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As you pointed out , CR wants to be around 10.5;1 & above with alu heads , anything much less will soot & can be a PITA to tune , more power will be had increasing CR from 9.9 to 10.5 than from 10.5 to 11.1 all being relative........cutting the heads .040" should net around 78cc bringing SCR up to around 10.5/1 , piston to valve should be around .080" , may not need to cut those pistons.

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The simplest thing to do would be to shave the heads .040 or so. The cc,s of the head with that shave can end up anywhere between 76 and 78 cc,s That will put you around 10.5+ comp.

With my old 906,s every .040 shave = a solid .2 tenth gain in ET. Did it 3 times

With a .040 shave coming from 9.9 you should see about the same. I had the same 509 cam too.

If I were you I wouldnt go any higher then 11.1 with pump gas. You could though, but you have to be Much more carefull with timing/tune and fuel.

If you do have your pistons flycut a .050 shave with a .030 gasket should net you around 11.1 comp.

There will be No need to rebalance with just fly cutting the pistons. You would probably only be removing about a gram or so, if that, in a favorable direction. mike

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Mike , the OP is using an ,027" gasket , those pistons have around 6cc reliefs?

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Adam, thanks , my comp estimates were with 4cc reliefs. My comp numbers are approximate within .1 or so or maybe looser . mike

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They are .0205" down in the hole.

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If I was you I would disassemble the short block and have the deck cut .010 to .015, depending on how much piston to cylinder wall clearnances you have now If your running .003 or more piston to wall clearnaces cut the deck .010 and reuse the head gaskets, do the math on that with your current head CC and see what that gets you for a compression ratio, check both KB pistons sight and Wallaces, they do not come up the same using the same specs on both sites If you have less than .003 piston to cylinder wall shoot for .000(zero) down in the hole, BTW, make sure you check every piston in every cylinder for its piston deck hieght, especially if you haven't already stock Mopar forged rods are not that close to each other on the lengths a lot of the time My message is to set the deck hieght of the block based on the highest pistons on each side, not just the (only) one you checked on one side of the block

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FWIW, my eddy heads have been cut .100"

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Thats illegal, Eddy recommends a Max cut of .060

Your heads are going to break in half the first time down the track.









Mines .080

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Your heads are going to break in half the first time down the track.

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It wont break till run # 5




BTW..............

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TRW actually says the reliefs are 7cc.

Hmmmm...I wonder if I could get away with cutting the heads and still have enough clearance. Guess I could always cut them and bolt them up without gasket to see what the p-to-v clearance is and then figure out what to do then.

Would cutting the heads .040 mean my ptv clearances would become .080" intake (.120"-.040") and .134" exhaust (.174"-.040")?

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It is way better to measure them to make sure, Remember that the valves are on angle in relation to the piston tops so the angle will affect the actual clearnances, that being said I run my piston to valve clearances .060 on the intakes, or less sometimes and .080 on the exhaust on a motor with steel rods and a automatic trans and race converter and good valve springs. I do run a little more clearances(.100 and .120) on a stick shift motor with steel rods, just in case they miss a shift

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Would cutting the heads .040 mean my ptv clearances would become .080" intake (.120"-.040") and .134" exhaust (.174"-.040")?

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Well , i know it's a funny angle but i would say yes. ...........you could always retard that cam a couple degrees & gain .010" , are the piston to valves #s with zero lifter preload?

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I know these things because I am a Keyboard Racer. As I havent raced at the track in 4 years. mike

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