deck height on a 250

[gary6768]

building a 250 short block and all the info i get says to shoot for 0-.012 deck height. with the 56 cc combustion chambers in the aluminum head this would get me close to a unusable 12-1 compression. what do yopu other 250 guys do ?? thx Gary

 

[Bort62]

Dished pistons

 

[Hot 6t Falcon]

Howdy Gary,

Your estimated compression ratio of 12 to 1 seemed way too high, so I went to the "Compression Calculator" in the left bar of my web site. (Click on the url in my signature)

I changed the pre-set 200 numbers to be a 250.
Put the stroke to 3.91
Put the gasket thickness to .045
Put the deck clearance to .100
Put the combustion chamber cc to 62. I know - that's the stock cc - but I want you to see the baseline.

Compression is 8.2:1

Change the head cc to 56. The compression is now 8.7:1

Change the deck clearance to .045. The compression is now 9.6:1

Change the deck clearance to .015. The compression is now 10.2:1

Notice that so far I've left the piston dish at 7cc. (stock) There is also a "Califronia" piston with 13 cc which brings the compression down to 9.5:1.

Copy and paste my answer into a word processor so you can print it out. Then goto
http://falconperformance.sundog.net/compcalculator.asp
and make the changes for yourself. It's a lot of fun to play with the numbers

Hope I helped.

 

[gary6768]

thx. I was figuring flat top forged pistons (which I wanted to use but don't know if they are available) .040 over bore and .025 gasket. I can't seem to find info on how much power is lost by the deck height (quench height)? being more than .050 including the gasket. Gary