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Discussion Starter · #1 ·
I bought a 1981 sunkisst stripped out with a berkley pump, witha droop snoot an A impeller. Put it together, dropped 396 dome pistons, big cam single plain intake, and a holley dominater 750. Boat runs good but it will pull 5000rpm at quarter throttle and 5400 at full throttle. My uncle had this boat when i was a kid. He had a small block 400 in it, nothing major down to it. He said it would pull out 6400. I dont remember as I was too young. Shouldn't a 396 pull it easier than a 400?
 

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mo balls than $cents$
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you added weight and lost cubes:D classicccccc,lol
 

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Discussion Starter · #4 ·
A balanced 396 punched 30 over 0.300 dome pistons, 629/605 260/266 on 108 LSA, solid lift cam, big valve round port factory heads. My uncle had a 400, 501/501 244/244 on ? LSA, Torker II intake, and an 800 holley double pumper. Im pretty sure they were 305 heads, maybe flat top pistons, ain't sure. Been a long time ago. Pump is still the same. I think the pump will have to be rebuilt this winter. Thanks
 

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Welcome to PB, you will find a lot of info here. Alot of very knowledgable dudes here (the best in the business hang out here).
 

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mo balls than $cents$
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I bought a 1981 sunkisst stripped out with a berkley pump, witha droop snoot an A impeller. Put it together, dropped 396 dome pistons, big cam single plain intake, and a holley dominater 750. Boat runs good but it will pull 5000rpm at quarter throttle and 5400 at full throttle. My uncle had this boat when i was a kid. He had a small block 400 in it, nothing major down to it. He said it would pull out 6400. I dont remember as I was too young. Shouldn't a 396 pull it easier than a 400?
the simple answer is not really. if the 400 had more compression and made more hp, or even the same hp as the 396, the 400 will move the boat along faster, its simple power to weight ratio:)bulb you're uncle may have been runnin the boat alot higher outter the water than you're able to do with all the added weight, therefore the shoe/loader may be digging deeper on you than it did him, resulting in the pump being loaded harder, and pulling down the rpms. you can't jack with weight without adding power, and to me an outside observer that's never seen the boat run, it sounds like you're down on power and up on weight compared to how your uncle ran the boat. just my imo:D
 

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Are you sure your uncle was running an a impellar? seems like youd hafta have a ton of wieght to make 1000 rpm difference, quite a bit more weight than the difference between a big block and a small block especially if they where putting out close to the same hp. sounds to me like the impellar may have been changed at some point. just my .02
 

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Could the pump being wore out have anything to do with it? I might have to build a new motor too.
Not likely. With a worn pump you'd typically see higher RPMs as the pump is operating less efficiently, thereby not loading the engine as hard as it was when it was new.

In regards to boat weight, weight affects MPH, not RPM.

Higher than normal RPM = Jet problem

Lower than normal RPM = Engine problem (unless the pump is about to lock up and is loading the engine down as a result lol)
 
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