What would the maximum safe RPM for a 12v engine be? Is there any chance of over revving this engine, I have heard of governor springs being used to upgrade so I was just wondering.

 

This is just my opinion. If you want high rpms get a power joke or a gasser. The govenor is there for the good of the motor. An inline diesel motor is designed to turn at relatively low rpms. That is why they are so reliable and efficent. I know there are trucks out there running 3000 and 4000 rpm springs. Not me, i'm pushing for the 500,000 to 1millon mile mark in my truck. I know my stock 12v isn't a hot rod, I didn't buy it for that, but it will tow anything a modified truck will, just not as fast. If i want to race someone, i've gota '79 Trans Am sitting at the house . As sung by the great group Alabama " I'm in a hurry to get things done, I rush and rush until lifes no fun, all I really got to do is live and die, I'm in a hurry and don't know why." It's kind of like the tortise and the hare. I may not get there first, but I will get there. Well anyways. I dont know what the max rpms are for this motor. Welcome to the site. Maybe I'll see you one the road one day. It's always nice to see a fellow Alabamaian on the site.

-Kyle

 

I was just reading where the Cummins starts harmonic distortion around 4100 rpm. Not sure if the applies to the 12v or the 24v.

As for no modifications because of the hopefull 500k mile mark. I dont see where a few helpfull mods to speed things up a bit and improve towing will hurt anything. They say the more HP you add to the Cummins the less miles youll get out of it. Well really who wants a truck for 500,000+ miles??? Talk about a worn out piece of junk by the time you decide to spring for another!

 

I Didn't say that i wouldn't get another one before then. But I plan on keeping my truck after i get another one. Cummins of course.

-Kyle

 

Thanks for the replies. I am mostly wondering for when I am not in high gear and want to know what the engine red-lines at so I can stay below that. I am not really interested in pushing this truck FAST, just want it to stay together when I push it hard.

 

If your govener is stock & working correctly you shouldn't have to worry about over revving cuz the gov starts defeuling around 2,500 rpm.With stock valve springs you can go to 3,200 rpm
Bob

 

Thanks, Thats what I needed to know!

Jason

 

Cummins industrial set max RPM at 2,500-2,700RPM.

THe motors in our trucks, supposedly can turn 3,500 and 3,200 under full load. Earlier motors were governed at lower RPM, although the bottom ends are all the same.

1st Gens only run to somewhere in the 2,300-2,500RPM range.

If you can make it past the harmonic resonance at 4,100-4,200RPM, the motor will live untill 5,200-5,300 when the bottom end will let go.

Upgrading the valve springs, pushrods, and cam will get rid of the 4,100RPM harmonics.

Cummins recomends (on 24V's) that Exhaust brakes be used at 3,500RPM for maximum retarding power.

Merrick

 

it is strange, mine blows right past 41 or 4200 like it isn't even there. i have seen other trucks that had a noticable studder going through that rpm range. i guess i just got lucky, i put on new valve springs but that is it.
hey merrick wasn't it your truck that spun that dyno to 160ish? mike

 

Yup. Sure was.

I've made it passed 4,100 several, several times. My truck just sails right pass 4,100. Almost too fast! LOL


What I've been told, is,, if you are going to be loading the motor down to hold a steady RPM (like Sled pulling) to avoid that RPM. If not,, as in a dyno, drag racing, or burnouts, then that RPM is okay.

When I get my truck back on the street, it'll be seeing that RPM on the street, the track, and the dyno. Of course I do have double valve springs, and lots of head work to keep the valves from misbehaving.


Here's Jim Fulmer on the dyno...
Jim Fulmer puttin' down 800HP



Merrick

 

It is my understanding that the problem is the harmonics in the heavy lower end. There are trucks that have broke the crank and block when holding those RPM's. I have ran over 4,200 RPM's several times with no problem, but have never held at those R's.
Bruce