My buddy and I are new to bracket racing. How many thousandths do we shave the head on a 225 slant to go from 8 1/4 to 9 1/4 comp. Will this interfere with the push rods and valve clearance? Also what is the max that can be shaved and not interfere with the push rods and valve clearance. Thanks.

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I'll bet you $1 you're under 8.25:1. To go from 8.25:1 to 9.25:1 requires a combustion chamber volume reduction of 10.25cc. This is about .068" off the head, but if you're using a thicker composition head gasket you'll have to find the thickness difference (about .018" usually) and take that much more off the head. Now you're up to .086", but since you probably started at less than 8:1 you're still under 9:1. You must measure the deck height and combustion chamber volume so you know where you are now and can determine what you need to do to get what you want.

How much you can shave off the head without needing shorter pushrods depends on how much of the rocker adjusting screw is below the rocker body.

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Joshua

OP
you need to measure, the bore, stroke, deck height, gasket thickness, and combustion chamber CC's. That will tell you the CR, you have now. From there it can be determined how much to cut the head/block, to get what you want.

Also please sign up and log in. Please don't request tech help using the
userhelp log in. If you are having trouble logging on, use the userhelp login, and post a help request in the "how to use this message board" section. Thanks

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I am signed in with a pass word. The site would not leet me sign in. The userhelp was the only way I could post.

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Put a post in the "how to use this message board" forum, listing you user name, or send me a PM, and I will try to fix the problem
http://www.slantsix.org/forum/viewforum.php?f=15

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Hi, sorry I'm abit new to this.

How come it wouldn't be 8.25:1? Guessing it's something to do with aging, or factory specs weren't 100% or some slants were different so they might have a different model? Or is there something else?

Thanks

Spec compression ratio is 8.4:1 for most slants. Production tolerances were such that most were below 8:1. The pistons are almost always lower in the cylinder than spec and the head volume is larger than spec.

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Joshua

The generally agreed upon number, and what I used to get the compression up to approx 9.5:1 is a whole .1" off of the head.

Best of luck,

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

Sorry, but I disagree. You must measure the deck height and combustion chamber volume to determine how much to mill from the head to achieve a target compression ratio. .100" off my current head would not have gotten me 9:1 let alone 9.5:1. I had my head milled .080" which left it with 50cc combustion chambers. With a FelPro gasket on my untouched '67 225 I am at 8.5:1.

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Joshua

The head chambers and heights of the deck of the engine vary a bit.


Greg

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