Just finished the engine, 468, 10.5 to 1, TRW forged domed pistons, roller setup, cam is 290, 520, 800 cfm Rochester, mallory ignition, edl performer 2 intake. The motor was balanced, and line honed for the crankshft. 110 Octane, and 36 degree advance, The only thing I am not sure of is impeller size.
I cannot turn more than 4800 rpms, and it is best between 3000, to 4500. After that it feels as though it has a governer on it and no more hot foot either, the pedal and carb are at full throttle and or full travel.
I should be able to run 6500 all day long with this engine, but something is holding it back.
American Turbine pump.....
Any suggestions?
Thanks in advance.....
I am not gear head, I cannot guess how much HP you have. But if you have about 400+, that is where you are gonna be spinning with a "A" imp in a jet. Try uping the HP or cut the imp down to a "B". That will get you more RPM.
Others with more knowlage will jump in, but I think I am on the right track, or not! LOL
How big is the boat? Did you run it before the engine build and get 6500 rpm?? These numbers seem about right for a tight pump. It takes alotta HP to turn an "A" impeller over 5000, and it has to make it in the right RPM range. If your power level is "peaky" and tops out at 6500 then you may not be reaching it with that impeller...
When you say Rochester 800 carb, do you mean Quadrajet? If so, only a highly modified QJ could do what you are asking.
You may have a AA impeller in there. Pull the bowl off and find out whats in there.
We need to know what boat, speed, results before and after?
And your cam specs. If you got a cam to make power at 6000 rpm you are outta luck.
The carb is off a 455 buick and been tricked out and jetted, the boat is an 18 foot Wriedt Maverick and it ran like sh1t when I bought it so I have nothing to compare it to, the cam is 290 duration, abd 520 lift
If you have a smaller lightweight boat a good starting point would be a A/B cut impeller and possibly a B cut impeller. Remember it is hard to add material to an impeller once you have cut it down. If you can borrow an impeller from someone that is even better before you cut down your own.
If you have larger heavier boat a AA impeller would be a great impeller for your application.
If you are in neighborhood of 475 - 500 hp your impeller would probably be around a AA in size.
If you are lower in horspower like around 400 you are probably running a A impeller.
Both of these are assuming that you have a tight pump with correct tolerances.
This information is based upon your engine is able to get high enough on its horsepower curve to spin the impeller to 4800 rpm. It is possible that you have a smaller impeller such as an A or a B impeller and your engine creates horsepower much higher in rpm and it is not able to make enough horsepower at 4800 rpm to get to where the motor makes its peak horsepower.
Hope this helps, There are lots of guys in here that will be able to help you out.
way too many factors to consider here. since it ran like crap before, you could have a hiden problem. maybe a bad driveline, or ? you just need to check everything. then again at 4800 rpm, you could be maxing out your set up and all is correct. in the engine, the camshaft is key to making power were you want it. that 290 dur? is that advertised or at .050? im guessing advertised and if so id say thats about in the 2500-6000 rpm operating range. that doesnt mean you will get 6000 rpm out of it with your set up.
just because your only spinning 4800 rpm doesnt mean you can get some good speeds. in my 18 rogers i spin 5000-5100 rpm with an A/B cut impeller and it GPSed at 81.3MPH. and at 4800 rpm it is still hauling pretty darn good. matching all the components for optimum effieciency has been an ongoing battle from day one in the boating world.
I appreciate all the help i can get as I live in Indiana and there are not many jet boats around here.
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