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Carb Size

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    Default Carb Size

    BBC 454 Snails and logs. Wot 4050 With newly rebuilt engine and pump. SS AA with Stage 2 and stuffer plate. My Question is, currently I have a 750 cfm Holley vacuum Secondaries. 1)would I benifit from a Manual secondaries and 2) would a larger Carb net me any more RPM. Just wondering as it runs fine now. Currently runs 59 Mph. Not bad I thought for a heavy 22 ft. boat.
    Last edited by BAJA JA; 09-28-2012 at 12:27 PM.

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    Senior Member Schiada 201's Avatar
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    Most likely no.

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    Super Moderator HammerDown's Avatar
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    HELL NO...and stay with the vacuum secondary too
    <img src=http://www.performanceboats.com/gallery/data/500/medium/06-30-11_1234.jpg border=0 alt= />

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    Senior Member EVILFORCE's Avatar
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    Well you did not say how much H/P. But only turning 4050 on rpm 750 should be more then enough. Vac sec sould be fine as well. Might be sure to check what it takes to get sec to come on.
    No Fool Like A Old Fool is there?

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    Cool. Will stay where I'm at. More ching for other things.

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    Quote Originally Posted by EVILFORCE View Post
    Well you did not say how much H/P. But only turning 4050 on rpm 750 should be more then enough. Vac sec sould be fine as well. Might be sure to check what it takes to get sec to come on.

    The cam in ur boat will determine what kind of vacum you're going to get. If its a marine-specific cam, you're making almost no vacume and would run better and most importantly have a smoother transition through the rpm range with mechanical secondaries. Next time you go out, get it up to about 2500 rpm, and stomp on it. if it falls on its face for a second and then picks back up, youre not getting enough vacuum, and would be better compensating with your timing(lock it out), and run mechanical secondary. Oh and you should be running around 4500-5000 rpm. you might see that if you get the bugs worked out... 65 mph??
    Last edited by WesMark Racing; 09-30-2012 at 02:08 PM.

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    Senior Member EVILFORCE's Avatar
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    Black print is my take on this.
    Quote Originally Posted by WesMark Racing View Post
    The cam in ur boat will determine what kind of vacum you're going to get. If its a marine-specific cam, you're making almost no vacuum Tell me why a marine spec cam makes no vacuum ? Marine cams can make 20' of vacuum or 5's. and would run better and most importantly have a smoother transition through the rpm range with mechanical secondaries. You might unless you know how to adjust a Holley carb. Next time you go out, get it up to about 2500 rpm, and stomp on it. if it falls on its face for a second and then picks back up, youre not getting enough vacuum, and would be better compensating with your timing(lock it out), True. Slow timing can cause a hesitation. But a hesitation is not always caused by slow timing. and run mechanical secondary. Or learn how to adjust a carb. Oh and you should be running around 4500-5000 rpm. Only if he is making enough hp and torque.you might see that if you get the bugs worked out... 65 mph??
    No Fool Like A Old Fool is there?

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    Senior Member EVILFORCE's Avatar
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    Quote Originally Posted by BAJA JA View Post
    BBC 454 Snails and logs. Wot 4050 With newly rebuilt engine and pump. SS AA with Stage 2 and stuffer plate. My Question is, currently I have a 750 cfm Holley vacuum Secondaries. 1)would I benifit from a Manual secondaries and 2) would a larger Carb net me any more RPM. Just wondering as it runs fine now. Currently runs 59 Mph. Not bad I thought for a heavy 22 ft. boat.

    I just noticed it has a "AA" impeller. You might want to change that to get your motor to a sweet spot. If you know where it is.
    No Fool Like A Old Fool is there?

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    Quote Originally Posted by EVILFORCE View Post
    Black print is my take on this.
    It has just been my experience that the marine cams dont make any. im sure there are some more mild grinds that would be couterary, but maybe is is the duration to lift difference... what do you think??
    and my take on the timing is due to the common practice of vacuum advance on lake boats. i removed mine and locked out my timing and found that it ran much better through the rpm ranges.
    Last edited by WesMark Racing; 09-30-2012 at 03:01 PM.

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    Runs fine no hesitation anywhere. I can hear the secondaries closing when letting of of full throttle. It really runs great all the time. Was just wondering. motor is set up fine for me. Was built from ground up to be a lake cruiser not a racer.

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    BTC cardcarrying member sunkisst's Avatar
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    Quote Originally Posted by BAJA JA View Post
    BBC 454 Snails and logs. Wot 4050 With newly rebuilt engine and pump. SS AA with Stage 2 and stuffer plate. My Question is, currently I have a 750 cfm Holley vacuum Secondaries. 1)would I benifit from a Manual secondaries and 2) would a larger Carb net me any more RPM. Just wondering as it runs fine now. Currently runs 59 Mph. Not bad I thought for a heavy 22 ft. boat.
    Tunnel ram, w/ 2 1050 cfm Dominators. BLING is worth at least minus 3 mph.

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    Quote Originally Posted by EVILFORCE View Post
    I just noticed it has a "AA" impeller. You might want to change that to get your motor to a sweet spot. If you know where it is.
    I was thinking the same thing, but not knowing what cam or compression, how mild or wild. If he's running a fairly mild engine, wouldn't an AA be a little too big?

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    Senior Member EVILFORCE's Avatar
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    Quote Originally Posted by wolfie View Post
    I was thinking the same thing, but not knowing what cam or compression, how mild or wild. If he's running a fairly mild engine, wouldn't an AA be a little too big?

    Yes it is pretty tight to ma as well. Any mild BBC I would think you would want it to turn 45 to 4600 rpm maybe 5k. If you leave all as is you would probably get by with a 650 carb. Might gain a bit of milage. Your speed seems real good for that size of boat and the R's it is turning. Maybe Tom or some jet guy could give better advice.
    No Fool Like A Old Fool is there?

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    Senior Member TNYoungblood's Avatar
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    Quote Originally Posted by BAJA JA View Post
    Runs fine no hesitation anywhere. I can hear the secondaries closing when letting of of full throttle. It really runs great all the time. Was just wondering. motor is set up fine for me. Was built from ground up to be a lake cruiser not a racer.

    If it ain't broke, don't fix it

    Run it and enjoy it ?????

    JMO



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