alright i have a 1989 trans am gta with the 350 l98 engine. i just bought a garrett t25 turbo for it but have no prior experience with turbos. i already have a blowoff valve and turbo timer but was hoping to get some advice on intercoolers, turbo manifolds, etc. i was also wondering about how much power i should be pushing with 8-10 psi on an otherwise stock engine ( have full bolt ons). any advice would be much appreciated.

 

u would need about 6-8 of those t25's . that turbo is way to small.u need something around a t4 61mm turbo at minimum, and most would run 2 of those

 

The T25 is small for sure, but depending on the specifics it could support up to about 250 crank hp (so figure roughly 200 rwhp). You'd need two of these and that would support something in the range of 350-400 rwhp.

As for boosting an otherwise stock TPI, I have an automatic so I don't have true peak numbers but at roughly 12 psi I'm making 302 rwhp/418 rwtq, however my peak torque occurs lower than I am able to dyno (due to downshifting at WOT in lower rpm ranges).

Assuming the unobtainable figure of 100% efficiency, 14.7 psi of boost on a stock 230hp/330tq engine will produce exactly twice the power, or 460hp/660tq. So 7.5 psi would give you a 50% power increase minus inefficiencies. Turbos are fairly efficient though and your real world number could be close to 90% efficiency I believe. I'm getting a 55% increase in torque at 11-12 psi and my tune is very conservative on the timing (16-18 degrees total at full boost). Measuring it a different way, my car went from 9.30's in the 1/8 mile to 7.90's by adding 12.5 psi. It will see 7.6-7.7 with a more agressive tune. At 8 psi non intercooled it ran 8.6's. I have zero mods to the engine except removed the smog pump and of course larger injectors & a megasquirt ecm.

 

Ok like I said I have no turbo experience so I dont kno what a good size is. I didn't but anything yet because I was gona buy it off my friend. would at t28 b much better?

 

You are in the mild 4 cylinder world.. you need a much bigger turbo... in garret terms, thats GT35 or larger

I have a pair of T4 T60's for sale that would work ok for a twin setup (would support 800+whp so alittle big for twins on a mild 350TPI motor) and definately be ok for a 350-400whp single setup that would spool instantly with .96 a/r housings. I have .68's on them now, a new housing is 150 bucks to swap out.

Most guys target 64-70mm for a 350 inch motor for a single turbo. that will cover 400-700whp in some builds.

 

Alright thanks man ill have to look around