# Turbo/super charging a 2 stroke.



## Kneejerk Bombas (Jul 20, 2005)

Why doesn't this work?


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## Stihl 041 super (Jul 20, 2005)

*what you mean*

What do you mean. I supercharged my leafblower with the tube running off the blower tube. It didnot work very well because you could dump as much 
fuel as you wanted into it and the revs wouldnot go up it would just get very 
very hot. you could boil water in a spoon on the muffler. the only reason why 
it wouldnot work because you couldnot feed it enough fuel to make a difference. But it would be a hog on fuel.


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## Sylvatica (Jul 20, 2005)

> Why doesn't this work?



It sure does work.

Two cycle GM-Detroit Diesels (series 53, 71, 92, 149) and GM electro-motive Diesels were blown, and turboed & blown. They were the performance Diesels from the end of WWII to the early 80's.

The Roots blower with an aftercooled turbo boost supplied charge intake and forced scavenging.


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## ErrolC (Jul 20, 2005)

Several things to consider..as with 4strokes the overlap between intake and exh timing needs to be optimised..a 4 stroke has an induction stroke to allow time for the cylinder charge to be pressurise before the inlet valve closes for compression..a 2stroke does not have this luxury so the exh port/transfer port overlap has to be drastically altered and you still won't have positive pressure as the exh port is closed by the piston..2stroke diesels either have an exh valve in the head (with intake ports in the bottom of the cylinder skirt)..or they run slidding sleeve valves that are activated and timed from a camshaft/cranked arrangement which allows the intake ports to close after the exh ports..this is not possible with piston actuated cylinder ports.

If you supercharged a conventional 2stroke design you can get positive pressure in the cranckcase fine..but all the pressure does is blow more charge out through the exh port through the transfer phase..no advantage gained


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## Al Smith (Jul 20, 2005)

The GM/Elecromotive diesel engines are in fact scavenging air diesels.The porting is entirely different than on a 2 cycle gasoline engine.All you are doing is boosting the air above atmospheric pressure,the fuel is injected in the cylinder and does not have to enter via the sealed crankcase as in a gasoline engine.Historically,the Cooper-Bessemer diesel was in operation much before GM and used a piston type pump for aspiration,instead of a Roots positive displacement blower.The idea does intrigue me about supercharging a 2 cycle gasoline engine.The only case I can think of would be the McCulloch BP model saw.Conceptually I think it would be possible,but I have not yet figured a practical way to retro fit an existing engine with one.


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## McC (Jul 20, 2005)

Mike, you'll have some competition in the 50cc and under class at West Bend this year, and they will be supercharged. Mac BP1's, 44cc, 4.2hp, with balance piston that also acts as a supercharger by stuffing the crankcase on the upstroke. Your chain will be your advantage as the 2 we're bringing run round filed chisel. Hope to see you there.
Scott
Here's a link to Acres site for the BP1
http://www.acresinternet.com/cscc.n...378fb4451b521bbb88256b6100149cd3?OpenDocument


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## shtoink (Jul 21, 2005)

Anyone know where to find some diagrams on how this principal works? I'd love to see more. My curriosisty is definately piqued.

*Edit*

I did find some information about turbocharged two stroke engines, but they were all diesle.

http://www.greencarcongress.com/2005/05/fev_developing_.html
http://www.bath.ac.uk/~ccsshb/12cyl/

It didn't help me much, but it was still interesting.


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## CNYCountry (Jul 21, 2005)

Nitrous is a form of forced induction also:

http://www.madsens1.com/hotsaw.htm

The page says they did play with true turbocharging also...


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## TimberPig (Jul 21, 2005)

Nitrous is a way of adding more oxygen to the air fuel mix rather than a true form of forced air induction. Turbocharging or supercharging aim to flow more air through the motor by packing more air/fuel mix into the chamber and burning it.

As to turbocharging a 2 stroke, it is actually fairly common in 2 stroke snowmobiles for people to mod their sleds up by turbo'ing them.


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## Stihl 041 super (Jul 21, 2005)

*ya*

Ya because they have tuned exhaust's that act like a valve. Except they use 
a resonance pulse or back pressure to push the air fuel mix that tries to flow out the exhaust port back into the combustion chamber. Most stock saws
dont come with that kind of exhaust.


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## Sylvatica (Jul 21, 2005)

shtoink,
Aren't those pics of the assembly of that GIANT Sulzer marine Diesel awesome?! I've seen them before and I'm still amazed by that degree of engineering and power.


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## shtoink (Jul 21, 2005)

Yeah! I was blown away by the sheer size. I hadn't ever thought about what drove those barges before, but after seeing them in mid construction it bring them into perspective. You just have to step WAY back to see it all.

Any other links to information on how the turbocharging of an ordinary 2 stroke? I'd love to see some of the inner working of that BP-1.


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## ozflea (Jul 21, 2005)

Stihl 041 is right, yes other forms of turbocharging and supercharging have been tried but i suppose in the end the Tuned pipe is the answer as it pushes back excess fuel into the chamber before the piston closes the port, now if the pipe is setup correctly and the pulse wave is right great gains can be had. 
Try running a Hotsaw with and without the tuned pipe and you'll understand where that power has been made.
Next the Tuned pipe is easier made and less weighty and can be finely adjusted and once set requires little maintance.
But understanding how and why true Tuned Pipes work is a bit of a black art and many will not devolge their secrets.
Don't blame them really as it takes a very knowledgeable person to get it just right and get you into the top competitors.
Just unbolting one off a motor bike and sticking onto your saw doesnt work as their characteristics are completely different.

Mc Bob.

Here's a formula to help those who know how try to work it out.

http://www.camaa.org/tpipe/TunedPipeDesign.html


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## Stihl 041 super (Jul 21, 2005)

*Want to know*

If you want to know how to make a tuned pipe go to PSI,and Starting Line Products their the foremost designers in snowmobile racing pipes.


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## Al Smith (Jul 21, 2005)

Now then,ye olde tuned pipe.My buddy,Louis Baughan was national #3 in points during one season in the glory days of 2 cycle kart racing.Hopped up Mac 101's, of course,about a dozen of them,with different porting,for different power curves,He designed by seat of the paints,so to speak,a tuned pipe arraignment whereby the main barrel was changeable in 1/4" increments.It worked very well for him.He could adjust his power band from around 7 thousand rpms up to about 14 thou,depending on the porting and race conditions.As a normal rule I do my own work but if I ever were to get into hot saws,he has already said he would build me a pipe.


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## McC (Jul 21, 2005)

My cousin Paul owns the BP1's. He has a bare block and crank assembly. I'll see if he can bring them along next week so I can take some pics of it.
Scott


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## ozflea (Jul 22, 2005)

*Mc BP-1 Pics*

This should take to another thread containing the pic's requires on the BP-1.

Mc Bob.

http://www.arboristsite.com/showthread.php?t=19072


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## spacemule (Jul 22, 2005)

I just wonder how they start those behemoth ship engines.


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## Stihl 041 super (Jul 22, 2005)

*start*

They start them with compressed air from huge compressors. Source Super Ships Discovery Channel.


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## average joe (Jul 22, 2005)

Turbos work well on two strokes.


> a 2stroke does not have this luxury so the exh port/transfer port overlap has to be drastically altered and you still won't have positive pressure as the exh port is closed by the piston.


 A two stroke can be ported to have port overlap and also be ported so that after the exhaust port is closed the transfers can be still open. So a turbo will work just fine, provided the motor is ported properly.
Their are tons of blown snowmobiles around, btw.


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## Stihl 041 super (Jul 22, 2005)

*Yep*

Average joe the reason why turbos work on sled engines is that they have tuned pipes that help hold in the boost. Most 2 stroke saws donot have that kind of exhaust so when you put the boost to them the boost just goes right out the exhaust I know I tried it with my leaf blower.


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## average joe (Jul 22, 2005)

a turbo would work fine without a tuned pipe. In most sled turbos I have seen the pipe is rube goldberged to death to the point where it doesnt function fully as a tuned pipe any way.
Likely the reason your blower didnt work had to do with fuel delivery and more importantly the porting.


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## ErrolC (Jul 22, 2005)

Dear Joe..lets think about it for a minute..pertainant to piston ported petrol engines..with the piston on the power stroke (on the way down) whats going to happen if you open the transfers before you open the exh..because to close the transfers after the exh (on the compression stroke, on the way up) which is what you need for the intake ports (transfers) to continue to pressurise the cylinder before compression begins, the top of the transfer ports HAVE TO BE ABOVE the exh port..the engine won't run..

Sure you can supercharge a piston ported 2stroke but you only end up running 1-2 lbs of boost at the most..the end result is that a piped engine can give the same performance..you can only get a level of boost equivalent to the reversion pressure wave a pipe reflects back..any more pressure from within the engine just continues to flow out the pipe..no advantage....unless you run direct cylinder injection..then the excess intake air (which is air only, no fuel mix) can be used to more completely scavenge exh gases from the cylinder


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## average joe (Jul 23, 2005)

Here you go Erollc:http://www.mullerperformance.com/snowmobile.html#snow
Notice the boost figures of 8 and 12lbs? Turbos do work on two stroke.
FWIW I was speculating on the port timing differances of a turbo two stroke vs a traditional two stroke. I know what your saying about the engine not operating if the transfer ports opened before the exhaust port on the exhaust stroke, but these turbo kits do exist and do work.


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## average joe (Jul 23, 2005)

Here are a few more:
http://www.lako.com/turbo.html


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## klickitatsacket (Jul 23, 2005)

I love this thread. For all those who hate these types of discussions becuase all people do is argue... I love them because the ideas that are floated back and forth and the differant perspectives that people think from plant seeds of thought into my brain. Here is a what if question. What would happen then if you turbo or super charged a piston port engine knowing that you are pushing the fuel through and across the piston crown,(cooling it) and then used a pipe to stuff it back into the cylinder? Just a thought using Both perspectives. Also if the duration is too long and you are wasting too much fuel, just close up the bottom of the port and widen them or add more transfer ports to optimized the effect right before exhaust port closure. Heck you could do that with out a pipe. The pipe would though help with the scavenging if you were that tight on timing.


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## Lawn Masters (Jul 23, 2005)

While some of this is WAY over my head, its interesting. MAybe someone will try some of this stuff and see what happens.


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## average joe (Jul 23, 2005)

Its already been tried, along with almost everything else.


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## Al Smith (Jul 23, 2005)

You could do it with a direct injector. Long intake port with a tough reed on the intake. Stuff air with the blower after the piston clears the exhaust on the up stroke,inject before top dead center,hope for the best.It's all theory,who knows.I haven't quite figured out how to oil the lower end.  You would have to have a real high volume blower with a fast acting waste gate.Any thing is possible,however it may not be practical.


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## ErrolC (Jul 23, 2005)

Woo Hoo..I take it back..looks very much like they've sorted things..my experience and knowledge has been based on developments in the 80s/early 90s..things have moved along a bit since then obviously..thanks for the info and enlightenment.

The last of the Yamaha TZ fornula750 bikes for Daytona were pumping 180hp in the late 80s..race shops had tried turbos and found little performance advantage for the complexities added...a problem being the level of backpressure needed to hold the flow at the exh port as I explained.

Those turbo units must be getting reeaal small

Jeese thats a lot of hp "245" from something you'd be able to pick up..push that Canadian V8 saw...single handed if you could hold it!!!!!


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## ErrolC (Jul 23, 2005)

reading on..

Quo:System back-pressure must be kept within narrow limits if reliability and power are to be achieved..

must be a fine balancing act


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## shtoink (Jul 24, 2005)

Al Smith said:


> You could do it with a direct injector. Long intake port with a tough reed on the intake. Stuff air with the blower after the piston clears the exhaust on the up stroke,inject before top dead center,hope for the best.It's all theory,who knows.I haven't quite figured out how to oil the lower end.  You would have to have a real high volume blower with a fast acting waste gate.Any thing is possible,however it may not be practical.




You could also have a specially shaped piston top. I remember reading some info a while back that involved fuel being pumped in just before TDC and the special hollow shape on the top of the piston was designed to maximize the process and use less fuel. The piston actually had an inverted "V" shape and the hollow was on one side. The top of the piston nearly kissed the top of the cylinder. It was on a 4 stroke motor, but the principal is the same. Puff in vaporized fuel, and cram is as much air as you can after the exhaust port closed for a bunch of compression and there is a nice big bang.


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## Kneejerk Bombas (Jul 24, 2005)

ozflea said:


> This should take to another thread containing the pic's requires on the BP-1.
> 
> Mc Bob.
> 
> http://www.arboristsite.com/showthread.php?t=19072



Awesome pictures and really cool saw!

Are there many of those around?


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## Kneejerk Bombas (Jul 24, 2005)

klickitatsacket said:


> I love this thread. For all those who hate these types of discussions becuase all people do is argue... I love them because the ideas that are floated back and forth and the differant perspectives that people think from plant seeds of thought into my brain.



Me too. Fun read.


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## Al Smith (Jul 24, 2005)

*More food for thought*

What would happen if a person were to install,somehow a turbo charger with a spring loaded pressure activated discharge gate or perhaps differential pressure activated?Put the discharge directly over the carb[a big one].At start up or low rpm the saw would be natural aspirated.When the pressure came up from rpm's the waste gate would close pressurizing the crankcase etc.On the power side of the turbine,perhaps as the pressure wave decreased it may in fact reverse the exhaust enough to act like a tuned pipe.If this would work,you would still have the impulse cycle to pump the fuel,oil the bar etc,but a lot stronger pulse.In my madness I am thinking a reed valve engine would work best[Mac man ya know  ]Alas if good old J P McCulloch wouldn't have went off the deep end,he would have figured it out 30 yrs ago.For that matter,the ole boy may have and kept it secret.Oh yes,how to oil the turbine? Impulse from the bar oiler,maybe.


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## jimbo1490 (Jul 25, 2005)

Crankcase scavenged two-strokes, like the ones in chain saws, hate exhaust back pressure. That's why turbocharging is not feasible for them. Actually, all piston engines hate exhaust pack pressure, but with an Otto cycle (four-stroke with valves over the piston), the higher exhaust back pressure from the turbine side is compensated almost completely by the increased intake pressure from the compressor side, so that the engine still runs like it should, mostly anyway. There are still some changes, like the need for shortened overlap of intake and exhaust events and shortened exhaust duration, generally. But these changes are easily made and can mitigate most of the problems that exhaust back pressure would normally cause. 

The Otto-cycle engine depends somewhat less on the kinetic energy of its operating gas to charge and scavenge the cylinder than the crankcase-scavenged two-stroke. A crankcase-scavenged two-stroke uses a gas at a low pressure and depends mostly on velocity to get the charging/scavenging jobs done. An Otto cycle can vary the proportions of pressure and velocity to suit diffierent conditions, by changine valve timing. This can be changed somewhat with a two-stroke with port timing, but not nearly to the same extent, and the adiabatic losses will always be greater since the two-stroke engine favors a low-pressure/high-velocity type of flow.

On top of all this, the crankcase-scavenged two-stroke engine has lower peak exhaust temperatures. The turbine is essentially a heat recovery device, so with less heat available in the exhaust, the turbine has less waste heat to work with and consequently spins slower. In selecting a turbo, when it is found that a particular turbo will spin too slow, the general solution is to install a smaller unit, or one with a more restricted turbine inlet (lower A/R ratio). But this produces more back pressure, possibly compounding the problem.

Both port uniflow (Cooper-Bessemer, Fairbanks-Morse, etc.) and valve uniflow (Detroit Diesel, EMD) use turbocharging successfully. Note that these engines ALWAYS use pressure aspiration with a positive displacement pump as part of their design, even when a turbocharger is not used. So when a turbocharger is used with a uniflow two-stroke engine, it still has a seperate positive displacement scavenging pump, so it has both a turbocaharger and a supercharger. These engines will not run without pressure aspiration as there is no scavenging/charging force otherwise.

Crankcase-scavenged two-stroke engines have been successfully turbocharged, but success depends on the ability to carefully match the turbo unit with the correct event timing. In an Otto cycle engine, you can easily make even very radical changes to the event timing by simply changing camshafts. It's not nearly that easy with a crankcase-scavenged two-stroke; you wind up havig to make new cylinders.

Crankshaft-driven supercharging can be more easily adapted to small two-stroke engines, but lacks the advantage of consuming some engine output to drive the pump, whereas the turbo uses waste heat from the exhaust. This is not a trivial amount of power; in a truck diesel engine for instance, more than 50HP is dissipated across the shaft of the turbocharger, so a shaft-driven supercharger of similar capability would have to subtract that kind of power from the crankshaft to get the job done. 

Jimbo


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## jimbo1490 (Jul 25, 2005)

Sylvatica said:


> shtoink,
> Aren't those pics of the assembly of that GIANT Sulzer marine Diesel awesome?! I've seen them before and I'm still amazed by that degree of engineering and power.



If you liked those, the check this monster out!

http://www.lexcie.zetnet.co.uk/delticengine.htm

This is port uniflow since there are not poppet valves, only piston ports with one intake piston and one exhaust piston running in each cylinder.

Jimbo


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## jimbo1490 (Jul 25, 2005)

Al Smith said:


> What would happen if a person were to install,somehow a turbo charger with a spring loaded pressure activated discharge gate or perhaps differential pressure activated?



Or how about a device that timed the exhaust pulses to compress intake air and then supply it to the intake side at precisley the right moment:


http://www.kfz-tech.de/ComprLader.htm

I could not find one English language page with a picture or diagram this good; I hope it will be worth a thousand words  

Jimbo




Jimbo


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## CNYCountry (Jul 25, 2005)

TimberPig said:


> Nitrous is a way of adding more oxygen to the air fuel mix rather than a true form of forced air induction. Turbocharging or supercharging aim to flow more air through the motor by packing more air/fuel mix into the chamber and burning it.



Right, that's more correct than the generalization than I posted, I thought nitrous did something to the density of the air as a function of cooling it or something also?


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## t_andersen (Jul 25, 2005)

I used to work with design of large MAN/B&W ship diesel engines. The principle of turbocharging is to make the engine "believe" that it lives in denser air with a pressure of, say, a couple of atmospheres. The engine sees a thicker air on the inlet side and at the exhaust ports. Because of the thicker atmosphere, you can burn, say, twice as much fuel in the same cylinder. As also noted by "Stihl 041" above, this calls for better cooling plus a lot of other stuff. Seems hard to do on a chain saw...


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## DanMan1 (Jul 25, 2005)

How about trading in the cost, weight, bulk, and complexity of a turbo saw engine for simply more CC's??  I know, I know... that's no fun.


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## Al Smith (Jul 25, 2005)

DanMan1 said:


> How about trading in the cost, weight, bulk, and complexity of a turbo saw engine for simply more CC's??  I know, I know... that's no fun.


I think you are on to something.


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## ErrolC (Jul 26, 2005)

DanMan1 said:


> How about trading in the cost, weight, bulk, and complexity of a turbo saw engine for simply more CC's??  I know, I know... that's no fun.



Thats a bit radical..maybe a motorcycle motor...maybe a smal GP engine..say 125..or even a 500mx..or even a V8 ..baby!

Horsepower=heat..pac more into a smaller package and things get hotter..anyone tried shielding the hot bits from the hot stuff..say, ceramics could work..or is my thinking twisted 

A point to account for in small turbos is the smaller they get, the faster they have to spin to get comparable boost..everyone remember the CX500 Honda..2" turbo impeller (200k rpm full boost)..bearings and oils begin to have a problem at these speeds and thats with 250cc cylinders feeding..perhaps ceramics again!! Then again I've been out of the picture for a while, playing catch up.


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## average joe (Jul 26, 2005)

> You could do it with a direct injector. Long intake port with a tough reed on the intake. Stuff air with the blower after the piston clears the exhaust on the up stroke,inject before top dead center,hope for the best.It's all theory,who knows.I haven't quite figured out how to oil the lower end. You would have to have a real high volume blower with a fast acting waste gate.Any thing is possible,however it may not be practical.


The Krauts beat you to the punch, AL. They had a aircraft engine of simualr design in the 30's.
In regards to pison shapes for DI, 2 stroke engines. The one that I have seen has a small bowl with a cone shaped device in it design to take the injection plume and diffuse it. As for lubrication. These no DI 2 stroke outboard engines use a injector type sytem that has lines or ports so as to direct the lube directly to the bearings, and pistons, etc. The use much less oil than usual because there is no fuel dillution and the oil is directed to the exact areas needed.


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## drmiller100 (Dec 3, 2006)

t_andersen said:


> The principle of turbocharging is to make the engine "believe" that it lives in denser air with a pressure of, say, a couple of atmospheres. The engine sees a thicker air on the inlet side and at the exhaust ports. Because of the thicker atmosphere, you can burn, say, twice as much fuel in the same cylinder.



resurrecting an old thread, the above exactly describes why a turbocharger cna work very effectivelyl on a 2 stroke, and why a supercharger has such a very hard time.

I built a supercharger for a 2 stroke snowmobile. I learned a LOT doing it. I believe I am one of the very few to ever add a supercharger to a 2 stroke and have it end up making more horsepower when done. But when all done, it was very incremental gain. The secret was to plug the exhaust to build boost, counterintuitive at first.

Turbos by definition build back pressure as a function of front pressure, which is circular logic, and brings us back to t_anderson's excellent description of how to think about it.

Also, on sleds, you need to think big. stock 800cc's is 150 horsepower. If you want to add a turbo to one of these, the Holset turbo off of a dodge cummins is a good size to start with. 
all that being said, turbo or supercharging a saw seems pretty counter intuitive.

-doug


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## blis (Dec 3, 2006)

drmiller100 said:


> resurrecting an old thread, the above exactly describes why a turbocharger cna work very effectivelyl on a 2 stroke, and why a supercharger has such a very hard time.
> 
> I built a supercharger for a 2 stroke snowmobile. I learned a LOT doing it. I believe I am one of the very few to ever add a supercharger to a 2 stroke and have it end up making more horsepower when done. But when all done, it was very incremental gain. The secret was to plug the exhaust to build boost, counterintuitive at first.
> 
> ...




Just that the biggest problem with turbo´ng chainsaw is that they are too small for almost any kind of turbo to kick-in and even with turbo small enough to work, it still would need oil circulation etc... and in the end it would weight too darn much to be usable... hotsaws are different thing thou...

off-topic, how much hp´s you got out of your sled with turbo?? i´ve myself seen a rotax kart with 500 or 600 engine turboed, man, it was fun thing around ~150hp and tons of burnt rubber :hmm3grin2orange:


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