I tried searching, but could only come up with some guesses. I'm wondering what the O.D. size of the small pipe coming in to the passenger side of the stock intake is. I think it's called the intake bypass? it connects to the bottom of the throttle body. and would it matter if there was a restriction on this pipe, say to an I.D. of about 3/8"?

 

bigger than 3/8" That's the size of the breather line....

most likely 5/8"

 

3/4" works well. I routed it for the turbo setup yesterday.

 

So just to be clear, the intake bypass i.d. will fit onto a ¾” hose barb? And my question about the i.d. of the hose barb: I have a fitting I could use that I could screw a ¾” hose barb onto, but the i.d. is kind of small, around 3/8”, maybe ½”. Will that affect anything negatively?

 

I doubt that reducing to 3/8" would affect anything negatively is you readjust your idle. You might have less physical adjustability via screw, but it should be fine. Airspeed will probably just increase to maintain proper flow through.

 

ok sounds good, I was going to weld a 90 degree fitting onto my intercooler piping so it would fit and look a little better. thanks all

 

What does this "intake bypass" do exactly anyhow? I've always wondered..

 

I believe that it provides filtered air for idle purposes when the TB is closed.

 

That makes sense...I've always wondered too but never looked into it.

 

Ahh, so Miatas essentially bypass the TB altogether at idle?

I figured it was like my CRX had, just a notch in the TB plate to let a little air in.

 

Bypassing rather than notching the TB is supposedly a tiny bit better for initial throttle response...