Building a motor and use of NOS
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Building a motor and use of NOS

  1. #1
    MLC - Mid Life Crisis probablecause's Avatar
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    Default Building a motor and use of NOS

    I am going to build a BBC tall deck motor (525) that is going in our 21 foot open bow jet boat. I want to add a 100-150 shot of NOS whenever the hell I want. The motor will be from 9.5-1 to 10-1 compression (pre NOS) and running on pump gas. Is there anything I need to be aware of during the build for the use of NOS? Will be running 049 or 781 heads on it. Just a daily driver motor that I can kick in the nuts every now and then. Thanks, Brendan

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    go by whatever the ring manufacturer you use suggests

    Dare to be different, if it turns out great you can claim you planned it that way.

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    what kind of tall deck block do you have ? 427 t/d truck production block or bowtie? or ? what bore stroke combo ? might be cheaper to find a used 502 block or used bowtie block and start out with a larger bore and thicker cyl walls.. all the other components cost the same. guess you already have the block or you wouldn't be asking.

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    MLC - Mid Life Crisis probablecause's Avatar
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    Quote Originally Posted by havasubyou View Post
    what kind of tall deck block do you have ? 427 t/d truck production block or bowtie? or ? what bore stroke combo ? might be cheaper to find a used 502 block or used bowtie block and start out with a larger bore and thicker cyl walls.. all the other components cost the same. guess you already have the block or you wouldn't be asking.
    Got the block 427T and it is std bore right now. Looking at a 4.28 or 4.31 bore with a 4.5 stroke. Like I said, I am not looking to kill it with NOS but just want to romp on it some times. Maybe a blower would be a better approach (but $$$).

    Just my opinion, but maybe it's time for the government to take down the bird feeder!


    Quote Originally Posted by Rexone;
    Try to ignore the haters, they are everywhere, just as in life.
    Quote Originally Posted by Pronstar;
    Liberalism: Logic's retarded cousin.


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    Senior Member jetjunky's Avatar
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    Any cam nuances to consider? I know it's not "build" related but how much timing do you need to back out with 150 shot, 2*, 4*, not enough n02 to worry about? Just curios

  8. #6
    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
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    Quote Originally Posted by probablecause View Post
    I am going to build a BBC tall deck motor (525) that is going in our 21 foot open bow jet boat. I want to add a 100-150 shot of NOS whenever the hell I want. The motor will be from 9.5-1 to 10-1 compression (pre NOS) and running on pump gas. Is there anything I need to be aware of during the build for the use of NOS? Will be running 049 or 781 heads on it. Just a daily driver motor that I can kick in the nuts every now and then. Thanks, Brendan
    For a shot that small, there's nothing really exotic to do.

    The ring gap should already be a tad on the wide side for an engine dealing with an open cooling system. Put it somewhere on the upper (wider) half of the specs range for the ring gap, and it'll not do anything bad.

    I'm running 150 on cast pistons and stock rods, no issues.

    There's no absolute need to run any dedicated fuel setup either, unless you just like complexity. I have plenty of excess capacity on my mech, fuel pump, so T'd off the fuel suply and fed the plate.

    The comon wisdom for Nitrous is to retard the timing about 2 degrees for every 50HP or so, so you might set the base timing accordingly to take a few degrees off the top, won't really notice any difference off the bottle.
    It's either that, or add a retard box, more stuff to wire up and mess with.
    I don't retard my timing, from 35*, but, I am only running about 8.3:1 on flat-tops, I generally try to run premium if there is any chance of me cranking the Nitrous on, just for the sake of "cushion".

    Best of luck to ya.

    Oh, just a note, FILTERS ON THE SYSTEM (especially fuel).
    Clog the nitrous jet, no big deal, runs rich and slobbers all over itself, no harm done.
    Clog a fuel jet, instant leanout, instant detonation, and likely instant expensive parts burnt up.
    Last edited by SmokinLowriderSS; 09-20-2009 at 07:54 AM. Reason: correction
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  9. #7
    About 500' AGL MudPumper's Avatar
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    Quote Originally Posted by SmokinLowriderSS View Post
    The comon wisdom for Nitrous is to retard the timing about 2 degrees for every 100HP or so, .
    The common wisdom is actually 2* for every 50hp, not 100.
    Last edited by MudPumper; 09-19-2009 at 11:29 PM.

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    Quote Originally Posted by probablecause View Post
    Got the block 427T and it is std bore right now. Looking at a 4.28 or 4.31 bore with a 4.5 stroke. Like I said, I am not looking to kill it with NOS but just want to romp on it some times. Maybe a blower would be a better approach (but $$$).
    production 427 t/d
    that block is a big gamble @ 4.5 stroke and i have never seen anyone make it that far.i have read people on the net say (my friend) bla bla. but never seen it in person, ever.
    4.250 stroke is the norm with a lot of grinding on a older type block and you may get lucky with 4.375 stroke
    core shift and sonic test before you put to much into it is all i can say.

  11. #9
    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
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    Quote Originally Posted by MudPumper View Post
    The common wisdom is actually 2* for every 50hp, not 100.
    Thanks, I wasn't sure if I was remembering it correctly or not.
    "As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron."
    H.L. Mencken

    OBAMA: Some people deserve this.
    The rest of us are being dragged along kicking and screaming.

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