Differences in Int / Exh installed height
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Differences in Int / Exh installed height

  1. #1
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    Default Differences in Int / Exh installed height

    Looking for some thoughts on some stock heads I'm working with. The motor isn't really anything special, but an 8-71 is going on it, and I'm following a build done by chevyperformance some time ago.

    I'm working on freshening up some stock 454 heads, where I found valve rotators on both the Exh and Int valves. I didn't know they put them on intake valves as well... but oh well. So, I was planning on using some Comp .300 eliminators when I got down to measuring.

    My springs call out for a 1.9" installed height. From the head, the spring retainer measures in at 2.2" on the exhaust valves - so I'm good there with the rotator eliminators, bringing be back to the needed 1.9" installed height.

    On the intake, I'm getting anywhere from 2.160" - 2.175", which when using the eliminators, puts me in the 1.860" installed height range.

    The cam has a .3220 lobe lift and I'm using summit 1.72:1 roller tip rockers, putting me at .5538" lift. Coil bind on the springs is at 1.2" per Comp. Even at the 1.860" installed height, with the .5538" lift, I'm looking at 1.306" compressed height at valve lift - .1062" away from coil bind.

    The reduction of the .04" will add about 15# of seat pressure which per comp is 122# @ 1.9", making seat on intakes 137#.

    Is the .1062" from coil bind acceptable?
    Is the additional seat pressure on the intakes acceptable? There is a blower on this motor.

    I think I've seen offset retainers that come in at .05", but then I'd need a shim on the bottom with the valve rotator eliminator, correct?

    Retainers: Comp 748-16
    Locks: Comp 612-16
    Springs: Comp 911-16
    Cam: Comp 11-404-4 .3220" Lobe Lift
    Rockers: Summit 1.72:1 roller tips


    Thanks to anyone who responds!
    Last edited by st cloud rustoms; 04-10-2013 at 08:38 PM.

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  3. #2
    Bostick Racing Engines six-oh-nine's Avatar
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    Personally... I'd either put the eliminators in the lathe and whack .040 off them... or get some +.050 locks.

    You may not have a problem... but 137lbs on the seat of a hydraulic flat tappet is getting towards a bit much and possible wear issues.
    The Bostick®

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    137# seat pressure wear concern just on break-in or even continued concern on normal use?

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    Senior Member MACHINEHEAD1's Avatar
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    I would stick with the 137 on the intakes. .100 from coil bind is fine. Break the engine in with Comp zink additive and their break in oil. Break the cam in with the outer springs only. This will provide about 90lbs on the seat during break in. Install the inner springs and enjoy. Your springs will come down to about 130 in a couple hours of run time. Comp also states their rates and preasures are +/- 5%. So if you have access to a spring checking tool you can mix and match inners and outers for a consistant batch. Or make a set of low and high sets for the intake and exhaust.

  7. #5
    gn7
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    Quote Originally Posted by st cloud rustoms View Post
    137# seat pressure wear concern just on break-in or even continued concern on normal use?
    Break in will be tricky. After that I wouldn't want to idle it any more than I had to. And it better have a good set of lifters from a known source.
    I/ve run Iskys 8005A spring at 135 on the seat and 380 over the nose. It wasn't in a boat that was idled much and the cam still started to wear at an excellerated rate on 2 lobes after about 3 years.



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    Last edited by gn7; 04-10-2013 at 08:58 PM.

  8. #6
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    Quote Originally Posted by MACHINEHEAD1 View Post
    I would stick with the 137 on the intakes. .100 from coil bind is fine. Break the engine in with Comp zink additive and their break in oil. Break the cam in with the outer springs only. This will provide about 90lbs on the seat during break in. Install the inner springs and enjoy. Your springs will come down to about 130 in a couple hours of run time. Comp also states their rates and preasures are +/- 5%. So if you have access to a spring checking tool you can mix and match inners and outers for a consistant batch. Or make a set of low and high sets for the intake and exhaust.
    The comp 911-16 springs I said i was using in my OP are single springs, not duals.

  9. #7
    Senior Member MACHINEHEAD1's Avatar
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    Never run a single spring in a boat. Get a new set of dual springs. 130seat/300 open. Follow the same steps I had outlined above. I agree with GN7. I have also run into the same thing with 340lbs over the nose and 145 on the seat, takes a while, but will happen. My flat tappet max is 135/310 max max. BTW havnt run a aggressive flat tappet in 10 years. I have done some resto 283/289/327 vette/mustang stuff with parade idle and soft springs. 100 seat/240open. I strongly advise a roller of some sort.

  10. #8
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    It's not going in a boat....

    Truthfully, I'm only on this forum because I've scored some great parts and met some really awesome people on this forum. That, and ya'll build some really crazy motors for boats and seem to know what you're talking about. I would love to have a sweet performance boat one day, in fact I keep trying to convince the wife that we need one this summer - but apparently, her having our twins (any day now) is way more important than a boat??? LOL... hopefully I'll have one for next summer then.

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