I'm still new.... so go easy. I have a '96 25' Hawaiian Euro w/Dominator and Marine Power 454. With a 1/2 tank or so, and 4 people it goes mid/low 40's via GPS spinning ~4200 rpm. I checked out the impeller from the grate and it looks a bit eaten up, I think it would be considered cavication errosion (?). It seems obvious, but would a new impeller (or clean this one up), increase the top speed? The boat pulls fine from plane (has hyd place diverter), but the top end seems a bit low. I realize this is a big heavy boat, but I would think it should run a bit more on the top end. Thanks for your input, I'm still learing (and just today I realized I need to lube the u-joints, clank-clank-clank).
Is 4200 RPM flat out? My 18'6" Taylor makes similar speed, mid 40's at 4,000 on an "A" cut impeller. My top RPM on my 350HP 454 tho is 4,800, which put me at 64 last summer on a badly rough hull. With a big boat like that, 4200 may be it spinning a "AA" impeller to help accelerate the bhemoth, an AA Dominator should eat up 300 HP at 4,000 RPM or so, 340 HP at 4,200. Want to go faster, more HP
Yup, ~4200 rpm is as much as she'll spin. It sounds like there really isn't a need to clean the impeller or get a new one? I would be willing to sacrafice a bit on accelleration to gain some up top, will a "A" impeller do this? Thanks again for the reply... still learning!
It SHOULD ....... but.
I's sure that 454 is not topped out HP wise at 4200 RPM, so allowing it to spin higher should get you to where you can apply more HP to the impeller, thus generating more bowl pressure, thus more thrust from the jet. Now, that may gain you only a couple MPH tho, and aprox 300 RPM. Like I did say earlier, to really gain speed (well, as much as you are going to in that heavy boat) you will need more HP, I'd want a couple hundred personally, especially on a boat that heavy. A 500 HP 454 isn't that hard to build and make reliable, I am trying to get there myself, on a budget, 1 step at a time, nitrousing to 600. My Taylor is a lot smaller and lighter than yours, but she is still a hard working ski & tube towing lakeboat, not a racer. I want more top speed.
On an impeller reference program I have (lots here have it) 43 MPH @ 4200 RPM ... 340 HP. Change nothing else but to 540 HP, impeller speed is just under 5,000 and speed should be aproximately 60. That's on the AA impeller. Then changed to an "A" cut, spin 5300 and make 65 maybe.
If you do not have a diverter, I consider one a mandatory for a lake-jet. The nozzle down settings help cope with rougher water and increase holeshot acceleration, the nozzle up settings try to lift the bow to get more hull out of the water and into the air, reducing drag and adding speed, perhaps 4 or 5 MPH in your heavy boat, more with more HP. With your long heavy boat, a nozzle extension (a "snoot") might add bennefit there to the diverter giving it more leverage to lift and carry the bow.
I hope this is clear and helpful. The folks here are good peeps, many are quite knowledgable and like to help a fellow jetter. Best of luck to you.
Thanks, your responce is appreciated. I do have a place diverter, so getting on plane isn't a problem. Before going the 500 hp route (and $5,000 route), I was looking for a "simple" fix; hoping to use existing hp with a different impeller to spin a bit faster and being able to cruise in the mid 40's to low 50's. Like you said, I'm not looking for a racer. I/we enjoy the lakes cruising around, skiing, etc. BTW, what is the program you're referring to... I'm sure it can help fill in my information gaps.
A freshened pump usually makes a noticable difference. That being said, A good tune up also sounds in order. 4200 for any BB is wheezing at best. Take the time to do a compression or leakdown check. check your advance curve and advance mechanism. make sure all the butterflys are fully opening on the carb. With todays gas prices a top shape impellor/pump and well tuned motor will pay off in both $$ and enjoyment. R.B.
Jet Performance Calculator, or JPCalc, normally available here:
http://www.liquidaddiction.net/pump.html
from LVJetboy. It's really just an electronic compilation of factory impeller HP/RPM curves with a computation for speed if you can give it a reference RPM & speed for your boat. Very easy to use.
For some reason, the site isn't opening for me this AM. If you can't get it, PM me & I can e-mail you the installer.
Yea, my 500HP is costing me arround 5-grand, eventually, incrementally tho.
Cam, Intake, engine rebuild, better rod bolts, main studs, K&N filter $2k
Lightning Headers (used), 4" outlets, MSD no-box distrib. $2k
Next winter heads ported Stage 1, with bigger valves. about $1k
Sounds like there is some work ahead of me... Looks like I'll be getting the hands dirty in the next few weeks! I haven't worked on this stuff before, it should be a great learned experience. I couldn't get the program running either. I'm guessing that the engine (new) was ~320-340hp, so this all appears about right. Thanks again.
Legal Chemistry, ask around. there are a few guys in your area who might have the few specialized tools it takes to make pulling the pump apart easier. That would be a big help. Every 100 extra rpms makes a difference so don't rule out the tuneup issues. If the boat is new to you, getting a good looksy at what you have is also a bonus in it could help with selection of parts choice and what is going on with your pump. 10 years could be alot of good or bad with it. Another thought is to have the impellor you have cut down. This saves a considerable amount for a new impellor and it can also be cut for an undersize wear-ring. Your current imp just might need a cleaning up. above all ask ask ask. there are alot of knowlagable folks on this board who are just lurking. Have patience and you will be rewarded imo.
Your numbers sound ok.
The advice above is sound.
But, consider that trying to make a big boat fast is not a great investment. If you want to go fast and spend $5k you could buy another boat that goes fast.
If you keep your boat, I would not size down on the impeller. Think about getting some heads/work to up the compression a little and get a few hundred more rpm.
The JPC will probably show 400 rpm = 100 hp = 6mph
Is it worth it?
Good luck
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