air fiter pipeork diameter

[torqueofthedevil]

right hopefully somebody here will be able to help. I have a new air filter for my 306 - it is an enclosed system with a cold air feed.

The throttle body on the car has an OD of 80mm, however the neck of the air filer is only 70mm.

Do you think there would be much difference with

a. reducing to 70mm at the throttle body, and running all pipework to filter at 70mm, or
b. taking the pipework through at 80mm and reducing at the filter?


i know either way at some point the air will have to get through a 70mm opening, but i was thinking about the size of trumpets on individual throttle bodies and bigger is not allways better, a slightly thinner and longer intake can increase air pressure, air speed and torque etc.

I know there might not be much in it but would like to get it right first time.

Cheers.

[littleredrooster]

The shape and length of intake stubs can have a dramatic effect on power and where it occurs in the rev range, but to have something downstream which is smaller than the throttle body can only ever serve to strangle the engine. It will never be able to flow as much air as the rest of the system.

I think you may have just wasted your money......

[torqueofthedevil]

cheers. I am worried i may have done. However, i have seen there i a K&N filter which has a 70mm neck which is used for this model with seemingly good results.

Surely the oe air box and ducting which flattens out to fit through a thin gap above the front bumper would be more restrictive!?!?

[torqueofthedevil]

right well it turns out that the proper pipercross model for my car has a 70mm opening!!! Shame i decided to order one, reckon i'll end up with exactly the sme filter!