My Trans Am is getting ready for another motor. What is the safe compression ratio I will need for my motor?

355 LT1
Vortech S-trim, non intercooled
NOS 100 shot
AFR 190 heads, 56cc chambers
LT4 hotcam for now, might go blowercam if I find one I like

I am going forged this time. What would be a good CR for my setup? I have a t-56 tranny and 3.42's (possibly going 3.73). This is going to be a street car, but not a daily driver. I will be using a boost retard system of some sort and NGK tr-6s.

 

9:1 would be a good setup and be streetable with the charger. I just dropped in a 383 with a 9:1 setup that i'll be running 7 to 10 psi on all the time and be dropping a 150 shot on at the track. I'm also running a non-intercooled S-trim. Don't have it running yet though cause i'm waiting on a tranny, but I feel pretty comfortable with a 9:1 setup. It was always nerve racking at the track running 6psi with a 75 shot with my stock internals at 10.75:1, but she held up, until my oil pump let go, which induced this current setup. I'd atribute it's past health to a good tune somewhat on the conservative side though. Hope that helps.

Ken R.

 

yes, that's a good starting point for me. Thank you!

 

Roguedriver: IMHO 7 - 10 psi without some kind of cooling is going to generate very high intake temps that can lead to detonation. Might want to review that; there are alky injection systems for around $500 if you don't want to go the innercooler route.

 

Why not just pulley up the S trim instead of running only 6 PSI + N2O?

 

I am itching to use this nitrous system that's sitting in my shop...got the urge to purge...

I might end up not keeping the juice on, but I am going to give it a shot and see how much I like it.

 

Cruising around town, i'm never really in the boost, so not worried about intake temps. The occational street light to street light trip still doesn't get the temps up too bad and sustain them, so still not worried there. And whenever i'm at the track, i'm spraying at the same time, so my temps go WAY down. I've scanned while in the boost quite a bit when at 6psi alone, and they've never got too bad. I've already considered meth injection, but it's on the temporary back burner till I pay this project down a bit.

Ken R.

 

I have a Scanmaster and monitor my intake temps regularly. When I was running 9# of boost, non innercooled with my Vortech S trim I could easily see 160F temperatures around town just cruising (no boost).

 

Altitude must have a lot to do with it then OBE cause at the track when I would scan on 6psi and no nitrous, I would see around your NA temps. I don't see anything near your NA intake air temps out of the boost. Even in the heat of summer, I don't remember ever seeing anything even pushing 200. That plus I keep the timing pretty low also, so i've never had any problems with detonation. I plan on keeping the timing low in this setup too, so on top of dropping to 9:1, thats why I wasn't too worried about it. Was planning on scanning when I get it up and running to see what my temps are with this setup, and if they happen to be up there, then I was planning on a Snow stage 2 kit.

Ken R.