Compresson Question X Heads

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lucahemi

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Purchased the Kieth Black Hyper Pistons that talks about .018 out of deck. Stock Compression of 10:2:1. Everything I read on X heads shows 72c.c. At 72 c.c the compression is 9.5:1. The piston is a stock replacement. How did Mopar achive or claim 10:2:1. What am I missing ????.
At 9:5:1 how can I bump up the compression or do I have to purchase the 62 c.c Aluminum head ?:prayer:
 
manufacturers applied their ratings for NHRA regulations.
i'e'..you could build to 10.2 : 1 and race legally...that was the factory rating
 
Are you just using numbers out of a book, or have you actually measured how much volume is above your piston, the volume of your head gasket, and combustion chamber volume?

It's best to actually measure what you have, than go by books...
 
krazykuda said:
Are you just using numbers out of a book, or have you actually measured how much volume is above your piston, the volume of your head gasket, and combustion chamber volume?

It's best to actually measure what you have, than go by books...
Click to expand...

This. We have members that have measured "X" heads. You can come up with an average but the reality is that they are all over the place. An average (of production heads) is useless for what you are doing.

You need the actual measurement of the heads you are using.
 
..if you use 72 cc's you'll be close.
9.5 seems about right for a stock hi compression 340.
 
That is what I am having the shop do c.c the heads. I wanted to see if I was missing anything. Do it once and do it right!!!
Does any one know how many thousands are left for milling??
 
hi, the minium chamber volume is 63.3 cc If you cut deck so pistons are out + .045 with 63.3 cc, .036 gasket, comp ratio is closer to 11.5 actual.
remove .0048 per 1 cc of volume.
 
You're also assuming that the decks are at blueprint height...most of the time, they're not.

I'm in the process of helping my brother build his +060 340 with the KB243 slugs as well...the decks on his were definitely taken down some because they were actually out of the hole about .030". With his Edelbrock heads and their gaskets, it's calculating out to ~10.5:1.
 
This was my frustration when i built my 340. I have 9.4:1 compression.

10.2= (figured on a 62 cc head) most heads are in the 72 and higher cc
11.5= racing piston.....Yeah they are figure on a 74cc head.:violent1:
 
I run the same set up as you are describing x heads and same k B pistons and with A good tune you are getting close to limits of pump gas...cam profile also plays a big part.
 
Honestly, I would leave it where you have it now so it will run on pump gas.
My 340 has KB 243 and x heads compression is 8.98.
I also have a 360 with KB 107 and eddy heads compression is 11.37.

Also I am pretty sure the closed chamber Eddy heads will not work with pistons sticking out of the block.
 
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