Combines Cummins RPM IJIJ

Your 1680 should have the high speed Cummins. I think it's 2720 rpm high idle, but 2750 should be fine also. I wouldn't worry about it. The lower speed was introduced in the 1688.

I may not be as mechanically inclined as others on here, and this probably doesn't pertain to your question but I was always told by my CIH mech. that the IH 466 engines in the early model 1680's should not run over 2550. They use to run at 2750 but the engines didn't last very long so we had ours turned down to 2550. As to the cummins I honestly don't know, I do know that 2 of my neighbors have the cummins engines and they are only running 2550. JMHO. Brad NC. IN.

You may want to do some more research on that ihman, I'm running a 1680 with a 466, and everything else on the machine is designed to run at over 2700. A common issue of confusion on these engines is the pyrometer thermocouple location. On the 466 it is in the exhaust manifold before the turbo. Its basicly still in the fire. It will run a lot hotter than one that is after the turbo. I forget the acceptable difference right now, but I will try to look it up and let you know. As far as lasting longer, I have found that the fuel injection system seems to need service a little more often to keep from scorching the pistons. If you keep a good clean air filter in it and keep the fuel system in good health, they should last a long time even at the higher rpms.

My book says 2720. An injector west bad in mine. I would recommend having them checked every 1000 hrs. Can't hurt

I have very late model 1680 which is technically a 1688 as it has the updated hydraulics, fan, filters, etc. from the factory. My no_load RPM is only 2410 and loaded I run from 2300-2350 and it seems to have plenty of power etc. It doesn't seem to use any more fuel per acre then my 1460's.