Box Stock

Temps

alvin l nunley said:
I've been preaching this stuff, air density, EGT, compression pressure and other stuff for years and have made no inroads that I know of. I will not give up!
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You might try including some supporting data with your preaching Al, maybe it would be more convincing!
Keep preaching..................

Steve
 
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alvin l nunley said:
Thank you for that. I don't get the connection. But there's a lot of things I don't get.

I'm curious, what is this venture effect?
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The Venturi effect is based on Bernoulli's principle. A carburetor is a Venturi. On the carb, the air filter side is a diameter, the engine side is a diameter (that may or may not be the same size as the filter side) and in between the two sides is smaller than both. For the middle to move the same amount of air as the larger diameter ends, the pressure of the air decreases and the velocity of the air increases. With the decrease in pressure (less than atmospheric) , this is a great place to put the introduction of fuel (at atmospheric pressure) as the fuel is "sucked" into the throat of the carburetor and mixed with the high velocity air.

I guess for the exhaust, they were trying to "pinch" the diameter of th exhaust pipe somewhere along the length to increase the velocity of the exhaust.

Clint
 
A venturi is required in a carburetor to cause the low pressure, that atmospheric pressure can pushes fuel toward. A venturi is always a restriction to flow but it is required to get that fuel. It was once thought that a venturi in the exhaust could help to evacuate the crankcase, in reality the exhaust flow will do that without the venturi. The venturi being a restriction there is no reason to build one into an exhaust system if it is properly sized to begin with.
 
Kart43 said:
A venturi is required in a carburetor to cause the low pressure, that atmospheric pressure can pushes fuel toward. A venturi is always a restriction to flow but it is required to get that fuel. It was once thought that a venturi in the exhaust could help to evacuate the crankcase, in reality the exhaust flow will do that without the venturi. The venturi being a restriction there is no reason to build one into an exhaust system if it is properly sized to begin with.
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Thank you. I like that you know about "push", I've been telling people for years, "there's no such thing as "suck" in the intake event. Everything gets pushed!! High pressure to low pressure.

"Properly sized", that is the question. Gem used to make an exhaust header for the KT100 that had a venture. I always thought is was faster.

"crankcase"??
 
Kart43 said:
Al 2 stroke exhaust technology does not transfer to 4 stroke very well.
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Are you sure about that? How much exhaust do you want to release and when and at what point should it be shut off as it relates to incoming fuel air charge?

Steve
 
Kart43 said:
A venturi is required in a carburetor to cause the low pressure, that atmospheric pressure can pushes fuel toward. A venturi is always a restriction to flow but it is required to get that fuel. It was once thought that a venturi in the exhaust could help to evacuate the crankcase, in reality the exhaust flow will do that without the venturi. The venturi being a restriction there is no reason to build one into an exhaust system if it is properly sized to begin with.
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Think more like the exhaust tip on newer diesel pickups.

Clone rules began with a spec pipe. Altering spec parts make for shorter times in the tech barn.

I suspect when the big pipe was allowed, most had never saw this device. A surfacing of this technology will make that rule reappear.

JMHO
 
steve baker said:
Are you sure about that? How much exhaust do you want to release and when and at what point should it be shut off as it relates to incoming fuel air charge?

Steve
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I have to say you want to stop the outward flow, when all of the non combustable byproducts are gone and prevent any of the incoming charge from escaping into the exhaust system. This is very hard to perfect for all RPM so we often have to compromise. Are you suggesting that there is a reason to retain exhaust in the cylinder other than emissions control?
 
alvin l nunley said:
What's your understanding for that theory? With 50 years playing with both, I think I know a few things. Still, I'm willing to change my mind. Read my sig.
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Al the tuned pipe dependent on acoustics works well on the 2 stroke as the exhaust pulses occur very close together, the same principles could be utilized on 4 strokes but I think shape and size will be the problem.
 
95 shaw said:
Think more like the exhaust tip on newer diesel pickups.


JMHO
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The diesel tips cool the exhaust, by mixing with atmospheric air,
especially during the Regen process, without it they will melt the pavement or scorch the paint off the car beside you.
 
Seems like I remember back in the olden times the ASA stock car group mandated mufflers on all their race cars, at which point racers started looking for bridges to jump off. ASA did a lot of testing and shocked everyone by discovering that the added backpressure actually made cars faster. Maybe that's the thinking behind altering the pipes?
 
Last clue

Breathe through a straw, making sure all air comes through straw.

now, let some in through your nose.
 
Kart43 said:
I have to say you want to stop the outward flow, when all of the non combustible by products are gone and prevent any of the incoming charge from escaping into the exhaust system. This is very hard to perfect for all RPM so we often have to compromise. Are you suggesting that there is a reason to retain exhaust in the cylinder other than emissions control?
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Agree with you on this and no I'm not suggesting that there is a reason to retain exhaust in the cylinder other than emissions control.

Steve
 
ive had a exhaust reducer in a flathead exh port before and with a stock wka flathead it ran better so better i could feel from the drivers seat also had to drop a few teeth off rear gear
 
Kart43 said:
I have to say you want to stop the outward flow, when all of the non combustable byproducts are gone and prevent any of the incoming charge from escaping into the exhaust system. This is very hard to perfect for all RPM so we often have to compromise. Are you suggesting that there is a reason to retain exhaust in the cylinder other than emissions control?
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Your close.
Instead of thinking of incoming charge escaping, think of reversion with air returning into cylinder from short exhaust. Works best on engines with restricted intake system.

Was thinking of cam changes needed this afternoon when I realized I had owned a cam designed to take advantage of this phenomenon.
bought from a dominant builder of the time. I remember him not running exhaust gaskets in his engines and needing exhaust valves lapped on weekly basis.
 
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