Ok, I'm rebuilding a s5 t2 engine. The rear housing is scarred all to hell so hurray. I'm going to get fd housings to replace both housings but I want to know if I should keep the same rotors (9.0:1) or throw in my set of s4 na rotors (9.5:1) in. I'll be streetporting this engine and I want to run about 10-12lbs of boost off the stock turbo and tmic. Does this sound good, or should I just stick with the s5 t2 rotors?

 

uhhh, i thought the S5 rotors had higher compression, and the number diff was more like 8.5:1 for s4 and 9.4:1 on S5, atleast thats what ive read around here

 

Na rotors will generate more power with less boost while turbo rotors will allow you to run more boost with less power/fuel.

The s5 nas do have 9.7:1 ratio while s4 nas are 9.4:1. Higher compression rotors should save you some off boost mileage too.

Do you have both sets of counterweights?

 

if you never plan to run more than 10, i say go for it, but the stock turbo sucks so bad i think you'll get sick of it and want a bigger turbo and more boost eventually and if you want to run higher boost its a better idea to run 9:1 in the long run (this is EXTREMELY disputable). on the other hand, you can sell those 9:1 rotors for a lot more than the s4 n/a ones are worth....

 

Ya, I have both sets of counterweights and both sets of rotors in good condition. I'm just looking for more power. What is keeping me from running the same amount of boost that I would on 9.0:1 rotors, on 9.5:1 rotors? Is it the octane of fuel or the housings just can't handle that much compression, the ratio and the boost together? If the problem is the fuel detonating early because of all the compression + boost, I have a haltech and can easily retard the timing.

I have s5 t2 rotors 9.0:1 and s4 na rotors 9.5:1

 

I have friend running 9.4 84-85 se rotors in his T2 block. Its tuned on the conservative side for longevity. He also had his rotating assembly balanced with the heavier rotors. question being would you need to have everything rebalanced if you used the 9.7 s5 na rotors, being that they are same weight. or is every rotating assembly balanced separately from the factory .

 

9.7 rotors are lighter than the 9.4 rotors

maybe you should consider water injection with this setup

 

+ 1 on the water injection. I want to try methanol then maybe nitromethane injection. Just not sure how many engines it will take to get it right if my math is off.