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Thread: engine power

  1. #1
    I have a 22ft 9ftwide flatbottom handbuilt boat. It has berkeley jet AA impeller and 350 chevy all rebuilt . Moter has flattops 78cc heads and comp cams XM 262 marine dur 218I 224E .460I .477E lift. The moter runs goods but stops pulling at 4000rpm. I would like to see 4500rpm. Thinking of putting 64cc heads to rising compresstion .

  2. #2
    Hi there,
    Sounds to me like a cam is the key to your happiness. Yours sounds a little small, might want to lolok into a cam/lifter change rather than pulling the heads. You can get a kit for around 100 bucks. Do you have a four barrel, headers, good ignition? I would tune these before a head swap. You also want to be able to burn 92.
    hope this helps,

  3. #3
    spectras only
    Rod, besides you have a relatively good cam [if duration given at 0.050 lift], you should change your impeller to an "A" or "AB" to get the RPM where a 350 makes the most HP.
    [This message has been edited by spectras only (edited April 26, 2001).]

  4. #4
    The problem is not in your engine!!! It's in the pump!!!! An "AA" impeller is very much too large for any naturally aspirated small block. I have been there before, with a small block Olds and an "A" impeller. Jet pumps take large amounts of torque and HP to turn at higer rpms. My best recommendation is to have the impeller re-cut to a "B" size, and see how it runs at that level. You probably want to spin that small block to around 5000 rpm in order to hit the HP peak, if not higher. A "B/C" cut may even be needed, but the "B" is a good place to start with a small block. If in doubt, call one of the professional shops (MPD, Walts, or GS Marine are all great places to deal with), and listen to their recommendations.

  5. #5
    spectras only
    Rod , I've cut a lot of impellers down to a "C", but before you do that,try an "AB".You can always go lower but not the other way around!

  6. #6
    Big Block It!!!

  7. #7
    This just proves what I always say "When in doubt, BIG BLOCK IT!!!" Seriously though, if you really want some performance, go a size or two up in cam, go with the smaller heads, PORT THEM! Then make sure you have a carb that will flow enough as well as a good intake. If you don't want to yank the heads, then I agree with the others. Go with just a bigger cam and smaller impeller. Just remember though, your motor's only as good as it's weakest link. And I mean the heads. A big cam won't do anything unless to ports can handle the increased flow. Good luck!

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