I think I spoke to you at the Long Beach races
Not exactly a newb question here.
A couple questions that you need to ask yourself about your actual usage model with this in mind, you do indeed want to tune your pump to your engine:
How long will the engine last if you set it on kill? We had a few customers that were spinning over 9000 RPM. These combinations were capable of more RPM and more power but were ultimately operated at less than peak potential. The difference in operating expenses is changing a $1000+ set of valve springs every weekend vs. every pass. How often will you have to tear it down to inspect and refresh?
How are you going to run this boat? If at the river, are you going to wear out an engine every weekend making passes all day, every day or on the anchor enjoying socializing and cold beverages?
Lastly, you will eventually break your Berkeley suction housing.
Assuming that you will run it on kill, the pro stock boats run a Lenco gear reduction box to slow the impeller down. If you can spin a BC impeller around 7500 +/- RPM, you will be right around where you want to be. You will need your actual uncorrected numbers, RPM, and gear ratio, before you can't make a proper selection.
You want to run the largest impeller that won't stall your engine. A larger impeller will help your launch. Picture 1 illustrates the the difference between a 30-degree "A," or a "Large A" and a 33-degree "B" cut impeller. This is a difference of over 5/8" in vane length. Picture 2 is an attempt to illustrate impeller vane area.
As you cut the impeller down, you loose efficiency, but there is less load on the engine to allow it to rev to peak horsepower RPM. More work is getting done, but only when the impeller is completely loaded. Ultimately, it's about the total combination, not about optimizing one component at the expense of everything else.
Turbo engines make brutal torque. If you don't balance impeller cut with engine output, you will blow a hole in the water. Even then, you will most likely need some kind of launch profile. The impeller won't start properly loading until the boat is moving.
I have been thinking a lot about how to maximize the launch of a turbo boat. Even with minimal boost, you will probably be able to bounce off the rev-limiter on the hit. If I were doing this, I would ramp in boost using an electric blow off valve so that engine output closely approximates power absorbed by the impeller.
I would not try to pull timing because it takes more time for the engine to recover once timing is reapplied.
You could do it with the waste gates, but you might have lag when the turbo(s) slow. Opening the blow off valve(s) will reduce resistance against the compressor wheel, allowing the turbo to spool without resistance. Then reduce the amount of bypass, increasing the boost as the impeller hooks.
We talked about adding a clutch in the mix. I still think this is a terrible idea unless you employ some type of slider clutch that you can ramp in the power. If the pump is engaged, accelerating the impeller from zero to 9000 RPM in a nanosecond, you will blow the pump apart. I saw the carnage after a Jet-A-Away accidentally engaged on the trailer, supposedly at idle. The Jet-A-Away exploded, the suction housing broke, a good 17-4 shaft bent and twisted, and the impeller keyway sheared. There is just too much mass (11.5lbs.) in a stainless "B" impeller to dump it like that.
Cheers,
Joe
