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Old 10-01-2011, 01:36 PM
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Blown 496 cam recomendations

I'm convinced my cam is wrong for my combo. a 8.5 496 with 420 megablower 1-1 ratio. Dual holley 4777's. Goal was cruising 2000 in 5th gear. Engine came with a hyd roller .640 lift 114lca on 109 icl. Has 10hg idle vac. at 1000rpm locked at 32. Don't know duration but must be big. Engine builder and I don't talk anymore, another story. Chevelle with 29" tires, 390 gear and tko600 trans. Will not boil the tires on rolling start. Leak down good, 140lb cranking. Runs like a worn out small block. It idles shaky like too much timing. It runs best at 20 degrees but is really a dog then. This winter it comes out and something changes.

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Old 10-01-2011, 03:30 PM
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I'd start by talking with the tech guys at Blower Drive Service...
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Old 10-02-2011, 07:36 AM
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You need a little cam to run well at 2000 rpms. Which would have about 17 to 19 inhg of vacuum at idle (not 10 inhg). I would guess you have about 30 or 40 degrees to much cam duration.

However, 8.5:1 cr in a blown BBC would be very high compression for a mild cam.

I think you would need to drop the compression into the low 7's:1 and install a cam with 215-220 degrees at 0.050" on the intake, another 10 degrees on the exhaust, on 114 lsa.
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