What Compression with Boost?

[Turbo98]

What compression is everybody running with boosted cars. How much boost on pump gas and how much power? I was tthinkinb about a 10:1 set-up to help get some more low-end power but don't know if that's too much for 93 octane with moderate boost. I know all set-ups are different but I'm just trying to get an idea if anybody is running upper 9's-10:1 with boost on the street.
Thanks.

 

[98 Saleen Cobra]

It all depends on the type of s/c. With lower compression you can get away with more boost safely on 91/93 pump gas. Most people with Centri cars will run about 9.7-.8 and guys with TT or screw type blowers will run 8.6- 9.1.

 

[Turbo98]

Just wondering what everybody tends to run.

 

[Toasty]

Read 98 Saleens post again.

A centri blower works best with close-to-factory compression ratio. Flatop pistons in a rebuild will get you close to 10:1 compression.

Turbo and PD blowers like lower compression, 8.5:1 to 9:1 are common ratios in these applications.

Asking 'what everyone tends to run' is a misguided question. There are people like me with a KB, centri, or turbo on a stock shortblock (so 9.8:1 or so compression), and there are people with built shortblocks running the appropriate boost for their SC application.

You dont pick the compression ratio and then pick the blower/turbo afterwards. You design the engine parameters around your forced induction choice.

FYI, 03-04 Cobras have 8.5:1 compression to make the most out of their factory Eaton setups.

 

[busta]

I'm running 8.5:1 with my turbo.

 

[fourvalvegt]

It all depends on the car, blower, fuel, and what its used for. If you think about it if you bolt a kennebell on your running almost 10 to 1 where most people with a twin screw want around 8.5. Centri cars can get away with higher cr because of when the boost comes on.
I was running 9.85 to 1 with a procharger and that was a factory longblock, it was a blast to drive and never detonated or pinged

 

[Turbo98]

It all depends on the car, blower, fuel, and what its used for. If you think about it if you bolt a kennebell on your running almost 10 to 1 where most people with a twin screw want around 8.5. Centri cars can get away with higher cr because of when the boost comes on.
I was running 9.85 to 1 with a procharger and that was a factory longblock, it was a blast to drive and never detonated or pinged

Thanks, this is helpful.

I'm just trying to see what everybody is getting away with and how the low-end torque is due to the lack low RPM torque with the B heads.

 

[Turbo98]

Read 98 Saleens post again.

A centri blower works best with close-to-factory compression ratio. Flatop pistons in a rebuild will get you close to 10:1 compression.

Turbo and PD blowers like lower compression, 8.5:1 to 9:1 are common ratios in these applications.

Asking 'what everyone tends to run' is a misguided question. There are people like me with a KB, centri, or turbo on a stock shortblock (so 9.8:1 or so compression), and there are people with built shortblocks running the appropriate boost for their SC application.

You dont pick the compression ratio and then pick the blower/turbo afterwards. You design the engine parameters around your forced induction choice.

FYI, 03-04 Cobras have 8.5:1 compression to make the most out of their factory Eaton setups.

I read his post.

I'm not trying to determine compression on what everybody else is running or trying to pick a number off of a Kenne Bell car when I have a turbo set-up. I currently have a turbo set-up and am trying to maximize the efficenecy/throttle respnse/turbo spool with these heads. The turbo's respond similar to the centri's. No blast of low-end torque. I've been around for a bit and I'm more interestted in how the B heads respond to higher compression to help overcome some of the low-end lack of power. I know what compression the turbo Terminators run on their turbo and PD blower set-ups. There are a lot of centri guys in here with the same heads as I have and they respond somewhat similar to turbos (not exactly though). So, that's why I posted the question and that's why I posted it in here and not somewhere else.

 

[Toasty]

I read his post.

I'm not trying to determine compression on what everybody else is running or trying to pick a number off of a Kenne Bell car when I have a turbo set-up. I currently have a turbo set-up and am trying to maximize the efficenecy/throttle respnse/turbo spool with these heads. The turbo's respond similar to the centri's. No blast of low-end torque. I've been around for a bit and I'm more interestted in how the B heads respond to higher compression to help overcome some of the low-end lack of power. I know what compression the turbo Terminators run on their turbo and PD blower set-ups. There are a lot of centri guys in here with the same heads as I have and they respond somewhat similar to turbos (not exactly though). So, that's why I posted the question and that's why I posted it in here and not somewhere else.

"It all depends on the type of s/c. With lower compression you can get away with more boost safely on 91/93 pump gas. Most people with Centri cars will run about 9.7-.8 and guys with TT or screw type blowers will run 8.6- 9.1."

 

[98 Saleen Cobra]

Ok well I'm running 9.1 CR with my T-trim. The only reason that I am is because I bought the motor here on SVTP. It was originally made for a TT Cobra.. If I would have built my own block I would have gone with a 9.8CR..