BBC Decking Cylinder Head?
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BBC Decking Cylinder Head?

  1. #1

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    Default BBC Decking Cylinder Head?

    Hello,

    I just picked up a nice set of 049 cylinder heads. I measured a few of the chambers and got a volume of 121-122 cc. I'm running flat top pistons with a 14081045 head and a have a CR of 8.2 with 118 cc. I'm contemplating decking the 049s to bump the CR back to to 8.2 or maybe higher but i don't know how much i can expect to take off. (also my valve lift is about 0.48 but i'd like to maybe got to .54 some day)

    I figure if i go more than a few thou, i'll be looking at machining the bottom and sides of Intake Manifold but given that, how much is reasonable to take off? Has any one done this before? How if so how much can i expect to take off without screwing up the head?

    Thanks,
    Ted

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  3. #2
    Senior Member 78COLE's Avatar
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    I think you can count on about cutting 1cc per .005 mill. You could flat mill .020 and that should get ya pretty close to where you were. Wont have to mill intake either. Shouldnt have any problem with goin up to that .540" cam either. I'd say if you pistons alredy have relief it should be plenty for that. Just my .02

  4. #3
    Cantard 71hallett's Avatar
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    Not an answer to your question but had a good laught tonight.....putting a set of heads on my motor and was measuring piston to head and piston to valve clearances. When my buddy wasnt looking I stuffed the head on, (no gasket)torqued a couple studs to 30 lbs put in a pair of lifters set the valves and gave it a roll. The look on his face when I pulled the head and he saw the puddy was awesome.


    You should be able to get them down to about 112-114cc
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    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
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    You can go well over .540" lift with stock flat-tops, I am running .565 hydraulic setup, and still have a lot of clearance room to the pistons.

    IMO, the few 1/10ths you will gain in CR are not going to be of much notice. If the engine is fairly old build, I'd just assemble, and plan to put decent pistons in it in an overhaul one of these winters.
    Your call ttho, best of luck to ya.

    The only milling I had done was to pick back up a bit lost to a valve enlargement due to opening up a bit arround the intake valves to help breathing, and it wasn't enough to make me get the intake milled (very close tho).
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  7. #5

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    Default Decking Heads

    Thanks for your help.
    Looks like the consensus is .020 to .040 which will be enough.
    I'll post my results but i will be a while.
    Ted

  8. #6
    steelcomp was here
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    Half a point will be worth going after if all it takes is milling. .005/cc is about right. You can also look into a thinner head gasket than you're currently running. Cam timing plays into valve/piston clearance as well, but where you're at, I wouldn't worry.
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  9. #7
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    Are the valves sunk from wear or too many valvejobs? This will increase the chamber size too. The cure is larger valves, the new seats will be higher in the chamber and lower the cc size, helping both airflow and compression. Also, airflow is much more importtant than a half point of compression ratio, so.... with the big valves, unshroud the chambers and borenotch the block. TIMINATOR
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