Hi,

I have a Vauxhall Monaro (basically a 2005 Pontiac GTO in states-speak) and plan to go forged / stroked to 402ci. Manual T56 to be built to Magnum spec with LS7 clutch. Car will be a weekend warrior mainly for street but with occasional track time.

I'm looking at a pair of T4 Rev9 TX-72-68 T72's with the following specs:
Compressor: 72mm/103mm
Turbine: 68mm/79mm
BorgWarner compressor maps of similar size wheels suggest around 1000 at the flywheel @ 15-18psi - which is plenty LOL.

I'm guessing (confirmation or disagreement welcome) that a forged motor should realistically spin to 7000rpm.

My question is what AR should I go for on the turbine side? I appreciate lower numbers offer faster spool / more top end choke... but what would be best overall for a street car turning up to 7000rpm? Options are .96 .81 or .68

I'm inclined to go for the .96 personally as a 402 even with around 9:1CR produces plenty of torque off boost. I really don't want to be choking it at 5,500rpm with the wrong AR. Advice greatly received.

Thanks.

 

Looking at turbine flow to RPM is likely the wrong way to go. If you're making 500HPish (What you'd be looking at to make 1K at 15 PSI) Would be a lot better indicator. That said, being a street car with a manual I'd be thinking the smaller turbines would be better to drive. I would also think that a pair of 72mm turbos is going to push you higher than 1K at the flywheel. I'd be looking more towards 62-66mm range personally.

 

Appreciate the input. Any recommendations on types of turbo's in that range... along with the turbine wheel size / AR?

 

couple of borg warner S366s with the .91ar would work good on that motor. Much more efficient turbine wheels than those china rev9 turbos