Two-strokes; octane boosters, lubercants and racing fuel

[kach22i]

Let's say you have a two stroke engine that you would like to goose a little more power out of. Short of adding a Turbo or Nitrous system which are way beyond my abilities, what your you do?

1. Clean the air filter.

2. Change spark plugs and gap the plugs.

3. Make sure you have fresh gas and the proper oil ratio mixture.

4. ?

5. ?

6. ?

I don't want to damage the engine with any weird octane boosters, lubercants or racing fuel. However if these items work, or can be made to work in moderation I wish to know how to do this right.

Operation of engine may vary from climates of hot to cold as the engine is in a hovercraft.

Link of interest (info) - 1:
http://www.off-road.com/dirtbike/rick/gas2/

Link of interest (product) - 2:
http://www.hiperf.com/acatalog/Online_Catalog_Lubricants_190.html

[Nostril Cheese]

different reeds, pipe, what kind of motor?

[Jeff Higgins]

Snake oil for the most part. If your engine does not detonate with your current fuel, there is nothing to be gained. Just like any four stroke, octane requirements are dictated by compression ratio. More octane with too low of a compression ratio does nothing, and may even overheat and lose power. Kind of like running the timing too retarded.

Easy tricks for two strokes start with tuned pipes. If you don't have one, the addition of one will add significant power; probably the biggest "bang for your buck". You do have to pick the right one, just like headers or other exhaust modifications on four strokes. The engine manufacturer probably has some recomendations.

Another easy mechanical change is in the height of the exhaust port. Higher port, more top end power; lower port, more low end power. It's tough to lower the port without welding, as you must lower both the top and bottom. Combined with lowering the peak power, most folks won't ever do that. Raising the port only takes a die grinder and some experience; the top is raised, but the botton stays put. There's probably some dirt bike tuners that can do this for you pretty cheap.

A reed valve induction motor can pick up some power with different reeds. If you have a common motor, the same guy that can grind your exhaust port can probably supply some reeds. If it is a rotary induction, with a timed port through the crank. the same guy can alter that crank port pretty easily as well. The motocross guys have this stuff pretty well figured out. Find a shop that supports them, and you might get some cheap power with just a few proven mods.

[LakeCleElum]

When I raced go karts as a kid, a guy at the track told me to use "white gas". I'm not sure what is was, but it went like hell.

Later I road raced motorcycles for six years; the first few being 2 stokes. What Jeff says about porting is true, BUT (as I found out the hard way): raising the exhaust port is also lowering your compression ratio. I went slower until I figured it out. It was then onto milled heads for higher compression.

I had a friendly machinist that also bored my carbs out 2 mm. Next was automotive coils and a little exhaust work.

Many run more oil in the fuel than they need. 40:1 is considered ideal for most used. Even a racing engine that runs really hard does not need more than 25:1.

I still dabble in snowmobiles. One must remember that carb jetting in a 2-stroke is much more critical and "touchy" than a 4 stroke. Ten degress difference in outside temp. or a change in elevation can make a difference. As always, go as lean as you can away with. As the old saying goes: "A two-stroke always runs fastest just before it seizes!!!" Many snowmobiles are modifed and run slower than a stock one that is well sorted with good (1) jetting, (2) Clutching, and (3) Gearing.

If applicable, gearing is often overlooked and can make a difference.

[Jim Bremner]

two strokes are fun!

port height I & E

squish,

barrel height

port size

compression

pipe lenght, expansion shapes,

carb


I say play with your fuel, look outside of gas

[M.D. Holloway]

I think you could do some cool things to the exhaust that might help. I know in go-carts they are able to boost it that way - maybe a supercharger? You won't see any help with oil.

[Tim Hancock]

Kach, what engine are you talking about? I am quite familar with 2 strokes on ultralights (as well as dirt bikes, snowmobiles etc). On an aircraft, low end power is a non-issue and basically a propellor is matched to load the engine so that maximum power can be reached in flight. IOW, too much prop and engine will never reach max power/rpm, too little prop allows overspeed.

I assume hovercraft (if that is what you are talking about) operate in a similar fashion without any sort of gear changing transmission. If your present engine is not able to reach it's powerband, maybe you might try reducing your propellor load. Or if you are able to reach the high rpms where your engine makes power, THEN you need to increase your prop load AND boost engine power to match.

Depending on what engine you actually have, you may be on your own when experimenting with porting and exhaust pipe changes as "driving a fan" creates a different power tuning than what the snowmobile engine tuners will probably have proven mods developed for.

Raising the compression ratio is the simplest way to achieve more power (custom exhausts and porting work too, but they are kind of an experimental black art), but then you may need to boost the octane to avoid detonation along with messing with your jetting.

Anything is possible, but there may not be any "proven" fixes for your situation.

[Porsche-O-Phile]

What those guys said.

Turbos aren't that hard. . .

Come to the dark side. . . BWAHAHAHAHAHA!!!

[Jeff Higgins]

I'm not sure you can turbo or super charge a normal reed or rotary valve two cycle. Is it even possible? It seems with the convoluted through the carb, into the crank case, crank case compression, squirt past the piston, combustion chamber compression process that forced induction would be a real trick. I dunno; maybe it can work.

[deathpunk dan]

The first link is great bc it's the legendary Rick Sieman of Dirt Bike magazine infamy. Super Hunky lives!

A friend of mine, tired of getting smoked by YZ250F (4 strokes) in the 125 class, had a 144cc big bore kit installed on his honda CR125. The thing is making ~40 hp now!

So, go big bore.

[LakeCleElum]

Forced induction bascially just blows your fuel charge right out the exhaust port duirng overlap. Very little success in 2-stroke applications.

[svandamme]

we used to overcook 40 cc mopeds...

standard they would do like 40km/h ( the legal limit for that class )
but it wouldn't take much mucking about to make em go 80km/h
just removing the exhaust restrictions


to get past that , wouldn't work easely (talking no gearbox mopeds here)
and that required boring out...

the really hot thingies were the Zundaps, 40CC stock
and gearboxes... those things were legally scooters, but there were 60 or 80 or more CC kit's out, that made em effectively motorcycles , not scooters


as for forced induction > what Bob says... don't make much sense in a 2 stroke... 2 stroke is about simplicity , they are not efficient with the fuel, and have poor emissions..
if you need more power, you oughto look into a 4 stroke motor

[kach22i]

Originally posted by Tim Hancock
On an aircraft, low end power is a non-issue and basically a propellor is matched to load the engine so that maximum power can be reached in flight. IOW, too much prop and engine will never reach max power/rpm, too little prop allows overspeed.

I overloaded a gas (Cox) powered hovercraft model once, it did not work out well.

After reading everything here I think that installing a more efficient fan for $200 is the way to go. I've been told that the new Hanson fans make almost 20% more thrust than the old Multi-Wing fan.

The big problem with fans is they are made for building HVAC systems and adapted to hovercraft and ultralights.

Engine: Two cylinder, one carb, air cooled Cyuna of 35 HP.

The Cyuna brand was once used on snowmobiles, bored out and first adapted to ultralights. This is what Scat Hovercraft used in the late 1980's before switching to Rotax.

[David]

It would really help to know what engine it is.

[LakeCleElum]

Originally posted by kach22i
I
Engine: Two cylinder, one carb, air cooled Cyuna of 35 HP.

The Cyuna brand was once used on snowmobiles, bored out and first adapted to ultralights. This is what Scat Hovercraft used in the late 1980's before switching to Rotax.

My first snowmobile had a Cyuana engine. It quit on more than one ocassion due to a bad CDI box. The previous owner had torn his hair out trying to troubleshoot this problem and thought he had it fixed with new crank seals. Hopefully the electrics have improved.

I'd never take to the air in one, although I doubt you "hover" very high....

[kach22i]

Originally posted by 125shifter
It would really help to know what engine it is.

ULII-02 Cyuna

[kach22i]

Originally posted by LakeCleElum
My first snowmobile had a Cyuana engine. It quit on more than one ocassion due to a bad CDI box. The previous owner had torn his hair out trying to troubleshoot this problem and thought he had it fixed with new crank seals. Hopefully the electrics have improved.

I'd never take to the air in one, although I doubt you "hover" very high....

I did have to replace the CDI and coil, twice in 15 years. Mostly it would not electric start which is how it is now, so I pulled the starter out to save weight.

The other time it was a problem was when it would just die without warning and not restart until it was cold again.

I still have just 90 hours on it after all these years because of the typical 1/2 hour flights on lakes (2 hours on rivers), or grad school, or under redesign/reconstruction as it is now.

[David]

Originally posted by LubeMaster77
You won't see any help with oil.

I'm sitting here at work, bored out of my mind baby sitting two less than A team machinists. Anyway, I'm passing time by looking for random topics to post on.

As for oil, there is some benefit in using as much oil as you can before you foul the plugs. There was an article in Road Racing World back in the late 80's or early 90's on F1 bikes that discussed it. I forget the reason behind it, might have something to do with sealing the rings better. In roadracing karts we run about a 22:1 fuel/oil mixture.

[David]

Squish is probably the biggest bang for your buck. Stock squish is usually too large for reliability. On 125's we run about 0.030", but we check it everytime we make a change. If it's air cooled and/or big bore, you'll need more, if it's smaller you can go even tighter.

You could raise the exhaust port, but that moves the power band higher and may make your power under the curve smaller which could make it slower overall.

Clean up the intake track, not bigger, just cleaner. Clean up the area in the case where the intake charge enters the cylinder and match these areas.

If you can widen the cylinder intake ports, there's a little power to be gained.

You can move the power around by changing the angle of the intake port roofs. It's been a while since I've messed with them to know which way to go, if your thinking about doing this let me know and I'll look it up.

Bigger carbs can help if it came with an undersized one, but you also loose bottom and midrange by going to big, for a minimal gain on top.

Advancing the ignition timing a hair will help everywhere but on the top.

More compression helps everywhere but on top were you want less compression so the engine will reach max revs.

[kach22i]

Since this old thread has new life, the way to get more power out of a 100 hours of use two-stroke is......................TIGHTEN ALL THE BOLTS!!!!!!!!!!!

Using the mannual I downloaded on-line I tightened/torque up all the engine bolts to original spec--------------what a difference.