Question for two stroke experts regarding port height and jetting

[Chaz]

Yes , he is a member here and has a hand full of YouTube vid's ...

Non asymmetric .... LOL


http://forums.autosport.com/topic/19...troke-engines/

[Mark75H]

I'm somewhat sad @ the moment .. >>> I just knew TorqueXrpm would come along with a non asymmetrical transfer system to make better use of crankcase pumping pressure from port opening to BDC and ex scavenging from BDC to the new closing number .
My guess is we will be stuck with the same opening and closing numbers for a while longer ....

Well at least until till I debut one like dis-heea ...

I drove it once in North Carolina at a race because the owner wasn't an APBA member and didn't have safety equipment. The boat was old and gaining weight from picking up moisture and all of the refinements weren't yet squeezed into the motor but it still ran around 85 mph. The motor was very peaky; when it finally got on the pipe it felt like it had been kicked ahead by an elephant. A year or so later a new boat was built specifically for a new version of the motor; the new rig was reaching for 100 mph in competition.

Oh, yeah. I took that picture

[Chaz]

Oh, yeah. I took that picture

I'm glad you got the peaky part out of the way , before "Instigator" comes along in the morning and says it needs "vari-length" cable adjustable pipes on it ...

Only saving grace is that your picture ...... is an OMC ....

PS ... Mr. Demeanor , feel free to join the conversation ...

[olboatman]

[QUOTE=Chaz;2843351]I'm somewhat sad @ the moment .. >>> I just knew TorqueXrpm would come along with a non asymmetrical transfer system to make better use of crankcase pumping pressure from port opening to BDC and ex scavenging from BDC to the new closing number .
My guess is we will be stuck with the same opening and closing numbers for a while longer ....

Well at least until till I debut one like dis-heea ...

[/QUOTE

I can see this with a tiller on my 11ft SLT! Gary

[dwilfong]

pipe eng have a very narrow power band as a function of the return wave bouncing off the reflecting rear cone.
Multiple rear cones have proven to broaden this power band and help with it coming on pipe to hard.
Adjustible pipes work to a point but it is hard to predict how it will respond. most are just a lever for adjusting as you drive in and out of the corners.
A ex port valve works on a governor and controlled by eng RPM only.
But the load and temps in the pipe are never part of the function of either system.
Multiple rear cones are a function of the wave speed controlled by EGT and load on the eng.
Water injection in to the pipe is a great way to control EGT to change the pipe tune and simple to do.
A combination of both would be the simplest way to tune for a wide power band.

[Chaz]

I can see this with a tiller on my 11ft SLT! Gary

So Fong , how many gal / hr will I need to inject into each of my six pipes to pick up 50 ft / lbs down low to pull a 36" wheel out of the hole ....

I'm puttin one of these under the dash ...

[dwilfong]

[Mark75H]

Computer controlled water injection was one of the final upgrades. I theorized it already had a slightly wider power band because of the unequal lengths to the ports with the single pipe below 2 cylinders.

[powerabout]

Computer controlled water injection was one of the final upgrades. I theorized it already had a slightly wider power band because of the unequal lengths to the ports with the single pipe below 2 cylinders.

Jet skis have been using that for a while, I think MSD made a box for it?

[powerabout]

did anyone mention double diameter pistons, or has all the old stuff been forgotten

[Chaz]

pipe eng have a very narrow power band as a function of the return wave bouncing off the reflecting rear cone.

All "engs" have an exhaust system . Some just a short header pipe , others quite involved . Blaming just a small section , and the part with the least effect is being quite short sighted. But if you must blame the convergent cone , then at least say that the steeper the angle , the narrower the power band .

Multiple rear cones have proven to broaden this power band and help with it coming on pipe to hard.

Back in the day , I built quite a few expansion chambers , mostly for short track racers , but a few road racers.
Every one I've seen or built used a single rear cone . Even the late model stamped steel pipes have little to no abrupt cross section change . Less angle is what calm's it down . Multi step divergent sections came about because of space limitations making it difficult to achieve the desired volume.

Adjustible pipes work to a point but it is hard to predict how it will respond. most are just a lever for adjusting as you drive in and out of the corners.

Since 1900 , there have been thousands of pages written about two strokes . In the 50's MZ in Germany brought pulse wave's to the lime light . Now there are inexpensive programs available to the public that make pipe tuning very predictable . Even if it is cable operated.

A ex port valve works on a governor and controlled by eng RPM only.

Not such a bad deal if you dont mind taking them apart to keep them clean and moving.

But the load and temps in the pipe are never part of the function of either system.

See , we agree on sumptin ...

Multiple rear cones are a function of the wave speed controlled by EGT and load on the eng.

Yes , Load or BMEP and temp control the column velocity . However the pipe builder control's the structure of the pipe.

Water injection in to the pipe is a great way to control EGT to change the pipe tune and simple to do.
A combination of both would be the simplest way to tune for a wide power band.

External pipe temp never really moves more than 300* ( 300-600*F ) If anything , cooling the ex gasses could have the return wave being less prone to detonation if it happens to find it's way into the cylinder .

None of this has anything to do with Chris's rich mixture , or V-6 outboards , which most of us run ... next time , you'll just have to settle for a photoshopped picture of a garden hose shoved in a stinger pipe ...

[olboatman]

[QUOTE=Mr. Demeanor;2842682]I gotta say this thread has a life of its own. Nitro, growing new body parts......

I guess it has BUT it has become one of the most interesting and informative threads in a while and Mr D your correct it could use some sub-threads! Thanks Chaz and others for the class time... jmo Gary

[Mr. Demeanor]

PS ... Mr. Demeanor , feel free to join the conversation ...

I feel like a one legged man in an ass kicking contest......

[Slimm]

I feel like a one legged man in an ass kicking contest......

Wanna learn the ropes from a pro?

Slimm

[Mr. Demeanor]

Wanna learn the ropes from a pro?

Slimm

Ahhh....you saw what I did there LOL. Im surrounded!!!