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Yikes !! even with a .035 quench and 9.7:1, you're still having detonation problems. These 906's have no quench, I'm hoping my cam will be my saving grace..

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I think you will be ok but you may need to pay close attention to your ignition curve to avoid issues.

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Call around to fine a veteinary supply store or one of the large animal vets and see if they will sale you a 500 CC syringe so you can CC your heads Having a thin 4.5 inch square plate of plexiglas helps also, you will need to put a small hole in it near the edge of one side to fill the chambers with what ever liquid you use. ( I use rubbing alchol with some food dye in it to see it better when filling) but some guys like a piece of thick glass(harder to put a hole in them without a diamond drill bit or cutter ) to use to seal the head combustion chamber up to check them. A little effort and not much money, you can do it to Don't be suprised to see a bunch of variences in the 4 chamber on each stock iron head and some variances between heads that are the same thickness on the outer head bolts I wouldn't run the compression up above 9.5 to 1 mechanical comp. ratio no matter what cam for pump gas, it(pump gas) ain't going to get any better than it is right now I've made 9.2 to 1 comp. ratio motor ping with iron heads and 34 degree timing and a cold plug when tuning on a hot day going up a slight hill at part throttle in high gear between 1700 and 2500 RPM in 75 degree weather here locally at or above 3500 Ft

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Hey guys; I know this topic has been discussed time and again on this forum, but even after reading all the replies using the search feature I'm still not sure. Because of budget concerns I'm using a set of upgraded 906's that i scored for a good deal. I don't have the coin for a set of closed chamber aluminum heads... (wish i did).

My block is at the machine shop right now.. Being set up with KB237's in place of the awful trw 2388's that were in there. They were .140 in the hole !!! .. netting me a 7.78:1 static CR !!!!!

I need to know if you guys think I will be safe
running near stock 906's with a 10:1 static cr on 91 octane ?? I know cam plays a huge role in the equation. I'm planning on keeping the .528 purple shaft i just installed less than 6 months ago.. Advertised intake closing on that cam is listed @ 72 ABDC.

If I plug the numbers into the Wallace Racing DCR calc using a 10:1 static CR it says i'm well within the "safe" zone.. "7.36:1 DCR" with 143 psi cranking pressure, but what i hear from some other posters on here is that I'm limited to no more than a 9.5:1 static CR to keep it safe.{avoid detonation}

Thanks in advance to anyone who takes the time to reply.

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Personally, I don't believe the results of Wallace dynamic compression calculator. The same calculator used on other sites state to put in the @ 0.050" numbers for intake closing. When I use the Wallace calculator, the cranking pressure is a lot lower than actual.

Checked one of the other sites. It has you at 8.2:1 dynamic, and about 165 psi. FWIW

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I have not CC'd the chambers.. I dont have the tools, or the money to get it done. So, i'm just giving it my best guess.. The heads have after market valves 2.14 int/1.81 exh and have been milled square. I'm really just guessing at an 88/89cc chamber. I'm thinking I'd like to zero deck the block for when I do come into the cash so I can just bolt on some closed chamber heads and easily dial in my quench with a .040 head gasket. The KB237's call for a +5cc for the valve reliefs. To achieve a zero deck I'd need to mill an additional .015 from the decks, but if I leave it, it may help with my no quench problem: shave a few points off of my static CR??? What do you guys think ??

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