I just measured my block deck to piston height and here's what I got; #1 is 0.186 and #6 is 0.183. First of all, what is it supposed to be? Second, since I want to raise the CR to around 9.2 - 9.5:1 should I take a cut off the block in addition to the head? If so, how much? My original thought was to take an equal amount from each but I understand that it is better from a combustion efficiency standpoint to reduce the deck height. I have essentially stock, flat top pistons if it makes any difference. My head gasket is a Victor (Dana) part which I measure at .045 uncompressed. I'm not necessarily tied to that gasket either, it's just what was in the gasket kit. If there's a better one for my purposes I'm not averse to using it. My goal is to build a good performing street car, not for racing other than perhaps a timing pass or two for testing purposes.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Measure the volume of the chambers in the head. Then do the math to see
what static compression ratio you have now. Also need to see if the
pistons you will use on the rebuild have a different compression hieght as
that changes how much you will cut.

Your measured deck height is a little farther down the bore than normal
for a stock 225 which usually is about .140 down the bore.

The block has been bored .040 and I measured with the new pistons, actually I used one piston and measured #1 then moved it to #6 and measure that hole so that I would eliminate variance between pistons. My thinking is to take maybe .080 off the block and whatever else I need to get it to my desired CR from the head. My intention is to put oversize valves in the head and do the necessary relief work to unshroud them then I can cc the head and see where it needs to be.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Just my opinion.....do your head work/relief work....cc head...deck block required amount to get target CR.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

So you're saying to get the head in shape with equal chambers on all six then raise the CR by cutting the block down? How much can I safely take off the block?

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

You can take at least 0.100 off the block safely. 0.185" down is a very typical piston-deck measurement on a real-world Slant. 0.141" is the factory spec, but I've never seen one below 0.170", most around 0.180". Sandy has the right idea.

Lou

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Home of Slant6-powered fun machines since 1988

I got to 'play' with member Ceej today working a bit on his '74 225...

Oddly... the 1974 225 had a chamber of 53 cc (standard), and the deck height was .187....(when we put the head back on after some massaging and new seals the CR with a fel-pro gasket came to be 8.05:1)...

He has a 1981 casting date Juice slant that has a deck height of .154...

-D.Idiot