I got my airfoil from Summit and Im looking at it and I notice two holes in the bottom center. Now Im new at this so help me out. I have a 91 formula with a 5.7TPI. I just had the plenum off over the weekend and ported it and I noticed that my plenum is different from some. I has two holes inside the throttle body openings for the EGR passage and some older models have an opening the front face of the plenum for the EGR passages. I am assuming that these two holes in the airfoil are for the type that has the opening on the front of the plenum. On mine they will lead to nowhere and cause turbulence again, right? I did not see two different model airfoils for firebirds. What if I plugge them up with some kind of metal filler and sanded them smooth? Is any of this making sense?

Larry

 

Are you sure they are not IAC passages?

I think the airfoil will fit any TPI car.

 

Im not sure what they are. What is IAC? something to do with Idle right? I havent' actually matched it up to the throttle body yet but I was looking at a picture of the TPIS airoil and it is different than the Jet airfoil like I have. See thesepics. Maybe Im just worrying about nothing but the TPIS airfoil does not have the two holes and I know that the plenums were different I think starting in the late 80's forward.

 

Idle Air Control. And thats what that is for.

 

Yes, it has nothing to do with the plenum or EGR. The holes in the airfoil are to let air into the IAC passages (bottom) and also for the valve cover breather port (top), which open into the cavities between the throttle bores.

 

OK, Idle Air Control. Do you see the small pic in the upper left corner of the photo, that is the TPIS airfoil and it doesnt have the two little hole in the bottom center. The Big pic is the Jet airfoil and it does have the two little holes. Why the difference? any idea?
Larry

 

It may not have the 2 little holes, but it does have that single notch in it, does the same thing.

 

Cool, I put it on last night and it fit fine. I was mistakenly thinking that those holes went into the Plenum somehow, just shows my inexperieince (which I admit from the outset). I ported the plenum and put on the airfoil at the same time. I noticed a difference but it seemed like the difference was more pronounced at medium speed as opposed to off the line. That seems right I guess, the more air flowing through there the more the difference will be noticed. I guess if I want a faster start I should put in a different rear end, I have the 323 in there now.

Larry

 

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