Are we "Over-revving" our engine?

[mhenon]

Ever look at the Cummins web-site. Click on "products" and check out the various uses of the 5. 9 ISB engine. Nowhere do the RPM's exceed 2600rpm. Doesn't matter if it's an RV, truck or boat... . the rpm range stays around 2500 max.

Why did the Dodge Ram ISB get rated to 3200rpm? Was this a DC requirement or did Cummins design an up-graded ISB engine that can be used nowhere else. Hmmmm!

While I did take my truck up to red-line a few time during break-in... . I've generally adopted a shifting pattern that follows the other ISB's: rev up to 2500rpm and an up-shift brings you right into the strength of the torque band... around 1600rpm. As I tow fairly heavy I don't want the RPM's to drop too low.

I wonder what problems might crop up from running high RPM's in an engine designed for low RPM's. I wonder if this has any bearing on our LP/VP44 failures. Any thoughts on this??

Mike

 

[Forrest Nearing]

are you sure you're not reading the peak HP rpm point?

 

[mhenon]

are you sure you're not reading the peak HP rpm point?

Pretty sure Forest. It's max "governed" rpm that they post. It looks to me that Cummins doesn't want the engine go past that.

Mike

 

[Forrest Nearing]

I was looking at the 370 marine engine (mechanical) and it was rated to 3,000rpm



to answer your question, I don't think we're hurting them running the revs we do.



Forrest

 

[DPelletier]

The ECM has a rev limiter and is supplied by Cummins, so I'm sure Cummins is OK with the 3200 RPM redline in our trucks. I imagine the difference in other applications has to do with duty cycle. For example: a boat or stationary generator may run at full throttle (and max RPM) for hours at a time, whereas that kind of situation is unlikely to happen in a motor vehicle.

The lift pump/VP-44 issues are completely different IMO. The lift pump is in the wrong spot and isn't a great pump and the poor VP-44 is just extremely susceptable to damage caused by insufficient fuel supply (like a lift pump failure).

I only ever rev to 3,000 during an empty acceleration run. Normally I keep maximum sustained RPM's at 2,800 or less.



Cheers,

Dave

 

[John - K5AWO]

I don't recall where I read it and since I am at work I don't have my links handy, but I did read a report by a Cummins engineer stating that the ISB would run at 3600 rpm all day long and not fly apart.



He did emphasize though that the torque and HP peak were at 2600 rpm and it was pointless to try and rev it up that much. The point he wanted to make though, was a missed shift or whatever that allowed the engine to rev up to 3600 was not going to kill the engine.



The rev limiter on mine is way up there above 3200 because I drove it home from Las Vegas the first day I had it at 95 mph and above 3200 all the way. That of course before I started to get interested in maximum MPG figures.



It still runs just fine and like the guy from Cummins said, it won't hurt it.

 

[ndurbin]

Most of these engines outside of the Dodge application run at their max'd rev limit for 90% of their life. From a longevity standpoint there is probably less wear at 2500-2600 rpms versus 3200 rpms. And going beyond the peak hp point is probably less fuel effiecent. I don't know about the other engines max. revs. are but a 12 valve can be taken upto 4100 rpms before stuff starts to fly apart.



Nathan

 

[Big_Daddy_T]

This pickup aint supplyin half the duty cycle this engine was intended to survive. I wouldnt worry about it one tiny bit. Its like using a d9 to push 3 yards of dirt.

 

[Thomas]

I don't recall where I read it and since I am at work I don't have my links handy, but I did read a report by a Cummins engineer stating that the ISB would run at 3600 rpm all day long and not fly apart...

Not quite the 3600 RPM you suggest, but from the August, 1999 Cummins Power Booster News:



... The new 24-valve engine likes to be driven hard. It performs best in the higher RPM ratings... For optimum performance while pulling a heavy load, run up to 2800-3200 RPM. You can hit the hill at 3000-3200 RPM and allow your engine speed to drop to 2300 RPM before downshifting...



And, from Dr. Diesel's Q&A section of the same newsletter:



Q: My 24-valve Cummins/Dodge is a work truck and I run at 3000 RPM all day long pulling a medium load (9,500 lbs. ). How is this affecting my engine?



A: The Dodge 24-valve will run all day long at 3000 RPM. This does not cause any problems other than increased fuel consumption...



I think you're good-to-go at 3200 RPM.

 

[nickleinonen]

i've hit 3800 rpm downshifting. and i'll pull 3200-3500 before upshifting if i am racing. don't worry. some of the P pump guys are running 4K with their new GSK's...

 

[mhenon]

Yeah. . I know it can go higher then red-line. Just found it interesting that every other application of this engine stayed well under 3000rpm. Seems it was really designed to run stay under 3000. Of course, the damn thing is so over-built it's hard to say what would actually "hurt" it.

Thanks for the feed-back. I'm still gonna keep mine under 3k most of the time. Shootin for that "million mile truck" ya know.

 

[Forrest Nearing]

those 2600-3000 RPM ratings are pretty much constant duty ratings... you'll be fine going over that for a few seconds 10-20 times a day...



Forrest

 

[MCummings]

Uh-oh. I better re-work my plans. I planned for a 5,100RPM redline.



Are "we" over-revving our engine? You, maybe. Me, I think so. :-laf



Merrick

 

[Tcolesanti]

I "heard" that Dave Mitchell bent a valve at 7200 rpm. But the bottom end was still fine, and stock, maybe balanced tighter.