Rev Limiter

[kaydano]

How do you know when you hit the rev limiter? Do you feel or hear it? Or does it simply mean you read the tach and if your at the high end of the manufacturers range, you're hitting it?

Reason I ask is I get 35 mph with 4 people (2 adults, 2 kids) and nearly full tank of gas and max out at 6400 rpm (which is the high end of the rpm range for Mercury). I went out this weekend by myself with just 6 gallons of gas (out of 24 gallon tank size, I know because I put 18 in afterwards) so only 1/4th tank, and I still could only go 35 mph at 6400 rpm, even with the bow gate wide open! I figure the boat was about 450 lbs lighter...

I also think I should have gotten more speed, because it climbed up to 6400 rpm a LOT faster than I ever have before. I was impressed. I mean the boat really took off with just me in it and not much gas on board (I weigh ~170-ish).

So, I assume I must be hitting the rev limiter, but I couldn't feel it or hear it...

Secondary question: Would a different prop (higher pitch) get me more speed? Not that I necessarily want to do that, just trying to understand. I assume a bigger pitch would lower my rpms, and so if I am hitting the rev limiter, I should get more speed due to the bigger prop angle. Right?

 

[ronfl]

I think if your getting 35 MPH out of that package your getting all it will give. I was looking for prop advise and got a ton and learned that the motors run best (when your running wide open) at the 6000 to 6400 range. If you change props you may loose speed because the motor may not get to the desired rpm range with the new prop. 35 out of a 115 is pretty good! I have a 90 and get mid 20's...

 

[Toonafish]

All you can do is try, try out a prop a pitch up this would probably be a 17 pitch (it looks like your running a 15)

this will bring your RPM's down and you may not gain much more in speed.

there are many different variables in props, pitch, cupping, diameter, 4 blade to 3 blade, aluminum to stainless, and even composition props (as i like to call them plastic)

I myself have been looking at props, i have a 75hp 4 stroke with a 14x13 aluminum and its all I can do to get 5100RPM's Mercury's website claims i should be turning 5500 to 5700 now I know if I drop to a 12 pitch my RPM's should come up, but i'm also told that if i go to a 14 pitch in a 4 blade this will allow me to gain speed and bring my RPM's up, Really dont know what to do at this time.

Might not be much help, but everyone says just keep trying until you find the right one?

I will say that my uncle has a 135hp Honda and thought he was hitting his rev limiter but come to find out he was trimming his motor like you would with a runabout, but was told by the dealer to leave the motor trimmed down and give it throttle, seems to be working.