Chain saw with forced induction

[timberwolf]

Many 4 cylinder gas cars now use turbos that can run many hours at a time hiway driving.

True most industrial diesel turbos may only spin 50,000-70,000 RPM while gas may go over 100,000. But the turbos they put on the small diesels like VWs can easily put out over 150 hp from 2 liters and those turbos see EGT teperatures much more like those from a gas engine, they also have variable geometry so so have spool up measured in fractions of a second.

I have 2 turbo diesel cars in the yard with a total of over half a million kilometers on them done nothing more than ajust the waste gate. Before that I had a gas turbo volvo which went over 400,000 with one rebuilt turbo.

 

[PLMCRZY]

Diesel turbos run much slower than a gasoline engine turbo. Gas burns much hotter too. If there's a continuous duty turbo for small gasoline engines I've never heard of it. I'd love to see one though, anyone have an example?

I dont think you have any idea of what your talking about. A diesel turbo makes more then double the boost a gas engine does.

 

[PLMCRZY]

Nitrous enables the burning of additional fuel. Thus the need even on carbureted applications for fuel solenoid opening in unison with nitrous solenoid.

I realize that, carbed v8s do why cant a small chainsaw do it.....

 

[drkptt]

YOU GUYS ARN'T LISTNING

A TUNED PIPE TO A 2 STROKE SAW IS WHAT A SUPER CHARGER IS TO A 4 STROKE.

Here are a few graphs of a 361 stihl muffler vs pipe on pump gas, on muffler the cylinder only sits at about 1.1 bar when the exhaust port closes, pipe moves it up 0.2 bar, also the pipe puts an extra 0.2 bar pressure in the crank case to help with transfer flow and nearly a -0.4 bar draw on the transfers. Also it puts an extra 0.2 bar draw on the carb. This works out to 2 to 5 psi working at both ends.

I'm listening--of course a tuned pipe is the elegant solution for 2-stroke. No moving parts vs a blower?--it's a no-brainer.

Note that you'd never get the high-boost power gains from a supercharged 2-stroke that you do from a 4-stroke. At high boost you'd be pushing a lot of air/fuel mixture out of the exhaust, which would give you great scavenging and no dilution of the trapped charge with exhaust gas. But after a point you can't increase the charge density because you're pushing air into the engine when the exhaust port is open. And when the transfers close your blower isn't pushing air at all--but the cylinder pressure is leaking down until the exhaust closes.

Yes, you'd see some power increase with a blown 2-stroke. But once you got to a few psi boost, doubling it would only waste fuel.

timberwolf: Those plots look like computed models and not measured data. Do you know anything more about their source?

 

[timberwolf]

NOS on a saw possible? yes. But IMHO the gains are not worth the trouble an there are other simpler ways to get the same kind of power.

 

[timberwolf]

timberwolf: Those plots look like computed models and not measured data. Do you know anything more about their source?

Yes computer models as for the source my C: drive. Both saws I built and tested and I have a fair degree of confidence that the plots are fairly representative of the actual performance gains I observed and spot measurments I have made of pressures through the engine.

 

[drkptt]

Yes computer models as for the source my C: drive. Both saws I built and tested and I have a fair degree of confidence that the plots are fairly representative of the actual performance gains I observed and spot measurments I have made of pressures through the engine.

Can you explain the last plot; what's 'inflow' and 'outflow' and where the theoretical pressure taps are?

 

[RPO-L78]

I had a supercharger on my rc truck it was this kind

It ran better but when i put it on i knew nothing about these little engines and it was low on compression and finally bit the dust. I swapped the supercharger for a brand new OS .15cvr i believe it ran great until i sold it.

Screw the supercharger, i would throw a bottle of nitrous on it.....

NOS on a saw possible? yes. But IMHO the gains are not worth the trouble an there are other simpler ways to get the same kind of power.

I'm not trying to be an armchair quarterback. I realize the experience gap between us, therefore knowledge gap. I should have explained or said more clearly, the added weight and bulk of components required to use nitrous would relegate the attached saw to specialized use. I don't mean to infer I know what is the ultimate power adder on a saw. I've read about and watched video of the most efficient placement of exhaust outlet to propel a turbo on tuned expansion chamber pipe mounted on 2 stroke powered RC cars. I don't know if a properly tuned, ported and piped version would have provided more power or vice versa .

 

[Coloradobum]

I dont think you have any idea of what your talking about. A diesel turbo makes more then double the boost a gas engine does.

Boost pressure is dependent on more variables than just speed. Diesel turbos do in fact spin slower (generally speaking). I'm not a turbo expert but no one has been able to give an example of a small, continuous duty gasoline turbo. In case I wasn't clear, what I claimed was that a turbo of that type would be heavy due to the necessary cooling system, etc. A car engine turbo, even for a four cylinder, is of a totally different scale than what you'd use on a 50-100cc motor.

 

[timberwolf]

Can you explain the last plot; what's 'inflow' and 'outflow' and where the theoretical pressure taps are?

Inflow would be at the exhaust flange which would be the interesting one, outflow at the stinger.

The last plot is different than the muffler plot just a software thing, when running a boxed muffler the software just looks at it as a single space, when running it as a pipe it looks at the exhaust in more detail along the length of the pipe.


As far as gas turbo engines there should be more than enough to convince that they are well used in automotive industry and have been for decades. Obviously under hiway conditions they will run for hours and are always spinning for hundreds of thousands of miles...
http://en.wikipedia.org/wiki/Turbocharger

 

[Coloradobum]

Sigh. Think maybe there's a reason they don't use turbos on chainsaws? Or mx bikes? Or ultralights? Just maybe those engineers know something? You can NOT say that because turbos work on a car engine they would work on a saw. I for one don't care to lug around a liquid cooled saw. I'd love a manufacturer to prove me wrong.

 

[timberwolf]

Exactly, same said for super charges. Thats why 99% of the time you see tuned freaking pipes on high output 2 strokes....light, simple, cheap and effective.

Another thing to think of in a saw is thermal limit, some of these air cooled motors are working pretty close to their 100% duty cycle thermal limit as it is, add much boost be it from a turbo, super charger or good old tuned pipe and the piston will want to become one with the cylinder.

:chainsawguy:

 

[drkptt]

Sigh. Think maybe there's a reason they don't use turbos on chainsaws? Or mx bikes? Or ultralights? Just maybe those engineers know something? You can NOT say that because turbos work on a car engine they would work on a saw. I for one don't care to lug around a liquid cooled saw. I'd love a manufacturer to prove me wrong.

This is the general statement you made that has been disputed, not the feasibility of turbocharged chainsaws:

Turbos are not meant to run for long periods of time. :

 

[PLMCRZY]

Boost pressure is dependent on more variables than just speed. Diesel turbos do in fact spin slower (generally speaking). I'm not a turbo expert but no one has been able to give an example of a small, continuous duty gasoline turbo. In case I wasn't clear, what I claimed was that a turbo of that type would be heavy due to the necessary cooling system, etc. A car engine turbo, even for a four cylinder, is of a totally different scale than what you'd use on a 50-100cc motor.

A turbo is a turbo, the stock turbo on my truck is a popular choice for a honda civic, etc. Diesels have more volume as far as exhaust gases which is going to turn the turbo faster thats why they make more boost. You cant tell me that the same turbo off of my truck is gonna spin faster on a gas engine only making 6 psi of boost.

 

[stihlkicken]

conundrum.

sorry if I seem stupid,but isnt forced injection completely opposite from basic 2 stroke therory?would forced air be blown thruogh all ports?

 

[dingeryote]

:hmm3grin2orange::hmm3grin2orange::hmm3grin2orange:

A Kid with a wild thingy and some RC toy parts, done started somethin'.....LOL!!

I love this place!

Stay safe!
Dingeryote

 

[discounthunter]

how about instead of forcing that air down the carb its blown across the cylinder,then one could grind of the cooling fins on the flywheel,taking work of the motor plus cooling down the cylinder would increase power and engine longitivity.

 

[WVshooter]

OK, Ok, Ok. As it turns out, some manufacturers have beat us to the punch here. They've got engines powering their saws with turbo or superchargers and they're made with longevity in mind. I found one of them here. It seems to have a few other neat features, too.
:biggrinbounce2:

 

[ironman_gq]

Ive seen some pretty small turbos including one that I think had like a 13mm inductor. Made for continuous duty on I think a cart engine, going from memory here so I might be a little off. Its not a problem to make a small turbo last a long time with the new ceramic bearings and synthetic lubes look at all the little european cars under 2L that are turbo'd and go for a couple hundred thousand miles without too much trouble.

 

[timberwolf]

I found one of them here. It seems to have a few other neat features, too.

I like the idea of a saw with skylight and USB port. :hmm3grin2orange:

look at all the little european cars under 2L that are turbo'd and go for a couple hundred thousand miles without too much trouble.

yup, they are pretty amazing, esp the variable geomettry one where the vanes can move to control boost. No more waste gate, to more need to wait for spool up. Hit the throttle and a little actuator sets the pitch on the vanes and boost jumps in a fraction of a second. Pretty nutso concept though of movable vanes spinning around in there at well over 50,000 RPM, yet they can run maintenance free for hundreds of thousands of miles if the engine oil is kept in good shape.