Chain saw with forced induction

[timberwolf]

Biggest problem with a pressurised intake is that the carburetor uses the partial vacuume created by the venturi to draw fuel in. Once you put enough boost on the intake to do much you will stop the flow of fuel into the engine and run it lean.

Yes a two stroke can be set up to work as a turbo or super charged engine, but it will require a pressurized fuel system that will be easiest to achieve with fuel injection.

Far far more to be gained by using a tuned pipe. But befor that more can be gained with good shapening and basic porting.

 

[PLMCRZY]

The turbocharger idea isn't too far fetched. They are in use in aftermarket form on two strokes from quads like Banshees to radio controlled cars. Rather spendy though...

Piping, oil sump, oil lines. The banshee has oil going thru the trans so its easier, rc cars i think are supercharged i have never seen a turbo kit for them. I had a supercharger on my Tmaxx back in the day it was ok.....

 

[ironman_gq]

regular atmospheric pressure is 14.7psi so roughly 15psi of boost will double the amount of air in the cylinders assuming an optimized intake and porting. Most bolt on combos only use 5-7psi of boost to keep the engines alive and warranty claims down. I have seen diesel rigs modded and running over 150psi of boost but usually only on pulling trucks.

 

[madhatte]

Knew a guy once put a leaf blower on the intake of an old Chevy pickup. Had some kind of jerry-rigged linkage for boost. It worked pretty well... for about a half-mile, before first the leaf blower and then the engine burst into flames. The truck burned to the ground. Not sure exactly what went wrong. Oh, well.

 

[timberwolf]

The venturi effect in a carburetor is the only thing drawing fuel into a simple saw type engine. This draw is only at a pressure of inches of water (well less than 1psi). if you place more than that on the intake it will stop fuel from flowing into the engine and the engine will sieze in short order.

An EFI car engine can deal with the boost better because the fuel is injected at pressure and the O2 and MAF sensor as well as fuel map will accomodate the additional air flow by delivering more fuel.

 

[drkptt]

The venturi effect in a carburetor is the only thing drawing fuel into a simple saw type engine. This draw is only at a pressure of inches of water (well less than 1psi). if you place more than that on the intake it will stop fuel from flowing into the engine and the engine will sieze in short order...

If you can apply the positive fan pressure to the outside of the metering diaphragm then the carb can still draw fuel. That could be done by putting the whole carburetor in the airbox, for example.

 

[drkptt]

why dont they modify the flywheel cooling fan so a divided or split housing pushes filtered air into the carby , it would not need to be that large and the boost would increase with revs and a spring loaded flap could limit boost to a reasonable pressure , even a few pounds of boost should give a large increase in torque . is it too hard to seal a separate fan

The maximum static pressure that the centrifugal cooling fan can generate is in the order of a few inches of water (fraction of a psi).

 

[Coloradobum]

Turbos are not meant to run for long periods of time. Adapting one to a chainsaw while keeping the weight down and keeping the engine/turbo from burning up would be a serious technical challenge. For a short race saw type demo it could be made to work. For an everyday chainsaw where you might hold it full throttle for 20 seconds, take a 5 second pause, and go another 20 seconds FT I foresee big problems.

Good for him for fiddling around though. My first mechanical project was figuring out how to bypass the governor my dad put on my minibike. That took about 2 seconds. Then the cops pulled me over (deadend country road). Asked me for my license (I was about 7 years old). I said sheepishly "I don't have one". Cop must have been LOL on the inside but he played it real stern and sent me home. I was so relieved, thought I wuz going downtown for sure :monkey:

 

[timberwolf]

If you can apply the positive fan pressure to the outside of the metering diaphragm then the carb can still draw fuel. That could be done by putting the whole carburetor in the airbox, for example.

Yep, I have done just that it would be exactly like tricking the intelicarb on the stihls to think the filter was casuing a negative restriction and adding more fuel. You still are limited to the 3-4 psi the fuel pump makes and tuning becomes difficult.

The problem with running the air over the flywheel is that it heats the air alot, and actually more air density is lost due to heating than is gained by pressurizing it. The Husky "Turbo" air induction system produces about 0.3 inches of water = 0.01 psi. Now there is a joke as it heats the air up a good 10f causing more harm than good.

Turbos sure do run at full duty cycle ask any heavy truck driver out there.


Its a cool idea and all but if you want to turbo charge a chainsaw build a tuned pipe. That is how the problem has already been solved.

 

[PLMCRZY]

regular atmospheric pressure is 14.7psi so roughly 15psi of boost will double the amount of air in the cylinders assuming an optimized intake and porting. Most bolt on combos only use 5-7psi of boost to keep the engines alive and warranty claims down. I have seen diesel rigs modded and running over 150psi of boost but usually only on pulling trucks.

I will hit 45psi in my truck thats pushing it for stock headstuds. Stock diesel engines usually hit around 25psi, gasoline engines cant take that much boost so even 4psi in some applications is alot.

 

[PLMCRZY]

Turbos are not meant to run for long periods of time. Adapting one to a chainsaw while keeping the weight down and keeping the engine/turbo from burning up would be a serious technical challenge. For a short race saw type demo it could be made to work. For an everyday chainsaw where you might hold it full throttle for 20 seconds, take a 5 second pause, and go another 20 seconds FT I foresee big problems.

Good for him for fiddling around though. My first mechanical project was figuring out how to bypass the governor my dad put on my minibike. That took about 2 seconds. Then the cops pulled me over (deadend country road). Asked me for my license (I was about 7 years old). I said sheepishly "I don't have one". Cop must have been LOL on the inside but he played it real stern and sent me home. I was so relieved, thought I wuz going downtown for sure :monkey:

That is not true at all, most turbos on semis especially, are boosting the entire time. When i cruise at 70mph im usually from 5psi to 10psi, depending on hills. Turbos are made to spin, infact they always spin.....

 

[Knuckles]

He's got the right idea, just the wrong side of the carb. A chainsaw would benefit from a supercharger, not a turbo.

I've seen guys at the hobby shop run miniature belt driven ones on their nitro r/c's with good success. It wouldn't be so hard to hook one up to a chainsaw.
You want to discuss tiny basic carburetors?

We just need you guys with machining experience to step up to the plate

Imagine the power:chainsawguy:

 

[Terry Syd]

Brian, that is something I hadn't considered - that the Husky 'Turbo' air induction would raise the temperature of the intake air. Has that 10F rise been measured on a saw?

Running a 10F temperature rise through an air density calculator, I get close to a 2% drop in air density.

http://www.denysschen.com/catalogue/density.asp

Since the 'air box' on a Husky isn't sealed (holes for adjusting carb, etc), there is no pressure rise from the system, only a pressure drop due to heated air. That's a fair penalty to be paid for having a bit cleaner air to the air filter.

Edit: It should be fairly easy to quantify any drop in power by simply removing the airbox cover and doing some cookie cutting with and without the cover in place.

I also note that the 'bleed' of intake air off of the flywheel, is air that won't be flowing across the engine. The hotter a two-stroke gets, the less charge density it has in the cylinder. That may be noticeable during extended cutting.

Crikey, I may block off the 'air injection' feature and drill a few holes in the air box.

 

[PLMCRZY]

He's got the right idea, just the wrong side of the carb. A chainsaw would benefit from a supercharger, not a turbo.

I've seen guys at the hobby shop run miniature belt driven ones on their nitro r/c's with good success. It wouldn't be so hard to hook one up to a chainsaw.
You want to discuss tiny basic carburetors?

We just need you guys with machining experience to step up to the plate

Imagine the power:chainsawguy:

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.....

 

[galde]

Could the output of the alternator of a saw with heated handles be used to drive a suitable fan?

 

[RPO-L78]

Biggest problem with a pressurised intake is that the carburetor uses the partial vacuume created by the venturi to draw fuel in. Once you put enough boost on the intake to do much you will stop the flow of fuel into the engine and run it lean.

Yes a two stroke can be set up to work as a turbo or super charged engine, but it will require a pressurized fuel system that will be easiest to achieve with fuel injection.

Far far more to be gained by using a tuned pipe. But befor that more can be gained with good shapening and basic porting.

Thinking draw through type. Any thoughts?

 

[RPO-L78]

Piping, oil sump, oil lines. The banshee has oil going thru the trans so its easier, rc cars i think are supercharged i have never seen a turbo kit for them. I had a supercharger on my Tmaxx back in the day it was ok.....

Micro Boost makes or markets both belt and exhaust driven versions.

 

[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.....

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

 

[timberwolf]

Edit: It should be fairly easy to quantify any drop in power by simply removing the airbox cover and doing some cookie cutting with and without the cover in place.

Crikey, I may block off the 'air injection' feature and drill a few holes in the air box.

I had a guy at a race ask if he could borrow some duct tape, he taped the heck out of the top cover of his turbo husky to try to seal up the air pressure. He suggested that I might tape the holes up in my covers. LOL, After the race he came over to ask why it was such a good idea to drill the crap out of the top covers over the area that may or may not have been occupied by an air filter.

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.

Sure if you want to go flow through then that makes the carb fuel system work easier but there are fuel problems to deal with in compressing a fuel air mixture is going to start dropping fuel out of suspension. Not that it can't be done its just that there is a much easier lower tech solution tried and tested.

 

[Coloradobum]

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?