Black_98Z

iTrader: (13)

I already have the ebay kit and I am pretty sure I am going with the tc78 turbo. My question is what size motor. Looking to run 15 psi max. Keep in mind this kit has a 3" dp. I think the 346 is more suited for the 3" hp, but with the larger motors I think the max hp would be higher, the spool quicker and more off boost power. Thinking of running 8.8-9.1 cr.

Thanks

black98ws6ta

iTrader: (77)

The max hp at 15 psi may be higher with a larger motor, but you should be able to make more max hp on the smaller engine. My decision would depend on what you want to use the car for and what your goals are.

Black_98Z

iTrader: (13)

The car will be used a lot on the street but will be taken to street nights at the strip. Looking to see which engine is best suited for this setup.

67Firebird455

iTrader: (27)

Larger displacement will have more off-boost torque, will spool the turbo faster, and will make more power for the same amount of boost, period. Even @ 15psi, you could set it up to run 9.25-9.5:1 and still be good to go. You're right on the 3" DP, it would work great on a 346, but you can get a good compact sized turbo that makes over 600whp and still uses a 3" downpipe!

Josh@KY-Turbo

iTrader: (120)

TC76
8.5:1 370ci, Stock 6.0L LQ9 heads, LS6 intake, TU1 cam
15lbs boost.
770rwhp through a TH400 and 9".

Went 9.80 in the 1/4 with a terrible 1.6 sixty ft.

Black_98Z

iTrader: (13)

Thanks Josh. Would you recommend more compression like 9.1 or would you have stick with something the 8.5 you had. I also have a set of stock 317 heads already.

Josh@KY-Turbo

iTrader: (120)

I like lower compression and more boost. Its more forgiving. My 370 wasnt bad when it was N/A. I drove it around for 1500 miles or so before the turbo setup went on. It had no problem spooling the turbo at 2200rpms eigther.

engineermike

This subject is debated a lot. I've tried several different displacements with the PT76GTS and wound up at 388 cid, which I like the best.

It's like this... if you plan on running lots of boost and making the most hp possible, then go with the smallest one. If this were the case, you might even consider a 4.8 liter build. But, you'd have to run 25+ psi boost to get the numbers. Conversely, if you want max hp at a lower boost level, like 15 psi, then go with the biggest one.

My goal was to maximize hp on pump gas (15-17 psi), so I went 388 even though I had already run 383 and 360 cid.