 grumpyvette
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 15641
Age: 65
Loc: FLORIDA USA
Reg: 03-16-01
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05-07-12 06:23 AM - Post#2223370
In response to rumrumm
I got a few emails asking why I suggested the crane cam I posted, every choice is a compromise the key is selecting a decent match,first keep in mind this is a 327 with a manual transmission, and close to 9.8:1 compression, the engines piston speed doesn't get to be a factor until about 7000rpm plus so its silly to restrict the engine with a hydraulic lifter cam that will not function well over about 6200rpm
IF WE LOOK AT THE DISPLACEMENT to VALVE SIZE we get 20cid so a 110 LSA is about correct
IF we want to be a bit CONSERVATIVE on duration because this is a street application and calculate BOTH dynamic compression to fall near 8:1 to allow crappy octane fuel and enough duration to allow restrictive heads to breath at mid and upper rpms we find your looking at 220-230 degrees of intake duration, adding extra exhaust duration tends to compensate for a restrictive exhaust most corvettes with mufflers are equipped with. while its very true that a 215 duration cam would increase the low and mid rpm torque it would run out of breath far sooner, again restricting the 327 engines potential strong point, its ability to easily spin 6500-7000rpm (with a cam thats designed to allow it too!)even a 228 intake duration is a compromise in this area, but it matches the combo well when trying to get the correct dynamic compression
POST SPEED WILL ALSO LIMIT A CAM WITH LESS THAN ABOUT 225 duration and having over .500 lift will help, hence the reference to the crane cam and 1.6:1 ratio rockers
http://forum.grumpysperformance.com/viewtopic.php?...
http://forum.grumpysperformance.com/viewtopic.php?...
lets look at the potential difference in two cams similar to what are suggested
HERES a cam with 216 intake duration
heres the result of the same engine with just the rockers and cam slightly larger
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Edited by grumpyvette on 05-07-12 10:16 AM. Reason for edit: No reason given.
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