Determine SCR with kb399 with j heads

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stumblinhorse

stumblinhorse

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Due to bad life choices my stroker build is out the window. So going standard rebuild on my 318. I am trying to figure CR with the KB399 dome pistons .030 over. My J heads measure to around 71-72 CC, they are the 2.02 variety. Using MP head gaskets .028 thick 4.06 bore.

the KB399 are .140 dome, how do you take that into the consideration with a CR calculator?

Trying to keep my SCR pretty high, since my DCR will be way low at my elevation (7000ft)

Thanks for the help.
 
Go to Summit Racing and use there CR calculator. 65'
 
You need to find out how many cc’s the dome is. If there are valve reliefs in the piston as well, you will need to figure out how many cc’s those are. Minus the smaller from the greater and enter that value into the calculator. Valve reliefs are a minus and a dome is a positive number.
 
Use the Wallace calculator, and out of the UEM book that piston is a negative 6cc volume. Do the math right, that means fills in the volume/space
 
Yes, I just came from the summit web site. I think it said 6.2cc. Double check that with the KB site. That is the value to enter, +6cc.

You’ll also need to know where the piston sits in the cylinder. If you don’t know this you cannot calculate the ratio. If the piston sits at zero deck height and the dome sticks up above the deck, you can guesstimate the ratio. Or have your piston set at zero deck height and nail it.

The calculator is great to know ahead of time to help figure out where you need the piston to sit. Below, at or above deck for its height.
 
Well, once you get into the calculator, it will all pan out and you’ll get a better understanding of it all.
 
Using the Wallace calculator, and the #'s provided, you'll have about 10.28 cr. Once again, the dome volume is entered as a NEGATIVE #, domes use up volume not increase volume, a positive number would give you an incorrect calculation of about 8.5 to 1
 
Did I mess that up? Dang! Sorry about that.
 
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