Reply With QuoteThanks Duane. Here's the numbers...
Engine Dyno run B:
http://members.cox.net/lvjetboy/DuaneDyno.jpg
Notice corrected power is similar (in the 900's) to Cyclone's as well as peak power rpm.
Here ya go Kojac, top speed and rpm's:
http://members.cox.net/lvjetboy/DuaneSpeed.jpg
Duane tested with his lake jet and verified speed by GPS and Nordskog speedo. The impellers were race-prepped. There was a tell-tale tach in the boat matched to computer data aquisition. Duane, if I've mis-quoted anything, please correct me.
Analysis:
First, notice the rpm change from Aggressor AA to A. +500 rpm.
I graphed impeller curves (maybe will post them later) to the dyno data adjusting for engine output power and estimated +450 rpm...close to test results. Yes, an Aggressor impeller's not the same as an American Turbine impeller. But consider Berkeley AA to A at the same power....impeller curves say 400 rpm. Consider also Legend AA to A at the same power...impeller curves say +380 rpms. Then consider Dominator impeller curves near the same power...+300 rpms. AT curves say over 450 rpm gain...similar to Duane's test data. So based on Duane's data and impeller curves from several different mfgs including American Turbine, I'd expect WAY more than a 150 rpm gain going from an AT AA to A reported by Cyclone. That's why I commented on that point.
Not challenging Cyclone, just questioning why his data on the AA to A is significantly different than other published results. There's stuff we don't know. There's stuff we don't account for. Then there's stuff we could know and account for if we took the time to think and understand.
Second, notice the impeller size for top speed. Was it bigger is better AT 9.5 or even Aggressor AA? No. In fact, if you look closely at the data, although the Aggressor A tested recorded top speed, an A- or A/B cut may've done better. Hard to say. But clearly, the big cut was short by about 10 mph. That's significant.
Finally consider, test data no matter who does the test, and impeller curves, no matter who presents those curves...both are subject to question. Does that mean we throw out one or the other? No. Just approach with an open mind. The point is not to dismiss either as bogus but to understand why a difference?
jer
Jer, Thanks,
I agree with you after looking at the dyno charts it appears that the horsepower and torque stop making maximum power at 6400 rpms and an a/b cut impellar may have put the pump at the sweet spot at about 6100 rpms and produced more top speed.
It would be nice to have been able to try an a/b cut impellar to see if this is true.
Great input from everybody.
Thanks to Duane for the data he produced.
I think this kind of input is critical for those of us looking for the most efficiency in our boats.
Were there any other changes made during the testing of each impellar. i.e. Nozzles, loaders, wedges, plates? If not I think at least the nozzle changes would have made significant changes due to bowl and intake pressures changes. I would think that at these different rpm's the pressures had to be different?
So much to think about hmm.
Kojac
Variations in DA and other test conditions hard to account for and may eat up (or exaggerate) a 2% power change? I'm thinking ya. But other things equal, in the simplified world where some underlying truth may be discovered before the haze of reality sets in...20 hp should be good for about 50 rpm's and 1-1.5 mph with a hull like yours or mine. Just trying to focus through the haze maybe see some nugget of truth.
