how to know if you need more fuel pump?
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how to know if you need more fuel pump?

  1. #1
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    Default how to know if you need more fuel pump?

    So, I have a 454 with 300cc aluminum oval ports, crane 731 HR Cam, Roller Rockers, IMCO Powerflow high flow marine manifolds, air gap intake, holley 800DP HP500 Carb in my 23.5' bravo 1 boat.

    I am not spinning the Prop to the RPM I should be. I swapped between the two props I had, and the RPM is equivilant for the respective prop's pitch. So it's got to be the engine.

    Only thing I didn't change is the fuel pump and I'm still using the small flame arrestor as others said the stock pump should be fine up to around 500HP and I doubt I'm too much over that.

    I can't find anything else wrong with the engine, timing is about 37* all in around 3000-3200, engine sounds strong, runs strong, gets on plane fine. But won't spin as fast as it should. Would it sound terrible, pop, backfire,miss, etc if it was running out of fuel? or will it just run out of steam? Is it possible that it does just need a bigger pump?

    Or, is the stock small flame arrestor not giving the air flow for a good enough vacuum signal?

    Or, I have no idea what size jets or PV that are in the carb, it idles fine, and starts fine. But, could it need larger jets? Carb is stock mercruiser off of the 500 HP 502, so I assumed it'd mate my combo very well. (I realize what happens when we assume things though )

    Could spark plug gap keep me that low on power?

    Its got new plugs, wires, cap, rotor, coil. it is a stock coil.

    I have not done a compression test or a leakdown test, I'd really doubt that'd be my problem judging by the vacuum reading, and also, how hard the damn thing is to turn over by hand. Its got compression.
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    Doubt it's a fuel pump issue. If your running out of fuel you will simply feel like your running out of gas. Based on what I read here seems like your getting all your going too.

    The guys here that know more than myself are going to want more details. Pitch & brand of prop at what rpm, speed per gps. Plug reading. Hull?

    In my experience if it sounds good and runs good that's probably all your gonna get.

    Good luck

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  4. #3
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    Only way to know if the fuel pump is up to the task is to know the fuel pressure at WOT, MAX RPM.
    If the flame arrester is too small, it will have the same effect as too much fuel.

    You make no mention of the size of the prop, or the RPM you are turning, or the type hull or make of the boat. Just that YOU THINK it should spin more.

    Chances are, the engine doesn't make the HP you think it should, and simply doesn't have the power to spin the prop you are running,
    Bottom line, what you are really saying is that the boat is slower than you like or wished. You are far from the first person that was ever disappointed by there boats performance.



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    Quote Originally Posted by gn7 View Post
    ...... You are far from the first person that was ever disappointed by there boats performance.
    And quoted only to add it's NEVER anything as cheap and easy to replace as a fuel pump
    Quote Originally Posted by gn7 View Post
    ....... David 519 is 100% correct........

    Quote Originally Posted by fuelinmyveins82 View Post
    .....I think people forget that racing is supposed to fun. Losing shouldn't be discouraging it should motivate you work on your pile to make it faster.....
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    more details:

    Boat is roughly 23.5' long, VIP Vindicator. Mini-Cig looking boat. It has Trim Tabs. My research shows 4000lbs dry. I had 4 people in the boat, cooler, tools, and half tank of gas and was spinning the 21p 3 blade to ~4800 RPM

    Previous engine that was essentially a stock mercruiser 330, carter carburetor, stock exhaust manifolds - had the air gap intake and some stock heads (just, oval port instead of peanut port) Turned the same prop to ~5000 RPM. 2 people, half tank, tools.

    This is why I am fairly certain I have an issue somewhere. Even with just adding manifolds I should have picked up some RPM. But instead, I'm down.
    Last edited by PowerAddict; 09-30-2013 at 11:34 AM.
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  8. #6
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    Quote Originally Posted by David 519 View Post
    And quoted only to add it's NEVER anything as cheap and easy to replace as a fuel pump
    How come when I read a quoted post of mine 15 minutes after I posted it I realize I used THERE instead of THEIR, and think to myself, what dumbf*&k did that?

    Yeah, I am sure there are lots of people that wish a fuel pump added 100HP. It would be the biggest bang for the buck in performance boating.



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    Quote Originally Posted by PowerAddict View Post
    more details:

    Boat is roughly 23.5' long, VIP Vindicator. Mini-Cig looking boat. It has Trim Tabs. My research shows 4000lbs dry. I had 4 people in the boat, cooler, tools, and half tank of gas and was spinning the 21p 3 blade to ~4800 RPM

    Previous engine that was essentially a stock mercruiser 330, carter carburetor, stock exhaust manifolds - had the air gap intake and some stock heads (just, oval port instead of peanut port) Turned the same prop to ~5000 RPM. 2 people, half tank, tools.

    This is why I am fairly certain I have an issue somewhere. Even with just adding manifolds I should have picked up some RPM. But instead, I'm down.
    Fully loaded it spun 4800 and half loaded it spun 5k after mods.
    Were conditions exactly the same? 20* air temp is worth close to 200 rpm on my deal. What would you think if it spun 5k fully loaded?

    Maybe the cam is done @ 4900.

    RPM is not a good tuning tool without mph.

    If the cam is done @4900 you could very well add more prop, loose 100 rpm and pick up 3 mph. With that much boat the mph/$ ratio will be rather high.

    When in doubt try running it with the flame arrestor removed.When in doubt about fuel pressure you will need a gauge and someone to watch it...or spend money on a pump to find out that wasn't the problem...
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    it spun roughly 5000 RPM essentially stock (maybe +30HP over stock) with say 300 lbs less in it with air conditions pretty damn close (both very early fall, low humidity, about 78 degrees F) than when it ran ~4800 RPM with Heads, cam, manifolds, and carburetor upgrades. See why that doesn't really jive? The cam "should" be good until 5600 RPM (pretty commonly used cam, most guys spin them at least over 5k) Cam is a Crane 139011

    I didn't mean to imply I think a fuel pump would solve the problem, it was really the opposite, I was trying to check that off my list of what it isn't. I think there has to be another issue - but it does seem that there is some sort of issue.


    Fuel pressure wouldn't really show the problem if it were a fuel pump right? It'd be fuel flow that i'd need to see somehow?
    Last edited by PowerAddict; 09-30-2013 at 12:57 PM.
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  11. #9
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    The fact that the cam is good for 5600 is no indication that the engine will run that with the prop and load you have on it.

    Are you 100% sure the cam is degreed in properly?
    By any chance these oval port heads happen to be ProComp heads?????
    Did you buy the heads assembled and install them as is out of the box?

    If you fuel line from the pump to the carb is large enough, then fuel pressure will tell you if you have enough flow. If you have high enough fuel pressure, 5-7 psi, and you know its not caused by small lines or small needle and seat, then you know you have enough flow.

    Low fuel pressure can be caused by a number of things. But high(enough) pressure can only be caused by 2 things. Sufficient flow verses demand, or a restriction of some sort.

    NOT KNOWING YOUR FUEL PRESSURE IS THROWING DARTS IN A DARK ROOM. You're just GUESSING!



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    Last edited by gn7; 09-30-2013 at 01:38 PM.
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    sooo...

    how much can using a .460" reach spark plug when a .750" reach spark plug is supposed to be used, effect performance?
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  13. #11
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    Quote Originally Posted by PowerAddict View Post
    sooo...

    how much can using a .460" reach spark plug when a .750" reach spark plug is supposed to be used, effect performance?
    In a pump gas compression deal, with a decent ignition, not a lot. Don't expect some big power increase with the right plug. Specially if the .460 plug was an extended tip type.

    But if you haven't already installed the longer plugs in the heads, I would spray the holes with some carb cleaner, and chase the threads to clear any carbon that might be in the exposed threads due to the short plug. If they are aluminum heads, I would do it for sure. Carbon in the threads will tear up the threads on aluminum heads.



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    Valve spring pressure?
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