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Thread: Mercruiser Ignition 454 vs. 502??

  1. #1
    Just finishing up a repower project on my 23' Powerplay. I replaced an older Mark IV 330 Horse 454 with a new 450 Hs/502 longblock. Among the things I changed were intake (used Merlins) and went with Edelbrocks marine carb'. The item I need help with is the Mercruiser ignition, is it ok to use the setup off the 454? The 454 box has 32 degrees total advance compared to the 502's 28 degrees, not sure how much different the curve is or if it matters. Also does the Thunderbolt ignition have a built in rev limiter. Appreciate anyone's input who has been there before, my mechanic isn't as worried as my wallet is.. don't want to melt a motor yet.
    Thanks in advance,

  2. #2
    If I were you I invest in an Marine MSD ignition.

  3. #3
    Racing Ray
    [This message has been edited by Racing Ray (edited March 12, 2002).]

  4. #4
    Couple of questions that I think you could answer-
    If sticking with the Thunderbolt could I just replace the ignition module with one from a 502 Mag'. You switched to the entire MSD system are you happy with it, much of a difference with it?
    Last question- if not using F.I. what carburator are you using. I'm not real happy with the Edelbrock version of Weber....
    Thanks for all your help!

  5. #5
    Racing Ray
    [This message has been edited by Racing Ray (edited March 12, 2002).]

  6. #6
    I set it up on a Merlin single plane intake (one of the only ones I found with bronze linings) and used a 1" spacer that was recomended from the builder I bought intake from. Boat is pretty hard to start and has a very bad stumble if I accelerate hard from an idle. From 1500 or up its fine all the way to 4600 where the ignition dies off. I think it has a bad accelerator pump as its stream is pretty weak compared to the Holleys I've had in the past. Very interested to see how it runs once I get the rev limiter raised and carb right as it is already 150% better than the 454 was.

  7. #7
    Racing Ray
    [This message has been edited by Racing Ray (edited March 12, 2002).]

  8. #8
    Thanks Ray appreciate the ideas. Look forward to sneaking out of work early to give it a try.

  9. #9
    Ray just checked out your HP'Car site...Nice. Nice looking Chevelle, knew you had to be a good guy especially if you race a BB Chevy. 71 SS454 Owner here.... http://free.***

  10. #10
    Racing Ray
    [This message has been edited by Racing Ray (edited March 12, 2002).]

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