Well my timing marks are dead on. Damn, I was hoping for something simple but like Raptor said it's the cam timing. After looking into it apparently the closing of the intake valves is one of the variables that affects dynamic compression. So the 30-40psi jump in compression came from when I went from non-degreed Crower Stage 2's, back to stock 2G cams because the stock cams close the intake valves a lot sooner.
Also I was crunching some numbers this weekend and I don't like the results. I should have been more careful when buying pistons (at least I'm learning a lot):
http://www.rosspistons.com/calculator.php
Here's the numbers I used.
Bore: 3.426
Stoke: 3.937
Head: 46
Gasket: .045
Deck Height: .015
Dish: -13
Num Cyl: 4
The one big number I don't know is the Deck Height. And the Head and Gasket numbers are rough estimates but should be close. With those numbers I get a static CR of 9.75.
I really want lower compression because I'd like to run pump gas and more boost. My options for lowering the compression (without swapping pistons) are:
1) Adjustable cam gears to tweak when the intake valves close.
2) Radical cams to keep the intake valves open longer.
3) Thicker head gasket.
4) Modify the head to create a bigger compustion chamber
5) Sell the damn thing to someone who wants to run mostly race gas.
Any advice? I would replace the pistons if I could do it without removing the crank. It's a 7 bolt and it seems to be holding so I don't want to F' with it. Anybody had luck doing that? I feel like that is just asking for trouble.
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