LOW RPM DAMAGING?

[lucas1]

I was wondering if lugging an engine at very low rpm (500rpm for a 4.0L 6 cyl) has an adverse affect on longevity, fuel consumption, etc. I often do this simply because the engine can pull quite strongly from those speeds. Any thoughts would be greatly appreciated.

 

[patdaly]

Lucas, I would suspect you are not harming the engine, as long as you hear no audible knock and it isnt bucking/jerking. About the only thing I could think of would be at 500 RPM, your oil pressure isnt where the OEM wanted the engine to be operated under load, however unless parts ( crank and rods ) physically touch each other, you should do no damage. If they do, high or low RPM will only be a matter of how bad it blows up.

 

[GregLocock]

You might run into driveline issues, since you will be operating in or around some resonances of the engine mounting system, but the engine itself will be OK. We often run full throttle from idle on the dynos. Cheers

Greg Locock

 

[Whittey]

Every time I read a magazine where they do a motor buildup (even in 4x4 magazines) they always start at 2500 or 3000rpm. I wonder why they never show rpms below that?


-=Whittey=-

 

[lucas1]

I agree with Whittey, I`m big into 4wheeling, and low rpm power is very usefull. Climbing steep hills on idle is what it`s all about, so somtimes the rpms dip a bit low and the engine has to pull itself out of the basement. I guess flywheel mass is also an important factor.

 

[patdaly]

Just a WAG as to why they do not show below 2500, would it be possible that they cannot "load" the Dyno and keep the engine running?

 

[Whittey]

Is there a minimum load on a dyno? I've seen a dyno chart of a friends 300cid inline six and it had over 150ft-lbs of rear wheel torque at 1000rpm. Thats more than alot of 4 cylinder engines come with peak.


-=Whittey=-

 

[evelrod]

You know? I never thought much about it before. I put my engines on the dyno for performance setup. Never saw the need to dyno a 'grocery getter' and I am not into tractor pulling or OHV's. My dyno operator sets low rpm on a couple of runs to get a baseline on idle and off idle but that is about it. Printout starts at 3000rpm and goes up to whatever the red line happens to be. Dyno time is very expensive and it is not at all uncommon to get 12 to 16 hours on the setup of a 'new' engine. My last engine this summer took 14 hours total over two days to get it right. Most of the time is spent changing stuff.
Anyway---I start at 3000 and go up because in my type of racing the engine will never (hopefully) see less than 5000 nor more than 8000 .

As to low rpm engines---some industrial (read that BIG DISPLACEMENT) engines used in Co-Gen or pump applications operate in the 200 to 600 rpm range under full load as a matter of course!

Rod

 

[Whittey]

Yah, but in this case its a 4x4 magazine. Or if you look in Truckin magazine, they rarely ever go below ~3000 rpm! 3000rpm on most truck motors isn't exactly what i'd call the low end of the spectrum, and oftentimes its only a couple hundred rpm lower than their peak torque. Hell, i've seen some import mags where they dyno down to a lower rpm than these truck mags i'm reading.


-=Whittey=-

 

[evelrod]

Sounds like it's time to whip up a "letter to the editor" type rant. The 4 bye crowd leaves me guessing. My son-in-law has a 2001 F350 crew cab with the powerstroke, nice truck EXCEPT he lifted it up so high I need a stepladder to get into the cab and I am over six feet tall (just real old)!!!
Oh yea! My Dodge/Cummins govenor is set about 3000rpm.


Rod