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EN331 (B-30) Engine Speeds Question


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The Mack literature I have found for the B-30 so far gives (max?) torque rating at 1400 RPM and max horsepower at 2800 RPM. Would 1400 be on the low end of shifting RPMs and 2800 on the upper end? Disregarding speed and transmission/rear end ratio considerations, about what RPM would that EN331 be happiest at cruising down the highway?

The reason I am asking is that I have been working out ground speeds for the various combinations and permutations of transmissions, rear ends and tire sizes for the B-30P. Wish I had the truck home or had at least known enough to get the transmission and rear numbers when I looked at it.

Calculation results are fascinating - one of the first things that occurred to me is that a buyer would really need to have a had a thorough understanding of what he was going to haul and what the conditions would be as it would otherwise be easy end up with what appeared to be a gutless wonder or a speeding snail. At 2800 RPM with the standard issue 9.00x20 tires, top speed would for the TR-85 trans with highest drive axle reduction (8.68) would give a top speed of about 34 mph. Same transmission with two speed drive axle (8.28 & 6.00) would allow top speed of about 53 mph.

Interestingly, the standard TR-73 transmission with the lowest drive axle ratio (5.37) would allow for nearly 60 mph while the optional TR-730 (overdrive) transmission and lowest drive axle ratio would have allowed for nearly 70 mph. This all assuming, of course, that the truck did not either run out of horsepower or get to its destination or stop signs before it got up to those speeds.

Thing is, I don't think 2800 RPM would be the happy cruising speed for that engine. Maybe 2400 or 2500 RPM? I need some expert guidance here as I work out what my options might be in restoring my B-30 while keeping it within the realm of what a B-30 could have been upon seeing its first light of day.

Best regards, Dennis

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If you can get your hands on a power graph (torque & hp vs engine speed) it would make things a bit easier to understand. I was always told that peak torque = peak efficiency....my assumption has always been shift up so the revs are around the peak torque and run it till the hp starts to fall off. Hence the usefulness of the graph.

Lack of planning on your part does not constitute an emergency on my part....

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Now, there, I have learned something new today - I did not know that torque/hp/RPM charts existed to identify optimum operating points for trucks - sort of like pump curves for trucks. I have no idea where to start looking for such a chart. I think I will probably just wait until I have the truck home and running and figure things out from there. It may be that it is already set up such that I can at least keep up with traffic on the highway. If not, I know what my options are to look for equipment to make it so that it will.

Best regards, Dennis

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