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Old 08-13-2008, 04:03 PM
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There are two common Dished pistons used in the popular typcial stoker kits.
One has a -12cc dish and the other has a-18cc dish.

if you have the 18cc dish and did not "0Deck" the block, your cr with 70cc heads is 8.78:1. {Assumes a stock .025" deck clearance}
The cure is to swap on 58cc heads (or have your heads angle milled to 58cc) and use the .028" GM performance head gasket.
This will give you 10:1 compression.

If you have the -12cc dished pistons, mill/Angle mill your heads to 64cc and again use the .028" GMPP gasket. Your cr will be 10:1.
{Again assumes a .025" deck height} yes it matters.

You'll want to pull the heads and check and verify your actual piston dish volume and piston deck clearance @TDC and accuratly calculate the nessessary finished cylinder head volume nessessary and machine as required.
But you can use these typical examples as a guide.

Most popular pistons from the typical stroker engine kits are "rated" for compression ratio when the block is "0 decked" machined. If your block was not 0 decked the actual cr will be lower. The edelbrock performer rpm Hyd roller cam with its 234 @.050 duration will not get busy until around 3000rpm.

If you really want the torque/power band to start at a lower rpm point, install a cam with less duration. Something around 218 like the GMPP Hot CAM would work well while still giving strong peak power. This cam is intended to use a 1.6 rocker ratio. {.525" lift}

Comp cams has some cool short duration (218 ish) but very high lift custom Extreme hyd roller cam lobes. This requires a custom grind cam job but may well be worth it if you really want a milder cam with more low end grunt but same/simular peak valve lift with a 1.5 rocker arm ratio.

Start by doing a simple cranking compression test. If it is lower than 180-190# then its a good bet the cr is probabily too low for the camshaft duration.

What is the rear gear ratio and rear tire diameter? Vehicle weight?
At what rpm do you want the power band to start?

Once the compression ratio is corrected and the camshaft is dialed in to your driving preference, you'll have a whole new opinion of your 383.

cr calc
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Last edited by F-BIRD'88; 08-13-2008 at 04:29 PM.
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