OUTLAW EAGLE MANUFACTURING

MOriverbum · Joined: 26 Jul 2010 Posts: 51

So I have 20ft step tec (gator) with a 383 . Dyno sheet says 436 at 5200. Running a 309 with a place diverter hp housing and 4degree up wedge with place diverer. Best run at 68.4gps at 4800rpm. It's a ss impeller, can't find a stamp on it. I think it's an "A". Would I benefit by going to a B? Don't really run over 4000 most of the time. Like the current cruise speed at 3800. But I am curious if getting up around 5200 would help at wot. Would it kill my. Cruise?

WILSON · Joined: 17 Jun 2005 Posts: 352 Location: Mexico City

According to Mr. Berkeley Jet and Mr American Turbine, 436 HP should be able to turn an "A" impeller at least to 5000 RPM's.

So, If your engine is properly tuned up, and your current WOT RPM is 4800 RPM's, Your impeller is likely an AA. (Not A)

The "higher" the letter, the more water is moved on each turn. So, going to a lower impeller (A or B) will give you:

a) Probably more speed at WOT, as you match the pump efficiency with your engine's HP.
b) More difficulty to get the boat on plane /step
c) Less boat weight carrying capacity
d) Less engine life.

If you can get a borrowed impeller to try, try it. But your current setup sounds good to me, and I would'nt bother if it was MY boat....

My 3 cents.

WILSON · Joined: 17 Jun 2005 Posts: 352 Location: Mexico City

Ooops It should rather read: The LOWER, the letter, the more water is moved: AA pumps more water than A; A pumps more water than B; B pumps more water than C, and so on...

Medicine Man · Joined: 02 Dec 2010 Posts: 66 Location: Medicine River, AB

You have an A Impellor, I used to have a 19 ft Step Tech with 450 hp sbc AT 309, and it spun an A at 4800 in Red Deer @3300 ft elevation. Switching to a B will increase rpm around 300 rpm and u will only pick up 2mph maybe 3 mph, but your fuel mileage will drop at cruising speed, and you will loose some whole shot. IMO A is the best all round Impellor for 383, 406, 421, 434 sbc's. I have tested AA, A, B, C Impellors.

Arthur · Posted: Thu Sep 27, 2012 6:25 am Post subject:

MOriverbum · Joined: 26 Jul 2010 Posts: 51

Thanks guys, guess I will just stick with what I have. My wallet will appreciate it.

Medicine Man · Joined: 02 Dec 2010 Posts: 66 Location: Medicine River, AB

At our elevation here in the Red Deer area, a good way to figure out how much HP you are making is this formula a guy told me about 15 years ago, Loui at AMS. 500hp spins an A at around 5000 rpm, every 100 rpm = 25hp. This formula at 3300 feet elev is quite accurate for naturally asperated engines. 5400 = 600hp, or 4200rpm = 300 hp. If you live at lower elevation you will rev 100 or 200 rpm higher. This is about 85% accurate I would say spinning a steel uncut A Impellor in a AT 309.