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Thread: 781 head question.

  1. #1
    Jet Novice
    I'm getting a set of 781 heads put together with new 2.19/1.88 valves. My head guy is telling me that the installed height with the stock length valve that I bought a few months ago is 1.750. Says he has never seen a BBC head with this low an installed height, and that I need at a bare minimum of 1.850+ installed height with the cam that I have. Cam is a Comp 11-324-4 with .568 exh with .578 Int.
    I'm being told that 1.900 installed height is pretty standard on a stock BBC head. Is there something different with 781's or maybe this set of heads that I have?
    Does this all sound right or does something sound out of whack?

  2. #2
    Senior Member
    Join Date
    Feb 2009
    what did Comp Cams say about the spring height for the cam u have?...i would go with there recommendations...they are usually pretty rite on...i run a set of 427ci 049/781 oval port heads with the L-88 valves & springs with a semi wild hyd cam with n/p

  3. #3
    Jet Novice
    Will definitely follow their recommendation and get it together right. I just found it odd that it was a 1.750 spring height when just about everything my guy had ever seen before was 1.900 or better. Just trying to find out if anyone had ever run into spring installed height issues with 781's or if this is a normal and common thing that has to be dealt with on any head. I know just enough about things to get me in real trouble so I figured someone here for sure would know.

  4. #4
    I dont know what it is about the 781s, but we find the spring heights vary a bunch from set to set. And its always the opposite of what you need. Makes parts selection a PITA for those heads. The exhaust is not too big a problem because we can just machine some rotator eliminators to the thickness needed, but the on the intakes it takes sinking the spring pockets, offset keepers and/or retainers and longer valves or a combination of those.

  5. #5
    Jet Novice
    It makes me feel a little better to hear that. It seems that every project I take on lately seems to have some aggravating and unexpected ($$$) quirk that takes a lot of the fun out of it. Thanks for the reply.

  6. #6
    ALLWAYS GO WITH THE CAM BUILDERS RECOMENDATIOS.... Spring bind is a bitch... And set closed and open pressures to manufactures recomendations. Lessons well learned.... :squiggle:

  7. #7
    Man, I dissapear for 2 days on a trip out of town and EXTREMEBOATS comes in here with all kinds of solid (IMO) advice. I gotta back him here on this one too. Just don't bind those springs, and unless you have solid lifters, it's a tough one to try to check for binding with it not running.
    There is another thread arround here somewhere where a guy up-cammed and (though he wasn't specific, and partly becuase he wasn't), I (and some others) don't think he changed springs to match, and promptly wrecked 2 hydraulic (non-roller) cams just after break-in. Sure looked like spring bind because his lifts were a LOT higher than stock, even higher than my jet-cam. My setup works, works really well, and was reccomended by ISKY to be set up at 1.875".

  8. #8
    Valve installed height must be known befor you can check for coil bind. When checking spring pressuer befor installing springs is when you can check for coil bind. Never wait untill your engine is together. You must have the right seat pressure as well as open spring pressure. By setting your tester to your cams max lift you now can make sure no binding is takeing place. If its questionable, get the right springs and recheck your pressure again. Seat and then open... It dont matter what kind of cam as long as your requirements are met. Mike :hammer2:

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