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#1
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906 heads shaved .060 how much cc do I have?
I picked up a 73 440 .040 over with TRW 2388 flat tops. It has 906 heads, comp ratio is about 8.5.1. with steel shim head gaskets that are about .020 compressed. My question is I just shaved the heads .060 and I'm wondering what cc these heads are now. I think 906 heads originaly have a 79.5 cc. I'm trying to determin the approx. comp ratio. I should have cc'd the heads when I had them shaved but I was to cheap to pay for this service. Anybody have any ideas.
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#2
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Stock 906 heads had 89 cc chambers. After shaving .060 off you will have around 79 cc chambers. The only way to be sure is to measure it though. I wouldn't pay someone to cc them for you because that can be done easily at home. Good luck.
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#3
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Hello all!
I got a shaving job for my 906´s a couple of years ago. First my stock chambers measured 90-91cc. Then I took them to a machinist and told him to shave as much as 2mm that equals 0.0785 inches! Yeah, maybe such amount is an overkill but a couple of racers that I know had done that before so I took the risk. I´ve had no problems so far but I wouldn´t encourage anybody to do that themselves, though. There is some pitfalls that you should be aware when shaving that much (ie. more than MaMopar suggests). So after this huge shave my combustion chambers measured 70-71cc. The chambers do not look like stock anymore, there is a LOT more flat surface around the combustion chambers, now. I think MP has got the formula and basically the math goes like this: with every 0.010 inch you shave you make the chambers 2,5cc smaller. At least that works till the 0.060 deep shaves. After that the chamber starts to "change shape" and the MP formula does not keep up anymore. Well, MP suggest no more shaving than 0.060, anyway ,-) Just my 2 cents, - BB70Challenge |
#4
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BB 70, how did your intake go on after the shave? I had my 906's milled only 15thous. and had to elongate the holes on my Edel rpm intake, what a pain! You were probably smart enough to mill the intake too? Oh well, live and learn! Would shaving that much work w/stock flatop slugs? What was your estimated comp ratio? Just curious <><
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#5
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My understanding is that for every .010 shaved of the face of the head, .0123 must be shaved of the intake mating surface, "on the head". I did this with mine, and me intake is sitting properly and is still interchangeable.
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#6
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Hello kingjr
Yeah, I got the intake side shaved, too. I ran into troubles because the amount that needed to be shaved on that intake surface of my heads was ALOT (0.0885") and if doing so the problem would have been that THE VALVE COVER GASKET MATING SHOULDER on the heads was getting too thin.... Go figure ;-) So I ended up shaving my heads so that the intake mating surface was indeed shaved alot but just above that where the valve cover gasket surface is it was not milled too much in order to retain the sealing surface. A hassle, yeah, I admit. I really won´t advice anybody to do that way ;-) A buddy who milled his #452 heads even more went the other way and shaved the actual intake. And he ran into sealing and bolt aligning problems. All that is taken care off and everything is running fine now but both of us are pretty much against all that "shaving too much hassle" nowadays. We learnt that MP has got some point in their recommendations. Something like live and learn... ;-) And to my compression ratio after all this: well the whole problem was that my ´75 factory replacement 440 had VERY low smog compression ratio to start with. You know, something like under 8:0, and I tried to be smart and manage to get away WITHOUT pulling the engine out and changing the pistons. I thought that I can just shave the heads to the max and use that 0.020" thin stainless MP head gasket to get my comp up. Well, that is what I did but at the moment my street engine still has got only something like 8.9:1 calculated compression ratio and something like 153PSI measured (I live by the sea so that figure should be right as long as the actual metering device can be trusted ;-) SO, what did I learn? Well, I don´t try to get "smart" the next time around and use the "easy fix" route again. Next time I will change the pistons.... ;-) Best Regards, - BB 70 Challenge |
#7
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Thanks BB, I tried the same thing to a lesser degree. I don't like the seal from the .020 steel gasket though, would've helped if I could've shaved the deck also. But like you, I didn't want to do a complete teardown. I have a small antifreeze leak and some carbon buildup on the heads, still there after re-tourqing. <><
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#8
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Hello kingjr!
Back then when I was putting my 440 back together I asked a racer buddy about that thin 0.020" MP steel gasket and whether it would leak and stuff. His opinion was: - my heads´ surfaces are ok because they have been shaved = dead flat and straight, so no problem there (as you kingjr already said in your reply, too) - my block surface is not so good but because of NO prior overheating or scratches or anything like that the steel gasket should be ok: the best way now would be to really carefully clean the block surface. I mean REALLY clean it ;-) - buy a spray can of that VHT COPPER gasket thing, and apply that stuff during the assebly to the steel gasket´s both sides, assemble when still a bit sticky So I did all that and the project was a success. No leaking of any kind, everything is fine! Hope that helps, - BB 70 Challenger |
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