Rev limiter question......

[Snobike Mike]

Now that my boat is mothballed I have a lot of time to reflect on the performance of my new bowrider (which I'm quite happy with as it went 54.5 mph on GPS with approx 60 gallons of fuel and 3 people aboard).

My boat is 21 feet with a 5.7 Gxi DP. I'm curious how "hard" the rev limiter it on these engines. A few times when I was running reasonably light (say 40 gallons of fuel, 4 adults aboard), the boat would seem to go faster when I didn't go completely full throttle, ie the motor slowed "slightly" when totally pinned.

RPM's showed right around 5100-5200 which is the WOT rpm range for my lump. I'm quite familiar with rev limiters on bikes/cars but the boat seems to be "softer" in its engagement - assuming I was even hitting the limiter.

Thoughts?

 

[a70eliminator]

Re: Rev limiter question......

Do you sustain 5000RPM ? That seems hard on the engine and the rev limiter is probably kickin in.

 

[CharlieB]

Re: Rev limiter question......

Generally, when a motor seems to slow slightly at WOT but tachs better at slightly LESS throttle, you will find a small restriction in the fuel supply, like a dirty filter or restriction in the pickup tube or check valve, which is failing to supply adequate fuel for WOT running.

 

[Snobike Mike]

Re: Rev limiter question......

Do you sustain 5000RPM ? That seems hard on the engine and the rev limiter is probably kickin in.

The WOT rating is 5200 for the 5.7 Gxi and the manual says after 10 hrs you can run WOT for as long as you want. Having said that, I only run WOT for very short runs and rarely go over 4000 rpms.

I'm just surprised the rev limiter seemed so "soft" and really just slowed the boat a little. As soon as I pulled the throttle back a little this condition would stop and I'd actually be going a little faster again.

 

[Snobike Mike]

Re: Rev limiter question......

Generally, when a motor seems to slow slightly at WOT but tachs better at slightly LESS throttle, you will find a small restriction in the fuel supply, like a dirty filter or restriction in the pickup tube or check valve, which is failing to supply adequate fuel for WOT running.

Thanks.

I'll have to do more testing next year. The boat is brand new and this happened at less than 20 hours so while you're ideas are good to check, I figure it's more like a limiter not a fueling problem due to the boat being new, but who knows until spring.

Cheers.

 

[Dave1251]

Re: Rev limiter question......

You will know if you hit rev limit on the engine. That being said, it still sounds like your boat is prop'ed wrong if you can hit 5200 rpm with this load.

Your dealer can change to the next size props under warranty this will lower your rpm to a more accecptable rpm range at wot.

 

[Don S]

Re: Rev limiter question......

What is the Volvo Serial Number for your engine.

 

[Snobike Mike]

Re: Rev limiter question......

What is the Volvo Serial Number for your engine.

Engine Serial Number: 4012245871
Drive Serial Number: 4202233600
Trans?: 4151182191

 

[Don S]

Re: Rev limiter question......

You have the 5.7GXi-J model.
Yes, the max WOT rpm for that engine is 5200 rpm. right at 5200, the ECM will start shutting off injectors to keep the engine from going over, at 5400, it shuts of the ignition until the rpm lower.
It may be that the ECM is doing it's job, and you could just have a tach that isn't 100% accurate.
I would be checking the rpm with a scan tool to see what the acutal rpms are, and if it is disableing injectors.