I have plugged a few numbers and came up with a 9.67:1 cr. SRP pistons inverted dome (-21cc) 4.145 bore, 3.75 stroke 62cc chamber .010 deck.

The questions I have is 9.7 cr @ .040 quench to much for a race gas non IC blow through?.

Is quench hieght as critical in a blown application as it is on N/A application?

Yes, it is as important (or not) depending on other factors.

The A/F mixture in the cyl does not care how it got there; all that matters, is the conditions it finds once it's in the cyl.

I ran a true 9.7:1 compression 468 with .042" quench (non-intercooled) on 91 octane without issue. It was an aluminum block and had the ceramic barrier coated pistons which help, but you'll be running race gas which is a huge advantage over the 91 octane I ran. I made 15 psi of boost and about 800 rwhp with that setup in a street setup (3" exhaust, conservative timing, etc).

Jody

Thanks guys. I need to tear down the motor and check deck hieght and CC it. The only unknown at this point is the deck hieght.

I think 15psi would meet or exceed my goals. At sea level the true ratio would be 15:1, atleast thats what I come up with.

Is there any prefered gasket thickness? I plan to run cometic gaskets, I've heard (wether true or not) that thick gaskets in boosted applications are more likely to let go now how think I dont know.

I gather .040-.045 is the optimum quench.

I like to gather info before talking to my machinist.

I don't know a whole lot about blown motors but I have learned some from working on a 532ci 2000+HP blown alcohol motor. We were making about 39lbs of boost with our last motor. We had constant problems with the DART (non-solid) heads and keeping the cylinders sealed.

Essentially we were seeing the heads gaskets move where they narrow between cylinders. We think was because of head bolt stretch and the heads actually flexing and "floating" slightly. The gasket was getting hot enough to deform and with the loss of clamping force was deflecting to the side.

We talked to Jim Oddy(sp?) about our issues and he said to increase our solid copper gaskets from .050 to .080 and we would see the issue diminish or stop altogether. He also stated in a blower motor this whould make more power because you are getting more air/fuel into the cylinder (more space). He was right. We effectively lowered our compression ratio almost a point and picked up a tenth and haven't had the issue since.

I'm only stating this because it seems quench isn't as important in blown applications. I don't know if the fuel (alc/gas) makes the difference or not. It may. Bottom Line - Talk to the blower manufacturer or someone like Oddy that's an expert if you aren't sure how to set it up.

Troy.

I theorized that more quench was better for packing more air into the cylinder with less resistance.

I currently dont plan on o-ringing. I here cometic gaskets are good, and plan on using them. More research to find out if race gas and cometic gaskets will survive.

More replies welcome thanks again.