Engine Power Curve

[chaparral442]

my 4.3 Carb Merc cruiser (2006) is supposed to run 4200-4800 RPM-- What does it hurt if the top end is 4900-5000?

 

[Bondo]

Re: Engine Power Curve

It just causes accelerated Engne Wear, That's All......

 

[Zackman]

Re: Engine Power Curve

Usually the concern is with the valve train and Newton's 1st and 2nd Laws of Motion, although there probably isn't an issue with just a few 100 rpm's higher. Check your tachometer, its probably reading high. If not you may want to consider changing your prop to get the engine back into the peak power band.

 

[Bry21317]

Re: Engine Power Curve

I'm not trying to Hijack this thread.

I also have one thats doing this, so I have gone up in pitch on my Prop. I have a Merc 5.0 2 Bbl with thru hull exhaust and its running with a 21 pitch prop at over 5000. I should be getting a 23 pitch prop today from UPS, and will try that.

My problem is that even with 7 people on the boat and it fully loaded I was able to run 5000 rpms. And the prop that I had changed from, I could run 5200 with the wife and myself. Both the same size pitch, the new prop had alot more cup and rake though. So I figured I would lose some more RPMS, but I didn't so now its up to 23 to test with.

Any other Ideas on how to get less RPMS? lol I know, not a normal problem.

Bryan

 

[John_S]

Re: Engine Power Curve

I wouldn't consider changing prop unless you were consistantly hitting that rpms with your worse case load. Your merc has a rev limiter that would prevent you from going much higher, but you can always use you right hand to adjust the rpms back down. I doubt that that few hundred rpms adds up to any significant additional wear. ( I am assuming you are not running for long periods at wot, 4800 or 5000) If you look at Mercs sbc 350's, they have models that specify to 5000rpms. The rotational assemblies are the same as the ones that are spec'ed to 4800.

 

[Zackman]

Re: Engine Power Curve

If you look at Mercs sbc 350's, they have models that specify to 5000rpms. The rotational assemblies are the same as the ones that are spec'ed to 4800.

John, I believe those have slightly different valve trains (stiffer springs, roller cam, etc.) to take the higher inertial forces from the increased rpm.

 

[John_S]

Re: Engine Power Curve

All merc sbc have roller cams, starting in '97. The V6 might have started even earlier. Valve springs are the same, unless you are talking a different head. All SBC mercs are vortec, since '98.

 

[RubberFrog]

Re: Engine Power Curve

Bryan, have you checked your tach for accuracy?

 

[QC]

Re: Engine Power Curve

What that gay dude says ^^^^