Chain saw with forced induction

[heathkiks]

Turboing, Supercharging, or other forced induction of any kind is not new with 2-strokes... Take a look into the snowmobile arena. Weight will be the largest factor, unless you use space age materials making it cost prohibitive. I can gaurantee that all manufacturers are aware of the posibilities that forced induction brings.

edit: That being said, the possibilities are only as good as ones imagination. Good luck!

 

[rmihalek]

Maybe the wave of the future chainsaw will be a supercharged or turbocharged, piezoelectric cooled 4-stroke? I believe Timberwolf's point about too much intake pressure in a 2-stroke is the key: at some point of increasing crankcase pressure, you're just going to end up blowing more raw fuel into the exhaust.

The resonance in a tuned pipe is pure genius: have the negative pressure wave draw additional charge through the engine, then return that charge with a positive pressure wave back into the jug before the piston closed the exhaust port. All done with no moving parts (well, except for the molecules).

 

[cwpoulan250a]

Maybe the wave of the future chainsaw will be a supercharged or turbocharged, piezoelectric cooled 4-stroke? I believe Timberwolf's point about too much intake pressure in a 2-stroke is the key: at some point of increasing crankcase pressure, you're just going to end up blowing more raw fuel into the exhaust.

The resonance in a tuned pipe is pure genius: have the negative pressure wave draw additional charge through the engine, then return that charge with a positive pressure wave back into the jug before the piston closed the exhaust port. All done with no moving parts (well, except for the molecules).

i see pulling the fuel through the engine with the charge from the pipe to be a useful thing but..... i just wanted to try something new
it seemed that all of my saws are restricted by small carbs and an inability to pull their full potential of fuel into the engine
so adding a positive pressure on the intake made sense at the time
being restricted on the intake side is hard to fix from the exhaust

 

[2000ssm6]

Good idea and one heck of a way to "think outside the box". I would not say you are wasting time but as mentioned porting and a pipe would be time better spent if the end goal is power. Check out some of your local GTGs or saw races, run a pipe saw. I'll bet you will change your mind and start to learn porting and pipe building. A saw that has been ported to run with a matched pipe, runs like a turbo car. Get one in your hands, you will see.

 

[cwpoulan250a]

Good idea and one heck of a way to "think outside the box". I would not say you are wasting time but as mentioned porting and a pipe would be time better spent if the end goal is power. Check out some of your local GTGs or saw races, run a pipe saw. I'll bet you will change your mind and start to learn porting and pipe building. A saw that has been ported to run with a matched pipe, runs like a turbo car. Get one in your hands, you will see.

i have ported 2 strokes and run pipes on them before
that was to easy
and the pipes always seemed to get in the way when i was in the woods
i want the power and torque but inside the chain saw case i started with

i have a 1980 IT175g that has been bored, ported, piped, and jetted
standard it ran 14hp
now it is right close to 22hp
piping and porting is all well and good but i just want to try a small turbo

 

[ironman_gq]

not too many turbo 2-stroke sleds but lots of 4-stroke ones. However a whole lot of supercharged 2-stroke detroit diesels out there still pulling trailers. I like this idea and once saw a gut who built a turbo powered yamaha blaster with a turbo out of a 2.2L van. I think he ran without a wastegate with something close to 20lbs of boost. not sure how it all ended up working but it did work at least for a little bit.

 

[timberwolf]

and what is wrong with trying???
new stuff is fun and tuned pipes are hard to manage
they are big and not exactly easy to keep with in the confines of the saw
my idea will fit inside the existing saw case and will hopefully work just as well as a tuned pipe
i don't mind u saying don't "waist your time" but it's people like you that really help me do incredible stuff

Yes, nothing wrong with trying... but when you're trying to do something many many others including manufactures and pro racers have decided was not worth doing. Then it is likely your time could be better spent on more conventional efforts. However, in the long run, learning that something does not work is just as importaint as learning what works. Just a bit more of a round about way to get there.

Honestly though, puting a custom turbo on a saw will prove to be far harder to manage than a tuned pipe. This is certainly one of these devil's in the details problems.

One of the hardest things to accept in the world of moddifying engines is that all the good ideas have been tried already and if you don't see it being done by others there is going to be a very good reason why. Where its at is using the good ideas out there then refine and combine them.

Anyway have fun, keep us posted. Maybe get some good video of the saw with just a full muffler mod in a little more substantial wood then if/when you get the turbo going you will be able to clearly document what gains were made.

 

[drkptt]

if you think about it the fuel and oil in the intake side won't burn
what happens when a saw doesn't have enough compression??
it won't run because the gasses aren't compressed enough
so being that the gas and oil on the intake side of the turbo aren't under 100psi of compression it won't burn
that is just my thinking

If that's true what causes a backfire in the intake?

Unrelated to that, when you continue working with forced induction you should put a boost gauge in the intake to see what you're getting. You could make a simple water manometer to do it.

 

[drkptt]

not too many turbo 2-stroke sleds but lots of 4-stroke ones. However a whole lot of supercharged 2-stroke detroit diesels out there still pulling trailers.

I believe those are uniflow 2-strokes with exhaust poppet valves that can be closed while transfers are open so boost can increase cylinder pressure, unlike piston-ported exhaust. I think they might also be blower scavenged--ie: wet sump and intake airflow not pumped by crankcase compression.

 

[heathkiks]

Fifteen years ago one never heard (I hadn't anyway) of a turboed or supercharged 2-stroke snowmobile. Now there are dozens of companies producing kits that are even intercooled and taking up less space than ever before. Supercharging a 2-stroke has obvious hurdles to overcome including exhuast issues, but turboed 2-strokes have a significant following and growing.

To get a better grasp of the concept I would research that area before tackling the issue by yourself. There is a wealth of information out there that I can not even start to explain on here.

 

[cwpoulan250a]

If that's true what causes a backfire in the intake?

Unrelated to that, when you continue working with forced induction you should put a boost gauge in the intake to see what you're getting. You could make a simple water manometer to do it.

i don't know how to make a manometer
but i can figure it out mathematically

if you jet the carb/ tune it right it shouldn't ever "back fire" it may pop out the exhaust but i don't believe a 2 stroke that is crank case driven will ever back fire
if it was split like my dirt bike motors ( 25% of the fuel air mix goes directly in to the cylinder and 75% goes into the crank case) i know that will back fire

 

[2000ssm6]

i have ported 2 strokes and run pipes on them before
that was to easy

You should get into building race saws then. Get a good rep and you could make some nice $$$$.

and the pipes always seemed to get in the way when i was in the woods
i want the power and torque but inside the chain saw case i started with

Good point here but most don't use their pipes in the woods to work. I don't see a turbo and all the related hardware needed being much less cumbersome. You have my attention though. I remember using a zero turn mower that had a small turbo diesel engine. Never seen a turbo that small. That thing had some power...

 

[stihlkicken]

just want to pet the rabbit george.

force all the air you want to thru a 2 stroke, watch the air leave where it wants.

 

[timberwolf]

i don't know how to make a manometer
but i can figure it out mathematically

A manometer is dead easy, its nothing more than a tube filled with water held vertically or on an incline to measure air pressures in inches of water. It will be perfect to measure the slight pressures the fans will generate. If you start to get some real pressure going then you will want a boost gauge.

Off the top of my head there are 27.7 in of water per psi. so you gan get quite accurate with a manmeter but even to measur 2 psi you need about 5 feet of water in a tube.

 

[olyman]

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.....

fact!!!

 

[olyman]

Diesel turbos run much slower than a gasoline engine turbo. Gas burns much hotter too. [ QUOTE]

mmm,NO--

 

[olyman]

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.

yup!!!!!!

 

[sachsmo]

Didn't take the time to read this whole thread, and if it was mentioned,,,,,excuse me.

By nature a two stroke is already force inducted.

As the piston travels downward, it compresses the gasses in the crank case, (probably the reason for crank case stuffers)

As the gasses enter the ports they are at a greater pressure,,,,,,

Two strokes are Kewl!

 

[timberwolf]

In a way yes, but because piston induction is a positive displacment system that works on partial vacuum without intake or exhaust tuning it can not charge the cyliner such that the volumetric efficiency =/>1. In simple terms the cylinder will never contain a greater volume of freash charge than it's physical swept volume. Typically volumentric efficiency is much less, getting the cyliner filled 60-70% is likely optimistic even in power band on a pro quality stock saw. With some muffler and intake work like on a stock appearing racer saw and it is possible to get close to 100% filling Add a pipe and filling to closer to 150% is in theory possible.

 

[drkptt]

if you jet the carb/ tune it right it shouldn't ever "back fire" it may pop out the exhaust but i don't believe a 2 stroke that is crank case driven will ever back fire

You missed my point entirely. You claimed that there was no safety issue with running air/fuel mixture through a turbo because it cannot burn until it is compressed. A backfire is proof that the mixture can burn at intake pressures.