Switched to SS from Aluminum of same pitch but now RPMs too low

[further]

Recently purchased a Ballistic Stainless Steel prop 14-1/2 x 19 pitch for my 1996 Chris Craft 18' bowrider Volvo 4.3L GS, SX Drive to replace the original aluminum. Went with the same size and pitch but now at WOT I'm topping out at about 4300 rpm and I should be 4400 - 4800. Has anyone had their props re-pitched by a prop shop? Is it an expensive proposition. Guess I'm asking if its worth the effort to re-pitch or should I just unload this one and buy a new 17 pitch to increase the rpm's?

 

[Sea Rider]

Which wot rpm did you achieved with original alum prop ? So 4300 rpm was your last SS prop wot run, was the wot test conducted with you alone and lightly loaded boat on flat calm no wind water cond ?

4400-4800 is your factory wot range. If you drop two more SS less pitch maintaining same diam probably will hit the mark. This is not exact rocket science. Best prop is dialed under trial and error. Usually at third prop change from factory delivered. The issue is that you will not know how many wot rpm will be increased dropping one pitch size. Could be 150-200 or 200-400 + rpm. Roll the dice..

Happy Boating

 

[further]

Which wot rpm did you achieved with original alum prop ? So 4300 rpm was your last SS prop wot run, was the wot test conducted with you alone and lightly loaded boat on flat calm no wind water cond ?

4400-4800 is your factory wot range. If you drop one more SS less pitch maintaining same diam probably will hit the mark. This is not exact rocket science. Best prop is dialed under trial and error. Usually at third prop change from factory delivered.

Happy Boating

Original prop had me around 4500-4600 if I recall correctly. Test was done not in the most ideal conditions - myself, wife and my two kids with some minor gear on board. It was very windy however and definitly not calm conditions. Maybe I'll try again next calm day I get before switching anything out.
Thanks

 

[Frank Acampora]

Too bad someone did not clue you in before you bought it.: Ballistic is an EXCELLENT prop but it is fully cupped AND has more blade area than a standard type prop. The net result is a Ballistic prop of the same pitch will always turn slower than the standard prop. Don't even think about re=pitching it. If it is that new and you really don't like the RPM, sell it and buy a different prop or a lower pitched Ballistic.

Back about a year or two ago I did some evaluations of Ballistic vs. stock stainless props. I picked up a brand new Balllistic 13 X 21 in the box at Cabela's. It was probably a return and I paid only $200. It consistently ran lower RPM on my outboard but top speed was the same

 

[Texasmark]

You nailed it Frank!

 

[FrizFreleng]

Frank - If you are getting the same speed at a lower RPM, why up your RPM's to attain the same speed? You are burning more fuel at the higher RPM. I went from a 13 pitch to an 11 to gain RPMs to manufacture's specs. Got the RPMs but lost the speed. Cruising had to use more fuel to maintain the same speed. Probably going back to a 13.

 

[further]

Great info guys! Thanks Frank. Gonna put back my original Aluminum so I can stay within recommended rpm's and sell the ballistic; try to get a different one. I picked this one up on eBay for 180.

 

[Frank Acampora]

Friz: I never really measured fuel consumption during the tests I ran with the Ballistic against stock stainless props. Unfortunately, the Ballistic put my RPM below the recommended range and my outboards are happier near the top of their RPM range. Also, because of the extreme rake of the Ballistic blades I could not use a standard thrust washer. I needed to customize the mounting so the blades would clear the exhaust snout.

 

[Outsider]

Probably going back to a 13

Any idea what your recommended WOT range is? That's where the OP wants to be ...

 

[Texasmark]

Frank - If you are getting the same speed at a lower RPM, why up your RPM's to attain the same speed? You are burning more fuel at the higher RPM. I went from a 13 pitch to an 11 to gain RPMs to manufacture's specs. Got the RPMs but lost the speed. Cruising had to use more fuel to maintain the same speed. Probably going back to a 13.

What Frank is telling you that the Ballistic grabs more water per rev. It is "loading up" more than the other prop and pulling his rpms down. Loading a 4 stroker causes the vacuum to drop and change the timing to more advanced to pull the engine harder......tries to get the rpms back. This causes the ignition point to be earlier in the cycle and does burn more fuel since firing takes place too long before TDC where the piston can reverse and go into the power stroke.

Ever notice a colored vacuum gauge with the 3 color scales, used for determining best driving condition for max fuel economy: Red for low vac, engine lugging, excess fuel consumption, yellow mid range, green which is like driving down a hill, engine loafing vac rises and timing retards and fuel consumption drops.

Backing off the pitch aka "grabbing LESS water per rev" puts the vac in the green and raises the rpms toward max rated. Besides you get the best hole shot and water toy towing ability as a bonus.