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Discussion Starter · #1 ·
boat specs.
16'
350 (.30) over
mild rv cam
big valves (2.02)
650 holley
hei
spun a old wore out pump with an "A'' impeller to 4400 rpm.
havent had the motor on a dyno, but i am rebuilding the pump right now. would it be safe to say that starting with a "b" cut would be a pretty good choice to pick up a little more rpms?
 

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Are there any visuals as ro what the differnt cut impellers look like? I've often wondered, what is cut to make the difference.
 

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Are there any visuals as ro what the differnt cut impellers look like? I've often wondered, what is cut to make the difference.
I actually have an impeller cut chart, I will try to scan it when I get to use my computer:|err

They cut the trailing egde, making the vanes (aka blades) shorter.....

I am sure someone will beat me like I owe them money on the scan thing..But I will try to beat them to the punch...:D

GT
 

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Discussion Starter · #6 ·
I actually have an impeller cut chart, I will try to scan it when I get to use my computer:|err

They cut the trailing egde, making the vanes (aka blades) shorter.....

I am sure someone will beat me like I owe them money on the scan thing..But I will try to beat them to the punch...:D

GT
glen i have seen alot of impeller charts, but since i dont know my actual horsepower, i didnt really pay to much attention, i wanted the "pros" opinion
 

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My concern is that you have a RV cam (torque not RPM), and big valve heads but you want to spin more rpm. If you want more rpm and take advantage of the heads, consider more lift in the cam.
My .02
 

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My concern is that you have a RV cam (torque not RPM), and big valve heads but you want to spin more rpm. If you want more rpm and take advantage of the heads, consider more lift in the cam.
My .02
Times 2 also what pistons/compression ratio ?

ps heres some info for ya courtesy of AT


H.P. 9.5 9.25 AA A B C
150 2900 3050 3200 3600 3800 4050
200 3200 3350 3500 4000 4200 4450
250 3450 3600 3700 4300 4500 4800
300 3800 3950 4050 4550 4800 5100
350 4050 4200 4300 4750 5100 5350
400 4250 4400 4500 5050 5300 5600
450 4450 4600 4700 5250 5500 5850
500 4650 4800 4950 5400 5700 6050
550 4800 4950 5100 5550 5850 N/A
*THESE RPM VALUES MAY VARY ACCORDING TO HOW YOUR BOAT ALLOWS THE PUMP TO LOAD
HORSE POWER REQUIREMENTS ARE AT THE PUMP SHAFT

AMERICAN TURBINE JET DRIVE IMPELLER SPECIFICATIONS
IMPELLER SIZE LARGE DIAMETER SMALL DIAMETER MACHINED ANGLE
9 1/2" 9-1/2" 8-1/4" 25 DEGREES
9 1/4" 9-1/4" 8-1/4" 20 DEGREES
AA 9-3/32" 7-13/16" 25 DEGREES
A 9" 7-1/4" 30 DEGREES
B 8-3/4" 6-3/4" 33-1/2 DEGREES
C 8-1/2" 6-1/2" 33-1/2 DEGREES
 

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glen i have seen alot of impeller charts, but since i dont know my actual horsepower, i didnt really pay to much attention, i wanted the "pros" opinion

Yeah I figured you have. I was trying to answer Gregs "cutting the impy" question...It was a shameless thread jack.

More RPM BTW does not necissarily mean more HP like Tom and slowride state, you will find that the performance of the pump is generally centered around the 5000 RPM mark, they will work at higher and lower RPM, but the curve really drops off, I like to stay near 5K for a BBC and 5.5K for a SBC as a general rule for "family boat" type apps...Just my preference from what I have learned by making assumtions and mistakes...

GT :)hand
 

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Ok so if you want to play around with the impellers is it as simple as pulling one out and putting another in Or do you have to change wear rings to mach each impeller?
 

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Yeah I figured you have. I was trying to answer Gregs "cutting the impy" question...It was a shameless thread jack.

More RPM BTW does not necissarily mean more HP like Tom and slowride state, you will find that the performance of the pump is generally centered around the 5000 RPM mark, they will work at higher and lower RPM, but the curve really drops off, I like to stay near 5K for a BBC and 5.5K for a SBC as a general rule for "family boat" type apps...Just my preference from what I have learned by making assumtions and mistakes...

GT :)hand
I hope Sandeggo doesn't miss the point as you did. It's not about "horsepower" (let's not get into a hp/torque thread again), it's about the cam not providing enough lift for a fully loaded engine at a higher rpm. That's why I didn't mention duration or lobe center (though they are also a consideration)..... my concern is that it'll wheeze without enough lift.
 

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Discussion Starter · #12 ·
10:1 is the compression ratio and the only thing i know about the pistons is that it is bored .30 over making it a 355. this is all going off of the previous owner, and the seat of the pants. dont know if it helps or not, but the boat gps'ed at 58.7 before the gps shut off
 

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10:1 is the compression ratio and the only thing i know about the pistons is that it is bored .30 over making it a 355. this is all going off of the previous owner, and the seat of the pants. dont know if it helps or not, but the boat gps'ed at 58.7 before the gps shut off
Do you know if this is a "flat top piston deal" and are they Old camel hump heads ? Tom
 

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I hope Sandeggo doesn't miss the point as you did. It's not about "horsepower" (let's not get into a hp/torque thread again), it's about the cam not providing enough lift for a fully loaded engine at a higher rpm. That's why I didn't mention duration or lobe center (though they are also a consideration)..... my concern is that it'll wheeze without enough lift.
slowride, where did I miss a point?, I was merely pointing out that with his current motor combo may not want to add some RPM and should remain at a taller impeller...The motor would hit a wall at around the 4800 rpm range, IMHO I would go AB and see where he ends up..The curve I mentioned was that of a pump curve, not HP/Tq..;)

Maybe I could have written the comment better.:)devil

I read the thread 3 times and failed to catch where I missed a point....

10 minutes I'll never get back...:)

GT :)hand
 

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Ok so if you want to play around with the impellers is it as simple as pulling one out and putting another in Or do you have to change wear rings to mach each impeller?
depending on if your dealing with new or used equipment.. Some impellers may have been turned if used to get the ring skirt surface true again.. If thats the case you would most likley have to change rings to get your clearances right.. Otherwise say youve got a ring thats gonna be on the loose side thus possibly causing cavitation issues. Best to match ring to impeller...


What i did was start fresh with an A2 and im going to go from there. cut it down if need be. As ive got the 455 i wanna keep the rpm down, but on the edge at the same time :D
 

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slowride, where did I miss a point?, I was merely pointing out that with his current motor combo may not want to add some RPM and should remain at a taller impeller...The motor would hit a wall at around the 4800 rpm range, IMHO I would go AB and see where he ends up..The curve I mentioned was that of a pump curve, not HP/Tq..;)

Maybe I could have written the comment better.:)devil

I read the thread 3 times and failed to catch where I missed a point....

10 minutes I'll never get back...:)

GT :)hand
By interjecting "horsepower", you completely missed the point. 500 ft lbs (for instance) of torque would have been required at 4500 rpm. Now you go to a smaller impeller and that same theoretical 500 ft lbs is at 5500. The load is the same (it's a dyno after all), but the increased rpm requires a greater volume of air. If the lift is insufficient for the increased flow at 5500, it won't achieve it. That's why I suggested more lift.... not for more HP.
Happy now? I had to waste 5 minutes explaining basics to you.:)sphss
 

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Discussion Starter · #19 ·
ok so try an AB, cool. now slowride, which cam would you suggest, i appreciate all the information and please guys lets not get this thread cluttered?
 

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ok so try an AB, cool. now slowride, which cam would you suggest, i appreciate all the information and please guys lets not get this thread cluttered?
Forgetting impellers for a minute , what SR was saying (I think) is if you want that motor to buzz to 5k your going to have to go with a cam etc accordingly. That said you might be surprized at what happens when you take a 10 to 1 or so sbc with "202" fuely heads and a "first off road Cam" with headers and two 450 holleys and try to then interject a "mild rv cam" into the mix.
"
The 17' "Syndicate" project motor (removed from another boat) we just finished originally had that combo and we spent alot of time coming up with a cam that would work with "thru hulls" (which our project and I belive yours has) and still allow the motor to survive on 91 octane. Josh knows far more about this than I and would be happy to help you call him
Tom

heres some interesting reading , on compression ratios
http://www.empirenet.com/pkelley2/DynamicCR.html

Just sent a B/C to a guy with 550 [email protected] rpms (6k is where he wants the motor to run)
 
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