DJK

iTrader: (2)

I'm not ready for a new motor but I was thinking that when I am, that I might consider the high compression 9.7 rotors for my next motor to help with response. Right now I only run 15-16psi on a GT35R (.82A/R) and my motor is stock ported so I don't rev it much past 7000-7500RPM anyway.
I'm wondering if anyone has any experience with something like this or has some usefull knowledge. My goal would be to keep around the same 350rwhp and lower the boost a little, but increase low end and throttle response (not like I don't have good throttle response now, but better is welcome). Open to opinions and suggestions? Thanks, Jerry

GUITARJUNKIE28

i have experience with that same setup, except a 1.06 hot side on the 35r.

pulls great, i found myself lugging out of turns at ~12-1500 rpm a lot of the time cuz i'm a lazy shifter when i'm in commuter mode. i'd definately bump up the hot side to a 1.06, and add some water injection. high-comp motors are really bitchy.

DJK

iTrader: (2)

See now that I'm thinking about it I'm not so sure it would be good for me cause I run an ASP medium SMIC and didn't want to have to run water injection(for simplicity reasons). Also I was thinking that anything lower than 15psi is getting out of the GT35R compressor's efficiency range. Just out of curiosity, how much power and at what boost are you running? Thanks

GUITARJUNKIE28

373 whp @ 12 psi without the water injection. i was shooting for 10psi, but it crept. i'll see if i can dig up the dyno sheet somewhere.

the thing with this is: it's the **** if you're running higher boost and race gas, otherwise, you sac hp for response. it did a little better down low, compared to a 9:1 engine, but not enough for me to justify me doing it again for that scenario. next high-comp motor i do will probably be with a stock s5 turbo. just ~250whp with awesome response. gas milage did improve by about .5-1mpg with the higher compression, though.

i went with the 8.5 rotors for my new engine.

DJK

iTrader: (2)

Those numbers sound awesome for what I'd be intested in. I'm not really looking to run high boost and race gas though, I'd just be interested in increasing the low end power and overall response and still able to make around 350rwhp on pump gas without decreasing my reliablility.

Not really sure if it would be worth it for me though, but I was thinking maybe for my next motor (hopefully at least a couple more years out of this one). But if you have the dyno sheet I'd love to see it! Thanks for the feedback, Jerry

the_glass_man

iTrader: (2)

What about 10.0 rotors?

t-von

iTrader: (8)

I feel harder RA seals are a must for higher compression boosted engines. Contact Crispeed on this forum. He's the high compression, boosting tuning expert.

GUITARJUNKIE28

ra seals will still break if you detonate.

and 10:1 rotors won't give much advantage over 9.7:1 rotors. however, in an n/a application, the renny rotors will allow you to advance the port timing a bit more.

DJK

iTrader: (2)

I'm not really sure higher compression rotors are worth me doing since I'm not going to be running high boost or race gas. Still, I'd like to experiment with the thought and see if anyone has done it or recommends it for my application(stock port, GT35R, pump gas, around 350rwhp) Thanks

GUITARJUNKIE28

stock port, 35r, 350 hp....ehhhhhhh, you can get away with it. what i'd do iiwy, is back it off to about 8psi and run it that way for a while, then slowly turn the boost up. egt's get out of hand REAL fast on the high-comp motors. and especially since you have a smaller hot side than i did when i did it.

instead of setting a "350" goal, don't expect any numbers. 300whp will come with ease, then just start slowly working it up from there.

DJK

iTrader: (2)

Well the spring on my wastgate is 12psi so unless I get a new one that's about as low as I can go. I guess I could still switch to the larger hotside turbine (1.06 I think). I just can't justify going through all the work and not get the same power I have right now and only gain low end response. Also do you happen to know what is the lowest of the GT35R compressor's effeciency range? I was thinking around 14-15psi, but I'm not sure?

GUITARJUNKIE28

10-12 psi is fine.

only problem with bumping up the hot side and doing higher compression is the effects will work against eachother. i started with the 1.06, so i don't have anything to compare it to.

RotaryResurrection

iTrader: (8)

I've built some high comp turbo motors ranging from stock to single turbo. It improves the low end slightly, but if you got into a car with high comp rotors and didnt know it, you wouldnt be able to tell...it is that small of a difference. Gas mileage does also increase. I have been getting almost 25mpg with the stock auto FD that I built with 9.7 rotors. I've even been running it with 87 octane, but then it's a stock auto so it's not like I go around roasting the tires in boost all the time...I just drive it like a regular car.

IF you're looking for a lot of power, it can be done, but probably isnt worth your time to fool with, especially since it requires a conservative tune to work properly and you have to worry more with intake temps and boost levels.

I'd be much more inclined to build a stock turbo rotary that will never see more than stock boost with high comp rotors, as there isnt much of a sacrifice there, only gains to be had. But with an already modded motor you have to watch your *** with how you set it up and how far you push it. That said, I have had high comp motors up to 22psi on a gt35 turbo and it held together.

R.P.M.

iTrader: (3)

Now how about a wild ported high comp motor?
I built a Half Bridge 4 port S5 T2 motor with 9.7 rotors in it to use as N/A for this year. Should I throw some boost to it next year?

BTW, I'm using JHB Cermet B rotor housings and the 9.7 rotors are thermal coated by JHB as well.

GUITARJUNKIE28

here's one way to look at it...

for any given octane rating, the lower the compression, the more power you can get.

but take octane out of the equation and the higher the compression, the more power you get.

i wouldn't do a high-comp bp with boost unless it was running race gas. there's just too much overlap in the thing and you'll have to compensate by using a huge turbine to lower the backpressure...but then it won't be any fun anywhere but up top, and the power will tend to come on all at once.

DJK

iTrader: (2)

So would you say it would be safe for be to go with high comp rotors and boost around 12psi on a GT35R (.82 hotside and ASP medium SMIC). And do you think it's even worth it in the end?

GUITARJUNKIE28

i can't answer that directly. each setup is individual.

as for it being worth it... that's up to you. take a little off the top and put it down low. if that's what you want, then yea, it's worth it. if you want something else, then you might want to think twice.