Rotating assembly question...
Thread Starter
Joined: May 2008
Posts: 91
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From: Muncie Dragway....Indiana
Rotating assembly question... I can get a pretty good deal on a forged crank with a 3.80 stroke. My thing is, I don't see many piston kits offered for that stroke. So does anyone know the correct compression height piston to use with a 3.80 stroke, or can someone give me the formula to figure it out myself? Or will the pistons for a 3.75 stroke work? I am not sure on how much of a difference .05 on the stroke will make. (Other than 3 more cubic inches)
Thanks,
Thanks,
I believe the 3.80 strokes were made so GM could sell 4.00 bore "383" crate motors. I also believe they were Cola which is a good piece.
I think you will get away with normal "383" pistons just going to need to be looking at thicker than usual head gasket.
Normally the pistons are .025" or thereabout down on a stock motor, seen .022-.032 myself and heard of examples outside those measurements so say the real range is .015-.040.
To figure out compression height needed take HALF the stroke, plus the rod length and subtract that from deck height usually a little over 9.000".
You might end up just using traditional 3.75 stroke pistons not decking the block and having the piston stick up say .005 which is like the thickness of a piece of paper. The you just choose a head gasket to get the right quench.
Sometimes when rods are rebuilt they can lose a little length so if you could score rods in need of reconditioning cheap it could maybe help you get the piston back down near flush with the deck. Ask your shop they might have something laying around.
I think you will get away with normal "383" pistons just going to need to be looking at thicker than usual head gasket.
Normally the pistons are .025" or thereabout down on a stock motor, seen .022-.032 myself and heard of examples outside those measurements so say the real range is .015-.040.
To figure out compression height needed take HALF the stroke, plus the rod length and subtract that from deck height usually a little over 9.000".
You might end up just using traditional 3.75 stroke pistons not decking the block and having the piston stick up say .005 which is like the thickness of a piece of paper. The you just choose a head gasket to get the right quench.
Sometimes when rods are rebuilt they can lose a little length so if you could score rods in need of reconditioning cheap it could maybe help you get the piston back down near flush with the deck. Ask your shop they might have something laying around.
just an fyi....stock deck height is 9.025".....just to give you an idea of what may or may not be needed....you won't know until you have the block measured and see whats up with it....
