RPM...how much is too much??

[.44 mag]

I know..... I need to get guages.

Just looking for a general opinion. My truck has the 4. 10 gears and slightly oversize tires. It's otherwise stock and it runs about 2200rpm going 65-70mph in O. D. If I step it up to 75-80mph, I'm getting to about the 2500rpm range. Any thoughts as to how much rpm is too much for sustained driving without much load??

The truck seems to be fine for the limited times I'm in a position to run for hours at 80mph ( no temp increase on factory guage etc ) but, I thought I'd try and get some feedback.

Thanks.

 

[Shovelhead]

I'm sure I'll be corrected if I'm wrong... but the CTD is designed to run a LONG time at, or near redline.

So our little highway runs at 2,000 to 2,500rpm are just a walk in the park for the mighty Cummins.

 

[Mopar-muscle]

my 2-3 shift hangs on occasion , dirty gov pressure solenoid , when it does and i don't lift i see 3500 no problem ...



2500 is nothing for the cummins , its just louder ...

 

[Racechaser]

Hank I have wondered as well how much is to much. with my auto & 3:55's, if I take it out of O/D at 70-75mph, she'll scream up to about 3k! It's almost like a second power-band up to about 2800 though. I can't wait to hear what it sounds like after I loose "muffy"

 

[KatDiesel]

Cruise set on 80mph = 2500rpm. (Speedo not corrected yet) Drove 8 hours like that recently. No big deal, racing and on the dyno I see it go all the way upto 3300rpm. Got 16mpg doing it.

 

[Boost]

A buddy of mine is a Cummins mechanic. He works on engines for a company in Alaska. Also drives a CTD. I asked him the same question and he said you could put the engine against the gov, set your cruise and run all day long without doing any damage except to your fuel mileage.

 

[Snow man]

I run mine at 2500+ for hrs on the freeway,no problems at all. My Dad bought his truck in FLa last december,put 400 miles on it there,then drove it to NY at 80-85 with 4. 10's. He was taching 2500+ the whole time,I think if anything it helped it break in right. I think the 24v likes to be run at or above 2000 IMO,the vibration is less,and mine smooths right out at 2100,Si Im glad ive got 4. 10's. I am confiden that the governed RPM is low enough to run it there indefinetley of until you run out of fuel.

 

[DHawthorne]

Let her eat PETE, that Cummins don't known its hooked up to anything. Put a little heat in the heads, keeps the valves and injectors clean. Mine is still pulling hard at 100mph, Strokes hate it.



Dave

 

[Vaughn MacKenzie]

Piston slamming food for thought

I know it has been said the B-series can run up against the governor all day long and not miss a beat, but do bear in mind that almost all the other applications our engines are used in have governor speeds of 2600-2800 rpm. 3400 rpm is quite a bit faster than that. I doubt it hurts anything to run sustained up to 3000rpm or so but going past that a lot may take its toll in the long run. I know I've shot mine past 3400 many times.



Here is something to think about. . . have you seen those pictures of how huge and burly our connecting rods are? And how HD the pistons are? And how many know what a long stroke (4. 7") our engines have?



Well at 3000rpm, those pistons and rods make one entire pass top-bottom-top of the cylinder 50 times per second (57 times per second at redline). Talk about serious piston slamming! Just think what sort of force is exerted on those rod bearings!! LOL

Good thing the Cummins is an inline 6 with massive rod and main bearings



I have an ISC owners' manual that sternly warns to never go above 2900rpm.



Vaughn

 

[RustyJC]

Re: Piston slamming food for thought

Originally posted by Vaughn MacKenzie I have an ISC owners' manual that sternly warns to never go above 2900rpm.

ISC? That's the 8. 3L engine, so I would expect a lower redline than the 5. 9L ISB.



Rusty