"supercharge" atc250r using V.E. and pressure waves.

[poppanitrous]

Returning pressure waves "super charge" the cylinder giving it more fresh mixture than if the cylinder were filled at ambient pressure. This is a similar result to turbo-charging or super-charging a four-stroke engine. If the mixture contained within the cylinder before combustion occurs were allowed to expand to ambient pressure, its volume would be larger than the displacement of the engine. This phenomenon is quantified as volumetric efficiency; it is calculated as the ratio of the ambient pressure volume of the fresh charge, divided by the displacement volume of the engine.

My question is:

How to calculate MASS AIR FLOW in gm/sec for ATC carbs 34mm-36mm-39mm so i can calculate volumetric effiency?
I own a 1985 atc 250r, i am doing a 72mm (re-sleeve)bore on a 77mm stroke (+5 stroker crank).I want to have a "tune pipe" fabricated to adjust pressure waves to increase volumetric efficiency. I live in Florida so Sea level pressure.

[CRAZY70MAN]

Returning pressure waves "super charge" the cylinder giving it more fresh mixture than if the cylinder were filled at ambient pressure. This is a similar result to turbo-charging or super-charging a four-stroke engine. If the mixture contained within the cylinder before combustion occurs were allowed to expand to ambient pressure, its volume would be larger than the displacement of the engine. This phenomenon is quantified as volumetric efficiency; it is calculated as the ratio of the ambient pressure volume of the fresh charge, divided by the displacement volume of the engine.

My question is:

How to calculate MASS AIR FLOW in gm/sec for ATC carbs 34mm-36mm-39mm so i can calculate volumetric effiency?
I own a 1985 atc 250r, i am doing a 72mm (re-sleeve)bore on a 77mm stroke (+5 stroker crank).I want to have a "tune pipe" fabricated to adjust pressure waves to increase volumetric efficiency. I live in Florida so Sea level pressure.

:wondering:wondering:wondering:wondering......man. ......this question may belong on final Jeopardy? I am sure somone can help ya here.

[dcreel]

Break out that American Express Black Card, and start making some phone calls.. :rolleyes: :lol:

[Billy Golightly]

You should do a search for Helmholtz resonator, which is a more typical term for what your talking about being put on the intake side of an engine.

http://www.3wheelerworld.com/showthread.php?65921-2-Stroke-engine-performance-resources.-Books-and-other-things.&p=474001#post474001

Also checkout Eric Gorr's Kinesethic Energy Injector as well.

[WilliamJ]

Returning pressure waves "super charge" the cylinder giving it more fresh mixture than if the cylinder were filled at ambient pressure. This is a similar result to turbo-charging or super-charging a four-stroke engine. If the mixture contained within the cylinder before combustion occurs were allowed to expand to ambient pressure, its volume would be larger than the displacement of the engine. This phenomenon is quantified as volumetric efficiency; it is calculated as the ratio of the ambient pressure volume of the fresh charge, divided by the displacement volume of the engine.

My question is:

How to calculate MASS AIR FLOW in gm/sec for ATC carbs 34mm-36mm-39mm so i can calculate volumetric effiency?
I own a 1985 atc 250r, i am doing a 72mm (re-sleeve)bore on a 77mm stroke (+5 stroker crank).I want to have a "tune pipe" fabricated to adjust pressure waves to increase volumetric efficiency. I live in Florida so Sea level pressure.


Now that is a hard question to answer. I believe you have to measure the flow using a flow bench. If you search for budget flow benches you should find some ideas on how you can do it for very little money. Commercial flow benches cost a fortune but a couple of articles I read by respected and successful engine tuners suggest you don't need them. I think the volume of air can be measured by using comparative pressures. Open suction tube vs your carb and a very accurate metering orifice.

Majority of fuel injected cars have mass air flow sensors measuring the incoming air. They use a heated wire and a resistor in the intake tract and measure the current used to keep the heated wire at a constant temperature. The ECU then calculates the mass of the air - but I don't know how you extract that information for your carb.

Bill

[RubberSalt]

Well your tuned pipe has relatively nothing to do with air temps. The temps you need to look further into are the exhaust. The higher the temps=more power=more engine heat=lower lifespan of engine.

Your tuned length of your pipe is determined by the temps inside, and your rpm range you want to hit. The fat part of your pipe is more relative to port size/type of pipe. Drag pipe, wider power band pipe, ect.

I've got some software than help design a pipe, It helped me design mine. I half assed it and made it at home, but it has made a MONSTER of a difference. I went for a lower temp pipe with a wider powerband with less hp. Being my engine was air cooled, heat was an issue. If you look into the thread, BGP helped me out a TON. I'm sure we can get you squared away on it also.

http://www.3wheelerworld.com/showthread.php?130209-Pipe-Design-!!Pictures!!-on-page-4!-Nasty-fast.

[RubberSalt]

If you get some measurements, I'll plug your information into my program and get you an idea what you'd want.
Here is what i need:
Bore, stroke, exhaust/transfer duration(or distance from top of jug to top of port), Port map + measurements would be nice, transfer duration, desired RPM for peak hp, use of bike(race, trails, dunes, ect), gearing(ratio).

The width/height of the port. Total surface area of the exhaust port(s) If you map the ports on graph paper, it's easier to measure.

To map the ports, here is a guide; http://www.macdizzy.com/cylinder_map.htm

[Billy Golightly]

Now that is a hard question to answer. I believe you have to measure the flow using a flow bench. If you search for budget flow benches you should find some ideas on how you can do it for very little money. Commercial flow benches cost a fortune but a couple of articles I read by respected and successful engine tuners suggest you don't need them. I think the volume of air can be measured by using comparative pressures. Open suction tube vs your carb and a very accurate metering orifice.

Majority of fuel injected cars have mass air flow sensors measuring the incoming air. They use a heated wire and a resistor in the intake tract and measure the current used to keep the heated wire at a constant temperature. The ECU then calculates the mass of the air - but I don't know how you extract that information for your carb.

Bill

In addition to what Bill said, I was thinking about this question a bit further, and it seems like I recall it being raised by someone else on another tech forum a few years ago, and a very knowledgable person answered that the VE has to be calculated for basically one specific RPM, because of how much it changes as the engine speed increases or decreases. So you end up with some stupidly narrow light switch powerband on a 2 stroke.

[BGP]

Not touching this one... The answer to this "loaded" question easily turns into a book! Forget the VE if you're looking for a pipe design, see Rubbersalt's post. This increse in volumetric efficiency is just what 2 stroke pipes pipes do by design, only, the length and shape determines where in the rpm range this "phenomenon" occurs. However, VE is tied to everything from carb/reed flow characteristics, primary compression, port time area, port shape and upsweep angle as well as pipe design. As Billy said, you need to pick a "power band" and tune for it... and not with different colors ;)

[Deathrocket]

Sounds like a cool idea, now can ya dumb it down for me?