Oil pump pressure question
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  1. #1
    Administrator blackpopracing's Avatar
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    Oil pump pressure question

    I have a Melling M55a high pressure pump (std volume) for the small block, rated at 70-80 psi max at high revs and approx 40-45psi at idle.

    I also bought a std pressure spring years ago (when I bought the pump) which would rate the pump at approx 25 psi idle and 60psi max at high revs.

    So the question is; should I swap the std spring back in or keep the high pressure one? Opinions on the net are divided on what is best.

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    Off the Xmas card list kapri's Avatar
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    Volume is more important than pressure . I now on the VW side of things many engine builders have know gone back to standard pumps and settings.

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    "call 0-800 Apocalypse" satan's Avatar
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    Quote Originally Posted by blackpopracing View Post
    I have a Melling M55a high pressure pump (std volume) for the small block, rated at 70-80 psi max at high revs and approx 40-45psi at idle.

    I also bought a std pressure spring years ago (when I bought the pump) which would rate the pump at approx 25 psi idle and 60psi max at high revs.

    So the question is; should I swap the std spring back in or keep the high pressure one? Opinions on the net are divided on what is best.
    depends on the application. more detail please.
    And I heard a voice in the midst of the four beasts, And I looked and behold: a pale horse. And his name, that sat on him, was Death. And Hell followed with him.

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    Administrator blackpopracing's Avatar
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    SBC,
    Rebored, new KB flat top pistons, std fully balanced crank & rods 20thou over on all bearings.
    Iron 64cc 'camel hump' heads with 1.52 roller tip rockers and Comp Cams 270H hyd flat tappet cam. Valley holes plugged above cam with screens in main drainback holes.
    Std sump.

    The general consensus of SBC owners in the states is keep the high pressure spring in, but Real Steel think the std pump pressure is fine & high pressure "may" present other issues. Nearly everyone agrees high volume (25% higher) is a big no-no for street use and std sump. Many recommend a 10% higher volume & pressure pump, but I dont have one of those & will stick to the the new pump body I have as it is the correct one.

    This all has come about from the big lettered instruction in the Comp cams roller tip instructions warning that high pressure punps will cause galling of the pushrod upper tips & rocker balls unless an oil deflector plate is fitted over the rockers - this might 'just' fit inside my sheet ally covers but may not leave room for the breathers or pcv valve fitting.

    Up till then I was quite happy with the higher pressure pump?

    Originally the engine was fitted with an adapted big block chevy pump - but that gave over 100psi cold and 60psi at idle hot & was too much (originally had solid lifters)
    Last edited by blackpopracing; 18-10-2013 at 12:10.

  7. #5
    "call 0-800 Apocalypse" satan's Avatar
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    yep that just about covers what I was gonna tell ya. Imo stick with the standard spring but strip and check pump tolerances are correct and free from defects[yes even a new pump can be faulty,] checking costs nothing,, rebuilds are spendy. some will agree. some wont. your motor,,your call.

    as a side note this is mellings take on pumps.

    http://www.mellingengine.com/Portals...lume-pumps.pdf
    Last edited by satan; 18-10-2013 at 12:25.
    And I heard a voice in the midst of the four beasts, And I looked and behold: a pale horse. And his name, that sat on him, was Death. And Hell followed with him.

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    Administrator blackpopracing's Avatar
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    Hi Satan,

    Good link, is there a similar paper on the high pressure pump as well please? be helpful to make my mind up.
    I'll blueprint the new pump as you say & I think I'll put the std spring in it (there must have been a reason in my mind for buying it extra originally).

  9. #7
    "call 0-800 Apocalypse" satan's Avatar
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    Quote Originally Posted by blackpopracing View Post
    Hi Satan,

    Good link, is there a similar paper on the high pressure pump as well please? be helpful to make my mind up.
    I'll blueprint the new pump as you say & I think I'll put the std spring in it (there must have been a reason in my mind for buying it extra originally).
    heres some more info from car craft. Small-Block Chevy Oil Pumps - Oil Pump Shootout: Which One Is The Best? - Car Craft Magazine

    some surprising results there .
    And I heard a voice in the midst of the four beasts, And I looked and behold: a pale horse. And his name, that sat on him, was Death. And Hell followed with him.

  10. #8
    Administrator blackpopracing's Avatar
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    I'll read that link, thanks Satan.

    Bugger, the test results page is not available????

    The answer from Melling tech support was to use the yellow #58 spring which is a little stiffer than stock but not to use the pink #78 high pressure spring.
    Apparently I should have had the yellow spring in the box with the pump but as I bought it years ago it does not appear to be there. Kept it all boxed though so maybe I swapped out the spring when I first bought it

    I'll blueprint the pump and pull the spring to see this weekend.

    Top marks from Melling for replying with 3 emails in less than 24 hours!
    Last edited by blackpopracing; 18-10-2013 at 20:26.

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    Pressure will also depend on the crank clearences, if large use the high volume pump/ pressure can also wear out the cam gera /dissy drive especially if its the bronze dissy gear.
    race engines.

  12. #10
    "call 0-800 Apocalypse" satan's Avatar
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    Quote Originally Posted by Adey View Post
    Pressure will also depend on the crank clearences, if large use the high volume pump/ pressure can also wear out the cam gera /dissy drive especially if its the bronze dissy gear.
    adey. did you read the link in post 5.?
    Last edited by satan; 19-10-2013 at 09:01.
    And I heard a voice in the midst of the four beasts, And I looked and behold: a pale horse. And his name, that sat on him, was Death. And Hell followed with him.

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