Looking for a formula to calculate compression ratio at 26#'s of boost

[turbo6x2]

How does one compute this? If you have this please let me know. It has been suggested that running 110 octane at 26#'s of boost is not high enough to support this. Trying to figure out what the compression ratio would be. Your help is appreciated....

 

[Lee Thompson]

?

A bunch!!!-----As far as 110 being enough octane, depends on static com. ratio and the amount of timing. DS will tell you if you have enough octane. I have be running 2 parts 93 and one part 116---with alky. That is enough to keep detonation away for me with 8.4 C.R. and 24 degree timing in 1-2 22 in 3rd. @ 24-25 psi

 

[turbo6x2]

I would hope with straight 110 and the alky we would be okay.. May have to play with using alcohol some more to get it dialed in. The bolts worked themselves lose from the turbo again. May have been a lot of the issue we were having to this point. I know running straight 110 at Nationals with the boost about the same (may be a pound difference) was netting no knock on the direct scan. But since doing some suspension stuff we are getting knock, trying to see if it's hitting or not. Seems to have a lot of tire chatter where you see it shortly after I leave the line.. Just trying to figure out where the unusual knock counts are coming from... I'm still running the same chip as Nats. For the time being...Not extremely high but we went from no knock counts to having knock counts. That's why someone mentioned I need more octane, just trying to see what everyone runs at higher boost levels.

 

[turbo6x2]

What octane is everyone running with what combinations??? thanks,

 

[Lee Thompson]

knock

I would think you are getting knock from something bumping (big DP) Reds chips will ignore knock for a few seconds( 1-3 ) if you ask for that option, on launch. 110 octane should be more than enough.

 

[cool 84]

I ran 24psi and 24 degrees on AV gas (somewhere around 108 octane) with no knock. Don't know if you need this since it was with an intercooler but I had the basic mods like ported heads and intake, 206 cam, TA49, and a 2.5" DP.

My dad's car ran 25psi @ 28 degrees of timing on pump 100 octane and alky injection. There was an occasional count or two but never more than 2 degrees of retard and usually none. We were told that was no where near enough octane but it worked and the only time we hurt a headgasket was when the alky jet got plugged during a run.

 

[turbo6x2]

Well that helps. I was having issues with this being a problem since we ran that all week long at Bowling Green and it seemed to run just fine. (no retard) Come home and do the modifications to the rear suspension and now I have counts. We're checking all possible causes. I just had someone get me a basic formula

1. boost + atmospheric pressure (ap)
2. "1" divided by ap
3. "2" multiplied by static compression ratio (SCR)
(boost+ ap)/ap)*scr=ecr

Example
boost = 26
assuming ap =14.7
Assuming SCR=8.0
(26+14.7)/14.7)*8.0=22.15
This is a rough calculation but will get you some idea.

Bear in mind how hot the air is getting at those pressures. There is a limit to the benefits of psi vs air temps.

(thanks Dean!)


Hope this helps someone else if they were trying to figure this out.