TOPIC FOR DISCUSSION... HIGH-COMPRESSION, LOW BOOST TURBO FOR 2 STROKE... HMMM.

[Turbotater]

I'd like to hear what Turbotater (Wayde Johnson, T8rz Porting and Performance) has to say in this conversation.

I don't need to say much, Tree Thrasher hit the nail on the head.
He described my old 2000 800 RMK aero to T. Lol
I can run 50/50-91/100LL with 10lbs all day long with no issues but run it on straight 100LL for simplicity and peace of mind knowing there's no ethanol in the system.

 

[o2bncamo]

I have a couple turbo 2-strokes. One is a low compression (11-1) high boost (25 map), the other is moderate compression (13-1) lowish boost (19 map). I would like to experiment with higher compression on the low boost setup. There are several things I like about the higher compression setup; more responsive, easier to drive in the tight trees, more engine breaking going down steep grades.
There is no doubt you can get more HP out of the low compression setup. On a deep bottom less powder day it's hard to beat. On most other days I prefer the higher compression setup. I think this thread is the motivation I needed to try the 14-1 head I have laying around. Whats the worst that can happen a couple more pistons.

 

[mountainhorse]

The benefits, from my perspective, of the Higher comp, with turbo, are the same as the benefits of the higher comp in a non-turbo application. The low boost and the 100LL keep things much less complicated.


I wish I could run 100LL in a stock sled and have it give me the same performance as 91... but it wont... pump 91 here and even a lot of the non ethanol fuel... is low quality and inconsistent at best.... 100LL, no ethanol or other weird additives... very consistent, easy availability (for me at least), and not much more than pump fuel.

The straight AV gives me the det protection, and ability to get the benefits of high compression, and run on 17.7 PSI MAP with the proper configuration to make the most out of the fuel. You can run 100LL without loosing performance in a high-comp/low-boost config.... where you cant in a low-comp/low boost config.


Wade... have you run any CFi sleds with electronic fuel management like that?








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[mountainhorse]

I have a couple turbo 2-strokes. One is a low compression (11-1) high boost (25 map), the other is moderate compression (13-1) lowish boost (19 map). I would like to experiment with higher compression on the low boost setup. There are several things I like about the higher compression setup; more responsive, easier to drive in the tight trees, more engine breaking going down steep grades.
There is no doubt you can get more HP out of the low compression setup. On a deep bottom less powder day it's hard to beat. On most other days I prefer the higher compression setup. I think this thread is the motivation I needed to try the 14-1 head I have laying around. Whats the worst that can happen a couple more pistons.

For me...Things are muchless complicated, set-up/tuning/componentry, at lower boost pressures... but some really want a lot of HP... and thats great too.




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[o2bncamo]

So you want to use lower boost just to get rid of the intercooler? Tuning doesn't seem like a big factor, at least for me. The main reason for me to do the high compression with low boost would be for the big bore affect, low end grunt, better compession braking.

 

[mountainhorse]

So you want to use lower boost just to get rid of the intercooler? Tuning doesn't seem like a big factor, at least for me. The main reason for me to do the high compression with low boost would be for the big bore affect, low end grunt, better compession braking.

Not to 'get rid' of anything... for me.... low boost is what I want... consistent performance from 2000 - 12000 feet... lots of grunt... able to get performance from a consistent fuel that does not absorb water, eat rubber/plastic, or degrade in a couple of weeks and not have to deal with the exponential changes that happen on the turbo kits, regardless of maker, that happen above those low boost numbers.... consistent 17.7 psi MAP... thats NICE. (IMO)

200 hp at 9000 feet compared to the 115hp you'd make without the turbo in the same sled... that is HUGE.... and only needs 3psi (or maybe less) above sea-level-pressure of 14.7 to do it.

Higher boost... more considerations in pumping efficiencies, gained heat, transitional variations with rapid WOT/chopped throttle movement etc etc..

I'm just not the rider that needs more power than that... some do... but not me.

190 - 200 hp at 9000 feet in blower pow is an ANIMAL.... more than that... sure, it's fun, but what are the extra considerations..

Some turbo sled people would say "Why run a turbo if you're not going to crank the boost up? 3 lbs... thats a waste !! "
My answer: 190hp - 115hp = 75 hp.... more than double the power improvement.

200 hp is what you could make, consistently, at all altitudes on straight 100LL, and 14:1 - 15:1 compression, 17.7 psi MAP (3 lbs) IMO & without pulling any timing

The difference between non-turbo (10.5 psi MAP) at 9000 ft. and 3 lbs (17.7 psi MAP) boost is much more than the diff between 3 lbs (17.7 psi MAP) and 7lbs (21.7 psi MAP).

Running More than 7lbs (21.7 psi MAP) and you are talking about a 'paradigm shift' in your way of looking at the sled of race fuel, intercooling, timing mods, low comp heads etc.... remember.... 7lbs-true (21.7 psi MAP) at 9000 ft is more than 11lbs reading on your gauge at 9000 ft. ... and you'll make 240 - 250 hp. IMO.

The bigger the intercooler, or turbo, or charge tract... the more it behaves like a turbo sled and less like a NA sled... Lag, more fuel tweaking, more sensitivity to humidity, more watching your plugs. etc etc.

My presentation here is the K.I.S.S. approach... with a twist to optimize the bottom end, keep the kit price lower, and give me the ability to run quality fuel



I know this is a lot for the 'turbo inclined' sledders to wrap their heads around and a departure from the norm... but ponder it for a while









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[LoudHandle]

My 2 cents; this would be the perfect setup for us Alaskans; IMO

This type of setup would be the Ideal setup for us Alaskans. As all of our riding is sea level and higher (most is sea level to 6500-7000 feet) although higher altitudes are available, most of us aren't scaling Denali or the other tallest peaks here in a weekend.

AV gas is also very readily available as we have the most small planes per capita in the USA.

I'm really liking the concept! It sounds like this setup would solve most of the issues people have here with the currently available turbo kits. The on / off throttle lag is a huge deterrent for me as well as the lack of lower altitude R&D on the mapping / run-ability.

I see it every year at our local hillclimb. The current turbos scream from the starting line to the first tight uphill corner gate, where they have to lift to scrub some speed to make the corner, at which point it is never able to recover and get respooled between the steep course and the tighter gates. A box stock sled will kick the turbo'd sleds azz, every time, because it can and will recover from the throttle chop.

I've always thought the turbo should be sized to start building boost at a point slightly below the engagement RPM to counter this effect, But upping the compression should have the same effect?

Subscribed and watching eagerly, Thanks MH!

 

[gmustangt]

I hear where your coming from MH , Some of the knowlegable engine builders have steered away from the higher compression in the past for fear of runability issues on the top end.
What your really after is cylinder pressure , the high compression is one way to get there, there are other ways to get there as well for more response and better bottom end.

 

[Spaarky]

I know as a "turbo inclined" sledder that can't wrap my mind around this.....

What is the difference between this and a Sidekick, except it runs in AV????

 

[gmustangt]

I know as a "turbo inclined" sledder that can't wrap my mind around this.....

What is the difference between this and a Sidekick, except it runs in AV????

Up the static compression , and achieve equivalent cylinder pressure to a side kick at "x" boost.
Have more exhaust energy to drive the turbine at lower rpm
Ask less of the turbo and more of the motor.

Curious to see how the correlation between 1# of boost and 1.0 of compression

 

[Spaarky]

I understand that. MH just appears to me to think it's something new and revolutionary. A nonadjustable, low boost is not new. Doing that on AV is a little bit....... But backyard/small shop guys have been messing with that for years and years. My old carb sled had enough compression to blow the head gaskets on a diesel truck.

Guess I am missing the point......

 

[Jaynelson]

How about the same idea, but on e85 ala the turbo car world? You'll need more fuel, but it gains you a ton of torque and lights the turbo quicker. And would take everything a high comp sled motor could ever throw at it; given a fuel system to support. It's pretty easy to come by an e85 pump for lots of guys south of the border, correct? Up here we would need to go the AV route cause it's the only way to go...other than race fuel, which has gone crazy on price.

 

[Turbotater]

Wade... have you run any CFi sleds with electronic fuel management like that?

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I've rode and been around them plenty. I've stayed out of that market mostly because I don't make my living doing sled work and to build them my way is more costly and time consuming.
I've consulted many but none want to spend the extra time or coin to try my mods or they try part of them and don't finish so they still don't see the benefits and that's fine. Most need a turn key set up and getting them to work should be the kit manufacturer's responsibility.
It's a tough racket to be in as there are so many ways to do things and some work in one application and not others. If my Wife would win the lottery I'd retire and we'd have a blast with this stuff.
Right now I have very little interest in the turbos. I've been riding my 962 stroker Axys and I'd rather ride it over a turbo any day of the week.

 

[mountainhorse]

Good Discussion !!

My old carb sled had enough compression to blow the head gaskets on a diesel truck.

Sounds like a crazy setup !!

Turbo'd ?
If so, what was your static compression ratio, how much boost/altitude and what race-gas/timing were you using?

MH just appears to me to think it's something new and revolutionary. A nonadjustable, low boost is not new. Doing that on AV is a little bit....... But backyard/small shop guys have been messing with that for years and years.

I would think this is NOT at all 'revolutionary or new'... but I don't see any kits offered this way in the age of electronic controls, EBC/EABC's, injection etc.
I can't find a single article/thread/discussion on a high-comp/low-boost turbo Sled (carb or electronic injected).... But I am open to any links or scans of them... or better yet, personal accounts of specific builds.

Non adjustable, LOW boost with stock or lower compression... seem to be a few kits out there, but just recently.

I know lots of people that run their low boost kits on Straight AV gas.... for 'peace of mind'... but, dang is there a lot left on the table as the fuel is not appropriate for the configuration.







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[Merlin]

I'm with LH on this one too.

I can definitely understand your(Eric) reasoning but curious as to how it would play out in the real world.

I'm really liking the concept! It sounds like this setup would solve most of the issues people have here with the currently available turbo kits. The on / off throttle lag is a huge deterrent for me as well as the lack of lower altitude R&D on the mapping / run-ability.

Subscribed and watching eagerly, Thanks MH!

 

[mountainhorse]

I know as a "turbo inclined" sledder that can't wrap my mind around this.....

What is the difference between this and a Sidekick, except it runs in AV????

Higher compression.

AND... the kit builder to take the time to tune the kit well on the AV fuel.



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[BILTIT]

Sounds like a good setup to me MH! I love my (semi-)high compression engines and have av gas around all the time. A small turbo and a few pounds of boost could only make it better!

I don't need/want a ton of power like most turbo setups have, but a few pounds would be great.

 

[jim]

You can do this by putting a butterfly valve in front of the turbo inlet and still getting the higher boost numbers on pump gas with the great throttle response. Valve in front of the turbo intake lets the turbo remain spooled up. And then you have the power on top with full spool up. This discussion is like anything with a traditional turbo set-up...what do you want to trade? Also, typically, one gets the best throttle response with lower octane on a standard motor. So why not just accommodate that as opposed to upping compression?

 

[Daltech]

MH
I have read up on the map vs gauge discussions when time has been available, and I see it is brought up here also. I will bring up a factor that has not been mentioned yet, as I have seen, and that is PIPE PRESSURE.
IMO, on a 2 stroke you need to take into account the pipe pressure.

I don`t think the power increase is linear with boost on a 2 stroke, much of that because of pipe pressure.
As you suggest to have a turbo setup at 17,7psi map. At sealevel that would be 3 psi gauge pressure. We know that most 2 strokes 800 today have a pipe pressure of 3-4 psi. With as low boost numbers as presented, I think there is almost no gain in power running only 17.7psi map at sea level.
At elevation it will change, because the gauge pressure goes down, and the pipe pressure follows the gauge pressure, meaning the engine sees more actual boost.

You will always have the 3-4 psi pipe pressure on your bottom line, but the delta P over your engine will raise with elevation if you run a constant MAP.

We live and ride @sealevel, and there has been countless 2 stroke turbos at dynos here. Typical cat 800 with boondocker kit get 220hp with 10.5 heads at 12 psi.

With stock head, the limitation is 6psi approx, where they are@ 180bhp.
All this on pump fuel thou.

What I am trying to communicate is, that I do not belive that any 2 stroke at 3 psi gauge pressure at sealevel will make anything more then stock or close to stock power since we are not adding more boost then just "zeroing" the delta P over the engine.
We will never see a positive delta P over the engine, that is for sure since we are always adding pressure to the already pressurised pipe.

 

[m7ascent]

MH
I have read up on the map vs gauge discussions when time has been available, and I see it is brought up here also. I will bring up a factor that has not been mentioned yet, as I have seen, and that is PIPE PRESSURE.
IMO, on a 2 stroke you need to take into account the pipe pressure.

I don`t think the power increase is linear with boost on a 2 stroke, much of that because of pipe pressure.
As you suggest to have a turbo setup at 17,7psi map. At sealevel that would be 3 psi gauge pressure. We know that most 2 strokes 800 today have a pipe pressure of 3-4 psi. With as low boost numbers as presented, I think there is almost no gain in power running only 17.7psi map at sea level.
At elevation it will change, because the gauge pressure goes down, and the pipe pressure follows the gauge pressure, meaning the engine sees more actual boost.

You will always have the 3-4 psi pipe pressure on your bottom line, but the delta P over your engine will raise with elevation if you run a constant MAP.

We live and ride @sealevel, and there has been countless 2 stroke turbos at dynos here. Typical cat 800 with boondocker kit get 220hp with 10.5 heads at 12 psi.

With stock head, the limitation is 6psi approx, where they are@ 180bhp.
All this on pump fuel thou.

What I am trying to communicate is, that I do not belive that any 2 stroke at 3 psi gauge pressure at sealevel will make anything more then stock or close to stock power since we are not adding more boost then just "zeroing" the delta P over the engine.
We will never see a positive delta P over the engine, that is for sure since we are always adding pressure to the already pressurised pipe.

I can't wrap my head around this one. Pipe pressure and gauge pressure are two different things. Gauge pressure is measured in the intake side between the turbo and the engine. I get that the motor naturally aspirated is making 3-4 psi in the pipe, but now with the turbo you are putting 3 more psi pre engine.

As an example, you CANNOT put 3 psi into the engine without added fueling with out blowing your motor. I think there are a ton of pump gas turbo guys running at sea level that would disagree with you when you say "I do not belive that any 2 stroke at 3 psi gauge pressure at sealevel will make anything more then stock or close to stock power". If your putting more air and more fuel into the engine, you cannot have a "zero gain" just because the pipe pressure was already at 3-4 psi.

Back to topic, I think that a properly tuned high compression low boost setup would be that cats meow for some applications. Should in theory make the sled have the bottom end of a big bore, with the top end of the turbo, best of both worlds. Lucky for us, turbo kit builders have come a long way with the development of tial exhaust with external waste gates, their clutching setup, and the way they are fueling the added boost. Gone are the days of boggy or laggy bottom end power, boost comes on quickly and smoothly. That said mountainhorse, can you ever have to much bottom end throttle response? I haven't been able to have that problem in any application yet.