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Discussion Starter #1
i ve got the motor apat and want to know what the max CR is that i can get away with on 94oct with a bottle of octane booster and 112oct at the pulls. turning the timing back to drive it there and back doesnt bother me. im running .030 trw 2443s with the domes milled off that are a couple thou out of the hole. a performer rpm cam 234 244 @.050 .556 .581 108* 4* adv. im going to cut the heads to get the CR to the max i can. Is 10.5:1 dueable on a good tune? that leaves me with an 89 cc chamber. whith means about .050 off the D3's right? (.0055 per cc) Or can 11:1 be done with polished 84 cc chambers? (about .075)
i know i have to cut the intake side the same amount.
I have a friend that works at a machine shop to cut them for me so theres no problem getting it done. would it be better to agle cut them than to flat cut them a big amount like that? then justy square off the intake side and spot face the bolt holes.
 

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Max CR for 94 Pump Swill

I built a 10.54:1 385c street/strip motor for a customer last srping.
It would rattle and ping on 94 octane when you leaned on it hard
(at about 37* timing). I added a set of FelPro block spacer gaskets
that lowered the CR to 10.08:1 and it no longer rattled or pinged.
I never tried Octane booster so its possible that might work at this
point? FWIW, I'm removing the spacer gaskets for this year and
going to E85 fuel.
 

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D3's can vary widely on combustion chamber size. It is on Scott J's website, something like 89-98cc's if I recall correctly. If you take more than .020 off the heads the intake or heads will need milled to fit.

Is the block decked? It is often said on here that decking improves quench properties and helps prevent detonation problems. It would certainly benefit you. It will also boost compression a little. It is also said thicker head gaskets hurt quench and not a good idea.
 

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Discussion Starter #4
the block has been decked and the pistons are out of the hole like .004 with a .039 gasket so thats .035 quech. ill cc the heads later theis w/e but i need to know how small i can go.
 

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It doesn't sound right but,

about 12.7/1 will be OK if you are sure not to put a hard load on it excet when you are using the 112 racing gas...
 

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Discussion Starter #6
so 11:1 should be no problem right?

now what would be the best way to get the chambers down to 84 cc's. cutting them flat (about .075) or angle milling them (0 to .100??)?
 
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