Upgrading my S475 T4
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Teching In
Joined: May 2018
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Upgrading my S475 T4 I’m thinking about getting the vs7875 1.25AR as an upgrade for my ls2 Sierra, current set up is ls2 6.0 with ls3 heads, tick ls3 turbo cam 10.5 compression. The current turbo set up is s475 1.10AR T4 with 3.5 DP and 3.5 muffler and exhaust. The car is making 650 whp @5090 rpm which is not efficient for my 3500 converter which goes to 5500 rpm immediately. Is it worth it to upgrade to a Vs7875 and upgrade to full 4 inch exhaust setup.
TECH Regular
Joined: Nov 2018
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I'm not sure a t4 s475 to a 78/75 is really an upgrade. I think those two turbos are nearly the same. You're only at 12psi. I have my t4 s475 at 19psi on a 5.3 sbe. Crank the boost up before opening your wallet again in my opinion. 12psi is not even in the turbos peak efficiency area, that's about 14-15psi. You have another 200+hp to grab from your current turbo. Maybe get a meth spray setup and get her up to the 17-20psi range.
Thread Starter
Teching In
Joined: May 2018
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I'm not sure a t4 s475 to a 78/75 is really an upgrade. I think those two turbos are nearly the same. You're only at 12psi. I have my t4 s475 at 19psi on a 5.3 sbe. Crank the boost up before opening your wallet again in my opinion. 12psi is not even in the turbos peak efficiency area, that's about 14-15psi. You have another 200+hp to grab from your current turbo. Maybe get a meth spray setup and get her up to the 17-20psi range.
Thread Starter
Teching In
Joined: May 2018
Posts: 24
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I'm not sure a t4 s475 to a 78/75 is really an upgrade. I think those two turbos are nearly the same. You're only at 12psi. I have my t4 s475 at 19psi on a 5.3 sbe. Crank the boost up before opening your wallet again in my opinion. 12psi is not even in the turbos peak efficiency area, that's about 14-15psi. You have another 200+hp to grab from your current turbo. Maybe get a meth spray setup and get her up to the 17-20psi range.
On The Tree
Joined: Jul 2013
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Why are you staying T4? Regardless of AR you’re asking a pretty good flowing combo to breathe out a 3” hole (your 75mm turbine wheel on the 7875). I’d say you’re kind of at the limits of single T4 stuff if it’s choking out at 5100 rpm. Oh and check out AGP, they have a 1.25 back housing for like $180 bucks for your current setup.
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Teching In
Joined: May 2018
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Thread Starter
Teching In
Joined: May 2018
Posts: 24
Likes: 0
definitely i'm upgrading to a 4" exhaust, i was just thinking maybe i should change the turbo as well, gonna do the exhaust and post the diffrence.
FWIW, I run an s475/83 t4 1.25 turbo on my 5.3. I’ve run 4” exhaust out the back through a Hooker MaxFlow muffler with the wastegate recirc’d to the downpipe. I refabbed the gate to a screamer pipe, then went to a 4” cutout and a smaller exhaust system for the street. I DO monitor backpressure and it dropped with every change I made. Changing the gate to a screamer reduced POST TURBINE BP by 2 psi. Every little bit AFTER the turbine helps. As it sits right now, at 23 psi I see only 1.6:1 drive pressure. With the cutout opening at 3 psi, it’ll go from about 2-3 psi to 20 in less than a second if a crack it while cruising. This is with a 2.25” hotside into a 2.5” merge about 16” before the turbo. Again, this is with a 1.25 housing. Don’t get hung up on needing a tight housing to get it to spool. I monitor everything and have logs to prove it all. Free up the turbine wheel as much as possible and you’ll see an improvement.
I've yet to see 78/75 outperform a "real" T4 S475. Also I agree with the T6 option. A v8 of any kind should have a T6 on it IMO. My 4.8 spools the 1.32 T6 S480 just fine, for my intended use anyway.
That said if you need to stick with a T4, go with the S400 frame and 75-80mm compressor, what ever you can afford. Make sure to use the big 87/96 exhaust wheel and modded 1.25 T4 Borg exhaust housing. Makes for a mean little T4!
Id run a 4" downpipe and 4" electric cutout. Best of both worlds. Cheap and relatively easy compared to a true 4" back exhaust anyway. I like to run 2.25 crush bent garbage to a stock muffler. Any exhaust shop should b able to hook you up cheap.
That said if you need to stick with a T4, go with the S400 frame and 75-80mm compressor, what ever you can afford. Make sure to use the big 87/96 exhaust wheel and modded 1.25 T4 Borg exhaust housing. Makes for a mean little T4!
Id run a 4" downpipe and 4" electric cutout. Best of both worlds. Cheap and relatively easy compared to a true 4" back exhaust anyway. I like to run 2.25 crush bent garbage to a stock muffler. Any exhaust shop should b able to hook you up cheap.
Teching In
Joined: Nov 2014
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Not to hijack the thread but what I have is s480 t4 96 1.25. my exhaust system is pictured above. It goes from 4 inch v band to 3inch back up to 3.5 through a race bullet muffler, I also put a 3 inch cutout on it. Do y'all think I am hurting post turbine flow? I really hate the way a open downpipe sounds so I want to keep this exhaust. Also that part I cut off I didn't like the neck down so I replaced it with a smoother 3.5 transition.
On The Tree
Joined: Oct 2012
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You are definitely hurting it by necking it down that much. That big of a turbine needs 4” minimum. Just put a 4” loud valve in it if you hate open exhaust and get any number of 4” resonators or mufflers to keep it quiet.
Teching In
Joined: Nov 2014
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I cant fit anything larger then a 3 inch in that section I have labeled in the picture. As soon as the exhaust goes under the car I could replace the 3.5 inch with 4 inch tubing and get a 4 inch race bullet.