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Old 02-01-2012, 09:26 PM
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SBC build ???

New here been doing a bunch of research on here and find lots of great info. But the more I learn the more I think I am starting to over think things.

I am looking at building a engine that is not a kit. The block I am using would be a 86+ sbc with a stock bottom end decked to 9.000" and bored .030 over. The plan is to use factory vortec heads with beehive springs and maybe 1.6 roller rockers or 1.5, 5.7 rods ( stock ), inverted dome 4 valve reliefs 10cc hypereutectic pistons, and I am still throwing around which cam to use but it is going to be a hydraulic roller and a .040 head gasket. That should give me a 9.84:1 cr static.

My confusion is on the cam selection when determining the dynamic ration and cracking pressure. If I was to use a comp XR252HR grind I would have a dcr of 8.55:1 with a pressure of 173 psi. If I go with a XR264HR I end up with 8.27:1 dcr and 166 psi. I also thought about going with a XR270HR to end up with dcr 8.09:1 and 161 psi. all of this numbers based off of 1.5 rockers.

I goal is to run this in a 83 k20 pickup truck stock tires size ( 265/75/16 ) and 4.10 gearing mated to a 700r4. and use pump gas 91 at most and if I could get away with 87 then run with that.

What I dont quite understand is the effects of dynamic ratio when determining octane selection and the pressure for low end response.

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Old 02-02-2012, 10:22 AM
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Here's what Crane has to say about it....
http://www.cranecams.com/faqview.php?s_id=10
I would add that a very tight squish (0.035" to 0.045") should insure detonation-free operation with the XR264HR cam timing. Use a Cloyes front cover so you can easily retard the cam for less cylinder pressure if you find yourself in trouble after you get the motor dialed in.
http://www.summitracing.com/parts/CLO-9-221/
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