Can you run for ever at rev limiter???

[macdaddy]

Can you run forever at the rev limiter???

Gentlemen

A friend of mine has a new Country Coach 40' pusher with the Cummins ISL rated at 400 HP and 1200 lb ft of torque and the Allison 3000. We were in Wa state and I had the chance to drive it. While on the road with me behind the wheel when pulling a 6 percenter he asked me if I felt it was sluggish and that it couldn't pull such hills in 6th. I said I felt he should be down shifting to fifth for such grades.



Soooooo a phone call to Cummins confirmed this and that the motor can safely be run at the rev limiter for how ever long was needed, and that it also helped with the torque converter's operation (allowing it to stay locked). My question is can the HPCR motor found in our Dodge Rams sustain this same operation (at rev limiter) for extended periods of time Cummins says it can. I guess with the motor right under your feet it only sounds like the motor is going to come apart



Mac

 

[cummins_crewcab]

I pull at 3k rpm up grades in 3rd and 4th. If I let it drop below 2500rpm the thing bogs down and I loose momentum. I've stayed at 3200 (redline) for over 10 minutes before in 3rd while climbing... It's probably not the greatest but with my gutless SO it's the only thing I can do to keep big rigs from eating my bumper for lunch.

 

[Gary - K7GLD]

These engines in construction equipment - backhoes, etc. , run up against the governor all day long...

 

[Deezal Man]

The quick answer is yes. . Simply because Cummins sets the rev limiter well below the point of any engine damage. Making the point, many aftermarket engine software tuners regularly allow a stock engine to turn another 500-1,000 RPMs without so much as a complaint.



Point being, the manufacturer has tested their engine under conditions you will never experience or place on it. . And they set normal operating parameters for the likes of you and I to live well comfortably within those limits.



And as always, if you lucky enough to be in the last generation to have it... Common sense goes a long way. .

 

[Vaughn MacKenzie]

These engines in construction equipment - backhoes, etc. , run up against the governor all day long...

One thing to consider though is in most other applications the B-series, ISB and ISBe are governed to 2600 or 2800 RPM.



I don't think it will hurt anything to run against the governor on our trucks as long as there's a load on it (it's a lot tougher on the rod bearings to free-rev at redline) but like anything else the laws of physics are at play and certainly it won't last as many miles as it would operated a 1000 RPM slower.



Vaughn

 

[macdaddy]

Thank you gentlemen.

Hey Vaughn I think the governer is set higher than 2600-2800 I've had the 05 past 3K on occasion when building speed for the next shift on an uphill while towing.



Mac

 

[FDavid]

I drove my truck at 3600 rpm (right against the governor) for over 5 minutes. I believe around 4300 rpms is where the valves start floating. If my truck would of went to 4500 rpms believe me I would of pushed it. I sometimes secretly wish my engne would blow apart so i can get a built engine in its place. I just can't justify tearing down a healthy motor Maybe if i throw on some banks products my wish will come true. JK :-laf



dave

 

[whamby]

Can you run forever at the rev limiter???



To answer your question- NO Not unless you have a really big fuel tank :-laf

 

[Big MAK]

As long as it isn't running too hot you can run it at limiter until the fuel runs out w/o ill effects

 

[Vaughn MacKenzie]

Thank you gentlemen.

Hey Vaughn I think the governer is set higher than 2600-2800 I've had the 05 past 3K on occasion when building speed for the next shift on an uphill while towing.



Mac

Correct Mac, note the word other in my last post



Vaughn

 

[Gary - K7GLD]

I believe Vaughn was correctly pointing out that in typical commercial/industrial applications, the rev limiter is set perhaps slightly lower than in our trucks. I dunno exactly what RPM my truck limiter is set for, but my '91 was set at about 2700 RPM, and you could put the pedal to the floor, and it never sounded as though it was in pain. But yeah, work it harder, and it will wear out or fail sooner...

 

[Cigar John]

A factory rep once told me that the ones in back up generators not only run at redline,but they do it cold :--)

 

[macdaddy]

Vaughn



Sorry, I went back and read it again.

DUHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH

 

[Beast2B]

A factory rep once told me that the ones in back up generators not only run at redline,but they do it cold :--)

I'd have to question the rep that said this (while pulling up my pant legs to stay out of the puddle). The gensets we run are mostly 4bt and 6bt engines, all of them are set to run at 1800 rpm. They have load banks on them so that if a load is not present on the alternator from whatever equipment is being protected, a 'false' load is induced to keep the engine loaded. Sooooo, if you consider 1800 RPM the redline for those engines, I guess he's right. But, if you bring the real world in and keep the sales world under control, he's full of manure!

BTW, all of our stationary gensets also have block heaters so they are never 'cold'. Mobile sets we try to preheat or run unloaded until warmed up.

 

[Cigar John]

I can't remember what we were talking about when he told me that,but thanks for (as Paul Harvey would say) "the rest of the story. " :-laf

 

[jelag]

Our engine will run at the rev limit with out a problem... . based on comments by the guys at Cummins I've met... I run our 04 with a 20K lb trailer up the grapevine and the siskiyou's at WOT for 30 min at a time... usually never letting much below 2900 rpm. . and that truck has 108K miles...



I'd personally never turn up the HP and do this... . as our trucks need to run 300K plus before we trade... .

 

[Gary - K7GLD]

AC generators prior to the new generation of "inverter" types currently popular, were mechanically/elecrtically strapped, or locked into rotating at 1800 or 3600 RPM due to rotor/armature structure that REQUIRED that RPM in order to generate 60 cycle electrical current. The same WAS true of smaller gensets as well - one reason the Onan and similar sets ran so quietly, was that their rotor/armature design allowed 60 cycle AC at that rpm, while other sets had to run at 3600 RPM to do the same. Even my older Honda EX1000 generator provided a vibrating reed indicator and carburetor adjustment that allowed precisely setting the engine RPM for 3600 to provide 60 cycle AC current...

 

[Windscreen]

Actual Cummins data on running at rated

Here are some actual Cummins data sheets for marine versions of the 6B:

6BTA5. 9-M (SW)

This one is 280 hp @ 2600 rpm, rated for full load 6 out of every 12 hours, 3000 hrs per year max. That's almost 58 hrs of running per week, 29 hrs per week at full load/throttle!



QSB5. 9-380 HO

This is a common rail motor, making 375 hp @ 3000 rpm, and more impressively, a stunning torque peak of 1218 ft*lbf @ 2000 rpm! It has a duty cycle of 1 out of every 8 hours at full load, 300 hrs of use per year. When not at full load, Cummins says you must be at least 200 rpm below rated speed, which on the propeller load curve they show, is still a stout 300 hp.



So, yes, holding the pedal to the mat for 30 mins to an hour should be no problem at all for our engines.



Steve