Reply With QuoteSure, Jer. Go ahead.
The point to of the story though was to say here is what these three different impeller sizes did to this particular boat's performance. It's to get you thinking which I'm glad it seems to be doing. Hopefully, there was at least one nugget of info in the article that will shed some light on your own boat's performance.
Haven't actually seen the article so can't speak intelligently about it (some would say I couldn't, even if I had read it LOL).
Just reading what's been posted here, it sounds as though a lot of what's been speculation to this point (at least to some degree) was proven out.
I was contemplating running a smaller impeller (currently an Aggressor AB) but realized I'd made a mistake on valve sizes when I ran the DD program. After making the correction it turned out that my impeller was right about where it needed to be (new max ponies were at a lower rpm than previously thought), and figured maybe I should leave it alone. According to this information...........that was probably a good decision. I'da been turning more rpm and probably lost speed (or at least not gained any).
Running my mill 500 rpm higher to get an extra 9 hp is not worth the effort.
Sure, Jer. Go ahead.
Thanks 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
"I think that where top speed is concerned, you have to pick your impeller based upon which one you think will get your boat into its "happy zone",which is to say, peak powerband. For my motor, that is around 6,500 rpm. Anything past 6,500 and the horsepower begins to fall off."
Makes sense to me. Neglecting impeller efficiency. But I have your dyno numbers showing peak power near 6.4 to 6.5k rpm and yet your HBM test best top speed at 6200 rpm, 20 hp below peak. Not to mention a 3+ mph gain over the smaller size which implies nearly 50 more hp. So a total of 70 hp discrepancy? Could be all impeller efficiency but maybe not?
"If you have to cut down the impeller to get your motor into its peak powerband where its' really going to come alive, you might not go faster if you are decreasing the efficiency of the impeller faster than you are increasing the efficiency of the motor."
Also makes sense. Pump efficiency's defined as Power out/Power in. (not torque out/torque in btw) Power out directly related to thrust. Power in? Lake power. I've posted on this before. If we had accurate pump charateristic curves, we could estimate impeller power loss with cut size from efficiency and balance that with engine power gain. But we don't.
First things first. Question the data...then draw conclusions. AT impeller measurements for AA in Seloc are:
Large: 9 3/32"
Small: 7 13/16"
A bit different than cut sizes mentioned in your article. I'm curious which is it? Have you rechecked the 9.25/7.50 dimensions with TP racing on this point? Could be significant. Also, Seloc published the AT impeller table showing a 450 rpm difference between the AA and A cut at 550 hp. As power goes up, so does the delta. So also your engine's power from 6200 to 6350 rpm since it's short of peak. All considered, those factors seem to support more than 150 rpm. And 300+ impeller deltas may make more sense compared to other mfgs. Yet you measured only a 150 rpm gain between an AA and A?
jer
This test and discussion has been a real eye opener. To highlight my most personal significant observation from the results, forget the RPM for the moment and consider that the different impellors produce similar bowl pressures but have a drastic effect on the top MPH.
Since the diverter hardware (nozzle insert) remained unchanged for each test, one may assume that GPM output(volume) and top MPH correspond with each other. Does anybody know of a way to measure GPM output in our application? (In the industrial power field, GPM can be measured in several ways, all of which require a substantial length of straight pipe.)
It appears that the larger impellors are more efficient. I like the idea of moving the bowl closer to the impellor, testing that would be interesting. Generally speaking, not disregarding all the variables that come into play, would it be better for those who have a quest for efficiency for a boat that is not "race only", to "tailor" the engine for a larger impellor?
Sorry Jer for the vane thing.
Joe
http://members.cox.net/lvjetboy/DuaneSpeed.jpg
ok, i'll bite.. how fast was the boat going with the a impeller, at 5400 rpm?
The AA impeller that was used in the article was cut to 9.000 O.D. to fit a berkeley bowl. And the diameter of the blade on the back end was cut to 7.812 at 25 degrees. If the impeller was 9.250 then it would not fit into a stock berkeley bowl.
"I think that where top speed is concerned, you have to pick your impeller based upon which one you think will get your boat into its "happy zone",which is to say, peak powerband. For my motor, that is around 6,500 rpm. Anything past 6,500 and the horsepower begins to fall off."
Makes sense to me. Neglecting impeller efficiency. But I have your dyno numbers showing peak power near 6.4 to 6.5k rpm and yet your HBM test best top speed at 6200 rpm, 20 hp below peak. Not to mention a 3+ mph gain over the smaller size which implies nearly 50 more hp. So a total of 70 hp discrepancy? Could be all impeller efficiency but maybe not?
"If you have to cut down the impeller to get your motor into its peak powerband where its' really going to come alive, you might not go faster if you are decreasing the efficiency of the impeller faster than you are increasing the efficiency of the motor."
Also makes sense. Pump efficiency's defined as Power out/Power in. (not torque out/torque in btw) Power out directly related to thrust. Power in? Lake power. I've posted on this before. If we had accurate pump charateristic curves, we could estimate impeller power loss with cut size from efficiency and balance that with engine power gain. But we don't.
First things first. Question the data...then draw conclusions. AT impeller measurements for AA in Seloc are:
Large: 9 3/32"
Small: 7 13/16"
A bit different than cut sizes mentioned in your article. I'm curious which is it? Have you rechecked the 9.25/7.50 dimensions with TP racing on this point? Could be significant. Also, Seloc published the AT impeller table showing a 450 rpm difference between the AA and A cut at 550 hp. As power goes up, so does the delta. So also your engine's power from 6200 to 6350 rpm since it's short of peak. All considered, those factors seem to support more than 150 rpm. And 300+ impeller deltas may make more sense compared to other mfgs. Yet you measured only a 150 rpm gain between an AA and A?
jer
Haven't had time to recheck the size of the impeller. But the rpm change is correct. The AA to A=150 rpm, A to B=350 rpm. Why such a non-linear curve? I can't be sure. The point was to get people thinking and I'm glad people are debating the subject.
As for the engine running under peak (-20hp) rpm with the larger impeller, I really don't think that 20 hp (on the dyno, not the lake) is going to make a measurable difference. I've tested other parts on other motors that added 15-20 hp on the dyno and once the motor went back into the boat and hit the water, there wasn't a lick of difference in terms of top speed or acceleration.
It appears that the larger impellors are more efficient. I like the idea of moving the bowl closer to the impeller, testing that would be interesting.
We have done this testing. And it does make a difference. I have produced a new bowl that works exceptionally well with a "B" or "C" impeller. It moves the vanes so much closer to the impeller, that you can not run it with an "A" impeller. Another thing that we have learned, is that you can get the vanes too close to the impeller. When you do this, it pulls HP off of your engine, just like setting a wear ring up too tight does. But that's a whole other can of worms. The vanes too close to the impeller blades works kind of like a torque converter. Too close like a truck converter, they tend to lock up. Too loose, and you increase your stall speed, just like a race car. That's not necessarily bad, it's just the trick of getting the set up perfect for your boat. These are the kinds of things professional pump builders work on and do for their customers.
Now, here's where it gets real interesting. We have run more tests since I sent these results to Jer. Here's what we found. When we cut the vanes back on the orignal bowl that we were testing with, we ran 5400 rpm with the 9.5 imjpeller @ 93.1 mph; Then we installed one of the new bowls and ran 6100 rpm @ 98.2 mph with the "B" impeller; and ran 6400 rpm @ 97.4 mph with the "C" impeller. We could not run the "AA" or "A" impeller in this bowl because it would not fit. Bottom line here seems to indicate that there is a perfectly matched area, that works for the relationship of the impeller blades to the bowl vanes. We think we have found it. (or are at least close).
Jer, It would be interesting to see you add these numbers to your chart for compairison purposes.
Any data on the intake and/or bowl pressures with the different impellers?
Brian
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