How many mm is an si trottle body?

[crx hf]

Do guys know how many milimeters an si trottle body.Also i have an extra SI TB and my friend wants it but he has an HF.i know it will fit the problem is will it idle right.Becouse he HF manifold is really small.

[91civicDXdude]

i dont know what size it is, probably around 54mm or so. but putting an Si throttle body on an HF manifold is probably not a good idea. He would be better off getting an entire Si intake manifold. I belive the Si throttle body would be so much bigger than the HF that you would have to port the manifold so big it would have nothing left to bolt the tb onto.

[crx hf]

That sucks he already orderesd a AEM CAI for it.Hes going to be pissed when i tell him it wont fit.

[crx hf]

Back then when his car wouldnt start we put it in.And it bolted right up.

[91civicDXdude]

yes it will bolt right on, but the question is, will the throttle plate even open? my guess is it will open about 1/4 to 1/2 of the way and then the throttle plate will hit on the very small intake manifold opening. Plus, there will be a HUGE step causing a major restriction. the car would most likely lose power.