just want to get some real numbers. my compression is supposedly 13.1:1 and only putting out 225 psi. i put down 222 hp and i think i am going to mill the head to raise some more cr out of it. i am only running 94 octane.

one thing to add, when i went to the dyno i used pump and 108. i saw no difference at all.

let me know what crank pressure you are running at what octane.

thanks, josh

 

supposed to be 12.3:1 CR in a B18CspecR stock 81mm bore. my cranking pressure is 245psi with ctr cams on stock gears. i'm using 91 octane. what cams are you running, that would effect your cranking pressure as well. are you doing your cmpression test with the throttle plate all the way open?

 

YEA I HAVE BIG CAMS AND LONG DURATION SKS2 CAMS. yea tbodies are open.

 

Long duration will effect cranking pressure, as pressure will bleed off. Although that does seem a little low.

-sander

 

yea i know... so what kinda crank pressure can i go to with 94 octane?

 

I sorta did 300-310, Light detonation at low rpm though.

(that was on 93)

Wouldnt reccomend it. Lots of accelerated wear on various parts, rings, bearings, etc... (detonation that is)

-sander

 

so i might be able to mill head about 25 thou. supposedly it brings it up to 14:1. i am going to try it i think.

 

anyone have other answers?

 

i think your compression ratio is high enough...instaed of millling the head try more agressive cams...why mill and than have clearance issues with the cams you already have.

 

my clearance issures are not issues . i have 125 thou piston to valve. i can only mill heada about 25 thou for correct piston to head clearance. i am trying to figure out crabking pressure to octane basicly.

 

did you break-in the motor yet and leak it down ? given the fact that you have big cams and your dynamic compression is much lower, you can prolly get away with a 15 to 20 thous mill ... as for comparing output iwht 108 fuel and 94 fuel, did you adapt the ign timing map to get more aggressive and say no more output ? perhaps you're out of injector and not realizing it ... could be a lot of things happening. Also, what heat range plug and what a/f ratios like ?

greg

 

Like Greg stated, with higher oct race fuel you need advanve ignition timming because the higher oct gas will actually burn slower than the cheaper stuff. It can even trck your wideband because all the fuel isnt burning and just blowing out the tailpipe

 

yea i advanced it up no more than 4 degrees than the map for 94. my timing i believe was at 26 or so. it made no difference. air fuel wise my aem ugo was reading 11.5 or so where i made the most power. i tried leaning it oua nd riching up with race gas. nothing.

my question really iscrank pressure is more important to octane than static cr right? if you think about it this is the only way it makes sense. my leakdown was 2%.

i am using stock heat range ngk vpower. what plugs do you recomend?

the reason i can mill only 23 thou was due to .003 piston to deck, .030 head gasket, and quechpad was about .035.

another reason i think i am seeing suck low numbers is due to pistons. larry said they are 11cc dome. i find this hard to believe. can any one vouch for this measurement? there are the rollerwaves in 89mm.

 

i still havent got an answer about crank pressure and octane. any other ideaS?