its not 100% accurate, but its within 3% of a stock ls, and a gsr, and my 11.3:1 c/r

 

Indeed I do. It's internals arent stock, so it's not a suprise to me. I have also done a compression test with a different gauge with the same results... I guess it's the cams that is throwing the formula off...

Jeff Evans (Evan's Tuning) gave me his rule of thumb:

8:1~8.5:1 compression: 150-170 psi per cylinder
8.5:1~9.5:1 compression: 170-210 psi per cylinder
9.5:1~11:1 compression: 210-275 psi per cylinder
11:1+ compression: 250+ per cylinder (highly depends on cams being used)

 

I have stock cams right now which I heard makes higher cylinder pressure...Im putting in crower 403's in the next few days.. Ill check the compression then and post up the numbers.

 

that rule is vague at best. every near stock compression ls i have done has put out between 175 and 180. 210 is close to 10:1

 

Also remember that ambient air is rarely a perfect 14.7psi; so in order to use this formula more appropriately, 14.7 will need to be replaced with a more accurate measurement of current outside air pressure where the compression measurement is taken. Anybody got a barometer??? BTW, 29.92 inches of mercury is equal to 14.7psi. But, 14.7 is a pretty good guess for florida air, but a guess nonetheless. This would explain your .3 parts chi town.

Also, as was said earlier, non precision analog gauges can be off as much as 10% when they leave QC from the factory. Precision gauges will cost you$$$ so if you paid around $40 for the gauge, chances are the highest quality standards weren't in place for it. Most of these gauges can be adjusted however, if you have a constant to use as a base.

I know this because I used to calibrate precision medical gauges among any equipment you can think of in a hospital for the military. So, you can trust my judgement. I am a Certified Biomedical Equipment Engineer. Car gauges are much more basic, as with most auto related test equipment.

This is why I explained earlier that judging you C/R based on Compression results is much akin to going around your elbow to get to your asshole.