Thread: Just dynoed my 396 BBC...how to get more HP?

Tweet

Well, in short standard atmospheric pressure at sea level is 14.7 psi so if your cranking compression is 160psi your dcr is 160/14.7=10.88:1... Just math... So it seems one of these numbers ain't right... That's why I mentioned it because you would be detonating with pump gas... I would expect a normal cranking compression to be in the 120-130psi range for a hot street motor... If your scr is closer to 9:1 you should be around the bottom of that range... I would also be very surprised if you could get 1.25 hp/ci out of a 9:1 motor... If you can post all the motor specs I can run it through desktop dyno for you but it sounds you've already done that... Keep in mind dd won't account for accesory drive (water pump alternator etc) which can amount to about 20hp... I'm not trying to beat you up or anything... The numbers just don't sound right.

-Chris

Originally Posted by skids72

Well, in short standard atmospheric pressure at sea level is 14.7 psi so if your cranking compression is 160psi your dcr is 160/14.7=10.88:1... Just math... So it seems one of these numbers ain't right... That's why I mentioned it because you would be detonating with pump gas... I would expect a normal cranking compression to be in the 120-130psi range for a hot street motor... If your scr is closer to 9:1 you should be around the bottom of that range... I would also be very surprised if you could get 1.25 hp/ci out of a 9:1 motor... If you can post all the motor specs I can run it through desktop dyno for you but it sounds you've already done that... Keep in mind dd won't account for accesory drive (water pump alternator etc) which can amount to about 20hp... I'm not trying to beat you up or anything... The numbers just don't sound right.

-Chris

I know you're not trying to beat me up... I'm not a math whiz but my 2-stroke dirtbikes putting out 8.5-9:1 static make 175PSI and I run them on premium gas. I know people that run them on 87 too. 110PSI is when they are just about dead, and need a cylinder, piston, and rings...140-150PSI is when I do a topend on them.

Thanks for the info, I will get it tuned up. It just seemed low to me. I guess if I was losing 20% through the tranny and rearend which is possible I'd be at 430HP 430TQ which is believable.