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Old 07-03-2008, 05:09 PM   #11 (permalink)
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all of the exhaust intake design books I have read have a formula for figuring out ideal intake size based of engine size and the speed that you want it to run most efficiently at, to keep air velocity up you want an intake that is long enough to maintain the pressure pulse between valve openings, but not so long that it creates drag, the higher you rev the engine the larger around and shorter the intake should be, if you want good efficient low end power then you want a small around longer intake, it's fallowing the same laws of physics as any musical wind instrument, change the size to much without changing the air flow and it will go out of tune and fight it's self.

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Old 07-03-2008, 05:43 PM   #12 (permalink)
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is there a simple formula for this? input target rpm and engine displacement, output intake length and width?

Are those theories taking into account low-throttle cruise, or only WOT?
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Old 07-03-2008, 05:54 PM   #13 (permalink)
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Quote:
Originally Posted by MazdaMatt View Post
is there a simple formula for this? input target rpm and engine displacement, output intake length and width?

Are those theories taking into account low-throttle cruise, or only WOT?
Tuning the intake on the upstream side of the throttle valve only impacts WOT operation. Tuning it downstream of the throttle impacts all phases, but is usually not a do-it-yourself project.
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Old 07-03-2008, 05:55 PM   #14 (permalink)
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So the original poster has done no harm because he will never be at WOT anyway... what good is a perfectly tuned intake system with a butterfly valve closing 90% of the way.
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Old 07-03-2008, 06:00 PM   #15 (permalink)
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It likely does cause warmer intake air that might improve FE, depending on the calibration, type of injection, that sort of stuff.
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Old 07-03-2008, 07:51 PM   #16 (permalink)
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To the best of my knowledge improving an air intake on a gas engine only gets you more power at WOT. It does little or nothing to improve mileage (This may not be true for cars with computer controlled EGR however, as there might be room for some improvement in mileage provided the computer is smart enough). On a diesel you get both more power and fuel economy as there is no throttle.

That said, improvements can be made


I found these articles on reducing intake losses. They are aimed at improving performance however.

The first gets better as you go a long. It starts getting good in part 3. Note its for a turbocharged car.

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This is revisiting it with a non turbo car.
Part1
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Part2
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Part3
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Part4
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Part5
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Done on an economy car
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Picking your intake location
http://autospeed.com/cms/A_1023/arti...popularArticle
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Old 07-03-2008, 09:54 PM   #17 (permalink)
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Basically removing the tube allows the driver to hear the throttle body and allows slightly warmer air into the engine. I do not have a clue if it increases power or economy, but it's basically no big deal.

You can play with as many formulas and math problems as you want, but that is just too much time to waste on the physics of a 55 horsepower engine.
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Old 07-06-2008, 11:08 PM   #18 (permalink)
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I agree with Johnny Mullet 100 %. Hope you are feeling better, Johnny. Remember, we are talking about metros.

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