Reply With Quotethat makes two of us. i'm lost now.
pops1:
Scarab Jet:
OK guys, this might sound like an obvious question but here it goes:
Let's assume we have the same boat with the same jet pump and the same impeller. Now, if we were to compare a 350 vs. a 502 motor in this boat and run each of them at let's say 4500 RPM, would both of them go just as fast at that RPM? ( or for that matter at any given RPM?
Thanx in advance...You must make a assumption based on your write up that both impellers are the same cut.
That is whare the two motors will fall apart- ON Torque! The small block is a lighter weight but that is all. The big block may even make the same HP but it make Torque at a lower RPM. To off set this, you are be forced to cut the impeller-Which shortens the duration of water ride (a critical producer). Also on the smaller impeller you cut the vane away (smaller) which causes the bowl pressure to become the offset for the lower thrust comming off the impeller. You now have a larger exit port opening on the smaller impeller(flushing) with a lower thrust entering into the bowl. You also now have reduced your frontal draft by flushing the water out the back (and so on). Torque is the answer or gear reduction to develop comp torque to run the biggest impeller possable at the highest RPM.
What you have developed to offset the torque to HP is design in slippage which is non-functional loss -Dave wink
I know there is some really good information there
that makes two of us. i'm lost now.
Scarab Jet:
OK guys, this might sound like an obvious question but here it goes:
Let's assume we have the same boat with the same jet pump and the same impeller. Now, if we were to compare a 350 vs. a 502 motor in this boat and run each of them at let's say 4500 RPM, would both of them go just as fast at that RPM? ( or for that matter at any given RPM?
If the answer to the above is yes, then can it be assumed that the only [noticeable] difference between the two engines is that the bigger engine has the ability to get to the given RPM quicker than the smaller engine?
Thanx in advance...I think 77Charger is right on. The only other differance would be, one expensive small block VS one stock junk yard big block........ How much RPM does anyones small block turn with an A impeller anyway's? Usually 3500 - 4000ish??
MikeC
Scarab Jet,
Are you the one that has shoehorned a 502 in your Scarab?
I thought it took "X" amount of HP to turn an impeller at "Y" speed.
If it takes 400 HP to turn an A impeller 5000 rpm, it shouldn't matter if it was powered by a bbc or a sbc or hampster running on a tread mill, as long as it was able to put out 400 hp at 5000rpm and had enough torque to power through the lower rpm range to reach 5000rpm .
[ October 02, 2002, 07:36 PM: Message edited by: wsm9808 ]
MikeC:
I think 77Charger is right on. The only other differance would be, one expensive small block VS one stock junk yard big block........ How much RPM does anyones small block turn with an A impeller anyway's? Usually 3500 - 4000ish??
MikeC[/b][/QUOTE]
My small block turns the B impeller 5200. Junk 383, logs, unported world heads. With an A it would be 4800 or so? Once I cut the heads, put a bigger cam in it and get it back together I'm thinking around 5500 or so with a B. Get Jungle Boy in on this. He's got a pair of bad-ass small block jets.
I think the BB will get more ladies on the boat no matter what RPM you produce! Tim
If it takes 400 HP to turn an A impeller 5000 rpm Is there a formula or a chart to figure HP needed to turn a specific cut impeller at a specific RPM ? I bought a Spectra 18 with a rebuilt 460 I have know idea what has been done to the motor internally . I know the pump has been blue printed and I have the receipt with the cut , I know If I take it out and open it up I can get the RPM with this info can the HP be determined ? I would think there would be many more factors to this weight , drag , ect. Thanks RH
rh, check this out,pump chart
"Junk Jet
My small block turns the B impeller 5200. Junk 383, logs, unported world heads. With an A it would be 4800 or so? Once I cut the heads, put a bigger cam in it and get it back together I'm thinking around 5500 or so with a B. Get Jungle Boy in on this. He's got a pair of bad-ass small block jets."
JJ, Thats pretty interesting, what hull and what kind of speed ya getting out of that mouse? Most people that have tried SB's seem to have had trouble about the 4800 mark.... Is your Jet Junk?
The only SB that I've seen run like hell is Blown Biskit from Havasue. I'd like to hear more about them mouses......
Thanks
MikeC
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