I'm curious what this change would do for me. I realize the change is not a major one, but I'm curious what this would change from an engineering standpoint. Would I have less exhaust backpressure? Will the GTX71 compressor flow enough on the top end?

The setup is a Benson's sleeved 84.5mm B18C at ~10:1. GT3076R w/ .63 now on a cast manifold. Stock 8100RPM redline. Never want more than 550whp. It is a daily driven 100% street car.

With my .63 GT3076 on the 2.0L and short cast manifold I can reach 30psi between 3500-3800RPM. I believe this is putting the turbo into surge (I can hear and feel it). Typically I run 22psi in 4th gear. And my power falls off sharply after 6K RPM. There's almost no sense in me reving past 7K.

I love the level of response I have now and want my full boost point to remain between 3-4K RPM. But I'd like to improve my power after 6K and especially 7K RPM (I'm assuming turbine backpressure is my culprit right now). I'm wondering if a GTX3071 with an .82 A/R might be just the thing I need.

What do you think?

 

Get a better exhaust manifold with a good collector like the full-race etc.. With that you will have power to redline and increase spool.. If that is not enough then you might think of changeing turbo..

 

I think that you would stil run into your surge problem downgrading a bit (regardless of these overlapped compressor map plots that you see), because of the fact that you still wouldn't solve your surge issue at over 30psi. If you got the GTX3076 (or equivalent) with a .82A/R turbine housing, you'd address both some backpressure issues and even though the shaft would be past efficiency, you would lessen the chance of surge on the compressor side a little as well.

Otherwise, you just need to step up the turbo completely, if you're trying to do 550whp at all. that turbo was not really meant to do that on its own.

 

Thank you for your replies. Due to the rest of my setup, my turbo manifold cannot change. I have everything exactly as I want as far as radiator/fans/turbo inlet filter/coolant lines/etc. Would be too difficult to change manifolds.

I should clarify my 550whp statement. I don't mean I have a 550whp goal. Just that I never want more than that. I wanted to keep the "Get a 6262 replies away" lol.

My power goal is whatever my current GT3076 can comfortably provide. By what I see on paper it appears the GTX3071 compressor wheel can provide at least as much as the GT3076, maybe more. And if I mated that to an .82 I could have equal flow capability with less backpressure (hopefully solving my upper RPM torque drop-off). At least this is what I am thinking. I would like to know if I am wrong or missing something.

I know you suggested the GTX3076 w/ .82, but I'm afraid I will lose response from what I have now. That response is precious to me lol.

 

That's fine, but I'd honestly stay in the GTX3076R range for this, and not drop down to the GTX3071R. There are billet upgrades to this without having to purchase a new unit entirely. PM me.