# Effects of removing plenum?



## minute rice sentra (Mar 21, 2003)

Ok, so I had this idea a while ago for my CA18DET, make an intake manifold that's designed like an exhaust header. I've been trying to think of what the negative effects would be of not having a plenum for the intake, all I can really come up with is maybe it would cause a decrease in low-end torque since there's a smaller mass of air available until the turbo spools up, and then I'm thinking why not have the intercooler act as the plenum by mounting the throttle body before it. I eventually plan on having the manifold(with or without plenum) mounted so that it sits lower than stock so I can put the IC above it between the engine and firewall utilizing a cowl induction hood. This pic might help to see where I want the IC http://www.uniqueautosports.com/Images1a/Subaru Parts/wrxtopcooler2.jpg

I would like your input on what effects(negative or positive) these modifications might have on my performance.


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## morepower2 (Apr 19, 2002)

minute rice sentra said:


> Ok, so I had this idea a while ago for my CA18DET, make an intake manifold that's designed like an exhaust header. I've been trying to think of what the negative effects would be of not having a plenum for the intake, all I can really come up with is maybe it would cause a decrease in low-end torque since there's a smaller mass of air available until the turbo spools up, and then I'm thinking why not have the intercooler act as the plenum by mounting the throttle body before it. I eventually plan on having the manifold(with or without plenum) mounted so that it sits lower than stock so I can put the IC above it between the engine and firewall utilizing a cowl induction hood. This pic might help to see where I want the IC http://www.uniqueautosports.com/Images1a/Subaru Parts/wrxtopcooler2.jpg
> 
> I would like your input on what effects(negative or positive) these modifications might have on my performance.


It might have a powerband thats more narrow and have nodes in it.

Mike


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## minute rice sentra (Mar 21, 2003)

What do you mean by nodes?


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## James (Apr 29, 2002)

Places where your power will drop or not climb.


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## lshadoff (Nov 26, 2002)

minute rice sentra said:


> What do you mean by nodes?


An intake like you describe will be a "tuned" intake. At certain rpms a resonance will be set up and a ram effect will generate more power. At other rpms there will be no resonance and the power will drop. This makes an uneven power curve with hills and valleys or nodes.

A CAI does this to some extent due to the length of the tube and its uniform diameter.

Lew


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## minute rice sentra (Mar 21, 2003)

k, I gotcha, how about the throttle body idea?


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