I was wondering how accurate

[roostwear]

The Berkeley impeller chart is. The Stevens runs around 4600 rpm with an A impeller, so according to the chart, that's around 310 hp (give or take). Not too bad for an old 390, but there should be more than THAT in that engine. Has anyone that has dyno'ed compared it to the chart?

[victorfb]

mike those charts a joke. maybe a guidline for back in the 70s, but no way would i design from them. use my rogers as an example. 5000rpm with an A/B cut impeller. according to the chart my engine (502 BBC) has about 370 HP. how it ever got 81.3 on the GPS is amazing with only 370hp. hull design, pump effiecency, engine torque curves, all play a huge roll in determining what the end result will be.

[CPBRIAN10THMTN]

mike those charts a joke. maybe a guidline for back in the 70s, but no way would i design from them. use my rogers as an example. 5000rpm with an A/B cut impeller. according to the chart my engine (502 BBC) has about 370 HP. how it ever got 81.3 on the GPS is amazing with only 370hp. hull design, pump effiecency, engine torque curves, all play a huge roll in determining what the end result will be.
That chart is not meant to judge horse power off of. It is simply a selection "GUIDE". As victor said, there are so many different things to take into account that you can't use it as a way of figuring hp. All its meant to do is give joe shmoe a way of picking his impeller, a broad guide if you will. If you run a really basic setup that is mostly stock then it would work for you, anything past that i would say call somebody and get some opinions and help.:idea:

[Sleeper CP]

Roostwear,
I haven't had any experience with the stock Berkley chart because I've never had a stock engine or boat. The extended chart that I posted has been fairly accurate. It won't work for every case, but on my 512 BBF, 565BBF and two 650 HP 502's and a couple of more combo's that I helped set up the chart was within 200 rpm's of the dyno #'s. Total of 6 combo's that I set up it has been that close.
Sleeper CP

[LakesOnly]

I would think the HP impeller chart can be very accurate, assuming the OEM pump as delivered from the manufacturer and not worn out. The calculations and principles used to figure power output are very much akin to water brake dynos, less the load variability.
But, once the jet pump is modified with add-ons such as loader, pre-impeller, trim rings, etc. then the equation changes and the chart may be far from accurate. But the pump can still be used to measure gains and losses, though.
I sent the JPC Program to a friend of mine with a Dyno cell. Some of his customers are jet boat guys. He builds engines and then dyno's them, and then the engines are put into the jet boats and the impeller charts compared. The results have always been within 3%. Depending on pump condition and/or mods, your results may vary.
I suspect the shortcoming that may pop up is the lack of load variability with a jet pump (vs. dyno); an engine may produce more power at a higher rpm, but one may never know this if using a jet pump as a tuning tool because maybe the pump will hold back the engine speed at a HP level that is less than if that engine were allowed to run the higher rpm where the power generation is more efficient and thus a higher number. If you cannot see that expected HP number (that the engine should be capable of), then you may think that the jet pump/impeller chart is inaccurate.
LO