Question concerning RPM vs. speed

[ELIMINATOR77]

I recently purchased my first jet boat. It is a 77' Eliminator with a Mondello built 460 Ford. I got bits and pieces of info from the previous owner, but no paperwork. I researched the numbers on the heads...super cobrajet 429's, D00E-R. The block is a 460 bored .030, I believe that to be 480ci now. It has an Offenhauser tunnelram with dual 600 Holleys. Here is my question. In the water, I get 5000 on the tach, period. The motor runs awesome, but will not rev any higher. My GPS reads 68.2 MPH. There is no rev limiter on the Accel dual point mech advance distributor, nor any other device of electronic nature. I cannot believe a jet outdrive could rob this motor so badly that 5000 RPM is it!! I am new to jets, but not to engines. The secondaries only begin to open at that RPM, I have watched them. They do fully open, but the motor does not increase in power. Can anyone please shed some light? By the way, it will dry rev well over 6000 RPM...hence, no rev limiter. Thanks

[Stitch King]

Had a 460 (with lots of work) in a copy of Semi Vee Sanger Bubble Deck jet before my current boat. Mine made the most torque/hp at 5650 rpm. It was 460 bored .030, offset ground crank, chrysler 440 rods (yes Chrysler) for 502 CID and heavily worked DOVE heads. Had a custom intake with a single holley 950. Boat ran 76.3 on GPS. You should be able to run near or above those numbers.

Sounds like your impeller is to tall or the boat is not properly trimmed.

First things first, do you have the ability to trim the Pump?

Next which impeller is in the pump? Check with the previous owner on that one. The number on the pump may no longer be accurate.

[Stitch King]

Forgot an easy one. What type of exhaust are you running. Seen many a jetboat choked to death by the "logs".

[ELIMINATOR77]

first, thanks for the reply. I have hooker headers. Tried them open, and with the super trap arresters...same. I have no idea what # impeller. I am on the search for a place deverter also..found some places to get that new..looking for a used one if possible. I will rip into the jet to find out whatever I need..I have no reservations to tackle anything. The guy I got this boat from seems to think it did 85 or better...I find that alittle hard to fathom. I have been seeing alot of olds 455's only hitting 4600-4800 R's. I think this boat launches incredibly..my last boat did 27..only if it was downhill though..no lie. I do know it is a JG berkeley. It has a Harman Marine (converter)?? Maybe I am just scared to go faster...doubt it though. Again, thanks for the input.

[ELIMINATOR77]

Oh, almost forgot..there is a ride plate on this puppy.

[Stitch King]

If it were my boat.....I would get the hydraulic place diverter first. Sounds like your are running flat on the water and need some positive trim to get the bow up and less wetted surface.

That will give instant gratification of 5-7 mph maybe more. :D

Hold on tearing into the pump until winter. Have it gone thru professionally. Seek professional help on the impeller selection. Lots of opinions out there but a guy that works on them every day will usually get you on the right path.

As far as 85 goes......Mine would do 86 with a 175 hp shot of NOS. The pump was fresh, the bottom was blueprinted and the hull was light to start with. IMHO, Unless you have 700-750hp and all of the above that aint going to happen. Good Luck, Ken

[ELIMINATOR77]

ok, I will continue on my mission to get the diverter..ebay has quite a few..just have to catch it at the right time. I am researching to find out what will work and interchange with the JG. I located an original Berkeley jetovator JC model..dont know yet if that will work. I agree with waiting till winter for the jet overhaul. Will have to find someone in Cleve ohio that does jets. Meanwhile, I am off work today..sounds like I'll be heading for the lake to get some heartpounding fun in. Thanks for your great advice Ken. Talk to ya later. Ron

[Stitch King]

Ron,

There is a Jet guy in Northern Ohio I think by the Toledo-Maumee area. I am pretty sure he's in the MHBA. I will see some of those guys this weekend and ask.

Ken