Baddest small-size T4 turbo out there? Want to upgrade my TC78
09-03-2013, 09:50 AM
#21
Isnt the GT91 the same size as an 88? I think someone on here has done 140 in a heavier setup with the tc78... Also, the 75 may not be much bigger, but with a billet wheel and the proper AR housing will make a huge difference. You may have some things working against you for cam and exhaust too, you might want to give your entire build befor pulling the trigger on switching your turbo.
Last edited by TT427; 09-03-2013 at 09:58 AM.
09-03-2013, 10:34 AM
#22
That's exactly why I'm researching new turbo now, because few lifters have eaten my cam, and I have to get new cam specced with some future growth in mind, if you see what I mean 
I see nothing wrong with my exhaust though, I have 3.5" DP with cutout on it and then into 3" exhaust. I could remove whole exhaust alltogether and leave just 2 feet downpipe if I saw gains in this Or I could fab new larger DP to the fender for 1/4 and 1mile events
I see nothing wrong with my exhaust though, I have 3.5" DP with cutout on it and then into 3" exhaust. I could remove whole exhaust alltogether and leave just 2 feet downpipe if I saw gains in this
Or I could fab new larger DP to the fender for 1/4 and 1mile events 
09-03-2013, 12:32 PM
#25
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I went from a tc78 to a pt7675 CEA and for me it was the best move. I was hitting so much backpressure on the tc78 with my 346ci that i'd spike up to 17psi and by redline i'd be down to 11-12psi. On my PT7675 I have no problem holding 17psi to redline. I'd push more but i'm out of injector so hoping i can get a bit more out of it once i get my pumps and fic2000's in and retune. FWIW I made about 40whp more however that is going from a dynojet to a mustang dyno so the gains could be quite a bit more. On 10psi I ran a best of 10.4@135mph but when I turned up the boost I started breaking up. Too wide of a plug gap so switched that out with newer plugs and will run again soon.
Here are some pics that I took between the two turbo's.
TC78 turbine.
PT7675 turbine
Here are some pics that I took between the two turbo's.
TC78 turbine.
PT7675 turbine
09-03-2013, 03:55 PM
#27
09-04-2013, 07:05 AM
#29
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Borg Warner S400 anything is out if you are tight on space. If you don't want a Turbonetics 76-78/75 or a pt7675 due to the 75mm turbine, your best bet is a Comp unit with the 79mm turbine or a S380 which has the 80mm compressor wheel and 83mm turbine but the race cover might be an issue due to your space constraints.
09-04-2013, 09:49 AM
#30
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Borg Warner turbo's are out if you have a tight space like me. Unless they came out with newer smaller outside dimension turbo's I don't know about. Here is a comparo with the s400 vs pt7675 vs tc78
09-04-2013, 10:12 AM
#32
09-04-2013, 12:21 PM
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09-04-2013, 12:29 PM
#36
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Thanks for the info. In physical size, how do they compare with the PT7675 shown above? Are they anywhere close to that or are they massive like the S400-75 that's shown in the same picture?
09-04-2013, 01:41 PM
#37
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On3 performance also a sponsor has released their 88mm T4 turbo with an 83mm turbine as well. Same physical size as their 76mm turbo that several on here have used. Cost like 850 I think.
09-04-2013, 03:42 PM
#38
09-04-2013, 03:43 PM
#39
