Rpms

im talking like 1900rpms

 

I think its unrelated.

I've never had a problem running a Jake at 1800-2000 rpm for up to an hour a day for years. In a series 60, dd15, c15, c16, n14, d16...

 

What kind of old timers? In the small Cummins? 262, 1,700 was practically lugging it!

 

Coming down hill i like toggle jake between low and mid usually 17 to 18 rpm ... Windy 6percent grade thats 8 gear on dt12. At about 35 mph. Straight 6 percent grade i can go 9 gear and let it ride my jake, hold around 45mph. Other day in montana on 90 eastbound . speed limit for trucks was 25mph. 6 percent grade windy . 7th gear with low and mid jake toggle . 25-30mph all the way down never touched the brakes. Rpm was about 17-19 . 72k gross.

 

The higher the rpm, the faster your oil pump will run, the faster your fan, the faster your coolant circulates and the less your oil heats up, the less cylinder pressure each hole bears, the less oil wedge pressure in the rod bearings and pins because each hole bears the load for a shorter duration of time. I have disected many dead engines.. Lugging is harder in every way than reving high under less load. You watch your boost an EGT. When they ease down, youre under less load. The governor is not gonna allow you to scatter an engine.

The best rpm for climbing for any given combo is the one where you get the best avg mpg which in an old mechanical injection is usually lowest boost and EGT you can get up. Only fuel and load can raise those gauges. In my turned up mechanical DT466 thats staying under 950 egt and dropping down to like 5th at 40mph even tho i could fly up in 7th at 1100egt going 65+

In the 3406E i drive now.. The computer is in charge and whatever program is in there, it gets best mileage at 1400-1600 up the grades depending on steepness. The ecm wont overfuel it when you lug the rpm. With my 466 that pedal pours it on no matter if the turbo is lit or not. Lugging drops the turbo down and excess egt and innefficiency results.

Basically you gotta just hand calculate the same route over and over to find the spot.

 

If youre all the way in it with no pedal left, youre probably in too low of a gear, not counting max effort crazy steep hills where efficiency takes a back seat to making it. Dont take cheap freight into the hills. Glance at your topo map when figuring which run to bid on. Crossing ridges from one valley to the next [TN, PA, etc] is always gonna cost you.

I dont know big rig autos but hard lugging a diesel auto pickup will smoke a trans. The motors made too much power at too low of an RPM vs where the trans pump could make full line pressure to keep the clutch packs clamped. Plus the atf cooling rate was too low for the slippage induced heat burden. Drop a gear in an auto for the trannies sake.

 

Used to be a time if you lugged it to 1700 the engine was banging out the bearings

 

I don't know about the bearings but I've heard about some of our company'S (that I used to work for) trucks getting valves sucked in.

 

If you pull the rods out and the bearing just falls out of its shell, meaning its been taco'd.. You put too much cylinder pressure into that rod. The center of the bearing saddle will show heaviest wear from the oil being squeezed out and youll be into the babbit. Turned up mechanical pump, extreme load and low rpm all combined will do this. The survival rate is much better with higher rpm. In a gas motor, especially one on nitrous with too much timing advance, taco'd bearings and ring lands blow downward plum off the piston usually go hand in hand. Its too much cylinder pressure around TDC. Diesel has peak BMEP much further in the power stroke and usually just turns the crank.

On crank bearings, Youll almost always see worst wear at number one journal and the least at the flywheel end. This is due to the very effective damping mass of the flywheel due to its large OD and heavy clutch plates/diaphram. The crank pulley is much smaller and lighter thus less effective at consuming and dissipating the cranks torsional flexing. The hill says no you wont, the cylinder pressure says yes you will, and the crank gets wrung up like a wet towel. The flywheel end less so than the pulley and thats what your seeing in that wear pattern.

Valves going into the motor could obviously be spring, retainer or keeper failure. If it comes with a mashed pushrod youre almost certainly looking at valve seals too tight or a loss of oil pressure into the top end that galls the valve in the guide. The valve hangs up, pushrod steps out from under the rocker, gets munched and leaves the valve open for demolition at next TDC. Ive bent pushrods in DT466C and 6BT. Dt466 cannot run oil seals. they take a little plastic deflector shield but every top end kit comes with both to cover the low flow top ends and high flow top ends.. But everyone just pops the seals on out of habit. My guides were almost cut thru in 4000 miles and the valves ate the top of the sleeves.