Help with rear-mount turbo sizing
Thread Starter
Teching In
Joined: Sep 2019
Posts: 19
Likes: 3
From: Ephrata, Pennsylvania
Help with rear-mount turbo sizing Hi I am new to the forums but I am looking for some advice on my current build. I have a 1999 trans am with an sts rear mount turbo kit. Stock bottom end with a cam and valve springs spec’d for boost. I am running a 67 mm eBay turbo on 9psi and was making 505rwhp on this setup. I just blew the turbo and am looking to upgrade to be at about 600rwhp. I was looking for some suggestions and what brand and sizing works best for this application. I was considering the precision 7667 and am looking to spend not much more than 1k. Thanks for the help.
Thread Starter
Teching In
Joined: Sep 2019
Posts: 19
Likes: 3
From: Ephrata, Pennsylvania
I have my turbo fed off of engine oil pressure by a -4 line off the oil filter housing port and a 12v tillton engineering scavenge pump returning it to the engine. It’s the same setup the sts kit came with just a different brand pump.
Thread Starter
Teching In
Joined: Sep 2019
Posts: 19
Likes: 3
From: Ephrata, Pennsylvania
I can’t say for a 100% bc I did not install this system on the car it was on when I bought the vehicle but the oil feed inlet does appear to have a restrictor just not sure on the size. Is a restrictor as important with a journal bearing turbo ?
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Depends setup to setup. For rear mount a check valve in the feedline is important to keep oil from sitting in the turbo after shutdown. If oil leaks out into the compressor and turbine you may need a restrictor.
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On The Tree
Joined: Apr 2017
Posts: 115
Likes: 6
Imo I would not use anything below 70mm exhaust housing. Vsr billet 7875 t4 .96ar is a amazing turbo for $500!!!!!!!!!!!. You dont want so much back pressure on that rear mount. You could even do a vsr 69/73 turbo as well. Viren at vsr 2yrs ago when I was talking rear turbo said no way on the 7665 he said that turbine is too small for a ls motor. Will it work yes will it make 600rw should but it will be working hard!!!!
. !Vsr billet 7875! In the butt!
I've ran the 76/65 on a front mount, and the boost was almost instant. I could get boost at part throttle, just getting up to 60 mph at 20% throttle opening. I could see a benefit on a 65mm turbine housing on a rear mount, or at least try it........but as of now, I'm along with everyone else, I'm running the rear mount 78/75 cast $400 unit from vs racing, and so far it seems to work pretty good!
I'll post some solid updates when I get them, right now we're still working some bugs out in the tune.
I'll post some solid updates when I get them, right now we're still working some bugs out in the tune.
Thread Starter
Teching In
Joined: Sep 2019
Posts: 19
Likes: 3
From: Ephrata, Pennsylvania
My previous turbo had a 65mm turbine housing and I had the thing maxed out at 505whp I think I agree with you guys that the 78/75 billet wheel is the way to go. I’d love to see what numbers you make.
On The Tree
Joined: Apr 2017
Posts: 115
Likes: 6
Yea viren said I'd I want 600rw only to go billet wheel 7665 turbo and that will work might struggle depending on setup but with e85 or meth will work.
The vsr billet 7875 is really amazing middle ground turbo for most. Then 75/83 imo
The vsr billet 7875 is really amazing middle ground turbo for most. Then 75/83 imo
Thread Starter
Teching In
Joined: Sep 2019
Posts: 19
Likes: 3
From: Ephrata, Pennsylvania
The turbo was a 67/65 and not high quality either so I believe that’s why it was maxed out. I am looking to add meth to the car pretty soon so I think the 78/75 billet wheel is gonna be what I should go with.
On The Tree
Joined: Apr 2017
Posts: 115
Likes: 6
Should have some more too it. But ok. Hey if you just buy a progressive meth kit now and spray 5-10gph pre turbo and watch your afr and iat to see if it effect it much being that far back I bet you can pump that turbo up some. It will increase that turbo efficiency big time. Been proven many times! I was gonna spray pre but I'm spraying at the outlet and pre tb cause I'm not running a fmic
Thread Starter
Teching In
Joined: Sep 2019
Posts: 19
Likes: 3
From: Ephrata, Pennsylvania
That’s not a bad idea however I am replacing the turbo because the bearings went out on it so I just figured I’d go with a bigger turbo that is capable of supporting my power goals in the future.
On The Tree
Joined: Apr 2017
Posts: 115
Likes: 6
What's your full setup? From manifolds to pipe sizing to fmic to oil system to wg/bov/controler to fuel sys
Thread Starter
Teching In
Joined: Sep 2019
Posts: 19
Likes: 3
From: Ephrata, Pennsylvania
It is 2.5 or 3 in back to the turbo without cats to a tial wastegate cant remember the size then it is 2.25 in front to the inter cooler then 2.5 out of the inter cooler to a tial bov can’t remember the size of it either then through the factory maf and to the throttle body.
Thread Starter
Teching In
Joined: Sep 2019
Posts: 19
Likes: 3
From: Ephrata, Pennsylvania
The oiling system has a -4 feed from the oil filter housing back to the turbo also has an upgraded mellings high flow oil pump then it’s got a -8 return line with a 12v tillton engineering scavenge pump back to the oil fill neck. Boost is controlled by a turbosmart manual boost controller at the moment but is usually done by the wastegate spring. The fuel system is a racetronix f99 intake pump with the Hotwire kit it is fed by a 3/8 hard line then a -6 an line to Aeromotive fuel rails with upgraded injectors which I forget the size and a Holley fuel pressure regulator after the rails with a 3/8 return line.
