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Discussion Starter #1
My brother has some old 460 heads laying around that I've been thinking about porting out to go onto my 460 sometime. I'm sure they're the larger CC (95cc) combustion chamber heads, I think they are off of a '74 Lincoln 460.

When he had the heads worked over for guide plates and a valve job, he had the heads shaved quite a bit to bump up the compression ratio. But, I don't know how much more compression they would actually be, and I want to be sure to keep it under 10:1. Is there a general rule of thumb as to so many thousandths off the heads equals so much increase in CR? Thanks.
 

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just cc a couple of chambers. You'll be dead on then.
 

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Without measuring everything is just a guess. However even with flat top pistons and 97 cc heads YOU WILL BE LESS THAN 10-1.
 

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Discussion Starter #4
Thanks for the replies. I thought about CCing them, but I wasn't sure as to the best way to do it. Seems like I've seen pics where they put a piece of plexiglass on the deck of the head, maybe some goo around the chamber to seal it, but then what do you do? Get like a graduated cylinder or maybe a syringe with graduations on it and start pumping water in there?

EDIT: Yeesh, I just looked through the paperwork that for my engine, and I found a part number 1143 for the pistons on the short-block. Did a search on the web, and found out that is most likely a Silvolite 1143 piston, which is a dished piston with 21cc piston volume, YUCK!!! Says with stock heads they will run 8:1 CR, so I'm thinking the heads can be milled all they want and I'll never see over 9:1 compression, lol!

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'86 Bronco fullsize, 460cid, E4OD w/ Baumannator TCS, 4" Rancho lift, 2" body lift, 35x12.5 BFG AT KOs, 4.56 gears, Auburn posi in the 9" rear, Digital instruments, 600watt Pioneer sound system

<font size=-1>[ This Message was edited by: Motorhead on 2/18/02 3:49pm ]</font>
 

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Yeap ... And with those "Open Chambers" it will not tolerate very high compression, so the milling hasn't really improved much of anything for you ...

Just don't go to flat tops ... Might drive compression higher than the heads can bear.
 

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Discussion Starter #6
Ok, now what's the difference between an "open chamber" and "closed chamber" head? I thought open chamber was where the combustion chamber on the head is like a complete circle, where on closed chamber the combustion chamber is just big enough for the valves and spark plug, so much of the milled surface is actually in the cylinder... is that right?
 

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You are right about the shape. A closed chamber can handle higher compression. The milled surface that you talked about is called quinch area. Quinch is good. It helps squish the air/fuel toward the center of the chamber. This effectively blows out any pre-ignition. An open chamber doesn't do this which allows pre-ignition to remain uncontrolled.
 

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Discussion Starter #10
Ok, I thought that was right, I was just confused as to why MonsterMach called them open chamber. The 95cc (D3VE) 460 heads are closed chamber, just a larger volume closed chamber than the older 75cc heads. I suppose it's six one way half a dozen the other, but still I think they'll handle more compression than open-chamber heads.

I guess one bonus to the low compression is I could thow on a blower and run lots of boost, but I don't think the cast rings would like that too well, lol!
 
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