RPM vs Speed

[JThomasLambert]

Just thought I'd throw some metrics out there and see if others have similar experiences. I understand there's lot of variables but for the most part, if I'm alone on my 215 HP 180 Challenger, this is about where I sit:

4000 RPM = 10 MPH
5000 RPM = 20 MPH
6000 RPM = 30 MPH
7000 RPM = 40 MPH
Max = ~48-52 MPH

 

[robertm]

That looks about right to me. I remeber ~32mph being just over 6000rpms. Its amazing how many revs you have to give it to get her going.

Top speed looks great.

 

[TnTLQ]

speed

shouldn't it be more like 50% rpm ie 50% speed?

 

[Craigmri]

Gps?

Did you get these speeds off a GPS or the Dream-o-meter?

Craig

Just thought I'd throw some metrics out there and see if others have similar experiences. I understand there's lot of variables but for the most part, if I'm alone on my 215 HP 180 Challenger, this is about where I sit:

4000 RPM = 10 MPH
5000 RPM = 20 MPH
6000 RPM = 30 MPH
7000 RPM = 40 MPH
Max = ~48-52 MPH

 

[JThomasLambert]

No, the lower speeds are very consistent. The exception is the listed max speed. I can always hit 47/48 but getting to 50+ depends on wind/current/gas type/etc/etc. Pretty much has to be perfect conditions.

The reason I put those out in the first place is because I boat in a relatively weedy area. If I'm not completely cavitating due to weeds completely stuffing the intake (happens more than I'd like) I've learned to tell when there are just a few sitting in there by comparing RPMs to speed. The RPMs are consistent enough that I know when it's clear vs a little blocked.

I also use those figures as a guide for towing wakeboarders and skiiers. You'll never keep the speed constant on one of these boats so instead I aim for keeping the RPMs constant around the speed they're comfortable. It's not perfect but better than trying to tweak the throttle up and down--boat just doesn't have enough torque to compensate for variations in the water.