so they must be hard to tune.
I just want to say before my criticism comes across as negative, the the MTNTK kit is on another level from any other kit out there. The Intercooler/tunnel cooler setup is sweet and no other kit is utilizing the EFR turbo. They'd all rather use junk non ball bearing 1990s Garrett tech and no BOV at all.
That being said, I'd love to optimize the EFR setup. The WG and BOV are areas that could be improved to make the absolute most responsive kit possible.
After seeing this video posted in another thread
<iframe width="400" height="225" src="https://www.youtube.com/embed/ScqT0jj9ZnA?rel=0" frameborder="0" allowfullscreen></iframe>
I noticed a lot of compressor surge (way less than the no BOV boondockers setup). I would love to see a Synapse DV setup with the EFR BOV blocked off to see if that fixes the issue. And improves on/off throttle boost response at all.
As far as the WG side of things, you're definitely leaving something on the table for mid range power and boost with the spring wastegate actuator. Once the spring begins to compress the wastegate flap will start to open, well before target boost pressure is reached. This would be bleeding exhaust energy away from the turbine wheel, slowing down the rate at which the turbo is building boost. Ideal setup would be a MAP based EBC with a 4 port boost control solenoid, paired with a dual port wastegate actuator with a light spring. This would allow you to build boost as quickly as possible and when desired boost pressure is hit (some threshold below target boost where it does not cause boost spike) open the wastegate as soon as possible.
I have been looking at integrating a setup like this on the MTNTK kit, but I've read the turbosmart dual port WG doesn't work properly. Also, I do not see many car setups utilizing 4 port boost control solenoids, so they must be hard to tune.
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