Need some piston help
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Joined: Oct 2006
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From: Huron OH
Need some piston help
To start the block is a stock chevy 400 with a 4'' stroke and 6'' rods. My questions are- With this set up what would my compression hight be? If the block has the stock bore 4.125 will 4.114 pistons work or will the rings be to wide to work?
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Joined: Sep 2000
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From: The Top of Utah
Originally Posted by 1Fast7R
If the block has the stock bore 4.125 will 4.114 pistons work or will the rings be to wide to work?
Where does 4.114 come from? The bore is meaningless for figuring the piston compression height. As with most all SBCs the center line of the crank to the deck of the block is a blue print dimension of 9.025". To achieve a zero deck, start subtracting. 9.025" (block) - 2.00" (1/2 the stroke) = 7.025" left for the rod length and piston deck height. 7.025 (block, minus 1/2 the stroke) - 6.00" (rod length) = 1.025" for the piston compression height.
In review:
Block, deck height. +9.025"
2.00" 1/2 stroke
6.00" Rod
---------------------------
8.00" 1/2 stk + rod -8.00"
---------------------------
Piston comp height +1.025"
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Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by 1Fast7R
To start the block is a stock chevy 400 with a 4'' stroke and 6'' rods. My questions are- With this set up what would my compression hight be? If the block has the stock bore 4.125 will 4.114 pistons work or will the rings be to wide to work?
Originally Posted by 1Fast7R
Sorry that was supposed to be 4.115'' piston. I wanted to know if it was to small to use in a 4.125 bore. Thanks for the explanation i did not know how to figure it out.
Now you want to know about it as a bore size??? That is an odd ball piston diameter, but it would be perfect if you want .010" piston clearance in the bore size you state. I'm confused.
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Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
details, need details....are those sbc pistons???...stock 400 crank is 3.75 stroke, your stock 400 small block will prolly need some grinding to swing a 4'' arm.
back to your Q; it will run like a striped ape with 4.115 pistons in a 4.125 hole...oil consumption above normal but not a mosquito-killer...need bunches of vents to relieve crankcase pressure due to blow-by at rings...will sound like a ferrarie (same as an old washing machine) at cold start due to piston slap, and winging it (revving up) before the pistons expand with heat will likely break the piston skirts.
verify your block has std 9.025 deck before jumping in, we have found several 400's with original numbers on the front pad that were only 9.010 high...no biggie if you get parts as reqd, but a major pita to correct if found at assembly.
back to your Q; it will run like a striped ape with 4.115 pistons in a 4.125 hole...oil consumption above normal but not a mosquito-killer...need bunches of vents to relieve crankcase pressure due to blow-by at rings...will sound like a ferrarie (same as an old washing machine) at cold start due to piston slap, and winging it (revving up) before the pistons expand with heat will likely break the piston skirts.
verify your block has std 9.025 deck before jumping in, we have found several 400's with original numbers on the front pad that were only 9.010 high...no biggie if you get parts as reqd, but a major pita to correct if found at assembly.
Last edited by redrose; Nov 3, 2007 at 07:01 PM.
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Joined: Oct 2006
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From: Huron OH
Ok i should have given more detail so here goes. I would like to build a 434 with some sb2.2 heads and intake. The intake will be converted to fuel injection. When looking at pistons they are listed by compression hight. I was not sure how to figure out what the compression hight was. With the figures posted i now that the pistons i was looking at will not work with the 6'' rods. The compression hight was 1.33? being a little tall. So i would have to go with a smaller rod.
The second question was to bore. I wanted to know if 4.115 was to small to run in a 4.125 bore. I was not sure if there was to much piston ring area making them problematic with blowing rings.
The second question was to bore. I wanted to know if 4.115 was to small to run in a 4.125 bore. I was not sure if there was to much piston ring area making them problematic with blowing rings.
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Burning Brakes
Joined: Sep 2005
Posts: 993
Likes: 3
From: Iowa
Why run SB2.2 heads? There's better out there for the money and they usually don't require as long of valves.... For a 434 to really last under tough conditions it's best to start with a tall deck block. Also, a 434 with heads that flow in the upper 300's to low 400's is capable of making around 900hp; an aftermarket block is a good investment at those power levels.
