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Discussion Starter #1 (Edited)
I am going to build a new motor for my jet boat. The impeller that I am going to run requires 550 horsepower at 5000 rpm. I would like to start with a pair of off the shelf new ford scj aluminums.

I am wanting to run this impeller because of wanting to keep the cruising rpm's low because of noise and wanting to hear the stereo.

I am thinking of a 4.5 inch crank. A pair of through the transom headers with 2.25 primary's. Wanting a long life but a bit concerned about running a crank with that much
stroke.

The chart for the impeller that I want to run.

HP RPM
150 3050
200 3350
250 3600
300 3950
350 4200
400 4400
450 4600
500 4800
550 4950

Any help would be appreciated.
 

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550 horsepower at 5000rpm will require a larger engine than a 460 so adding stroke and cubic inches is the way to go. I think you could reach your goals with an engine that's in the low to mid 500 cubic inch area. About 4 years ago I helped a guy build a 454 Chevy for a jet boat and it made 509 horsepower at 5200rpm with a set of mildly ported oval port cylinder heads so with some more displacement and a better cylinder head you'll be way ahead of his engine. In his build he used a Competition Cams street roller cam, I'm thinking that it was the 280R which worked great and it's caused no problems with the valvetrain. A single plane intake was worth 30 horsepower at the peak and it was much better everywhere we tested from 3000 to 5500rpm. For a carburetor we tested with my Competition Carburetion built 950HP and his 850 Holley. After some jetting they both produced the same numbers and cruising down the river it's flawless.
 

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boat motor build

Get with Paul Kane on the forum, He's a jet boat owner, parts manufacturer, and general 429-460 expert. He can really help you on your build.
 

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For that low of an rpm range i would go with a 4.5 stroke for sure, a mild roller cam and some CJ style heads with a Victor intake and 1050 carb. For what you want this will get you a lot of low end power for your dollar. :)
 

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Also remember that going with a impeller that is too big will kill your topend performance and will only save you 100-200 rpm at cruising speed. I have tried this, ran a "AA" impeller and it hurt my topend alot compaired to the "A" and saved me very little rpm at cruising speed.
 

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Discussion Starter #6 (Edited)
Also remember that going with a impeller that is too big will kill your topend performance and will only save you 100-200 rpm at cruising speed. I have tried this, ran a "AA" impeller and it hurt my topend alot compaired to the "A" and saved me very little rpm at cruising speed.
Going from an A impeller to a 9.25 should drop cruising rpm by over 500 rpm. At least that is what I am seeing from the chart. As far as top speed that is not really a major concern.

H.P. 9.5 9.25 AA A B C
150 2900 3050 3200 3600 3800 4050
200 3200 3350 3500 4000 4200 4450
250 3450 3600 3700 4300 4500 4800
300 3800 3950 4050 4550 4800 5100
350 4050 4200 4300 4750 5100 5350
400 4250 4400 4500 5050 5300 5600
450 4450 4600 4700 5250 5500 5850
500 4650 4800 4950 5400 5700 6050
550 4800 4950 5100 5550 5850 N/A
 

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I've got a 77 Hallett Jet 19' that i built a 460 for. It turns an A Agressor 5200 RPM. According to the charts that makes it about 525-550 HP. Its a 40 over 460, stock crank and rods, DOVE heads with only mild porting to the exhust side, roller rockers, the biggest soild lifter cam Crane makes, 2.25 intakes, 9.3-1 comp and 2 660's on a tunnel ram. Oh and MSD marine ignition. It also has the 9 Vein Aggressor Bowl, 2" droop and place diverter. A custom built stainless top loader grate. The boat runs high 12's in the 1/4 mile with all the interior and about 82-85 on GPS depending on water conditions.

Doug
 

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Going from an A impeller to a 9.25 should drop cruising rpm by over 500 rpm. At least that is what I am seeing from the chart. As far as top speed that is not really a major concern.

A
So what's your projected cruise rpm ?

edit:
Do you ever plan on running it really hard? What intake manifold and carb do you plan on running ?



G-
 

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Discussion Starter #9 (Edited)
So what's your projected cruise rpm ?

edit:
Do you ever plan on running it really hard? What intake manifold and carb do you plan on running ?



G-
I would like to keep cruise around 2700 rpm. I would like to be able to run hard and be reliable.
As far as an intake, a single plane with an 800 or 850 Holley if this will work. I know that running such a tall impeller will probably leave some mph on the table but a true 550 horsepower should give some good mph numbers in a fairly light 19 foot boat.
 

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a 9.25 impeller will be great for cruising but it will kill the performance of a n/a motor, but the nice thing is you can always cut the impeller down if you don't like it.
 

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I would like to keep cruise around 2700 rpm. I would like to be able to run hard and be reliable.
As far as an intake, a single plane with an 800 or 850 Holley if this will work. I know that running such a tall impeller will probably leave some mph on the table but a true 550 horsepower should give some good mph numbers in a fairly light 19 foot boat.
Been there done that many yrs ago, if I could do it over again I'd take tha mph up top and give up alittle on the cruise side.

It's a balancing act,


Years ago we ( brother and I) had a stought roller cam 472" Ford in the CP with a AA impeller. Engine broke because of abuse of the little button on the steering wheel, replaced that engine with a nearly stock 460, that 460 damn near used twice the fuel of the more powerful engine. It didn't have the power to turn the impeller so it took more throttle effort and used more gas.

I don't think I see 2,700 rpm being a realistic cruise rpm, the impeller is only going to move so much water. I've had a 9.25" AA it pulled like a AAA the 565" turned that impeller 5,200 and the boat ran 92-93 mph and 102 at 6,200 on the Nos. I wish I'd have let the engine rev out to 5,800 with that impeller. That pitch impeller is no longer made and it was the most efficeint impeller I ever had ( mph/rpm).

I don't cruise the CP as most people run there boats. Most people cruise at 3,000-3,200 kind of lugging the boat along I run my boat fully loaded up river 12-14 miles at 3,800-4,100 at 50+/- mph on top of the water with far less drag. It doesn't use anymore gas until the secondaries kick in.

I think an 850 carb might be a bit small for your engine. Here's another thing on the carb, since '93 the 565 has had the same 1,050 Holley Barry Grant carb. First the engine was 780hp, then 855 hp and now 935 hp the same carb with progressive linkage, the secondaries didn't open until 4,000 +/- depending on the laod in the boat. Last year I got a 1,200 cfm Pro-System carb with soft-progressive linkage (secondaries open sooner). Patrick told me because of the way the carb is balanced it won't use anymore fuel than the other carb, as of yet I'm not sure about that.

I can't write you all that I've picked-up since '89 trying to balance cruise rpm with performance, but I agree with what Filucky stated about giving up a 100 or 200 rpm in cruise and picking it up on the top end. I'd let the engine rev out a bit more.

Do you plan on putting this engine on the dyno?

More later but I have to go for now.

G-

Jon
 

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a 9.25 impeller will be great for cruising but it will kill the performance of a n/a motor, but the nice thing is you can always cut the impeller down if you don't like it.
I agree with this and your other post about rpm and top speed.

Got to run for now I'll get back to you.

G-

aka: Sleeper CP

Jon
 

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I am going to build a new motor for my jet boat. The impeller that I am going to run requires 550 horsepower at 5000 rpm. I would like to start with a pair of off the shelf new ford scj aluminums.

I am wanting to run this impeller because of wanting to keep the cruising rpm's low because of noise and wanting to hear the stereo.

I am thinking of a 4.5 inch crank. A pair of through the transom headers with 2.25 primary's. Wanting a long life but a bit concerned about running a crank with that much
stroke.

The chart for the impeller that I want to run.

HP RPM
150 3050
200 3350
250 3600
300 3950
350 4200
400 4400
450 4600
500 4800
550 4950

Any help would be appreciated.
You can use the impeller charts as a guide but they are not always so dead-on accurate due to changes in the pump (intake, loader, pre-impeller, clearances, etc).

Personally I would opt for the 4.300 crankshaft with a 6.800 rod for structural integrity and engine longevity. The beautiful thing about the 4.300/6.800 combo is that at BDC, the piston pin is only 0.030" lower in the bore than the OEM 460. You will make more than enough power and also improve the two points I noted above, will accommodate the small carb better, will run slightly smoother, etc. And pump gas combos are easy with slightly less stroke, although either can get pump gas friendly combos, I suppose.

Paul
 

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FYI,

A guy I know did some impeller testing some yrs back. This is what he posted on the boat site we post on:

I just stumbled upon some notes I took during a test I did about 6 years ago. Jack McClure of Marine Performance Designs installed an Edelbrock Qwickdata system in my old Rogers Bonneville TR to record rpm, speed and pressure numbers.

Tom Papp cut the rear flange off of three identically prepared stainless steel American Turbine impellers so that I could quickly swap them in and out of my Berkeley pump at the lake.

Brian Alber came to the lake with me to do the swaps and in the course of a few hours we made runs with each impeller in my boat. The engine was a blown 572ci BBC. Here's what I learned that day:

AA impeller
3000rpm 39.2 mph
4000rpm 60.4 mph
5000rpm 83.0 mph
max rpm 6,200 110 mph

A impeller
3000rpm 38.8 mph
4000rpm 57.4 mph
5000rpm 79.9 mph
max rpm 6350 107 mph

B impeller
3000rpm 35.0 mph
4000rpm 53.1 mph
5000rpm 75.5 pmh
max rpm 6700 105 mph
+++++++++++++++++++++++++++++++++++++++++++
 

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Good find Jon, i remember seeing that awhile back, it shows just how little speed is gained at lower rpm on a bigger cut impeller. Just want to point out that the topend performance will be the opposite with a N/A deal, boosted motors make tons of torque down low and that is what those big cut impellers are for.
 

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Yep the blown deal is a different animal then what he would be dealing with. I'm not against the big impellers at all, but it's a balancing act at far as the rpm, cruise speed and fuel use. In a smalll light boat I'd let it rev a bit, but unless he's going to dyno it and never let it rev to max hp rpm it's all just a guess.


Here's an article that's posted here:

G-
 

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impellor size

The impellor size debate has gone on for years. I run a 557" 'Ford with a 9.5" impellor. This year I splurged and bought some SCCJ heads. My boat now runs 108 mph at 5500 rpm. Thats without using my NOS. It goes to 6k with the Nos but I have not tried to GPS the NOS because I don't like to run it that fast for very long.
My thoery is to try to keep the rpm down closer to where the peak torque is. My motor made 802 ft pounds at 5100. I like it.
 

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The impellor size debate has gone on for years. I run a 557" 'Ford with a 9.5" impellor. This year I splurged and bought some SCCJ heads. My boat now runs 108 mph at 5500 rpm. Thats without using my NOS. It goes to 6k with the Nos but I have not tried to GPS the NOS because I don't like to run it that fast for very long.
My thoery is to try to keep the rpm down closer to where the peak torque is. My motor made 802 ft pounds at 5100. I like it.
Those are some nice numbers! What kind of boat ya running?
 

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Discussion Starter #19
I appreciate all the answers to my original question. As i stated before, leaving a couple mph on the table isn't that big for me as this will mostly be used for water skiing and cruising. But I will spend the bucks to dyno the motor to find out where I am at. At least a tall impeller can be cut down if it needs to be.
For sure I want this motor to last a long time as I have done a lot of wrenching in my past and have done a bunch at the lake which I do want to avoid. I am toying with the idea of running a real mild roller since it seems that juice flat tappets seem to be having issues with todays oil.
 

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cheyenne splash

boat is cheyenne copy, built by me. been runnin this one for 7-8 years. last yr it would run 103 and I had dove heads on it. of course it is faster with nos but i never run the nos long enough to get a top speed. I like the big impellors. most of my friends run blown alcohol chevies. thats when I use the nos. they hate it!
 
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