i will be rebuilding my engine soon and i was just looking for some input from the DIYers around here who have done a rebuild. specifically on a 300+whp turbo motor. i am thinking i want the extra leeway from detonation with the 8.5 rotors, but i also want the lighter weight 9.0 rotors.......

 

S5's
More low end power and more torque overall... and if you run turbo, then faster spool of the turbocharger.
Good Luck

 

yes, definently go with s5 rotors

 

S4 n/a rotors, duh. And I'm serious too

You have standalone and a bunch of fuel, you should be able to tune it just fine with higher comp N/A rotors. I mean they're only 9.4:1, not *too* much more than the s5 TII ones. Now s5 n/a ones might be too much to tune with, but s4's are lower, I'd go with s4 N/A rotors.

 

ok, how about some BENEFITS of using the lower compression rotors?

 

Yah yah. Sure it's less prone to detonation or easier to tune, but come on man you have standalone and a bunch of fuel, get NA rotors

Kevin is building a half bridge FD with NA rotors from what I recall

 

i'm gonna drive down there and roll it up on one rotor

 

I think you've been "rolling up" something different by the sound of it...put the pipe down y0.

 

l0l

 

you can run more boost on the lower compression rotors ultimately.

you can also run more timing advance on the lower compression rotors.

However, 8.4 is pretty low. 9:1 is not exactly high, I would prefer the 9:1 setup especially considering you are probably not going to be pushing the boost limits, and will probably prefer the quicker spool up, improved response, and also improved part throttle performance higher compression will net you. These cars are already pretty dead @ low rpm without boost, a bit more CR will help.

Just be careful with the tuning like always.

so yea, my vote goes for the 9:1 rotors, hell even the FD came with this CR from factory.

 

I have a 87 T2 with a blown rear apex. Since Im gong to be doing a rebuild...are you guys saying its better to use S5 rotors from a t2 or S4 na rotors over stock? I dont have a stand alone so is this still something I should consider?

Want:
13b t with street port/polish
T04
dp, mp, e
720cc injectors
tandom fuel pump

 

Please tell me you didn't pop the new car already.

 

Yep...

 

i would put the 9.0's in my engine and i only have a SAFC and MBC, the difference will not be huge but enough to make it well worth it, the drawbacks are not enough to compromise anything.

 

I have a pair of low comp turbo rotors I'll part with. Think one needs a bearing. I'd have to look at them to be sure. I might also have the low comp NA rotors. I'd guess at least one of your current rotors is good. So the cheap thing is probably going to be finding a high comp turbo rotor to match.

 

i also have a blown jspec s5 TII engine sitting in the garage with a good rotor and housing and plates. so i have 2 good 9.0 rotors and 2 great housings, i was just thinking of downgrading for "safety" purposes. and i'm sure the low-end torque increase going from 8.5 to 9.0 is neglegible.

 

I've built all kinds of engines with both and I'll tell you that I can't really tell that much difference in either. The older rotors and flywheel are a hair heavier, and that (to me) gives the sensation of more low end torque and ability to pull out from a stop (more rotating mass stores more energy). But you can tell a slight difference with the s5 rotors and flywheel, the thing tends to have a bit more throttle response, which I attribute to the weight difference (think lightweight flywheel vs. stock flywheel). Generally, higher compression makes for a slightly quicker spool, too. BUt, with all else being the same, if I were going for high power, I'd run the 8.5's. If I was running a stock or mildly modded car, I'd run whatever I had in my hand.

 

well, at most it will see 320whp, so it doesnt need to be crazy or anything... and i was thinking about getting a lightweight flywheel during this project so i'm sure that would cover up any loss of throttle response. and the s4 TII parts are a dime a dozen. kevin you wanna buy some s5 TII stuff?

 

You just bring everything you've got and we'll talk it over

 

lets talk it over with some sex. oh god

i was actually planning on doing a rebuild myself to gain a little more experience/respect for my engine/setup....... that and i cant afford any labor this time.

 

 

I know it's not an apples to apples compairison, but I went from a stock port s4 motor, to an agressivly ported, s5 engine with a 9lb flywheel. The difference was huge, turbo spools much faster, throtle responce is far better, im very happy.

that said, go w/the s5 rotor/light flywheel setup.

Kevin, I dissagree about the loss of low end tq. If you mean, starting from a dead stop, up hill, yes the s4 setup felt stronger. However if you mean pull from 1500-3k, from my experence, the s5 setup w/light flywheel is a lot better.

 

i was planning on doing a lightweight flywheel regardless... i'm still not sure what to do

 

use the low compression rotors if you plan on boosting 25+ psi

 

i dont plan on going over 15-16