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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