I have a slant 6 in a 1980 van on 4 speed OD. Once in a while I pull a large trailer. I learned the hard way that constant tugging around dead weight is hard on OD gears so now I pull the trailer in 3rd.

Ok so what is the rpm range you would stay in for say an hour constant drive. I stay between 2400 and 2500 sometimes up to 2600 for short bursts. What is the safe range for a stock motor for long duration runs like 50 to 60 miles.

Depends on the history of the motor, but I have felt fine running mine for days (cross country) at about 3500 or less. Those are forged crank motors and yours would be cast crank. I doubt it would matter. I have run for a few hours at 3800 on occasion - tall gears 2hrs one way to a dragstrip.

I would say 3000-3200 should be totally safe, assuming all your oiling system is clear in an good shape.

Lou

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Home of Slant6-powered fun machines since 1988

As Lou said, as long as the motor is in good shape it shouldn't be a problem.

Towing in 3rd is a wiser choice with the A-833OD as 3rd is 'direct' which means it locks the main shaft to the input shaft bypassing the countershaft... in the other gears and OD when under load the power has to be transmitted through the countershaft gears and heavy loads tend to spread both shafts apart from each others eventually egging out the countershaft hole in the aluminum case, widening the clearance and causing other problems with gear mesh....

If you are set on towing in OD, changing you rear ratio to a kinder gear will help there, especially with a heavy vehicle... going to something more like 3.55's or 3.91's will help te load on the engine, but might make 1st gear when driving without the trailer a bit tedious....

Thanks for the replies.
What I pull is so heavy that the OD ratio would get chewed up. I know about the eat the case but van has cast iron case tranny but 3rd is only locked mainshaft choice so when pulling it's 3rd that's why I asked.
Van is already at 3.55 rear end.


Reason I asked is - there is a point where load factor and piston speed exceed the oiling available. Under light load that speed is way up there. Under heavy load not so high.
Add to it the long stroke of the slant puts the piston speed way up there for the same rpm as a modern engine.

If 3000 on long hauls has been no issue then I'm not to worried. 2500 ends up right about 58 to 60mph.

Motor has now 67K and runs like new but yes it's cast crank and solid lifters.

Since this is recent and answered, please allow me to hijack.

crustycar, in third "direct" how does that rig pull at 55 to 60? What kind of mileage are you getting with and without your load? And, if you don't mind, about how heavy is your load?

I ask all of this because I am researching towing with a slant while getting the best mileage when not towing. The build may be a ways off, or may be stepped up due to unforeseen incidents.