What is throttle body mod???
 

What is this stuff I hear about a throttle body mod? Is it hard to do and is it possible to do myself? how much gain will i get?

are you talking about putting a S5 (89-91) throttle body or intake(not sure which one your talking about) on a S4(86-88) if so you will need a throttle body theres a full writeup somewhere i cant find it right now but apparanly its not a direct bolt on you will gain about 10hp i think try searching throttle body(my search doesnt work)

search:
http://fc3spro.com/TECH/HOWTO/TBM/tbm.html

Interesting...

http://i16.tinypic.com/48p7fox.gif

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/frequently-asked-questions-2nd-generation-rx-7-faq-fc-494667/

I always wanted to know if you could use a 13B-RE TB in a TII. I don't even know where to find out which flows better. I can clearly see the 20B TB might not fit but I can't tell with the RE.

The RE throttle body is bigger and (I think) the air inlet elbow is a 4-bolt pattern instead of 3 like the TII. Lots of people have used the RE upper intake and throttle body, but to use it with a TII lower intake, you have to match the bolt holes with a die grinder or dremel. Oh and if the only mod you did was the throttle mod, you probably wouldn't notice the power increase as much as if you did other mods along with it. Some of the more noticeable gains with rotaries is accomplished with exhaust system changes, as the stock system is restrictive.