30p vs 28p ware on drives
 

Guys, I just had Wesco Racing Engines build me a pair of 575s out of my old hp500 blocks. The powerplants rock, but I'm now trying to dial in. Just ordered a set of 30 pitch four blade props to replace my 28s (need to lower the RPMs), but am concerned that this will put added stress on my stock bravo drives. How much harder will 30s be than 28s?

Before you answer – yes, I know that I am putting too much horsepower through these drives. You don't need to rag on me for that! I'm just interested in knowing the difference in ware and tear between the two.

I think it is more a matter of slip. Probably pretty similar between the two if they are both four blades.

I don't see either one being harder on the drives. You will have less acceleration with the 30P and may be out of your targeted RPM range. What I do is run the 28P and then have BBLADES tweak the 28's to align with your targeted RPM. It is not that many more $ if you buy a used set of Bravo 1 28p, and then use Brett to set them up to meet your goals. In a high preformance boat, used props and BBlades provides the best value to gain max preformance.

Arcticfriends "Smitty" has some informative posts concerning his real life experiences with different pitch props on a Bravo drive. I believe he noticed a significant difference in wear going from a 30 pitch Bravo prop up to a 32 pitch Bravo prop. Do a search on his threads,

Ir you meant where... Thats easy put it on the splined shaft thingy thats sticks out of the back of the damn thing... Ir you meant wear i can not help.you with that

LOL

Damnit, you're right......'wear.' I'll blame it on speech to text....

575hp? if so at what rpm, if it is higher than the old motors you might not need the new props. Torque and shock load will kill the drive, HP would not be the first of my worries.

Also, i believe Merc stuck XRs behind 600sc motors

Peak horsepower is being made at about 5000 RPMs. Rev limiter is set at 5300, and I hit that at about 80% throttle. Need to lower RPMs to gain more top end. Not sure how the old set up dyno'd, but I had 80mph at 5250 RPMs at WOT. The new set up with 28 pitch props powers up to 80mph, but that's where it hits the rev limiter.

You're right about the torque and shock load. I'm very careful with it getting on plane and hammering down while running 3700 to 4000 RPMS or so, as that's where peak torque happens.

If its making peak horsepower at only 5,000RPM, then I would try the 30p props. My rough guess is you will probably see 84-85mph or so.

I find it hard to believe that a 575 Merc would make peak HP at only 5000 RPM. I would think it would be at least 5400. Were these engines built using 575 parts or something close? If it was me I would raise the limiter to 5700 and see what it does.at 5400.
I spin my 509's 6000 RPM and they love it. I wouldn't worry about 575 HP going through a Bravo drive. I was using 28 Bravo props on my 34 SCARAB and the only part I broke on the drives was a design failure of the IMCO vertical shaft in the -2 shorty's.