Hideing in the shadows

[nitrochief421]

Hello to all, been lurking in the shadows now for about 4 months, reading and learning. First off Ive seen alot of nice boats from everyone and have picked up alot of good info. Ive always been a I/O guy but have always loved the jet boats since the time that my buddys dad brought home their 79 cobra with a 460, WOW what a ride. 20 years later the kids are grown up and I find that I dont need my 94 Fourwinns gas miser anymore, especially since they're not boating on my fuel anymore. After 15 years of racing injected nitro and supercharged alcohol dragsters on the NHRA circuit its time to kick back with the wife and have fun on the lake again.
In January I got rid of the Fourwinns and picked up a 79 16' Cobrajet outfitted with a 350 olds and Berkeley 12JF pump. The motor was toast, and the pump needed some TLC, the boat itself and trailer are in VERY good condition so 950.00 later its mine. Parts for the pump will be here Monday so now the pump will be 100%.
Now this is the part that I would like your opinion on. I can tell that most everybody on here is like me...there is no replacement for displacement...but, here is the motor thats going in. It is a 350 chevy high nickel large jounal block with special main bearings so we could run a small journal Luannatti crank, its a 350 that can run the RPM's higher than most 327's to be precise its a 331. Other goodies include,Crower rods, tapered wrist pins (for lighter reciprocating mass), dished Venollia blower pistons, Crower roller cam, Crower roller lifters, Harland sharp roller rockers, Crane stud girdles, Pete Jackson gear drive, Dart 2 cylinder heads, Edelbrock Victor Jr. intake, Paxton Supercharger and a few other goodies Im sure you dont care about. The motor itself really starts to wake up at about 2700 RPM thru redline at 9000 RPM, but because of the Paxton redline of 7400 Rpm, I keep it to under 7000. 15 pulls on the dyno netted 360 hp @5400 and 375 ft/lbs torque @ 5150. Base compression is 9.2-1 so this is all on pump gas. This years goals are to get it in the water have fun and then next year the second Paxton goes on which should net me 20 lbs boost total.
I have no idea what to expect out of this in a boat, I know that when it was in the car it was very content to cruise the streets or to pull the skin off your face at the track. Im hoping that it will still be very happy to cruise in a boat or to atleast run 50 mph and toss my buddy out the back....what do ya think is 50-55 mph realistic.
Here is another question, I know on our roots style and screw blowers that you can get to a point where all pumps (air or water) go whats called supersonic and will actually decrease in out put. Do jet boat impellars experiance the same? At what RPM range does this start to occur? As you can see from the motor info it will carry some ungodly RPM, maybe to much for the pump. I dont know thats why i signed up here.
I apologize for this being so long, I promise you wont see another like this.

the bridge is yours over and out
Ron Potter-AKA Nitrochief421

[nerve damage]

Welcome Ron It all sound pretty trick but as for how it will work you will have to wait for someone else to help with that. Do you have any pictures yet, if so post some. Back to you

[thompy]

dont know what the max rpm for the impeller is but it sounds like a 383 stroker would be cheaper to build with better performance

[nitrochief421]

Nerve damage- thank you for the welcome, sorry i dont have pictures yet I should have it presentable to all in about 2 weeks. Its always good to hear from a Canadian neighbor Ive did alot of raceing and beer drinking (Bradours & XXX WOW good stuff) with some awesome Canadisn fellows.

Thompy- Yes a 383 would have been cheaper by 15000.00 but negative on the performance. I had the exact clone to this engine in a 2600 lbs 23 T-bucket altered that ran 8.90's in the quarter. The difference in this one and the race one, is that the compession on this one is WAY lower. The clone had 13-1 compression and this one is 9.2-1 static and with the paxton spooled up its its approx 10.2-1 the paxton I have is a early model so its only putting out about 8 lbs boost. Next year the second one I have will go on and between the two should give me around 16 lbs. In all seriousness this mouse will roar, the motor will handle major compression and has blowen many a 383"s on the bottle into the weeds.

Nitrochief421

[OldSleekOlds]

Welcome to the frustrating world of jetboats. Do yourself a favor and find out what you will need for clearances so that this motor can live in a marine environment. The engine that does very well at the dragstrip will usually last minutes on the lake. It's all about clearance. Cold lake water goes through the block. The block cannot expand very much. The rotating assembly is operating under full load......NOT FOR A FEW SECONDS......but for minutes at a time. Everything that's moving in the motor WILL expand. Think about it. If you want to avoid throwing away a lot of money, do a lot more reading.

As for pump rpm, it's determined by the impeller you use. Pick a number you like from the chart and go for it. It's just like the water brake on a Dyno.

Considering that this is a 16' boat, it might be OK with the "little" motor. Power is very important, but any problem with the hull (like a hook) or setup will kill performance.

Old

[Duane HTP]

My suggestion would be to go get a crate 383 and have something you can use and enjoy, (and save your high dollar engine). The killer drag strip motor will not be welcome in the jet boat enviroment for long. As far as the 7200 rpm, give me a call and I'll explain some of the jet boat characteristics to you. 417-858-8616.
Duane HTP