Turbo Engine Question

[BigRedChvy355]

hey guys, new to the board and loving ever bit of this site. i have two questions. what would be a safe compression ratio to run with twin turbos, and what size turbos would be good for about 700-800hp from a 355. i havnt bought heads yet and my pistons are rated for 10.3:1 with 64cc heads and 9.0:1 with 76cc heads, would it be safe to run at 9.5?

[camcojb]

hey guys, new to the board and loving ever bit of this site. i have two questions. what would be a safe compression ratio to run with twin turbos, and what size turbos would be good for about 700-800hp from a 355. i havnt bought heads yet and my pistons are rated for 10.3:1 with 64cc heads and 9.0:1 with 76cc heads, would it be safe to run at 9.5?

No. A centrifugal can run fine with 9 to 9.5:1 compression. A turbo engine likes 8.5 to 8.75:1 compression. It could be run at 9.5:1 but may not meet your power goals because you would not be able to run as much boost..

Jody

[TurboLark]

9-1 would be fine, it would just limit you to running lower boost. My motor is 9-1 and I am shooting for 850rwhp. As long as you are careful with the tune you can do just fine. I didnt want less than 9-1 because I dont want the sluggish off boost performance I would get with my cam/cylinder head package.

[BigRedChvy355]

like how low of boost would i have to run at?

[RSX302]

Although there are many variables, this is a rule of thumb I go by. I think I put this out before but I don't recall where it was at.

Non-intercooled w/ factory timing and 91 oct
10.5:1 = 4 psig
9:1 = 6 psig
8.5 = 8 psig
8.0 = 10 psig

Intercooled w/factory timing and 91 oct
*Add 2 psi to each of the above

With either non-intercooled or intercooled, upping the octane will allow you to increase boost or timing. 2 points oct = 1 psi boost or 2 Deg timing above baseline.

Here's the disclaimer: As with any motor, there are limit's before meltdown. Just because you throw a ton of oct. at it, don't think it will survive.

Hope this made sense.
Ron