Im planning on swapping out my 88 T2 rotors with NA rotors from a 91. I've heard the compression rate is higher. Has anyone done this before, and what was your experience with it?

 

S5 NA rotors are 9.7:1 compression, while S4 TII rotors are 8.5:1. Higher compression rotors will have the most significant effect on off-boost power, but it also requires much more precise engine tuning. A programmable computer will be required to retard timing under boost and increase fuel delivery to prevent blowing the engine.

 

How drastic would the timing need to be adjusted if running S5 TII rotors in an S4 TII??

 

I also have a question/inquiry:

If you use s5 NA rotors in a t2 since you have to retard the timing a significant a mount will the added com

 

*compression offset set increased low end and spool?
Will it help increase mpg?
Would 9.4 rotors be better suited for higher comp turbo?



-Kyle

 

I wouldn't run more than 10 degrees total advance after about 10 PSI on the 9.7:1 rotors. The stock TII ECU runs in the high 20s under the same circumstances.

There would be a definite improvement in spool, and a mileage improvement as well. But only in an ECU tuned properly.

On a stock TII there shouldn't be an issue spooling the turbo anyway.

Honestly, my opinion on building a 9.7:1 turbo 2nd gen is to not do it. You're not going to gain much over the 9.4:1 rotors, which can be very reliable in a turbo application if tuned correctly.

 

Aaron, would there be an issue running 9.0 rotors instead of 8.5?