WOT #

[tonyiiiafl]

I have a 1994 390 CPMY with 454 gas. Plate states WOT is 4400. We are running 22 x 22 props high are the line ticket builder specs. I BARELY hit 4000 under ideal conditions and she is a hungry gal for gas, because I believe teh engines are working too hard. I was going to swap out to a 22 x 21, that should give me 1550/200 more revs to. Put me in the middle of the range. My prop shop said he would rather go to 22 x 20 to allow. Me to hit the 4400.

What are you all running for pros and WOT? I know numbers don’t lie, but do i want to hit 4400 or stay in the middle.

[bud37]

The original sea trial specs from the builder are on a light boat with no extra anything and brand new bottom with shiny clean props and running gear, also brand spanking new engines.

The question you have to ask yourself here is how much do you really drive this boat at wide open throttle and the more important in my opinion is do you really want to push 26 year old engines like that. If you are considering saving any fuel, it won't happen......if you use all the HP the engines have available you will use the same amount of fuel, just physics. You may go a little faster therefore get there sooner, but what does the prop shop say....they have all sorts of calculators available to them nowadays to spec things out within reason I would think. You lower the pitch you will have a higher RPM at hull speed as well, so consider how each advantage applies to your needs.

There are many opinions about this WOT thing, this is just mine for an older boat.....new boat would be completely different IMO.

[tonyiiiafl]

That is what I am thinking. First I run HEAVY! Always go out 330 gallons gas, 70 gallons of water, and or course enough provisions for at least a week.

I NEVER run at WOT, usually between 2800 and 3200 for cruise. The prop shop said I would need to pitch to a 20 for WOT to happen. However, I am not looking for more speed, just a step at what the engines will not be working hard, hence the 21 pitch.

I am leaning towards leaving these at the 21 pitch and trying them as such next season. Then I can better decide if I want to go to a 20, stay at 21, or go back to a 22. Make sense?

[km1125]

Going down in pitch will also help your ability to plane, even if you never got to WOT. You'll run at a marginally higher RPM at your preferred cruise speed, but that doesn't necessarily equate to lower MPG, as the engine would be also running with slightly higher vacuum.

[g36]

Your 390 is much the same size and weight as my 405. I have the 22x21 props and 454 crusaders 454 although tbi. I can reach 4400-4600 . Very seldom do this maybe 1 -2 times a year just to check. Anytime rpm's have been low or have me wondering i ve changed /cleaned my 3 fuel filters and then bam back to normal revs. Have you done any tune up or filter change recently?

[tonyiiiafl]

Yes, tune up (plugs, cap, filters yearly. Bottom paint yearly, ablative type. I just think my engine are working too hard for the level I am at. IF I open up to the highest I can get to, (4050, max) I am using 65++ GPH both engines. Even cruising at 3200 I am in the 40 range. So I am going to leave the 22 x 21 as they are, and just have them tuned. THANK YOU!

[Viper]

I agree with the guys and g36 brings up perhaps the most important part; before you come to ANY conclusion about your current WOT and the necessary changes required to achieve spec, you need to ensure first that your engines are properly tuned for both ignition and fuel delivery. Only then should you consider making changes to your running gear.

While not applicable to a lot of Carver models, one also needs to ensure hull and transom cores aren't soaked and adding an enormous amount of additional weight to the equation.

[tomschauer]

As usual, the guys are on top of it. If it comes up to plane in a reasonable amount of time i wouldn't bother with the pitch. In the end you are moving x amount of weight through the water at x speed. At a steady cruise your fuel consumption should be very close no mater what the pitch at a given speed (rpms will vary with pitch but total energy consumed (fuel) will be near constant). A bit less pitch may bring you up faster and save a couple quarts each time, but that's about it.