supercharging a 2 stroke

[drmiller100]

the sled boys have been trying for years.

in the strict sense a turbocharger is a supercharger, and they are dead easy. lots and lots of them out there.

aerocharger is pretty famous cuz they don't need a pressurized oil system to keep the bearings alive.

for a belt driven superchargeron a 2 stroke, it gets a LOT harder. I've only ever heard of on belt driven supercharged 2 stroke that made the buggy faster then bone assed stock, and I am the one that built it.

And then I gave up.

Belt driven superchargers are a waste of time on a 2 stroke.

as a HUGE HUGE HUGE hint, take a chain saw, duct tape the throttle WFO.

turn the crank so piston is half way down (or up).
now hook a compressor to the carb, and observe.

If i had done this, it would have saved me 2 months and 5k dollars.

 

[joesawer]

I didn't do your test, but I know that it will blow the charge out of the muffler.
What is your point?

What if you used a pipe with a strong impulse and a low pressure intake charge, would it make more power than it used to turn the supercharger?
If fuel consumption is not an issue, what does it hurt to blow the charge out of the exhaust? Are we already near enough to 100% efficiency that forcing air into the case doesn't help?

 

[Dibbs]

in the strict sense a turbocharger is a supercharger, and they are dead easy.

No, they are not the same, appart from the fact they compress air.

Turbocharcer is a fan rotated by exhaust gasses which in turn rotate a compressor fan to squeeze the air/fuel mixture into the engine to give more power. The pressure can be increased or decreased by bypassing (or not) the exhaust gas from the fan to the muffler/pipe which may be done while the car is in use.

A supercharger is driven directly by engine rpm through ribbed gears and a toothed belt. Therefore a low rpm will give a low boost and high rpm will give a high boost. Problem is the compression at high rpm may blow the engine or be too low to be of any use at low rpm depending on the gearing ratio to the compressor ad is fixed while the car is in use.

Now, I'm no mechanic but even I know the differences!

 

[drmiller100]

I didn't do your test, but I know that it will blow the charge out of the muffler.
What is your point?

What if you used a pipe with a strong impulse and a low pressure intake charge, would it make more power than it used to turn the supercharger?
If fuel consumption is not an issue, what does it hurt to blow the charge out of the exhaust? Are we already near enough to 100% efficiency that forcing air into the case doesn't help?

a good piped NA 2 stroke is already well beyond 100 percent.

the experience everyone has is that changing pipes doesn't help.

physically turning the compressor eats horsepower that cant be put back.

Prove me wrong!!!

 

[timberwolf]

How much pressure you thinking of putting on the intake side? One major problem is that raising the intake above atmospheric will quickly nullify the venturii and overcome the fuel pumping ability of the carb. Either going to need to go to injection of some sort or put pressure from the supercharger or turbo into the fuel tank (potential bomb) to get the fuel to flow out into the carb.

Agree volumetric efficiency is over 100% in a good piped engine and the higher it can be pushed the beter in terms of output.

 

[Al Smith]

The subject can be kicked around some more I guess.I suppose in theory a two cycle can be super charged buuuuut the charge would have to stuffed after the exhaust port closes to be of any benefit.Most likely a diaphragm carb would not be the best choice.Then comes the problem of getting the thing started in the first place.The whole concept would have to employ rotary or reed valves or some combination there of.

There are likely as many theories floating around as Carter's have little pills but none other than the Mac bp-1 has ever had much documented success.

If you just wanted to move massive amounts of air through the engine ,the old magaphone exhausts work just dandy but it takes a huge amount of carboration.A tuned pipe works much better. Nothing is impossible but it may be impracticle or it's time was just not right.

 

[drmiller100]

you can't put ANY pressure to the intake side. you can put a huge frigging air pump there, but you don't build any boost.

if you DID build boost, I was using mikuni flatslides, and just vented the boost pressure into the floatbowls. i also used a pulse pump.

all this worked just fine. eventually I managed to make 3 psi boost, and for sure she ran faster then bone stock, but it was a HUGE PITA for limited amounts of gain.

What was the secret to getting boost???? I threaded a bigger bolt into the stinger. stock pipe pressure was 3 psi.

as I raised pipe pressure, I raised boost pressure, which is intuitive in retrospect. eventually i had about 5 psi pipe pressure, and 3 psi intake pressure. engine ran strong, but acted really rich.

The really rich part surprised me a lot. after all, i took a good running engine and stuffed a blower on top of it. you'd expect to need more fuel, right?????

well, eventually i figured out the mikuni carbs, with float bowls properly vented, compensated just fine for increased air. and, i was mostly pumping fuel/air on through the engine at a high rate of speed, so the engine was PLENTY cool.

when all done, i couldn't keep belts on it. spinning the blower at 65,000 rpm with a belt was hard on things.

lots of thoughts here for those willing to consider new paradigms.

 

[drmiller100]

i would have figured tw or someone would post telling me what i did wrong....

 

[joesawer]

The subject can be kicked around some more I guess.I suppose in theory a two cycle can be super charged buuuuut the charge would have to stuffed after the exhaust port closes to be of any benefit.Most likely a diaphragm carb would not be the best choice.Then comes the problem of getting the thing started in the first place.The whole concept would have to employ rotary or reed valves or some combination there of.

There are likely as many theories floating around as Carter's have little pills but none other than the Mac bp-1 has ever had much documented success.

GMC supercharged and turbocharged two strokes, quite succesfuly, many years ago. They also ran on deisel, yes they were injected. They used poppet valves in the exhaust.

 

[Al Smith]

GMC supercharged and turbocharged two strokes, quite succesfuly, many years ago. They also ran on deisel, yes they were injected. They used poppet valves in the exhaust.

True statement with one big exception in the theory.The 71 series Gimmys or the big giants we had on the u-boats are considered scavenging air diesels.Those were either Fairbanks -Morse 38D8 1/8 or GMC 278A's .They won't even run unless the roots type blower or on later series,turbos are functioning.Those by the nature of design are actually considered to be natural asperated engines.

 

[romeo]

Two strokes are VERY superchargeable. I have kicked the idea around after we were screwing around with an old weed eater and an air compressor. We blasted air into the intake with a blow gun, that little motor was doing near 20k when it popped.
I don't know if its all worth it when you are talking saw racing, there isn't enough time in your run to make the gains work IMO.

 

[Goicoechea]

Don't know if this is applicable or not but I did see a video of a Turbo'd Vespa Scooter on Youtube once...pretty wild lookin creature that went somthin like 85 or 90....Video didn't show alot of details other than a functioning turbo and the scooter haulin a$$

 

[Al Smith]

Two strokes are VERY superchargeable. I have kicked the idea around after we were screwing around with an old weed eater and an air compressor. We blasted air into the intake with a blow gun, that little motor was doing near 20k when it popped.
I don't know if its all worth it when you are talking saw racing, there isn't enough time in your run to make the gains work IMO.

You must have had the muffler still intact .If not the you would have blown the fuel charge clean out of the cylinder with a huge overboost.Then also you most likely had a 5 hp compresser shoving air into a 1/2 horsepower weedwacker.It would be kind of hard to do using the weedwacker engine to drive that much air volume.

 

[Crofter]

You would not actually have to surcharge the pressure in the cylinder at the time of ex port closing to get an increase in power from a common 2 stroke. Generally there is almost 20% contamination of the charge by the previous exhaust. If fuel consumption is absolutely no concern you can use a method like Romeo suggests and blow through several times the normal volume of fuel charge and flush out all exhaust contaminated charge and you will definitely see higher output; not from supercharging effect but just because of more complete scavenging. As Al suggested, when you consider the extra power input of compressing the intake and the loss of fuel charge out the exhaust, it is probably a net energy loser!

 

[Al Smith]

If you run a huge megaphone exhaust ,you basically get the same results.The biggest problem is having enough carboration to supply enough fuel.A big old meg acts like a giant vacuum cleaner on the exhaust.I think if you could get enough fuel it would literally suck a golf ball through a garden hose.

 

[romeo]

You must have had the muffler still intact .If not the you would have blown the fuel charge clean out of the cylinder with a huge overboost.Then also you most likely had a 5 hp compresser shoving air into a 1/2 horsepower weedwacker.It would be kind of hard to do using the weedwacker engine to drive that much air volume.

I wouldn't have even bothered taking the muffler off. It was sitting in the junk pile with a busted, uh, whatever the heck the string thingy is. The customer didn't want to spend $70 fixing his $59 weed wacker. My brother started it up and said "check this out", and blasted it with a blow gun. It sounded COOOOOOL, so we played with it until it didn't work NO MO.

 

[Crofter]

would literally suck a golf ball through a garden hose.

Al, that sounds like an add for a hooker not a pipefitter!

 

[Al Smith]

Al, that sounds like an add for a hooker not a pipefitter!

Well,Mr Pipefitter just where do you think I first heard that term? It certainly was not from the director of the church choir .An old terbacker chewin fitter during a refinery shutdown many moons ago laid those words of wit on me.:hmm3grin2orange:

 

[stevethekiwi]

Well,Mr Pipefitter just where do you think I first heard that term? It certainly was not from the director of the church choir .An old terbacker chewin fitter during a refinery shutdown many moons ago laid those words of wit on me.:hmm3grin2orange:

it was off full metal jacket in the '80s

 

[SnaykeByte]

efficiency??

a good piped NA 2 stroke is already well beyond 100 percent.

the experience everyone has is that changing pipes doesn't help.

physically turning the compressor eats horsepower that cant be put back.

Prove me wrong!!!

I don't understand how you think ANY engine can ge 100% efficient.......let alone more than 100%. This would be beyond perpetual motion, which as we all know is impossible. What about energy losses through drag or friction, heat, gravity, and so on?