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What size a/r

3359 Views 26 Replies 10 Participants Last post by  Chris1374
This is for a local 10.5 class.
02 camaro on 275s
The new X275 88 turbo
10.5:1 [email protected]
Solid roller, probably spinning to 8k max.

Not sure what A/R to get this turbo to make it right? All suggestions are welcome with a reason why. I really like learning about this stuff.
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Well it depends on which hotside it is. If it's a gt55 you'll go tighter on the a/r than you would if it's a GT47 because the bigger wheel will allow you to. If you are going to a bigger housing because of drive pressure issues I don't think you will solve your problem. The wheel is the restriction, the housing just dictates where in the rpm band spool happens. I think that is the key to these limited size combos. Big wheels, tight housings, so the spool happens early and you can use your power management device ( ams1k ) to put the power down like you need it.
A wheel that big is gonna need a tight a/r so you can get it to spool and not be lazy the first 330. That's gonna be you key to getting down the track. Make it spool early then use your boost controller to back it off however you need to. If the a/r is too big, you won't be mechanically able to make to boost. And if you can't do that, the Ams or whatever contoller you're running, has nothing to control.
Shearer, nice hypothesis maybe, i would rather know that it's a correct theory you know. I sit behind the wheel thinking about this crap all day going over things I read, comparing combos to the way it runs at the track, but people like you who do this stuff for a living have way more information to base things off of. If I am on the right track, thank you for the compliment.

Coolrayz, I think a 1.00 would be a good place to start for you. I have that same
Turbine wheel going on 496 inches and I'm thinking about using a 1.32 IF I ever get the chance to race the car competitively. That reads win the lottery. That wheel has a 113 or 114 mm exducer, I can't see you having backpressure issues on 427 inches. If the 1.0 works, and you do, I'd look at everything else in the system first before I changed it. If you wanted to order your turbo with a 1.32, I have a 1.00 that I would trade, sell ya. How much room do you have for exhaust? It's been suggested to me to try and fit a 6 inch downpipe on my setup, might work for you too.
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Guess who, on yours with fewer cubic inches you might try an F trim wheel instead of a g trim with a 1.00 housing.
G trim is 114mm F trim is 108mm. GT55 is 111mm, and the GT47 is 92mm. For 376 inches, the gt47 is too small and the G trim and GT55 are too big. The F trim is the closest one to what I think would be ideal for your motor which would be around 100-102mm.
It was an opinion like i said. I know of 2 people that are having what they feel are backpressure problems with GT47's on high 300 inch motors. the GT55 is a big wheel, along with the G trim. I've seen countless guys pull G trim wheeled turbos to replace with ones with F trims on 400+ inch small blocks because they cant spool the G trim like they wanted.
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