Hi,
do you need to have a lower cr when using a paxton or vortch ? is 9:1 ok ?

Dan

more information on the use would help but in general yes 9/1 is fine depending on the boost you want.

9:1 is fine. I ran 6psi of boost on a cast piston 440. Make sure you have enough fuel and your carb is boost referenced and you'll be ok. FWIW it took a mild 3900lb b-body from 12.90's to 12.0. Probably could have run 11's w/ a little tuning.

I used a Paxto SN-2000 w/ a modified impeller. I ran a boost delay box and dropped timing out as bost went up. If you go over 8psi you should use a meth/H2O injection or a cooler.

You can run boost with 12:1 compression if you want to. All comes down to how much octane and/or meth injection you want to run.

School me people !!!! meth injection? what is that?

I have a supercharged 408 with 9 to 1 compression and I run 11 psi with an S-trim Vortech. I just started using meth injection to keep down the air inlet temperatures. You can run without the meth, but you need an MSD boost timing master to take out timing under boost. Also, it is critical not to run lean of fuel under boost.

I have a 440 with the cheapie Speed-Pro 9:1 forged pistons. It measures out to 8.7:1 on my engine. I've run 7.5 psi for years on pump gas with no problems. When I was injecting a little rubbing alcohol I could crank it up to 17 psi and have all kinds of fun.
Pull timing out under boost. More boost means less timing.

Keep it out of detonation and it'll last forever.

Here's my old set-up. I fabbed it myself. I had a total of $2100 in the entire system, from carb prep to fuel system upgrades and gauges.