Piping and throttle body sizing

[IndigoMKII]

I keep seeing how people are using the apexi air filter adapter and switching over to Q45's huge throttle body but something comes to mind. Has anyone else thought about the bottle necks elsewhere inside the system?

Does just simply tossing a apexi air filter adapter really give you an increase in power? The stock filter box has a 2"x3" opening which is 6" squared while the stock throttle body is only 60mm diameter so that's 3.14(1.18x1.18) which is 4.37 squared. So with that information, the stock air box flows more than the stock throttle body. The Q45 is 80mm diameter so that comes out to be 3.14(1.57x1.57) which is 7.73" squared. Most people only use 2.5" intercooler piping which is 4.9" squared.

So with all of this on my mind at the moment, wouldn't light porting on the stock throttle body make a better match than a Q45 if you're using 2.5" piping?

Would having too large of a throttle body on a setup hurt performance?

 

[supraguy@aol]

Well, part of the oem restriction is the path that the air has to travel. Oem, it travels up into the top of the airbox, then down through the restrictive filter, and then towards the maf, going from square at the box, to round. That can cause turbulence.

 

[IndigoMKII]

I would think the minor turbulence at that point would almost be negligent because of the straighten fins inside the AFM, plus it has yet to go into the turbo.

Doesn't the stock box just open at the bottom for direct access to the filter? I haven't seen but one stock air box and it was in many many pieces.

But on topic, with the engine being basically an air pump you'll want to keep the diameter of the pipe the same size going to the throttle body. So in a perfect world, wouldn't it be best to run a 4" inlet to a 2.5" outlet and use 2.5" piping the whole way, even in and out of the intercooler to a lightly ported throttle body?

I wish I had a bench flow tester..

 

[jetjock]

Restrictive filter?