Can someone please explain to me the physical differences between the 85-88 TB IAC and 89-92 TB IAC? How does the flow work since the later TBs do not need the hole in the plenum while the earlier ones do? Hopefully someone knows enough and can maybe share some pictures with the details. I am looking for a third gen throttle body for a drag application limited to stock size and trying to figure out which is superior. Going to use a custom manifold that is completely open so either should work. Throttle cable difference means nothing to me. The only concernable difference I have been able to research is the IAC difference but have not been able to find any detailed discussion on how the change affects anything.

 

Don't know about any IAC differences but the hole behind the TB on the early plenums supplies air to a port in each runner for the CSI which was deleted on the later setups

 

https://www.thirdgen.org/forums/tpi/...t-iac-use.html
A 89-92 tb can be used on any year plenum. if you only have a 85-88 tb you can drill a 3/8 through the plenum to get the manifold vacuum signal. Or remove the section in the throttle bore to the iac passage like the 89-92 tb uses.

 

Sorry I was pretty tired last night when I propsed this question and I guess I did not ask correctly so I will try again. I am not interested in IAC motors/solenoids or housings.

To put it plainly, the 85-88 TB needs the hole in the manifold to sense vacuum (thanks Tuned) so it cannot work with all manifolds as is. I get that. What I don't get is what is different with the 89-92 TBs. So how does the 89-92 TBs get vacuum? How does this flow/sensing of air work? What is the difference between the two? I've never had either in my hand to compare and I am coming up empty finding pictures of the back side of a 89-92 TB.
Next question: does the fact that the 85-88 TBs need a hole make any performance difference due to air flow compared to the 89-92 that doesn't need a hole?

Hopefully that reads better??

Thanks!!

 

this is the back of a bbk, stock 89-92 is the same there is a cut out about 1/4 deep to connect to the throttle bores from the iac port to the throttle bore. It have converted a few tsb be careful at the bottom it is thin the angled piece at the bottom next to the iac coolant port.

 

https://www.thirdgen.org/forums/engi...y-89-92-a.html
Here is a actual 89-92 tb pics
No performance differences with how the iac controls the idle with a controlled vacuum leak.

 

Awesome! That is exactly what I have been searching for! Thanks a lot!!