i will be tearing my engine down yet again this weekend and i was contemplating tossing in some S4 n/a rotors to up the compression, anyone who has done this or seen it done please list the pros and cons of doing it, i know it would increase the top end power band increasing overall horsepower but i would also need to run premium pump gas and it would need to be finer tuned than with the lower stock compression rotors.

well what i'm wondering is there any other issues or non obvious drawbacks to using n/a rotors in a S4 T2?

 

I did it in my vert's first engine. I used GSLSE rotors that I had laying around, due to the 3mm seal grooves stock. Anyway, it ran really strong, and I always ran 93. I had a knightsports chipped ecu with no fuel cut or rev limiter and routinely took it to 8500rpm. It will make your turbo spool quicker, and you'll find yourself in boost before you know it on the highway. I thought I could get the best of both worlds, decent highway gas mileage plus strong pull under boost, but I didn't experience that, because the thing would want to go into boost at the slightest hint of throttle. I don't see any reason not to do it, though. I plan to run 9.7 rotors in my FD's new single turbo engine.

 

thanks for the info Kevin, i think i may just pop em in there.

 

ahh and one other question, would the S4 n/a rotors be in balance with the S4 T2 flywheel and front counterweight?

 

bah, after thinking it over the n/a rotors are 9.4:1 which is a little higher than i originally thought they were, ideally i would want some 9.1:1 rotors which would give a bit more reliability for street driving, the GSL-SE rotors were 9.1:1 right? too bad i don't have a pair of those lying around..

 

13b rotor choices are 9.4 and 9.7 in stock NA form, and 9.0 and 8.5 in stock turbo form. SE rotors were 9.4 just like s4's, just heavier with thicker sideseals and apex seals.

Any s4 rotor works with the s4 flywheel and front counterweight, so long as both rotors are within 2 letters of each other you're fine.

 

thanks, i'm still contemplating it. i guess i will make my choice by tomorrow. i plan on driving the car for the most part daily so i don't know that upping the compression ratio that much is practical.

 

i made my decision today, i have some spare 4 port T2 irons lying around and quite a few n/a housings so when in doubt build BOTH!

i will use the lower comp rotors for my DD and in the future or when i'm bored or when it's not so much a DD i will swap the engine out for the higher compression one and have a little fun.