Volvo rev limiter?

QC

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Mar 22, 2005
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Friend's new boat: Chapparal 236 SSi with a Volvo 5.7L GXi DP. We took it out this weekend and broke it in. Seems very good, great hole shot w/ the Duo-prop. Anyway, we put enough hours on it to allow full speed runs, so of course we did. When trimmed out just right at the best speed we could make (52 MPH) it missed slightly a couple of times. I was watching a GPS for a speed reading and not the tach. My frined says it was around 5000 RPM. What I am wondering is whther we were possiblly bumping up against a rev limiter? Would it be set that close to recommended WOT RPM i.e. 5150 or so? What is the rev limter set at? Does it have a rev limter?
 

Don S

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Re: Volvo rev limiter?

The rev limiter is in the ECM. and it is fairly close to the max WOT rpm and it sounds like you are just bumping it. <br />If the boat was real light, (Low fuel, no water, no normal gear on the boat etc.) it may still be ok. But if it's how the boat is going to be most of the time, it needs the next size larger prop set.
 

QC

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Re: Volvo rev limiter?

Thanks Don, I wanted to confirm that there indeed was a rev limiter and that it might have been the "miss". With the excellent hole shot from the Duo-Prop, I am thinking that the next size LARGER prop-set is the answer. I am sure that is what you meant. The boat was indeed lightly loaded, but full of fuel AND I would expect that it would loosen up a little too. Also, this guy is known for holding at WOT most of the time. A little decrease in RPM would be a good thing for him . . .
 

Don S

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Re: Volvo rev limiter?

Yep, larger is what I meant. I even went back and changed it in my first post.<br />It's also hard to say how far over the limiter it would have gone, but with a 52mph speed, I would say it's close to the right size prop.
 

QC

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Re: Volvo rev limiter?

Agree on the close sizing too, although my understanding on top speed is that you are faster when propped in the middle to low end of the range. If you look at those GM bhp curves we were discussing on the importance of torque thread, it does show that the bhp falls off slightly toward the top of the range. I still think the Duo-prop helps solve the trade off of hole shot for top speed.
 
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