Forced-induction on a saw?

[beingeasy769]

I would like some feedback on a forced-induction saw motor. Use a larger saw, 80+cc, and use a very small turbo, perhaps from a small Kubota turbo diesel. The lag would be severe, but once the revs got past 6000rpm or so, the boost would take over. Also,a small nitrous container (the ones used to charge whipped cream dispensers) could be used to cool the turbo piping for brief periods of time. I believe with proper porting, a correctly tuned expansion pipe, 109 octane, and a high discharge coil, a 15HP 85cc saw could rule the world. ANY SUGGESTIONS!!?

 

[ckelp]

well this has been hashed over before, it won't work
basically an expansion chamber acts as a super charger..

 

[beingeasy769]

Ahhh, but I disagree. It doesn't aView attachment 265924ct as a supercharger. A supercharger forces air in, expansion chamber uses echo-reverberation to to minimize air-fuel escaping from the exhaust during scavenging. What about the nitrous?

 

[watsonr]

You haven't address the issue of fuel, nitrous requires extra fuel.

 

[Uncle John]

I would guess it's possible, but not practical.
It'd be fun tho!

Saw Races- AA/Gas class................:msp_thumbup:

 

[cpr]

You haven't address the issue of fuel, nitrous requires extra fuel.

As does a turbo. Fat enough on boost would never idle. Delivery curve isn't linear.

 

[sawfun9]

Why bother with nitrous oxide, just use nitromethane. It carries the air with it. The more you add the better and cooler it runs. That's why top fuel engines evolved to use such large quantities of it.

If your gonna put more air in, then you need more fuel. That would require a separate fuel pump, with a known fuel curve, that would match the fuel type and amount you are going to ATTEMT to run.

Then you have to deal with what static compression ratio you need and sometimes radical igniton timing changes.

You could try gunpowder as well but that's probably better suited to a non 4-mix 4 stroke. I tried it with a 3hp Briggs (too low compression) and got some interesting results that were about what you might expect with slow and fast burning fuels. Fast pistol powder behaved more like gasoline (a quick flash with less spark and compression required) and slow rifle powder behaved more like diesel or nitro. The slow stuff needed more volume and energy (spark amperage and compression) into it to get the power out of it.

 

[tpope]

Ya reckon that one could use a computer on an Auto Tune to inject extra fuel?

 

[sawfun9]

It depends on the programing algorithm of the Autotune. I'm guessing were talking about a lot more fuel than that is meant to cover. But your on the right track. A computer is essential to cover the fuel spikes that WILL occur with an unknown supercharging application and even a few known ones. Maybe it would be known as Super Autotune or Autotune II or something like that.

 

[cpr]

Also, particularly with a turbo, you won't get as much cylinder pressure because the transfers and the exhaust are open at the same time. The case will be pressurized, but then you'll have hp loss by the piston trying to blow down the case. Also, you have only one pressure pulse driving the charger at a time. It can be done, but I wouldn't expect much more than a couple of pounds of manifold pressure. Oh, and if you're blowing through the carb, you'll need to increase fuel pressure with boost so it keeps feeding.

Nitromethane/methanol mix with a pipe would be far easier.

 

[Scooterbum]

Why not a dual carb setup with the second using a vacuum control setup similar to a 4 barrel with vacuum secondaries. Additional fuel would be supplied on demand.

 

[jeepyfz450]

Anything can be done absolutely anything.......... Forced induction just wouldnt be the easiers way to make big power. as stated above i think the fuel delivery would be the greatest feat to overcome (when building boost). you can buy mini-turbos. it would be cool to hear your saw whistling.

Now nitrous that would be fun. have a 2 hp shot for those long pulls on the butt log...... here again fuel delivery will be the issue.

A buddy of mine once said "you gotta eat if you want to poop"

 

[bluestripes]

How you planning on lubing the turbo? Plus most small diesles dont run over 4000rpms if that and the turbo spins somewhere around 140,000rpms. Wouldnt it spin about threes times that fast on a saw? I wonder if it would stay together? It would be cool if you could get it all to work tho! :smile2:

 

[T0RN4D0]

Even if its doable it wouldn't be in any way practical or rational or any of that. A lot of other irrational but way more effective ways to make a fast saw.

 

[cpr]

How you planning on lubing the turbo? Plus most small diesles dont run over 4000rpms if that and the turbo spins somewhere around 140,000rpms. Wouldnt it spin about threes times that fast on a saw? I wonder if it would stay together? It would be cool if you could get it all to work tho! :smile2:

Total cfms the engine is moving and, more directly, turbine nozzle size affect turbo rpms more than engine rpms do. Think of nozzle size as trying to spin a toy fan blade. Open your mouth big - large volume, low velocity, the blade doesn't really spin. Close your lips - higher velocity and the blade gets going.

Oiling would be a problem on it.

 

[Rokon]

The title of this thread says 'Forced-induction on a saw'.

In two-stroke terms it has too many obstacles to overcome, as noted above. If and when 4-stroke technology reaches the practical application for chainsaws, then possibilities may open up.

Years ago in moto-x, two strokes were the only way to make snappy power. Don't see many two-strokes on the track anymore. :msp_unsure:

 

[Billm67]

Wouldn't it be easier to just get a bigger carb and run it on NitroMethane that is used for RC cars. The little nitro engines are two stroke with a glow plug. They already have 2 stroke oil blended in. I would think for 30% nitro would really make one of these saw sing.

 

[beingeasy769]

View attachment 266244

 

[sawfun9]

30% no way, come on, tip the can man, tip the can. What are you afraid of. It only has one cylinder not eight. HaHaHaHa

 

[MCW]

There is a hotsaw on the Australian racing scene running NOS.