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

mountainhorse · Jan 13, 2017

Heres a thought I've been pondering for a while.

A high compression, low boost turbo for 100% AV Gas (100LL) use.

We all like the great bottom end 'grunt' of a high compression engine.

Good gas is getting harder and harder to find...100LL is consistent and cost effective.

Turbos are great when they are designed and integrated well.

Why not make a kit that pulls those all together.

Say 17.5 PSIa MAP pressure (equal to 3 lbs boost at sea level)... held consistent with excellent boost control.
A well designed 14:1 Cylinder head.

This would be one fun sled to ride IMO... and give a lot of benefits for the owner... The 100LL (which is about 103 MON BTW).... would run this sled, IMO, no problem.

A stump puller and consistent 190-200 hp.... and no need for complicated turbos, intercoolers etc.

Please comment if you have something to add.

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Spaarky · Jan 13, 2017

Why? 6-7lbs is a cake walk on 91 and easily meets your hp requirements. 80% of people want to pull up to the pump. Look at sales of Sidekick, Mtntk lower boost, and Silber 7lb......

I have messed with high Comp turbo. Mine was fairly finicky. Ran like a scalded dog, but cloud came through it would change. Playing the high octane game isn't as easy as you may think.

The PG kits right now are easy and pretty reliable.

Rosslbz · Jan 13, 2017

Pump gas would be out the picture and det would be in the picture! Tuning would be tough, too many changing factors. Lower comp gives you more room to add some fuel and boost. I think variable vane turbos will be the bee's knees sooner that later!

mountainhorse · Jan 13, 2017

Ross,
You must have missed the part that said 100% AV Gas 100LL.

So pump is not even a consideration in this scenario.

I would prefer to use AV 100LL as it is a better QUALITY fuel... Throttle response is not ideal, but workable and disappears with higher compression.

Justin,
6 - 7 LBS [Gauge] at what??? 10k feet on pump fuel... thats 16.7 - 17.7 PSIa MAP (what I referred to as '3 lbs at sea level... 17.7 PSIa MAP).

At 6-7 lbs (20 PSIa MAP) at lower elevations.... say 3K feet...Too high for pump gas without pulling timing (performance detractor) or pulling compression (performance detractor).

I've seen people also run higher comp turbos and watched them get finicky... but NONE of those were running low boost...

IMO...This would be a great combo for a mass produced, non adjustable, non intercooled, FUEL SPECIFIC Consumer friendly sled-turbo-kit.

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mountainhorse · Jan 13, 2017

my 2¢

If you run 100% 100LL... it is too MUCH octane for for 3 lbs (held consistent at 17.7 PSIa MAP) boost... And not all people need to run more than that...

100% 100LL is too much octane for stock compression and 3 lbs boost (17.7 PSIa MAP).... And by increasing compression... you would give a significantly stronger bottom end... and transitional throttle response IMO.... and complete compatibility with the 103 MON fuel (100LL is approx 103 MON).

The desire would be to get some serious performance increase compared to non-turbo sleds... and be able to use fuel that will give very consistent performance.

At elevation... a good NA sled is making what, maybe 110 -125 hp... This high comp, low boost turbo sled would run 190 - 200 all day long not be taxing the motor/reeds/bearings too much....Charge temp at the lb/min required flow rate, at 17.7 PSIa MAP, to support the 800 CFi engine would be kept low with a simple fresh air intake and no intercooler needed (3 lbs)

Now.. for you power hungry guys.. that need the huge power (200 +)... this hi-comp/low-psi is NOT your scenario, at all... and hey... not all strokes for all folks !!

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Spaarky · Jan 13, 2017

6-7lbs at 10,000 is 3 lbs at sea level with boost control. It may pull a little timing but barely noticeable. It also burns hotter on pump.

High compression is high compression weather it's 3lbs of boost or 30. It's all finicky. It's a race motor on boost.... It's going to be finicky. Even with efi.

100% AV..... It's just not realistic for a kit builder that wants to make money. People want pump. Shoot most people don't want to change weights anymore. Non adjustable is out of question too.

The juice isn't worth the squeeze...... Meaning the minute performance gain isn't worth it. No offense .... But you said none adjustable. 3lbs at 10,000 ft is nothing. A 6lb sidekick will eat it for lunch all day. I will take a big bore 910-960 everyday before a 3lb sled on high comp.

Spaarky · Jan 13, 2017

If you want non adjustable with tons of grunt and want to run straight AV. Why not run a supercharger?

mountainhorse · Jan 13, 2017

14.1:1 comp... I've run those sleds all day long on 20% AV/pump (or less) ... no issues... not finicky 'pull and go'...
Plenty of 14:1 (+) CFI-800's running well and consistently.

And I DO agree with you a real RACE motor IS finicky..but for lots of other reasons than the compression alone.

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mountainhorse · Jan 13, 2017

GREAT conversation... and thank you for the input so far!!

3 lbs... which I put on a level field by specifying the MAP reading in PSIa ... gauge reading depends on elevation...

PSIa-MAP... your always talking apples/apples regardless of elevation. "Non Adjustable" does NOT mean "non compensating" it simply means that the user does not have control over changing boost or fuel (like with the new MPI G4 kit).

I really prefer to talk MAP pressures because you can then stop talking about the 'sliding scale' of figuring out elevation influences over PSIG readings...
An EBAC keeps MAP consistent ... not Gauge pressure readings. When someone says '7 lbs' or '10 lbs' ... you are alway asking, or should be asking, "At what elevation".... MAP readings pull that question out of the discussion.

Non adjustable means that the user cannot play Ricky-tuner and get things out of whack.

IMO... Solid 190 hp at ALL elevations IS very marketable.... it is the higher HP kits that will sell less and less.

I think you might be discounting the benefits because it is counter to the 'traditions' of sled turbo kits and "high boosters"

Low boost turbo kits, IMO, in the next 2 years will account for 90% of the turbo sled kits sold.

This was a good discussion I had with Tony a while back...

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Spaarky · Jan 13, 2017

I have a pretty good idea what your trying to accomplish. 14:1 will not cut it. How do I know that? Experience. To get the gains you are looking for has to be more on the 16:1 range.

I discount it.... Because it's not realistic. Guys that want to run something other than pump will want higher boost. If I ask the 8-10 guys I know that run Sidekicks if they would switch... They would laugh in my face. They have a 190-200hp sled at 10,000 ft. They aren't going to switch from pump to AV. Basically what you have described is a Sidekick, silber kit or Mtntk kit just on straight AV.

It's a great idea. I have spent a bunch of years working on it. It's not as easy as you think. Somethings just don't work well with boost period.

Again if it was me and I wanted that sled. I would go to a supercharger. Matter of fact if Speedwerx/Carl's comes with one for the Axys. I will go buy a Axys.

This is just my opinion with a bunch of time and money spent trying to accomplish what you are talking about. I am done now ..... Hahahahahahaha

TreeThrasher · Jan 13, 2017

This is where my opinion differs.

From my experience the sled works far far better with bumped compression, a re designed and tighter squish and I actually like a couple degrees of advanced timing as well. You make the same peak power as a pumper or even a bit more with less boost and have far far better bottom end. Now combine that same concept with a big bore and you have ahold of a rock and roll package. And for the record if your head is designed well its amazing how much boost 100ll will support with a relatively high compression head. I climbed at 12 lbs all the time no det issues on 100ll. Your cross a point in boost pressure where lower compression makes more power. But, right up until that point compression makes power on the bottom middle and top.

I just got off the phone with a guy talking about his pump gas turbo. Loves everything about it except how it rolls into boost. It's a tad slow and that bothers him a bunch. If there was a kit available that pulled a fair bit better right off the bottom and he had to spend the extra 20 bucks a tank to run straight av it would be a no brainer for him. So I think there could be a market

JJ_0909 · Jan 13, 2017

I like the idea but I think others are right, its a niche product. Its not even that 100% AV gas is that expensive, its that its a pain in the *** to go get sometimes.

I love my turbo setup in that if I can't find AV gas I can just swap a waste gate spring, reduce weight in the primary and go have fun.

I think we could have much better performing low boost turbo sleds. I can attest to the bottom end being a bit of a bummer, and often exhausting. But gains will come from turbo selection, plumbing, mapping, ECB "map" etc.

meathooker · Jan 14, 2017

I've always described what we have now as high compression low boost setups. Stock sleds are decently high compression (12.5:1) and we're running pretty low boost levels.

I'm sure you could go higher comprsssion and lower boost but at some point the weight of the turbo doesn't justify the ultra low boost (3lbs). At that point build a ported big bore high compression motor that puts out 190hp and weights 20lbs less.

If you were to go with more compression and timing why not go e98?

We tried to do the same thing with our hillclimb car and built a 10:1 (stock motors are 8.8 or 9:1) so it's considered high(ish) compression and running around 23lbs (not very high boost). Honestly the bottom end isn't that much different from a stock car. Perhaps it's in our tune??

mountainhorse · Jan 14, 2017

I hear ya Meat.... but it's not about "3 lbs"...It's about not loosing performance at altitude.

A ported big bore, at 9k feet... makes, maybe, 130 hp... maybe.

I'd bet that a 14:1 CR (or even 15:1), 17.7 PSIa MAP turbo 800 AXYS...would make 200 hp at all altitudes on straight AV Gas 100LL and, with all of the electronic control of the CFi system and turbo kits these days... be pretty darn pull n go IMO.!!

For me, and to most of the places I've visited...AV gas, 100LL is pretty darn easy to get, AND... pretty reasonable in cost... usually about $1.50-$2/gal more than the crap fuel we're getting out of the pump. Easier, much, in my area, than finding E85 too.

2 stroke turbos and cars share some things... but the departures beteween the two are pretty clear. I agree, the automobile situation would be difficult... plus, I don't know many people with turbo street cars that run race/AV fuels.

On an 800CFi with 15:1 domes and AV gas.... the added 'grunt' was noticeable, and very easy to run/dependable keeping the fuel consistent.

Keeping the engine fed with an 'artificial air density' of below sea-level... hmm.

This is a lot to wrap our heads around and IS a departure from the norm.

Running AV with Higher boost also brings on the issues that higher boost introduces.... hence the low boost.

Digging the conversation !!

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diamonddave · Jan 14, 2017

I'm in the process of building, and tuning this same exact scenario right now Eric.

However, I have to say the Silber set-up's (2012 kits, 2013 kits, and 2014 and newer reflash kits) that I have installed, worked on and tuned, and others I have ridden do not exhibit any real noticeable decrease low end, tip in throttle perfomance issues with stock compression, motors, etc. I have not ridden a Sidekick yet and my experience is only from 2,000-7,000 alt's. Maybe this low end decrease is much more noticeable at higher alts?

My 2863 Sliber reflash set-up has a few, very small extra tricks but it feels exactly like stock performance on the low end. But only feels stock until boost comes on.

sumtinwong · Jan 14, 2017

200 hp at all elevations with no low end grunt lost would be a dream come true! if the price we hade to pay was just running AV gas that's easy, and if we hade to keep a feu bottles of octane boost setting around for the chance that we cant get AV....that isn't bad...but I would still like to think that if I wanted to pump out 220 hp just to out mark my bud for a good laugh that Its possible. but to me it still seems like we are waiting for a supercharger!!! {as for getting AV gas just get a feu 55 gal drums it stays good for a feu years so it wont go bad if u don't use it the first year or the second year for that matter its prob the most stable fuel we can get}

mountainhorse · Jan 14, 2017

One of the big problems in sled turbo kits IS that most of the kits are user adjustable... IMO.

Now, some of the Turbo gurus on here would argue this... most of them love to run higher boost levels (say north of 20PSIa MAP) and tweak them all the time to run "on the edge" ... and for their use, I would agree that a non adjustable has no value to them.

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TRS · Jan 14, 2017

Kent Lundine from Casper was a master at tuning/running high compression engines on boost.

Scott · Jan 14, 2017

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

2XM3 · Jan 15, 2017

Having built a lot of 4 stroke and 2 stroke stuff, i'll say this, yes there is a market, however to really make it work well if you size the turbo for lets say the 4 pound level you can in fact use a much smaller turbo, this will in fact also spool much faster and produce less lag, you can also not use a intercooler and minimal pipeing and airbox volume too, all in the no-lag theme. (ie correct turbo would hardly ever use the wastegate as its spooling pretty much max all the time)

Another advantage would be that the mapping would be almost near factory, perhaps even just minimal tweeks and bigger injectors would get it done.

But I do believe the bad would be the fuel, maybe 95% of kits sold are the pump gas stuff (i'm guessing) and when I ran my turbo sled I ran 14 psi factory compression on 100% VP C14 never any issues and it was pretty snappy down low to boot lol

IMHO but at a low price point, it is a good idea I think :face-icon-small-coo

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

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