Author Topic: short compression height piston for a 440 block height 10.609?  (Read 1319 times)

Offline Riceman65

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heres my dilema had the block height checked today
and its 10.609  STD is 10.725 so its 0.116 short. shortest piston ive found has been the Keith Black/KB Pistons 1263-040 with a compression height of 1.969 in flat top no relief
not sure if im doing the math right but will this piston leave me in the hole by 0.005 ?
half the stroke plus rod lenght plus CH (2.067)= 10.702
half the stroke plus rod lenght plus CH (1.969)= 10.604

STD block height 10.725
STD piston compression height 2.067?
rod 6.76
stroke 3.75
my block height 10.609
compression height of piston i want to use 1.969 :banghead:
thanks Steve
« Last Edit: March 29, 2010 - 09:03:08 PM by Riceman65 »




Offline Changin Gears

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Re: short compression height piston for a 440 block height 10.609?
« Reply #1 on: March 29, 2010 - 09:10:28 PM »
I don't know the max you can deck a block, but I'll bet you are about there.

You will have to cut .125"+ off each side of the intake to get it to fit also.


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Offline Riceman65

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Re: short compression height piston for a 440 block height 10.609?
« Reply #2 on: March 29, 2010 - 10:56:19 PM »
the deck and valley were both machined by previous owner, motor was running before and everything fit great. i just rebored, magnafluxed, cleaned and rebalanced then tossed old pistons out when new ones arrived. new ones were out the hole so we checked the deck and shes short

Offline Moparal

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Re: short compression height piston for a 440 block height 10.609?
« Reply #3 on: March 30, 2010 - 06:44:48 AM »
What year is that block?   It kinda sounds like someone decked the block that had stock cast low compression pistons that was over   0.100 in the hole.  Instead of buying pistons, they chose to deck the block.  But you can have special pistons made. After market rods are 6.760.   Standard rods are 6.768.   At any rate,   .005 in the hole is great.  You can call kb and other manufacturers and tell them your deck height and they can tell you a piston that will fit.  Also the builder may have used a different rod length.  what  rods are in there now?   You do need pistons with valve pockets or you will not be able to run the bigger lift cams, also cometic head gaskets are made in any thickness if you choose to run the kb pistons you found would work with .005 in the hole. If your math is off a bit and they are zero or a bit above, an open chamber head and thicker hg would work.  I am not sure of the math formulas used but I do know you have to allow some for heat expansion for clearance. aluminum rods stretch more than forged steel. Sorry I didnt quite answer your question, but made helped you with a solution

Offline Bart

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Re: short compression height piston for a 440 block height 10.609?
« Reply #4 on: March 30, 2010 - 09:49:20 AM »
Got mine at Diamond cost about 900.00 a set will custom make any piston you want.

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Offline moper

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Re: short compression height piston for a 440 block height 10.609?
« Reply #5 on: March 30, 2010 - 11:55:51 AM »
The problem I see is that runnig a piston with no valve relief at close to zero deck means next to nothing for piston to valve clearance with a modern cam. Plus, a higher static along with that small cam. You could use a 400 piston which is shorter, but ends up around .060 down in the hole. Of course that .060" could be fixed with offset grinding the crank, and you'll need to re-balance... Or you can just order a set of pistons. If this was for a mild deal, I'd go with the 400cid KB-240s and accept the loss of quench and static compression. Rebalance, hone the bores to fit them properly, and run it. Otehrwise you have a custom set of pistons ($900) plus the rebalance. I think the KB240s and the hone/balance should only run around $800.

Offline Changin Gears

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Re: short compression height piston for a 440 block height 10.609?
« Reply #6 on: March 30, 2010 - 01:09:41 PM »
Maybe it's time for a new block.


The goal never changes - Stop the 60' timer with your back tires