deMideon Posted June 8, 2006 Share Posted June 8, 2006 I screwed my cam up (never adjust the valves on cold medicine! lol), so I am rebuilding my engine and I want to make absolutley sure I have the quench setup properly and everything will still run ok. Here is what I have: SBC 377 - 0 deck - 6 inch rods KB762 pistons Canfield heads - 59.2 cc Crane cam 114691 Mr Gasket Ultra seal head gasket .038 compressed thickness. I am thinking of advancing the cam 2 degrees to move the power band down from min 3800 rpm. But I do want to make sure I am still bleeding off enough compression to allow 93 octane gas to work. What do you guys think? Quote Link to comment Share on other sites More sharing options...
jt1 Posted June 8, 2006 Share Posted June 8, 2006 To make a motor more pump gas friendly, you retard the cam, thus delaying the intake valve closing a little longer, and lowering the dynamic compression. Advancing the cam will raise the DC. The best thing to do is find out the net cc's of the pistons and the intake closing point of the cam, and calculate the static and dynamic compression of your combo. Then you can play with the cam setting and see the results. Edit: Check this out: http://forums.hybridz.org/showthread.php?t=110913&highlight=dynamic+compression Grumpy covers it well in that thread. No big surprise there, huh? John Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted June 8, 2006 Share Posted June 8, 2006 I checked a KB catalog online and I don't see a KB762 listed, they have a 194, 195, 350. The 350 is a 18 cc dished, the 194 is a 7cc single valve relief trough, and the 195 is a 3.25 cc dome. Compression with your heads should be around 10.5, 11.5 and 13.2 respectively. The last one is too high for a street motor IMO and the second one is marginal. With that cam you should be fine and it should run like a raped ape from the san francisco zoo. I'm sure with a zero deck your quench is fine which is good and will help stop detonation with the compression your running. Quote Link to comment Share on other sites More sharing options...
deMideon Posted June 8, 2006 Author Share Posted June 8, 2006 Do you know where I can find the formulas for dynamic compression? Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted June 8, 2006 Share Posted June 8, 2006 http://cochise.uia.net/pkelley2/DynamicCR.html Quote Link to comment Share on other sites More sharing options...
deMideon Posted June 8, 2006 Author Share Posted June 8, 2006 Dr Hunt... it's under forged... it is a flat top with a 4.8cc head volume so my static comp with my head should be about 11.6:1 Thank you for the CR link!! Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted June 8, 2006 Share Posted June 8, 2006 Oh, I just assumed hypers, sorry. Let us know how it runs. Quote Link to comment Share on other sites More sharing options...
deMideon Posted June 8, 2006 Author Share Posted June 8, 2006 No problem... any idea how I can get the LSA and intake lobe centerline? I don't see that info on the cam card... Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted June 8, 2006 Share Posted June 8, 2006 theoretically, you can do the math and use the valve event timing. It's half the duration on the intake side for the intake centerline, do the same for the exhaust. You want the difference in degrees between the two for the lobe separation. Or you can put the valve timing events in DD and it'll do it for you. Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted June 8, 2006 Share Posted June 8, 2006 heres some differant calculators http://www.kb-silvolite.com/calc.php?action=comp2 http://www.wallaceracing.com/dynamic-cr.php http://www.smokemup.com/auto_math/compression_ratio.php http://not2fast.wryday.com/turbo/compression/cranking_pressure.shtml http://www.diamondracing.net/cocalc.htm average the results from ALL the calculators... any single calculator will tend to give you fauly info compared to averaging the five answers Quote Link to comment Share on other sites More sharing options...
deMideon Posted June 8, 2006 Author Share Posted June 8, 2006 I am challenged by the cam timing part... Dr hunt I do have DD2000 put everything in and it gives me a lobe center of 112(doesn't say if it is intake or not!), but doesn't give me LSA either. I tried the calculators from grumpy.. the KB gives me 8.8.. but they use ABDC@.050 +15 for a solid lifter shouldn't it be more like 20? Quote Link to comment Share on other sites More sharing options...
deMideon Posted June 8, 2006 Author Share Posted June 8, 2006 Heh.. I just called Crane... figured they would know, the lobe separation is 112 and the intake lobe centerline is 109. I just couldn't read the cam info correctly! That gives me a DCR of 8.5.. so I think I will be ok, 0 decked and a .038 head gasket should have me able to use 93 octane gas right? Quote Link to comment Share on other sites More sharing options...
jt1 Posted June 8, 2006 Share Posted June 8, 2006 http://www.cranecams.com/pdf/Page266-275.pdf?PHPSESSID=69ae0483719b080d67d3cddd73eb446a Crane doesn't really overwhelm you with info there, but it looks to me like the intake valve closing @ 0.050 is 55deg ABDC. Comp gives you a IVC at 0.015, which is what I've used for my DCR calcs. I'm not really sure how to deal with that????? jt Quote Link to comment Share on other sites More sharing options...
Pyro Posted June 8, 2006 Share Posted June 8, 2006 8.5:1 DC is easily in the 93 octane range. Since you have a light car with fast burn heads than don't require that much total ignition timing, I'm sure you could get by with 9.0:1 DC and 93 octane. Quote Link to comment Share on other sites More sharing options...
deMideon Posted June 13, 2006 Author Share Posted June 13, 2006 Well I guess it was good that I ground a few lobes off my cam... I have been having a problem with a water leak in this engine and I could not figure out where the water was going. Number 7 piston wall has a bunch of pin holes in it (only 40 over too!), guess I am going to have to sleeve it! Quote Link to comment Share on other sites More sharing options...
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