ITB setup opinions?
04-05-2011, 01:56 PM
#63
4 stroke 4 bangers, like sav said, only have one cylinder on an intake stroke at any one time, and at the top and bottom of that one stroke per 2 revolutions its hardly moving, and the piston is only 78mm, and its sucking through 2 30mm ports with valves only opened 7mm so why the hell would a completely open 60mm hole restrict this
In individual throttles, you do not have that problem. The charge is constantly traveling in one direction. Or at the very least, does not have to refill the vacuum created when the other cylinders are pulling from the same source of air.
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04-05-2011, 02:03 PM
#65
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If theres no vacuum guage reading difference at WOT between the sides of the butterfly how is there now a vacuum in the runner? If that were tru WOT would be like 80kpa, not 100.
Dann
Dann
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04-05-2011, 02:24 PM
#69
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And different chokes are great for changing velocity, but down choking itb's to result the same velocity as the stock TB would defeat the purpose completely of the advantage that you have argued it posesses. (ie inceased flow AND velocity...apparently).
Dann
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04-05-2011, 02:30 PM
#70
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The intake speed is higher on individual throttles (if they are tuned correctly) than any cast log manifold any day. Higher speed results in having more air/fuel in the combustion chamber. And THAT results in more power.
Did I make that simple enough for you to understand?
Did I make that simple enough for you to understand?
Heres the quote, intake speed is higher (on your larger total cross section ITBs) apparently. Only way this is actually possible is a smaller total flow area.
The reason that ITBs whether carbies or Quads are choked is that stomping them from low throttle opening fast results in a big flat spot due to not enough intake velocity. This is partially caused by fuel falling out of suspension but thats starting to get to e a long story.
Dann
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04-05-2011, 02:43 PM
#72
Displacement and rpm are generally what determines what choke size you need. There is a general graph available that determines the size, but good tuning is what is required to find out what is the best choke size needed to gain the most power.
When I tuned my car, I continued to go faster untill I used the choke size that I have currently. I tried 3 different size chokes. Unfortunately, I can not go any larger on choke unless I step up to the next sized throttle housings. However, with the rpm and discplacement I am currently running, I do not think I would go faster with larger chokes at this point.
My point is with a log manifold, I would be stuck with what ever runner diameter the manufacturer built, and I would be stuck with what ever results I was given.
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04-05-2011, 03:02 PM
#74
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Just to elaborate...I used Savington's advice:
Modern intake manifolds usually employ runners, individual tubes extending to each intake port on the cylinder head which emanate from a central volume or "plenum" beneath the carburetor. The purpose of the runner is to take advantage of the Helmholtz resonance property of air. Air flows at considerable speed through the open valve. When the valve closes, the air that has not yet entered the valve still has a lot of momentum and compresses against the valve, creating a pocket of high pressure. This high-pressure air begins to equalize with lower-pressure air in the manifold. Due to the air's inertia, the equalization will tend to oscillate: At first the air in the runner will be at a lower pressure than the manifold. The air in the manifold then tries to equalize back into the runner, and the oscillation repeats. This process occurs at the speed of sound, and in most manifold travels up and down the runner many times before the valve opens again.
Modern intake manifolds usually employ runners, individual tubes extending to each intake port on the cylinder head which emanate from a central volume or "plenum" beneath the carburetor. The purpose of the runner is to take advantage of the Helmholtz resonance property of air. Air flows at considerable speed through the open valve. When the valve closes, the air that has not yet entered the valve still has a lot of momentum and compresses against the valve, creating a pocket of high pressure. This high-pressure air begins to equalize with lower-pressure air in the manifold. Due to the air's inertia, the equalization will tend to oscillate: At first the air in the runner will be at a lower pressure than the manifold. The air in the manifold then tries to equalize back into the runner, and the oscillation repeats. This process occurs at the speed of sound, and in most manifold travels up and down the runner many times before the valve opens again.
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04-05-2011, 03:22 PM
#79
If you put a vacuum gauge on a plenum of a normally aspirated car at WOT, is it going to be higher than the ambient outside air? I think that it helps alleviate the symptom tremendously, but does it truely completely eliminate it?
I guess it would if you had a ram air affect, but that is not exactly easy to create. And certainly not cheap.
I guess it would if you had a ram air affect, but that is not exactly easy to create. And certainly not cheap.
Last edited by miata2fast; 04-05-2011 at 05:36 PM.
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