SoCal Jet Boats
Tech Talk => Jet Pumps => Topic started by: Ckaz21 on August 11, 2014, 11:14:32 PM
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At what point is switching impellers not worth it? For instance I running an A impeller and turning it 5,400 rpm if my engine makes peak power at 5,800 would it be worth switching to a B? Basically to gain a few hundred rpm would it be worth the loss in efficiency of a smaller impeller?
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At what point is switching impellers not worth it? For instance I running an A impeller and turning it 5,400 rpm if my engine makes peak power at 5,800 would it be worth switching to a B? Basically to gain a few hundred rpm would it be worth the loss in efficiency of a smaller impeller?
Gonna give you my best possible answer, but first, how sure are you that peak power occurs at 5,800? Do you have a dyno sheet? The reason I ask is because without gained torque, you would be taking a gigantic step backward...
You have two potential problems, if you can call them that...
The first issue you are going to have to deal with, the jet pump will begin to lose efficiency at anything above at or near 5,200 RPM, meaning that it will take "way more HP and RPM to make smaller differences above that point". You can definitely stay ahead of the curve, but instead of 20HP increases to sea a gain, you need 50hp increases...
Second, if your engine really does not make the torque at that higher RPM, it will all be for not.
When I set them up, I do everything in my power to build them to run between 5,200 and 5,600. It is my humble opinion that you will not see the speed change, just the noise... It will potentially lose MPH even though you would gain RPM...
Hope this at least helps.
These are just my observations and opinions.... Your results may vary (although I would be willing to put some skin in the game)...LOL
GT
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Thanks GT! I have no idea what my torque or hp curve looks like I still need to get it dynoed. My engine is a 454 .030 over 22cc dome pistons 10:1 XM 278 cam, full roller rockers, 049 heads with the bigger valves, air gap intake and 850 dp carb. I'm only assuming the peak power would happen higher than 5,400 but I have no idea about the torque. I'll probably just stick with the A cause my boat is ridiculously heavy for what it is, the old sales brochure says it weighs 1,800 lbs, don't know if that includes engine weight or not
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Thanks GT! I have no idea what my torque or hp curve looks like I still need to get it dynoed. My engine is a 454 .030 over 22cc dome pistons 10:1 XM 278 cam, full roller rockers, 049 heads with the bigger valves, air gap intake and 850 dp carb. I'm only assuming the peak power would happen higher than 5,400 but I have no idea about the torque. I'll probably just stick with the A cause my boat is ridiculously heavy for what it is, the old sales brochure says it weighs 1,800 lbs, don't know if that includes engine weight or not
I had a very similar set-up, (same heads, intake, pistons, 292AH comp cam, 750 holley and headers) and lost ~200 rpm (down to 5200) after the pump was built and detailed 'A' impeller. Wear ring to skirt was at .070"/ side, brought it back to .012"/ side.
Your pump may need some tightening up. A built pump should bring your rpm DOWN, but mph up and improve your hole shot.
What a difference, especially out-of-the-hole, and top end was at 72 (heavy azz sled)
Ridiculously heavy is 2900 lbs plus fuel and gear, well over 3600 lbs (21' daycruiser)
Dan'l