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Discussion Starter #1
Ok guys here it goes, me and my dad have the same exact hull both BBC engines, anyway we raced them this weekend and they run dead even but here is wear it gets strange he is at about 5600-5700 rpms with a AA impeller and according to my jet I have an A impeller but only is at 4400-4500, could someone of put a different impeller in my boat? Or can the way a jet is set up make that much difference? Btw they are both berkley jets. Thanks
 

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If your Dads motor is making over 700 hp, then something is wrong with your tach. If he doesn't make that much power, something is wrong with his. Assuming the impelled sizes are correct.
 

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Discussion Starter #4
I wish I knew the speed, I would guess 70-75. My tach might be junk, but then agian my motor doesnt seem like it's taching more than his. I wish there was a way to check the impeller I have wondered if someone put a AAA in mine.
 

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Are both engines built similarly? Meaning about the same Hp? There are many factors that could cause rpm differences. A loose pump with an "AA" could turn more rpm than a tight pump with "A". Do both boats get on plane about the same? I am pretty sure bowl would have to be modified to accept "AAA". Like Brendellajet alread said, more information is needed.
 

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Discussion Starter #7
19' mini day cruiser and the big difference in the motors are my dads has ported rec port heads and mine has unported large oval heads.
 

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from what you described, your dad's tach is bad. not terribly unusual to have that happen. loose or tight, if you're both going the same speed with almost identical boats, his with an aa and you with an a, there is no way he's turning 1000-1100 more rpm than you are. unless his aa is completely beat to shit. but then he wouldn't be going as fast as you are. we could postulate all sorts of things, like grass on the grate, plastic bag in the pump - all those things provide other symptoms. realistically, at the same speed as you your dad should be turning a few less rpm than you are. before diving into pump rebuilds, have him try another tach that's known to be accurate.
 

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Pretty sure his tach is right. Its a newer autometer?
You think because it's new it's correct :)bulb hummmmmmmmmm

Anyway how built is your dad's engine ? I ask because unless that impeller/pump is really screwed up it's going to take in the neighborhood of 700 ( observed) to spin a AA to 5,700 rpm's. How built is the engine?




If the engine isn't built to make approx 700 hp observerd or the pump isn't really jacked-up then the tach is messed up. Have the tac checked before you do anything else. ( JMHO )

S CP :)bulb
 

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You think because it's new it's correct :)bulb hummmmmmmmmm

Anyway how built is your dad's engine ? I ask because unless that impeller/pump is really screwed up it's going to take in the neighborhood of 700 ( observed) to spin a AA to 5,700 rpm's. How built is the engine?

If the engine isn't built to make approx 700 hp observerd or the pump isn't really jacked-up then the tach is messed up. Have the tac checked before you do anything else. ( JMHO )

S CP :)bulb
and with an aa turning 5700, it would be going a whole bunch faster than ANY boat turning an a 4400-4500. they wouldn't be anywhere close to even...
 

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Discussion Starter #12
Ok talked to one of my dads old friends, my dads boat might have a b impeller, would this make more sense??
 
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