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Thread: Slow to rise RPM

  1. #1
    filthyrat
    I have been having a problem with my RPM slow to rise at WOT. I can top it out at 4800 at wideopen, but once there it slowly will raise another 2-300 RPM over the course of 20-30 seconds. Of course I would like to have this RPM if not more without the delay, and am somewhat disturbed as to why it does this.
    I have a 82 eliminator daycruiser with Pre-Alpha, 21' prop. Small block 350, Alum heads w/ roller rockers, comp xtreme cam, bg carb 750, stealth intake, all MSD. Dyno's at 415.
    Any ideas?

  2. #2
    BDMar
    There is always the chance something isn't right, however I have never seen a boat that didn't creep up the last 200 - 300 rpm's. Especially a small block. An engine in a boat sees a lot of drag and will have to work harder than a car to get it's final few hundred rpm's.

  3. #3
    Ryan00TJ
    There is always the chance something isn't right, however I have never seen a boat that didn't creep up the last 200 - 300 rpm's. Especially a small block. An engine in a boat sees a lot of drag and will have to work harder than a car to get it's final few hundred rpm's.
    I agree. Mine is the same way. With the current 23p cleaver on the instant hit it WOT's at 5000 rpms and slowly rises after 10-15 secs to max at 5300 rpms depending on load.

  4. #4
    bikerboater
    I think it's because, as the speed builds, the hull gets aired out more thus alowing the engine to gain some RPM. A lot depends on how you trim it too. Plus the cam profile comes into play. May need to get to a certain RPM to come onto the cam so to speak. Lots of variables come into play.

  5. #5
    filthyrat
    thanks guys, at least I know this is normal. I really don't see any speed increase as those last few hundred RPM's rise, think this has anything to do with my prop??

  6. #6
    BDMar
    Could be the prop or the combination of hull, prop, drive height, etc.

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