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Thread: +1mm valve differences

  1. #1
    Supporting Member II Turbo Mopar Contributor
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    +1mm valve differences

    I have several different valve for my 8V some stock size other are +1mm.
    My thought is the intake stock are more nailhead design on the intake vs the SI +1 and the new vendor +1 as shown below
    https://drive.google.com/file/d/196W...ew?usp=sharing

    The exhaust valves are also quite different
    https://drive.google.com/file/d/1lEN...ew?usp=sharing

    So my question is which valves should I use?
    Regards,
    Miles

    DD '87 Sundance T1, 12PSI, SLH with rear disks
    '87 CSX #432

  2. #2
    turbo addict
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    Re: +1mm valve differences

    well, if all things are equal so to say as far as working valve locks and retainers go then , I'd go with the first valve on the left in the first pic and the second one from the right in the second

    the valves with the necked down stems

    from what I understand a flat face valve is wiser in a turbo motor but if the valve faces on those two are dished .. I still go with 'em

    (mine are dished but flat would be better .. so "people say")

    I'd consider polishing the edge of the dish to remove the sharpness where the flat and dished areas begin though

    I've found finding locks that fit my valves was challenging.. with the comp LS spring locks as the round little locking ridge in the comp locks doesn't come close to fitting my LRE valves

    comp ridge is U shaped and way to small (these were the part # pope recommended with the LS beehives and retainers I have no idea what valves he had with those U locking groves though)

    my valves need something like
    __
    ...I
    ../


    ^that

    the eye has a "thing" for seeing "flow"

    old layman's law.. if it floats , flies or flows
    if it looks good
    it probably is...

    more important than the valves though .. is the valve job applied to them

    if you're invested in the valves make sure to back it up with the valvejob

  3. #3

    Re: +1mm valve differences

    Yup, basically what Johnny Dodge says, but the devil is in the details. after porting and flow bench testing these 8 valve heads for 20+ years what I've found makes the most power is a shallow nail head intake, and a tulip exhaust.
    The valve angles and seat angles are IMPORTANT! The intake seat 45degree should be .100-.125 wide with a 30 degree back-cut, and a .075 wide and straight (almost sharp) margin. (the straight/sharp margin helps prevent back flow during overlap)
    The exhaust should be a large radius tulip, with a .125 45 degree seat and a .085 wide 30 degree back-cut. Also, the margin on the exhaust should be a .060 radius.(NOT STRAIGHT)
    For any 8 valve head with gross valve lift less than .550 the plus 1mm. valve is the best option. there is no gain with the big IMSA valves unless you have a "Huge" cam.
    the intake seat (in the head) should be a top 30deg. 45 sealing seat, 70, then 75 below the 45. exhaust seat in head 30-45-70. Hope this makes sense and helps; Don't know what others do, but this works well for me.
    PS. These metrics are for a G head, but I think I would do the same on a swirl.

    This photo should give you an idea what I'M talking about.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    best 1/8 ET-6.2 sec. best 1/8 speed-119.70 Best 1/4 MPH 145.5, Best 1/4 ET 9.73 sec. @144.26mph. 8 valve NO NITROUS!!

  4. #4
    turbo addict
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    Re: +1mm valve differences

    exhaust valve makes sense.. like a nice snug cattle run .. no turns sideways..nowhere to go but through and out

    ..no corners for a cow to stand in with it's rump blocking the flow of the herd...which brings to mind the word "stall"

  5. #5
    Supporting Member II Turbo Mopar Contributor
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    Re: +1mm valve differences

    Thank you Gentlemen for your thoughts.
    Regards,
    Miles

    DD '87 Sundance T1, 12PSI, SLH with rear disks
    '87 CSX #432

  6. #6
    turbo addict
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    Re: +1mm valve differences

    K, had a question on my mind for a few days.

    if the isma valves are semi useless without a really "big" cam , what would happen if one used the +1mm intake valves but still used the isma sized exhaust valves ??

    - maybe like using a duel pattern cam ?..or maybe WITH a duel pattern cam?

    if more goes in with the boost cranked up shouldn't we allow for more to come out when the only thing pushing is the piston like in a N-A motor ?

    as an asthmatic .. I fully understand not being able to inhale .. because I can't exhale first..

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