AA vs. A impeller

[BowTie Rick]

What king of RPM and HP difference will I get switching from an A to an AA? I am trying to lower my RPMs without losing any top end MPH (a gain would be nice too). How much a difference does it really make? Current set up is a 425 HP 454. Engine is still new so my rev limiter is set at 5000. Feels like it wants to climb higher and feels like there is little if any water resistance.

[HBjet]

What condition is the pump in? Is it brand new? I would say you stick with the A and I'm guessing your pump should be rebuilt. That will lower your RPM's by 400-500 and should give you a few extra MPH.
HBjet
Another question, what boat is this in? If it's a 22ft daycrusier, I wouls say the AA would be the impeller to run, if it's a 19-20 boat, stick with the A.
HBjet
[This message has been edited by HBjet (edited April 23, 2002).]

[BowTie Rick]

Pump is in good shape I believe, but am starting to question it. It was rebuilt a year ago and I just did some work to the intake, ground off some sort of casting seam. The boat is a 2001 Ultra 21 LX. Everyone tells me it should easily go 65 but at what RPM? I do not want to rebuild the motor every year because it runs at high RPMs on a regular basis. I built the boat from a bare hull. http://free.***boat.net/cgi-bin/imageFolio.cgi?action=view&link=Reader_Rides/Jet_Boats&image=KNmarine.JPG&img=0&search=kn%20marine&cat=all&tt=&bool=and

[HBjet]

Nice boat. I think 65mph on a stock 454 is a little stretched. I would say in the upper 50's for that hull. There are a lot of different things you can do. If you don't already have one, get a Plave Diverter. This will help you trim the boat, getting more of the boat out of the water, freeing it up. You can also play with intake grate and shoe setups. Once your loading the impeller properly, you can start playing with the motor if you still want more.
HBjet

[rivercrazy]

IMO - To go 65 in a heavy weight forward daycruiser is going to take a bit more than 425hp. You probably need more like 500hp and an AB impeller.
What brand of impeller do you have. I have a 400hp 454 and an American Turbine A impeller. My motor turns it 4,600-4,700rpm. If your turns it 5,000+ rpm you either have more horsepower than you think, a loose pump, or a smaller impeller.

[BowTie Rick]

I did put a loader grate in it and it seemed like it did make some water resistance in the pedal which made me think an AA impeller was the right direction to go. The motor is not bone stock, it has JE pistons, Manley valves, Milidon 10 qt. pan, GM Perfomance cam from a 502, GM performance valve springs, and the lower end is balanced. It is a copy of a GM 425HP crate motor. Don't you have to pull the intake out of the bottom of the boat for a shoe? That sounds like a mess. There has got to be an easier way.

[rivercrazy]

Actually for a ride plate and shoe, you have to pull the motor and intake. The intake then has to be machined for the shoe/rideplate, and reinstalled.
Originally posted by BowTie Rick:
I did put a loader grate in it and it seemed like it did make some water resistance in the pedal which made me think an AA impeller was the right direction to go. The motor is not bone stock, it has JE pistons, Manley valves, Milidon 10 qt. pan, GM Perfomance cam from a 502, GM performance valve springs, and the lower end is balanced. It is a copy of a GM 425HP crate motor. Don't you have to pull the intake out of the bottom of the boat for a shoe? That sounds like a mess. There has got to be an easier way.

[spectras only]

BTR, I sense that you're more concerned with longevity,than a couple of mph gain.I would check what cam you have ,and go for a bit more lift.Then install a "AA" impeller.With 450-475 HP on tap ,you should be able to maintain 60-63 MPH with your boat's design.I would also recommend the hydraulic place diverter setup,to get you on plane with some hefty friends aboard. http://free.***boat.net/ubb/biggrin.gif BTW,nice ride you have.
[This message has been edited by spectras only (edited April 23, 2002).]

[rivercrazy]

BTW, the difference in RPM between a AA to an A would be about 300rpm. However its also dependant on your peak HP/Torque curve.

[BowTie Rick]

OK, I am getting the jist. I do want longevity but also want more speed. I know it is a fine line to walk but with proper planning it should be obtainable. I do have a jet-o-vator now, would a place diverter really make that much difference in planeing and speed?

[spectras only]

Both ,place and jet-o-vator share the same principal,with the slightly different nozzle designs.The place comes with removable inserts for tuning,and the optional hydraulic trim ,with the botton mountable on the steering wheel to keep your hands on the wheel.With the hydraulic you can feel the trim in your pants when the boat runs it's best trim,especially whit 4+ people on board.I had a manual unit long time ago ,but got fed up with the short life of the trim cable,caused by some bad angles while trimming.The hydraulic cylinder pivots easily,so wear isn't an issue there.

[racingrascal]

AA would drop your RPM about 500RPM's, now that is fine if you are making peak HP/Torque at 4,500 RPM. See if you can borrow one from a shop that is used and see what kind of speed and RPM you get out of it. If you like it buy it if not just have your pump rebuilt by the shop of your choice, maybe MPD I don't know. Is you e-mail correct? I need to get a hold of you for a part we talked about at the L.A. Boat Show.
Andy

[BowTie Rick]

E-mail is correct... richardb@knfilters.com
Maybe we can hook up this weekend or next down at Elsinore. I want someone to run it with me and give me their thoughts on what to do. Tom Patterson from Rex did the pump "on the side" 2 years ago but one of those years it was idle while I built the new hull up. Looking at his ride, one would think he knew what he was doing.

[Banshee]

Hey BowTie, with a heavy boat like yours I would consider a droop snoot to get more lift out of it. Judging by the pic, that thing is running pretty wet. I know it’s not the question you asked but that’s the first thing I would do.

[wsm9808]

http://www.liquidaddiction.net/impeller.html
There is an impeller chart at this link, and I think MPH and CP have one on their web sites.

[spectras only]

[QUOTE] Judging by the pic, that thing is running pretty wet..Judging by the picture,he's not going wot,hence the long vetted surface .However a droop snoot is an alternative to the diverter [cheaper http://free.***boat.net/ubb/wink.gif].That boat is probably not an inch longer than 20.5 ,and being a newer hull ,it's lighter than most older daycruisers. BTR ,what's the specs on your boat?

[flat broke]

Rick,
There have been a lot of suggestions given and most of them will probably gain you something either in pump flow or unwetted area. One thing you should try to do if you're looking at wetted area as an issue is get some good film of your boat from the side so you can review it later and see how wet/dry you might be riding. That will give you a solid reference point to determine what may or may not help you out, and then post installation to verify if you made any gains in unwetted/wetted hull. (just scale the picture and take measurements)
As far as the A vs AA thing goes, from the charts it looks like 425hp would get you between 5-5200rpm on an A and 4600-4800 on an AA. Remember, these numbers are based on a stock Berk, so if you have has someone alter the contour or diameter on the impeller, the charts start to be come less reliable.
Last question, do you have a split(g or b) bowl on your pump? If so, I could hook up with you sometime and let you try out a droop to see what it does for your ride. I'll shoot you an email to give you some specifics.
Good luck,
Chris www.liquidaddiction.net (http://www.liquidaddiction.net)

[BowTie Rick]

Good eye on the amount of boat in the water. Unfortunately that is at a steady 35 MPH. I was out there for work, yes I know tough job, getting pictures for the catalog. I am leaning hard at a bolt on shoe and ride plate plus a diverter and the AA impeller. Not too much $$$ or work to do them. Keep the ideas coming, I am not a jet guru and appreciate all the help and suggestions. The pump is a JC so droop snoot is out. With the amount of forward weight on the Ultra, I think it would make it porpoise. It rides smooth as my bald head right now http://free.***boat.net/ubb/smile.gif

[spectras only]

With the JC bowl ,your choice is the Place diverter.If you want the snoop ,you have to swap to the JG.

[Bense468]

BowTie Rick. You want less RPM's but more top speed, with a more reliable setup? Thats not going to happen. I will tell you why, with the AA you will come out of the hole harder and you will probably pull to about 4,500 to about 4,700 )depending on if your pump is at stock clearances) harder then the A but the A will pull up to about 5-5200. The AA will lower your Rpm's about 500 which is one of the things you wanted. This will be a little better for the motor but you will not get any more top speed out of it. I would bet you lose 2 or 3 mph. Now you have to decide what is better for you. Coming out hard and being able to haul around people with beer or whatever or that extra 2-3 mph. If you want the speed stay with the A. If you want more, you need a little more in the motor dept. If you tighten up your pump which maybe it already is since tom set it up, then you will also drop RPM's but be going the same speed.

[bobz]

if you want the lower rpm and the same horsepower you can change the cam timing. the timing gear has 3 marks on it you want to advance to mark 4 degrees this will change the horsepower curve lower by 500 rpm on the cam sheet. all it will cost you are some gaskets and labor.

[Cole]

You may also check to see if there is a hook on the bottom of your boat,that was one of they first things i did and it made a huge difference http://free.***boat.net/ubb/biggrin.gif http://free.***boat.net/ubb/biggrin.gif Cole

[Licketty Split]

I'm running a dubble A imp. on mine and think it works well but I also amworking on a torker engine rather than a Horse Power engine http://free.***boat.net/gallery/Reader_Rides/Jet_Boats/DSC00965.JPG http://free.***boat.net/gallery/Reader_Rides/Jet_Boats/DSC00965.JPG[/URL]
[This message has been edited by Licketty Split (edited April 25, 2002).]
[This message has been edited by Licketty Split (edited April 25, 2002).]
[This message has been edited by Licketty Split (edited April 25, 2002).]