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  1. #1
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    Looper exhaust porting

    If I make my exhaust ports (bridgeport looper)wider, would that make low end torque suffer?
    I want to shape them like a letter "L", turned upside down...

  2. #2
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    If you just widen them, you'll make everything better. Just don't raise them unless you know exactly what you're doing.
    Tony Brucato


    (919) 718-0249

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  4. #3
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    .150 wider at the top and taper to orginal at the bottom but unless you do the right intake work it will not add any power

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  6. #4
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    Quote Originally Posted by racer View Post
    .150 wider at the top and taper to orginal at the bottom but unless you do the right intake work it will not add any power
    Thanks Racer!, will do that!
    The right "intake-work" are you referring to changes in duration on transfer/boost ports?
    I have already cleaned the intake mainfold up - taken away all sharp corners and added CCMS reeds. What is your opinion on shaving the heads? Boat is appx 2200lbs, prop is 22"raker, boat mainly used for skiing and recreation, no long wot-runs, maybe a minute max. I want to be able to use 91octane.

  7. #5
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    Quote Originally Posted by racer View Post
    .150 wider at the top and taper to orginal at the bottom but unless you do the right intake work it will not add any power
    .150 wider at the top overall or each window of the Bridgeport? Can you please elaborate on the intake work needed? It seems that these loopers are a black art when it comes to mild porting.
    1975 Hydrostream Ventura II
    1987 evinrude 200xp

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  9. #6
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    A couple of questions;
    .150 must be like 4mm, anyone to confirm?
    still trying to learn the inch system...
    When you guys write .150, you mean 0,150 of an inch -right?

    Any good tricks concerning cleanup after porting and honing?
    compressed air, what else?

  10. #7
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    Quote Originally Posted by Onetime View Post
    .039375 is your friend.
    Just FYI, 0.039375 is incorrect. 0.039370 is correct. Or 0.03937007874015748031496062992126 if you get picky.

    Much easier to work the other way since the inch is exactly 25.4 millimeters which I think is much easier to remember.

  11. #8
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    Quote Originally Posted by racer View Post
    .150 wider at the top and taper to orginal at the bottom but unless you do the right intake work it will not add any power
    Come on Mr Stoker, give up a little more info.

  12. #9
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    .150 wider on each exhaust port at the top, make sure you radius them when finished. Clean up the rod slot and match the intakes being careful to maintain original angle since you are not looking for a high rpm engine.

  13. #10
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    Just starting a v4 looper for a 15' allison,

    Any thing different on the V4 ?

    Will the V8 Finger ported piston w/ block mods work ok in the V4, or is there a better direction ?
    Last edited by thornl01; 11-26-2013 at 01:02 PM. Reason: spell

  14. #11
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    Quote Originally Posted by racer View Post
    .150 wider on each exhaust port at the top, make sure you radius them when finished. Clean up the rod slot and match the intakes being careful to maintain original angle since you are not looking for a high rpm engine.
    maintain the transferport angle is the most difficult part, -the alucasting is not nearly in sync with the sleeves, so it needs severe grinding!

  15. #12
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    Quote Originally Posted by racer View Post
    .150 wider on each exhaust port at the top, make sure you radius them when finished. Clean up the rod slot and match the intakes being careful to maintain original angle since you are not looking for a high rpm engine.
    Clean up the rod slot...
    on small high revving case-fed motors, I have ported/created a "direct passage" from the crankcase(rodslot)to the transfer boost/aux-port, this procedure has been succesful by allowing the fresh charge to enter direct into the boostport as soon as the piston starts its upgoing movement.
    Do you have any experience of this on outboards? In this case the boost port don't have to rely on the piston-window...
    The yellow tape in the pic is an attempt to describe my ideaClick image for larger version. 

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  16. #13
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    Quote Originally Posted by racer View Post
    .150 wider on each exhaust port at the top, make sure you radius them when finished. Clean up the rod slot and match the intakes being careful to maintain original angle since you are not looking for a high rpm engine.
    Any idea on how much hp's these mods can give me -if I manage to carry them out properly, of course...

  17. #14
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    Does anyone know what the max PSI for a blue printed V8 should be? Before we blue printed and evened out the ports on it the PSI was 135, this is an original 3.6 punched out to 4.0 liters. We now have 150-152 psi after raising the ports and the motor has not been broke in yet , only about 30 minutes at the dock, and this is with stock 4 liter heads, I have a pair of Taylor Marine and Machine heads and I am afraid to put the on with the PSI at this level? anyone? I have been told that the max PSI should be 145 to 155, but I have also been told that stock V6's are usually 150...HELP!!!!
    1987 Switzer GL-21 OMC V8 Prototype/ Replaced by another V8
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  18. #15
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    Quote Originally Posted by tomaprilsswitzers View Post
    Does anyone know what the max PSI for a blue printed V8 should be? Before we blue printed and evened out the ports on it the PSI was 135, this is an original 3.6 punched out to 4.0 liters. We now have 150-152 psi after raising the ports and the motor has not been broke in yet , only about 30 minutes at the dock, and this is with stock 4 liter heads, I have a pair of Taylor Marine and Machine heads and I am afraid to put the on with the PSI at this level? anyone? I have been told that the max PSI should be 145 to 155, but I have also been told that stock V6's are usually 150...HELP!!!!
    Are you checking the compression with the same guage? Porting can only lower the compression. Unless you ended up with a bigger cc' dome or the 4.0L heads have smaller cc' chambers than the 3.6L heads then the only gain in compression should be from a fresh bore and rings.

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