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  1. #1

    Default 1991 to 1997 7.4L Engine Swap

    I purchased a 1991 2400ssl Maxum with a 7.4L/bravo one towards the end of last season. Had a handful of good outings last year, and was hoping the same for summer 2019. Winterized it and stored it away for the Michigan winter.

    Got it out of storage this year and it ran great all of June, and then I started having issues in July. Somehow the engine took on water and I did not realize it (my guess is blown head gasket), out at the sandbar starter would only make clunking noise, finally got it started and it was knocking really bad so I think I broke a piston connecting rod. Turned it off, got towed back and brought it home. The engine oil was a milkshake and about 3” high on dipstick, pulled plugs and #8 cylinder poured out water, at this time engine would not turn by hand either (seized/hydrolocked). So I started looking at options, really did not want to pay a shop thousands and thousands to rebuild.

    I found on Craigslist a 7.4 carbed engine out of a 1997 Baja that the owner had just replaced with a 502. I went out and bought it as a replacement. Pulled the old engine out with a help of my neighbor and a steel gantry he welded together for his boat engine swap.

    Pretty much everything is swapping over fine except the fuel pump. The original big block has the hole mounted (bravo style?) mechanical fuel pump that’s mounted next to the raw water pump. The new block does not have this hole in the block, so I need an electric fuel pump. I have found a few online and would like input on which one I should go with, I will attach links. The new engine does have an Edelbrock high rise intake, so not sure if that matters on which fuel pump I choose (may need higher psi?). I realize I need to wire in a oil safety switch to kill fuel pump if engine stalls as well.

    I appreciate any input, and will keep updated through this process.




  2. #2
    Join Date
    Sep 2008
    Maryland - USA

    Default Re: 1991 to 1997 7.4L Engine Swap

    Sounds like the original engine was a MarkIV block and the newer one is GenV/VI...

    I think you are on the best path with the electric fuel pump and the switch....hard to say which one will be optimal as the flow ratings are unrealistic. I think as long as you can get 35GPH to the carb, at WOT, the engine will stay happy. I'd say the carter will be adequate unless you plan to run it hard and long....

    I think the only other item would be to cap off the sight tube connection at the carb....there should have been a tygon (yellow) tube from the old mechanical pump up to the carb....you won't need it with an electric pump...

  3. #3

    Default Re: 1991 to 1997 7.4L Engine Swap

    Thanks for the quick reply. I did notice the Carter pump did not have that “sight tube” connection on it, but the Holly pump did. My original engine did have the yellow tube from carb to pump, but new engine’s carb, like you said, had a rubber cap attached to it. I will get one ordered up. I’m sure I will have more questions along the way.

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