Over Revving

[Michael A D Green]

I just picked up a 2005 Larson Senza 206 with a 5.0L Volvo GL motor has about 12 hours on it now.

I am convinced the boat is over revving. When I pin the throttle it hits almost 6000rpm and tops out at 45 mph (gps and speedo). I'm not trimmed crazily either. The prop is an aluminum 14x21

Any ideas from the experts here?

Thanks

 

[Texasmark]

Re: Over Revving

Enjoy the ride. The overrevving you mention is apparently the hole shot and probably due to ports in the prop. You have a goldmine bro............stick with it.

Mark

 

[craze1cars]

Re: Over Revving

6,000 rpm is a suicide mission for a 5.0. Most likely the motor is rated 4,400 to 4,800. Motor and outdrive alike will live a very short life and likely meet a very violent self-destruct if the motor is actually turning 6,000....even for short spurts. If this is happening, it needs to be fixed immediately.

However I highly doubt you are actually turning 6,000 rpms. Is that full speed/trimmed out/wide open throttle? The math simply doesn't work.

Pretty sure you have a 1.60 drive ratio (can you confirm this please?) If yes, prop slip calculator says 6,000 rpm on a 21 pitch prop has a theoretical top speed of 75 mph. You're only going 45. That's 40% slip, and simply does not happen unless one of your blades is entirely missing from this prop....

My #1 guess is that your tach is not functioning properly, and you're not turning anywhere close to 6,000 rpms. Check your tach with another known good tach and report back....

 

[Michael A D Green]

Re: Over Revving

My #1 guess is that your tach is not functioning properly, and you're not turning anywhere close to 6,000 rpms. Check your tach with another known good tach and report back....

You could very likely be right. The boat's at my cottage right now so I can't check but this is not the original motor and it's possible the tach is set to V6 which would be comical I suppose.

Thanks for the reply