So why can our 4 strks handle way more boost then a 2 strk with the same compre

[samsquatch47]

So last weekend I had some crappy luck on my Impulse race gas Nytro. The fuel line ruptured at the stock fuel rail, spraying AV gas on the hot turbo. Sadly the sled went up in flames an damaged many things. Luckily the new 2871 is fine and the boost-it fuel controller is ok. So I'm thinking about trying a two strk either E-Tec (TSS kit) or Pro (Boost-it) kit once insurance pays me out. So my Nytro engine with Carrillo rods and head studs could handle 21 psi at elevation with 100 octane fuel every day without a hiccup. Why is that a 2strk can only handle 11 psi at the same elevation and fuel? What is the weakness?
I know this is the 4strk section, but it seems the most knowledgable turbo guys hang out here.
Thanks
Dustin

 

[Nytroboost]

Reeds are one of week spots.

 

[Backwoods M Max]

I would say for starters that since the yamaha sleds are more like an automotive engine with overhead valves/cams it will breath like one. I would dare to guess that on a blown 2-stroke you are dealing with the limits of what the reed valves in the case can hold for pressure. That 11 psi your squeezing in there first is occupying the crankcase and as the piston starts to come down it will reach a point where crankcase pressure exceeds boost pressure. Your now asking the bottom end to hold all this extra pressure that it wasn't designed to. The piston being driven downward by the other cylinder is compressing signifigantly more volume than stock, think about a blown head gasket but on the bottom end instead because of excessive case pressure.

My .02

 

[mike_s]

Many reasons a thumper can run more boost than a 2-stroke, but 1 big one that comes right to mind is, a four stroke engine has twice the amount of time to cool the piston/cylinder/chamber than a two stroke between combustion events. This makes the starting temperature of these components lower on each cycle compared to a two stroke, hence less chance of detonation/preignition. You can run whatever boost you desire in a two stroke if you can get enough octane, but your reeds will hate you for it, and at a certain point you will find deminishing returns.

 

[samsquatch47]

Thanks guys! Just looking to maybe trying something different this round. I've learned a lot about these turbo yami's in a few seasons would be cool to be knowledgable on 2strks too .
Has any one heard of guys getting Carrillo rods made to beef them up? They say they can do custom rods on their site. Most likely welding and balancing the crank would help too.
Keep the info coming!

 

[Wrenchmaster]

Gus runs some really high boost on 2 stroke race sleds. Guys are welding the cranks, triples for sure. I've seen some head mods to drop boost at high levels as well. I think the 10PSI max is for a mostly stock engine, with mods they can handle more boost.

 

[spoon]

Size for size a 2s makes same or more power on less boost because you have twice as many power strokes. M1000 with 10-12lbs boost is 280-320 hp depending on turbo setup. Same power from a 4s with same displacement is on nearly double the boost. There are guys running up to 30 lbs boost on 1000 2s and making into the 500 hp range. Racing only. Try to clutch for that and ride normally. One guy I know of running a 1200 cat motor with 35 lbs boost had very little engine mods other than big bore kit and welded crank and had years of racing on same engine. Reeds do need replacing more often with big boost. I can run a full season on reeds at 12-14 lbs. To make 300 hp a 4s needs more engine mods than a 2s to survive. I ran 8-14 lbs boost for 4 yrs on stock M1000 engine with turbo, replaced pistons after 4 yrs even though they still looked brand new and replaced reeds 2 times. Ran av gas and premium depending on boost. No race gas. Had some issues along the way but the motor was never one of them.

 

[HANDSOME]

Size for size a 2s makes same or more power on less boost because you have twice as many power strokes. M1000 with 10-12lbs boost is 280-320 hp depending on turbo setup. Same power from a 4s with same displacement is on nearly double the boost. There are guys running up to 30 lbs boost on 1000 2s and making into the 500 hp range. Racing only. Try to clutch for that and ride normally. One guy I know of running a 1200 cat motor with 35 lbs boost had very little engine mods other than big bore kit and welded crank and had years of racing on same engine. Reeds do need replacing more often with big boost. I can run a full season on reeds at 12-14 lbs. To make 300 hp a 4s needs more engine mods than a 2s to survive. I ran 8-14 lbs boost for 4 yrs on stock M1000 engine with turbo, replaced pistons after 4 yrs even though they still looked brand new and replaced reeds 2 times. Ran av gas and premium depending on boost. No race gas. Had some issues along the way but the motor was never one of them.

That is awesome, how many miles on it before you replaced pistons ? I have heard of some 2 strokes and they were all cats that have lasted 4000 km on boost.What is it that some are doing different to make them last. I just bought a carb turbo 2 stroke and cant wait to get it put back together and try it out but any hints on what to do to keep it alive would help.

 

[spoon]

That is awesome, how many miles on it before you replaced pistons ? I have heard of some 2 strokes and they were all cats that have lasted 4000 km on boost.What is it that some are doing different to make them last. I just bought a carb turbo 2 stroke and cant wait to get it put back together and try it out but any hints on what to do to keep it alive would help.

About 3000 miles on pistons. I think 2s turbo pistons last longer as they arent subjected to as much varying intake air temps as a N/A motor. I see lots of fatigued skirts on stockers.
Good luck with the carbed 2s, they make great power when they work but are more finicky in varying temps and air pressures. Fuel Injection is much more consistent.

 

[zebiraross]

Size for size a 2s makes same or more power on less boost because you have twice as many power strokes. M1000 with 10-12lbs boost is 280-320 hp depending on turbo setup. Same power from a 4s with same displacement is on nearly double the boost. There are guys running up to 30 lbs boost on 1000 2s and making into the 500 hp range. Racing only. Try to clutch for that and ride normally. One guy I know of running a 1200 cat motor with 35 lbs boost had very little engine mods other than big bore kit and welded crank and had years of racing on same engine. Reeds do need replacing more often with big boost. I can run a full season on reeds at 12-14 lbs. To make 300 hp a 4s needs more engine mods than a 2s to survive. I ran 8-14 lbs boost for 4 yrs on stock M1000 engine with turbo, replaced pistons after 4 yrs even though they still looked brand new and replaced reeds 2 times. Ran av gas and premium depending on boost. No race gas. Had some issues along the way but the motor was never one of them.

A 4 stroke only needs a $100 head shim to make 300 hp reliably with the right turbo set up. We have several with thousands of miles set up this way.

Boost is a arbitrary number anyway.

 

[up-high]

What he said.

 

[culvert]

So what are you doing with the old Nytro Dustin. Keeping it & fixing or parting her out?
Drop me a PM

 

[samsquatch47]

So what are you doing with the old Nytro Dustin. Keeping it & fixing or parting her out?
Drop me a PM

Hey man! Sold it last night $4500. I picked up a 2012 M8 going to try 2 strk boost out

 

[BigFish BC]

Hey man! Sold it last night $4500. I picked up a 2012 M8 going to try 2 strk boost out

better call the tss boys there turbo cats are fast + run great + a great fuel system.

 

[samsquatch47]

better call the tss boys there turbo cats are fast + run great + a great fuel system.

Already did! Just waiting for a final quote for turbo kit, C3 belt drive and Oil delete installed

 

[Wrenchmaster]

Lot's of good info on this thread if you haven't read it already.:

http://www.snowestonline.com/forum/showthread.php?t=149418