Reply With QuoteFor your 21' Daycrusier an A or A/B would be a good place to start. You can always trim more off an impeller but you can't add it back on.
Don't start with anything smaller than an A/B cut.
How high do you want to rev it?
Sleeper CP
565" Ford Lover
If your engine makes it's power at a higher RPM, you will need a smaller impeller like a "C"...in some cases being able to get to this power range will give you more top speed. Say for example that your engine makes 500 hp at 6000 RPM. With an A impeller you wont be able to reach 6000, so you wont be using all the available power, and your speed will be dependent on getting more RPM, which = pumping more water=more thrust...
Hope that helps
Yes, I think that does. Trade off between top RPM/MPH and engine acceleration. In looking at it, if I am understanding it, once your HP meets the Impeller RPM curve, you don't go any faster.
With the curve I said,
A2 would give me 5100 RPM
A = 5300ish
B = 5500
C = 6000
Which one accelerates quicker? Which one could have more top speed? Or is it all the same just hitting the engine at a different RPM?
Yellowboat said pulling a skiier I need an A - so an A would deliver more thrust to pull out a skiier? Or would the C just take more RPM to do the same?
Does anyone have the other impellor curves (a2/3/4 AB, etc)?
Sorry for all the Q's and such, I'm really trying to understand it.
For your 21' Daycrusier an A or A/B would be a good place to start. You can always trim more off an impeller but you can't add it back on.
Don't start with anything smaller than an A/B cut.
How high do you want to rev it?
Sleeper CP
565" Ford Lover
For your 21' Daycrusier an A or A/B would be a good place to start. You can always trim more off an impeller but you can't add it back on.
Don't start with anything smaller than an A/B cut.
How high do you want to rev it?
Sleeper CP
565" Ford Lover
Honestly, this combo is good mechanically for a pretty high RPM 7500-8500, KB external pump, really short and light pistons, large pan, etc. Difference between 5K and 6.5K is all a perception issue more than anything else (of course lower rpm is less strain). The cams I have to choose from (IE the ones in the garage), are a hyd 240/248duration (@.050) 510 lift, and a 312/320 duration .670 lift solid roller. The dyno curve I gave was simulated using real head flow numbers with the Hyd cam. I think the roller will be a little too much RPM, and not enough bottom end with the cubes I have in this combo (I'd probably only get 3K RPM out of it).
Are there flow numbers associated with an impeller, IE, a C flows 4000GPM @ 4000 RPM while an AB flows 4000GPM at 3000 PRM or such (made up numbers obviously). This could help me figure out what combo would go faster, assuming GPM = Thrust and speed for a given hull configuration.
Keep in mind that with a boat, you will always be running a "high" RPM, not just touching it for a couple seconds like in a car...therefore 4000 is fairly high. You dont want to be casually cruising around with the engine reving at 6K all the time...
Are there flow numbers associated with an impeller, IE, a C flows 4000GPM @ 4000 RPM while an AB flows 4000GPM at 3000 PRM or such (made up numbers obviously). This could help me figure out what combo would go faster, assuming GPM = Thrust and speed for a given hull configuration.
If I were you, I would figure out what the boat will be doing 85% of the time and set it up for that. I thought I read it was a 21' daycruiser. I wouldn't focus on the top speed thing. Put an A or A/B in it and if you want to go faster put a 125-150 shot of Nitrous on it and be happy.
Out
Sleeper CP
565" Ford Lover
Keep in mind that with a boat, you will always be running a "high" RPM, not just touching it for a couple seconds like in a car...therefore 4000 is fairly high. You dont want to be casually cruising around with the engine reving at 6K all the time...
Good point. *Very* good point.
If I were you, I would figure out what the boat will be doing 85% of the time and set it up for that. I thought I read it was a 21' daycruiser. I wouldn't focus on the top speed thing. Put an A or A/B in it and if you want to go faster put a 125-150 shot of Nitrous on it and be happy.
Out
Sleeper CP
565" Ford Lover
I just happen to have an extra (complete kit) 175 shot in the garage sitting there doing nothing that I know will work great, and I currently have an A impeller in my jet now. Certainly will be cheaper to keep what I have for now.
BTW - I love Nitrous
On other boards my tag is
bottles...they're not just for babies anymore
****
Thanks to both of you (and everyone else) for keeping me grounded. uh, watered. rivered?
quik street relationship to an impeller. A cut 538. c cut 373. hope this helps figure the rpm range and where you're torque will help most with a heavy boat trying to get out of the water. Or up on plain with a skier drowning behind you in the soup.
quik street relationship to an impeller. A cut 538. c cut 373. hope this helps figure the rpm range and where you're torque will help most with a heavy boat trying to get out of the water. Or up on plain with a skier drowning behind you in the soup.
what??
quik street relationship to an impeller. A cut 538. c cut 373. hope this helps figure the rpm range and where you're torque will help most with a heavy boat trying to get out of the water. Or up on plain with a skier drowning behind you in the soup.
Actually, wouldn't that be the other way around? The A being like a 373 and the C being a 538? 373's are a stiffer ratio than 538's...just as an A is stiffer than a C I would think.
quik street relationship to an impeller. A cut 538. c cut 373. hope this helps figure the rpm range and where you're torque will help most with a heavy boat trying to get out of the water. Or up on plain with a skier drowning behind you in the soup.
I guess that was humor, but an A is like a 2.73 gear and an D is like a 4.88 I would say
Sleeper CP
Big Inch Ford Lover
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