Well I've decided to just replace the 70 with my 71 S6 in my wife's dart. I'd like a little more power that what it has now. Right now it runs about 19.5 @ 60mph, not great. It does however get 20mpg. I'm thinking of just boring it out .030, milling the head to raise comp. Having a vavle job done. Just do a basic rebuild on everthing else. But I'm not sure what the engine has now, the 71 that is. What kind of comp did most have? What about the cam specs? With gas over $2 a gallon here I'd like to still get 20mpg. I've never done anything with a S6, except adjust the vavles. any suggestions would help. thanks

nobody knows the comp of a 71 S6, or the cam specs. No advice either huh?

If I remember right, the book spec for compression of a 225 was 8.4:1

Do some head "pocket porting" work and mill the block deck while you are at it.

Here is a link to the stock cam specs. - the 1969 cam specs are the same as what was offered in 71.
DD
http://www.dutra.org/pictures/engine/st ... -specs.jpg

mill the block? what about the head? stock length pushrods ok? with the adjustable rockers? I've seen rebuild kits in PAW ads, are they any good? Do they use a stock cam? Thanks

I like to leave the head deck as thick as possible so I tend to mill more off the block, the block is more stable.

Stock pushrods are OK up to about .150 of milling, many other things influance push rod length so don't worry about it, just measure and make-up custom push rods if needed. (don't design an engine around stock push rod length)

Rebuilds come with stock "regrind" cams unless you can "work a deal" for an up-grade to a performance cam.
DD

ok. so how much of the block do I mill? I'd like the engine to have 9:1 comp, is this alright with the cam? Is there a formula for milling the block to find the comp. i need to research this more. thanks