Slowest safe engine RPM

[joe117]

I always thought it wasn't a good idea to try to drive down the road at a very low RPM. With the stock 3.07 sixth isn't good for much less than 80 mph or so. The engine would probably keep the car going on a flat highway when turning only 800 rpm or so but I don't think this is good for the engine. I'm not sure why. Anyone know why it is or isn't a good idea?
What would be a good low rpm limit?
I use about 1400 as a low cruising rpm.

 

[CitySnake]

Joe:

I don't think the rpm is critical in and of itself. It is the amount of load that you place on the motor at a "low" rpm that is critical. The Viper has enough torque to cruise on interstates (relatively level) all day long at 1,000 rpm in 6th gear as long as you don't jump on it (in a high gear at low rpm). My .02

 

[Bad Asp]

It puts a heavy load on the crank journals and main bearings trying to accellerate from low speed. Answer? Go to 3:55s!

Bob W

 

[joe117]

Well, I have 3.55 gears as of about a week ago. Still, I don't think it's good to drive down the highway at very low rpm even if the car will just barely do it. I agree with you that it probably places heavy loads the bearings if you tried to accelerate. I'm wondering if the low oil pressure at low rpm would be a problem too. Seems like the engine would be prone to knock under these conditions.
I've also got a 96 Vette that's a four speed automatic. I notice that the automatic never tries to run the engine at less than about 1200 rpm. It will shift down to keep it above that. I know the 350 has less power but still, someone who knows what they are doing designed that car to stay above about 1200 rpm.
I'm trying to get someone who really knows if this lugging at low rpm in a Viper is a problem for the engine or not.

 

[Steve-Indy]

I PREFER to run our stock Gen I's and II's in the 1500-1800 rpm as a "crising minimum" range...and shift gears to avoid lugging as necessary...seems to me that I did read somewhere (here?) that one needs to be above 1400-1450 rpm to be in a "charging state", but I haven't tried to doccument that statement.

 

[joe117]

Weak? perhaps but a nice looking car.

 

[Gerald]

I pop that puppy in 6th gear ALL the time. Usually around 55 mph... runs nice and cool and the less RPM's, the less wear..


Gerald

 

[Chuck 98 RT/10]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Steve-Indy:
I did read somewhere (here?) that one needs to be above 1400-1450 rpm to be in a "charging state",

<HR></BLOCKQUOTE>

I've heard the same thing. Like Gerald though, I go into sixth all the time for the same reasons. Hell, it's the same principle as the 1-4 skip shift aint it?