496HO - Best RPM for Max HP
 

OK motor heads, I have a question for you. Throttle Up has my props right now for reworking. They are in pretty bad shape as suspected. Anyway, the question came up regarding the best rpm for max horsepower. For instance, I have noticed that my top speed does not increase when rpms increase from say 5100 to 5250. Matt called a racer buddy of his who has a lot of experience with our engines. His said that his experience was that best speed (in the 38 Scarabs) was attained at 4750 to 4850.

What are your opinions on this? And I know this group has an opinion!

thanks

Not sure where max hp @ rpm is, my single runs 5100 at top end.
You should be hitting the limiter at 5250? I've bumped it a few times myself when its cool out. I would like to know, 66 on gps is the best I can do. john

Your best HP rpm is dependent on many factors. The cylinder head flow is one, cam profile, intake, carb(s), exhaust, intake manifold...........If you give me more info, I can get you in the ballpark for what you have now. I can also help you set up for whatever power band you want.

blown1500, that's way more info than I am capable of providing. I am NOT a motor head. That will have to come from merc or someone else. My 496's are completely stock at this point.

fountain, yes i was bumping the rev limiter at 5250 in fall air. my typical summer rpm's were between 5000 - 5100 after labbing Bravo 28's.

It seemed to me that the motors ran (and sounded) much better after labbing as opposed to before when I was in the 4700 - 4800 range.

Macklin,
I am curious why you are having your labbed props done.
What problem are you trying to correct from the original lab job and who did that job.

Thanks,
Rick

If they are still stock give Mercury Racing a call in Wisconsin. I talked to a guy in the prop lab and he asked the weight of the boat drive ratio and engine model and then told me what the ideal max RPM was for my boat. BTW for me with HP500EFI and 1.5 ratio Bravos on an 11,500 lb hull he said the closer I can get to 5300 the better.

Fountain27ho496
I'm a bit surprised as to why you are only getting 66gps with the 496HO in your 27? With a full bag of gas and four onboard I'll slow down to 66. With a half bag of fuel and just myself onboard I've seen 69.2 gps...

BTW: 2002 Sunsation 288 -w- 496HO stock 24p Bravo-1

rv, after labbing I lost a solid 5 mph off my cruise speeds. NOT acceptable. Plus the props were not matched when they were labbed. They are 100 rpms apart which means I am always having to work the sticks to get the rpms matched up. I don't want to say who labbed them, let's keep this on subject. I will say that everyone agrees my props were bad out of the box.

I will make these my spares and am trying to decide which props to buy......the reason for this thread.

The 4750-4850 is probably the torque peak on the motor based on the Scarab comment. I know I am starting something with that comment. You might try running a higher pitch prop that the boat can turn at that RPM and see what the speed is. The larger pitch would also help the cruising speed. If you have the opportunity, it might be worth a try.

Just for some comparison figures...I have a 2001 Nordic 28' with the 496HO, 24p Bravo. The best I got was 67 with two people and 1/2 tank gas, rpms just below 5000. I had the prop labbed and repitched to 25 and lost cruise and wot. Total bummer. I'm trying a friends 26 labbed by Bronson Hill next summer. Finding the right person to tweak the prop is difficult and costly I'm finding out. This will be the last prop I deal with, if it doesn't work out, I'll just go back to a stock 24, these single engine 496 boats aren't fast enough to warrant the prop headaches in my mind...save your time and money :mad: