Just did a compression and leakdown test today on the car.

Leakdown was like 2% all across, looking good.

Cranking psi was 210 psi on 5 cyl, 1 cyl was 205. The other 2 i wasnt able to get readings on because the header blocked the tester. The engine was cooled off, but not stone cold, that was with about 4-5 compressions per cyl.

I did (dumb me) forget to prop the throttle body open. I have read that will produce lower readings. True?

Next question, is how does that relate to dynamic compression? Able to be converted back and forth? Using this calculator, http://www.rbracing-rsr.com/comprAdvHD.htm , it tells me cranking psi should be about 157psi, no where close.

Anyways, if someone has a different calculator maybe run the numbers or pass on a link it would be great, thanks.

11.3:1 static
6 inch rod 383
gm 847 cam, http://cranecams.com/index.php?show=...41&lvl=2&prt=5

 

I had a similar cam in an 8.5:1 357, and the cranking compression was around 175psi. Now it's 10.2:1, and it blows my finger off the spark plug hole when I'm finding TDC. I wouldn't worry about high cranking compression; that's why racing starters are built with high-torque motors.

 

My 396, with 11.7:1 static compression and a Comp XR282HR (282/288 advertised, 113 LS, +4) produces readings of about 215 PSI. That's with the throttle body closed and five compression cycles.

 

Thanks, good info to have there, means its fairly close to where i was.