Superbabi

Thanks Tom, I was not aware that the more top end RPMS avaiable would Reduce the prop size, someting I will check out with the motor builder. I thought the faster RPM motors would need rebuilds sooner ???

z.zuperboat

I bet the motor has a hydrolic cam. Thats Y the lower rpm range. My 540 likes 5900

FX10

Gary, I bet if you tried 5 different Merc 30's. You would get different results from each one. All props are not the same.

pi75

Dont mean to change the subject, but has anyone had any luck with a labbed merc Maximus. I have aB1 and a Max both 26P and want to get one labbed for the Y2K but cant decide on witch one, they both have good pros and cons. B1 4800RPM 69MPh GPS and the maximus is the same speed @4600.

Superbabi

Thanks John, getting my hands on a bunch of props is not as easy as the time merc racing had the box of props at Superboat to try out, I did not forget about your xr drive, I want to see how my mine holds up.

Pure Energy

[QUOTE=Superbabi;2618196]Thanks Tom, I was not aware that the more top end RPMS avaiable would Reduce the prop size, QUOTE]


Higher rpm does not reduce prop size. The faster you spin the prop the faster you will go. Spinning a smaller prop faster may be less strain on the drive as apposed to spinning a larger prop slower.

Pat McPherson

Maybe, but not likely.
Torque is Torque no matter how you slice it.

One other thing to consider is the higher the RPM the more friction and heat which can hurt the drive too.

I highly doubt that spinning a 28p B1 at 4000rpm vs. a 30p B1 at 3733rpm vs. a 32p at 3467rpm makes much of a difference.

Now if you change the slip of the prop significantly, that could change things. A 5 blade will in all likelihood be harder on a drive than a 4 blade on and off the throttle...

FASTERDAMITT

I run a hydrolic cam but using good valvetrain control (jesel rocker assembly, custom cam, ect) Here is what I used http://www.jeselonline.com/v2/index.php?categoryid=12

I also had my Mustang spinning 6600 with hydrolic but that's not same as a boat.

Pure Energy

Torque at 4000 rpm is not the same at 5400 rpm, where his builder said he wants WOT. I'd rather run a 28p B1 at 5400 rpm than a 30 at 5400 or a 32 at 5400 or any 5 blade for that matter. Sure he can spin a 28 to 6000 (just don't do it), but he won't blow the drive.

My point is why run a large prop and go WOT and blow the drive???? With that motor it is obviously not a matter of if!! Unless money is no object then by all means....run it like you stole it.

Use a smaller prop, don't go over 5400, enjoy the boat untill another drive option is figured out. Or, pull some power out of the motor. That's what I would do, and it's just my meaningless .02 cents. What do I know!

FASTERDAMITT

I don't know about all the anylizing about how much a XR will take. I only have proof my set-up has withstanded 800hp since late 2005 including a 100 mile offshore race and I still have not done anything but change oil. I still think it has alot to do with throttle control more than anything. I always have one hand on the throttle. If you want to just hammer the sticks and forget about it then you better spend the big bucks on a massive drive.
Yes, a smaller pitched prop will have less stress than a larger pitch prop at the same rpm. It's obvious as small props push less water a the the same prop speed than larger props do.
Therefore my 28p has less stress than a 30p prop at 5400rpm, however the 28p probably has the same amount at 6000rpm. The same goes for cruising speed I would think.
The increased rpm and heat come into play with a smaller prop as said before, but that is negated by cruising just a little slower. But hey, I haven't had to worry about that yet.