horse power per pound of boost

[Unfair Advantage]

This thread (original topic) is a loaded question in itself. There are so many variables that are not addressed in the question that would need to be taken into accont to make an accurate estimate at what your specific engine makes for HP "per pound of "boost".

 

[ruffryder]

the engine takes in as much air at full throttle (not counting turbo) as it does at idle.

not exactly.....

 

[DRD]

For the longest time I always thought you need a positive displacement blower on a two stroke diesel. I know better now, thanks, sorry for the BS info.

You're sort of right. A 2 stroke diesel will not aspirate on it's own. It needs air to be pushed into the engine. For example a Detroit will have a blower but it could also have a turbocharger, feeding into the blower. This is done since the turbo will not move any air until you start to burn fuel. The blower is engine driven so it will start to move air as soon as the engine is cranked, giving the air needed to start the engine. Some engines will also use some method to spool the turbo before the engine starts, either mechanical drive or external power and not use a blower.

 

[polarisfornow]

not exactly.....

umm actually yes exactly. For simplification purposes the way a diesel works is like any engine, its actually just a giant air pump. a diesel will pump in an unthrottled amount of air into the cylinder then compress it to high pressure. at the right time a specific amount of fuel is added to the cylinder. the amount of fuel is what regulate the speed of the motor. more fuel = more rotational speed in the motor because of the larger combustion.

when u add a turbo it essentially increases the displacement of the motor because you have to add fuel first and then tune with adding more air to the motor.

the key is realizing there is no throttle plate on a diesel to control motor speed. amount of fuel controls motor speed.

 

[milehighassassin]

The biggest difference is with a diesel you are only supercharging the cylinder with air, fuel is metered into the cylinder after the intake valves (or ports) are closed. A spark ignited engine is supercharged (normally) with an air/fuel mixture. You could increase the boost on a diesel engine and not increase the power, you increase the boost on a gas engine, since you are adding both fuel and air, you will get an increase in power. This is one of the reasons why most gas engines will have some method to control boost while many diesels will not. With a gas engine, you add more air/fuel, you have more energy to drive the turbocharger, this adds /allows more air/fuel, the cycle could continue until something bad happens. Also a diesel will see an A/F of say 20:1 at load but see upwards of 60:1 at light load. A gas engine has to be kept in a narrow A/F ratio to insure combustion. Either to lean or rich will cause a misfire.

I digress, what was the original question?

Correct, most diesels run off of injector pulse.

With the diesel like you mentioned, does run lean but you really can't hurt it by running it too lean, there really is no such thing. Lean on a gasoline motor produces power, but dangerous power. You lean it out too much and you will have some major unforgiving problems.

Since there is no throttle body, many modern diesels have a shudder valve which is in place to kill the motor after the ignition is turned. It is there for a safety device as well, because if your turbo fails and lets a seal lose, the turbo will pump the engines oil into the intake and eventually into the motor, the motor will burn its own oil for fuel, eventually burning up and siezing. That is not an issue on a gas motor.

Yes there are some differences, but it is the motor not the turbo (gas vs diesel). Many modern turbo chargers control boost electronically, on both gas and diesel.

 

[Robster]

Tractors competing in tractorpulling run up to 220 pounds of boost using sequential turbos. But that is Diesel engines of course. Still insane amounts of boost! =)

Sorry, back to topic.

//Rob

 

[milehighassassin]

I don't agree with the part about a diesel using the same amount of air at idle as under load.

Complete BS

 

[polarisfornow]

I don't agree with the part about a diesel using the same amount of air at idle as under load.

Complete BS

you'd be wrong then, look it up don't just shoot your mouth, not counting a turbo which is what i said a diesel uses the same amount of air at all rpms and loads. get an A/F guage on your own diesel and see for yourself.

 

[Boyko]

OK

At 14.7 psi boost you double your corrected HP because actual sea level air pressure is 14.7 psi. That is in theory and there is a wack of variables involved I think everone is ok with that. Some dyno numbers come close to that…….. providing it is a good kit, yet some dyno numbers exceed this theory. This can be because of some of the components of the kit brings the volumetric efficiency of the engine up, It could also be the Dyno operator. Your turbo steals power from your engine to make boost, it has to come from somewere it is not free.

I will like to through a idea out there about corrected dyno HP when you are playing with boost. I am not at all familiar with all dyno software but for the HP correction some software has no provision for boost. I think if boost is not calculated in you are getting a inflated hp number, 10 psi boost does not change at altitude but air pressure does and the software is adding HP to the HP that was made from that 10 pounds of boost. Am I wrong on this? How about some feedback.

Sorry about bringing the word Diesel to this thead.

 

[DRD]

Correct, most diesels run off of injector pulse.

With the diesel like you mentioned, does run lean but you really can't hurt it by running it too lean, there really is no such thing. Lean on a gasoline motor produces power, but dangerous power. You lean it out too much and you will have some major unforgiving problems.

Since there is no throttle body, many modern diesels have a shudder valve which is in place to kill the motor after the ignition is turned. It is there for a safety device as well, because if your turbo fails and lets a seal lose, the turbo will pump the engines oil into the intake and eventually into the motor, the motor will burn its own oil for fuel, eventually burning up and siezing. That is not an issue on a gas motor.

Yes there are some differences, but it is the motor not the turbo (gas vs diesel). Many modern turbo chargers control boost electronically, on both gas and diesel.

You've got me there. I have no idea what a "shudder valve" is.

I'm guessing you read something about a Positive Air Shut Off or a Rig Saver. These are commonly used when the engine is used around flammable gasses etc. to prevent a runaway. Old Jimmy's had them installed factory to prevent runaway since they were notorious for leaking blower drive shaft seals. The problems isn't the fact it will burn all the oil from the sump and seize, it's the uncontrolled RPM.

 

[Unfair Advantage]

Won't let me post a reply with "math" in it?

Figured it out...won't allow 2 running = signs...geez

 

[ruffryder]

you'd be wrong then, look it up don't just shoot your mouth, not counting a turbo which is what i said a diesel uses the same amount of air at all rpms and loads. get an A/F guage on your own diesel and see for yourself.

No, the amount of air is dependent upon the cam shafts, intake runner length, porting, and exhaust, not to mention cylinder shapes, piston shape, piston size, rod length, stroke of crankshaft..... An engine is an air pump... If you look at a volumetric efficiency curve of an engine, it is not a straight line..

velocity of the air coming into the engine is largely impacted upon the configuration of the motor...... there is some interesting wave theory (called tuning of the system) that happens with air and spent exhaust gasses....

Not sure if they make A/F gauges for diesels? Not sure why that is even important as a tuning guide...

 

[Boyko]

No, the amount of air is dependent upon the cam shafts, intake runner length, porting, and exhaust, not to mention cylinder shapes, piston shape, piston size, rod length, stroke of crankshaft..... An engine is an air pump... If you look at a volumetric efficiency curve of an engine, it is not a straight line..

velocity of the air coming into the engine is largely impacted upon the configuration of the motor...... there is some interesting wave theory (called tuning of the system) that happens with air and spent exhaust gasses....

Not sure if they make A/F gauges for diesels? Not sure why that is even important as a tuning guide...

You forgot rpm and it is a big factor to how much air is being pumped

A airfuel gauge only mesures the pecentage of oxagen present, it has nothing to do with the volume of air

 

[Unfair Advantage]

I'd like to hear some feedback on this also...

Ok to simply things, I will use an example. You just bought a new sled which is rated at 150 HP stock, your looking to add more power, say you want 100 more HP. You decide a turbo is the way to go. Here's some math.

Performance gain = Desired bhp / Original bhp - 1

Performance gain = 150HP + 100HP/ 150HP - 1 =0.67 -> 67 %

Ok, so an increase in base engine output of 67% will be necessary through the turbo system to achieve our results. Now to further it.

Boost required = Performance gain x Atmospheric pressure

Boost required = 0.67 x 14.7 = 9.8 PSI for the anticipated 100 bhp gain.

HP per 1 PSI = 100bhp/9.8 PSI = 10.2 HP

Note: This math is calculated based on a 4 Stroke engine, someone with a better understanding can easily apply this to a 2 stroke. In my understanding this does give a "general" idea as to how much HP you do gain per pound of boost in a controlled setting without taking variables into consideration.

Let's get some discussion going.

 

[Boyko]

Cool

or you could go the lazzy way

150hp / 14.7 = 10.2

10.2hp per pound of boost

 

[ruffryder]

You forgot rpm and it is a big factor to how much air is being pumped

A airfuel gauge only mesures the pecentage of oxagen present, it has nothing to do with the volume of air

I thought the rpm changing was assumed? Yah about the air/fuel gauge, but do they make them for diesels? I didn't think so.... since they are pointless for a diesel.. as compared to gas motors..

 

[Boyko]

I thought the rpm changing was assumed? Yah about the air/fuel gauge, but do they make them for diesels? I didn't think so.... since they are pointless for a diesel.. as compared to gas motors..

You can put a A/F gauge on any type of internal combustion engine providing the engine is large enough. Propane, alcohol, diesel, natural gas, hell even a wood or coal boiler, it don’t care what is being burned it still will measure the amount of o2 present. You might have a problem mounting one on your weed eater because of the size. Thay can be used for the same purpose on a deisel as a gas engine.

 

[polarisfornow]

No, the amount of air is dependent upon the cam shafts, intake runner length, porting, and exhaust, not to mention cylinder shapes, piston shape, piston size, rod length, stroke of crankshaft..... An engine is an air pump... If you look at a volumetric efficiency curve of an engine, it is not a straight line..

velocity of the air coming into the engine is largely impacted upon the configuration of the motor...... there is some interesting wave theory (called tuning of the system) that happens with air and spent exhaust gasses....

Not sure if they make A/F gauges for diesels? Not sure why that is even important as a tuning guide...

ok try to follow along here if you can, you might learn something. This only applies to diesels and not gas motors. a diesel doesn't have any way of limiting incoming air into the cylinder other than the valve train. no throttle plate or throttle body or any thing. so with no way to regulate incoming air it is always the same assuming no turbo boost.

an easier way to think of this is like an air compressor. just because an air compressor spins faster doesn't mean that each individual stroke takes in more air.

the same with a diesel, it doesn't magically become more efficient at a higher rpm. the engine is as efficient at 600 rpms as it is at 2000 rpms. the reason this is important is because if you know what volume of air the motor uses at one rpm you know what it uses at all rpms and makes for a much more precise tuning when you add fuel and boost to that engine.

this is first day diesel tuning stuff here guys not voodoo

 

[happylilcuss]

MHA Do a little research on the 12 valve cummins built in 98. I put a fuel torque plate on mine and installed a 30psi boost gauge. We took it out for a test drive and I promptly blew the gauge.
Went to summit and got a 100 psi gauge and I am running 60psi. Thats with nothing more than a fuel torque plate and opening up the airbox and a 4" straight pipe. Also had to put a south bend clutch in it to keep it from slipping.

From what I have seen with mine I can gaurantee that 100+ psi of boost is possible.

 

[polarisfornow]

MHA Do a little research on the 12 valve cummins built in 98. I put a fuel torque plate on mine and installed a 30psi boost gauge. We took it out for a test drive and I promptly blew the gauge.
Went to summit and got a 100 psi gauge and I am running 60psi. Thats with nothing more than a fuel torque plate and opening up the airbox and a 4" straight pipe. Also had to put a south bend clutch in it to keep it from slipping.

From what I have seen with mine I can gaurantee that 100+ psi of boost is possible.

curious if you tow with it at all and what sort of egt's you see while doing so. I have a 97 with a 0 torque plate 5 inch exhaust and a bunch of other stuff. i cant tow more than 9-10k with more than about 34-36 lbs of boost or its gets real hot real fast on inclines.