Re: Redline/Maximum Continuous Operating RPM - Packard 6 Cylinder Engines

Posted by Tim Cole On 2016/2/23 16:24:00

The term "redline" is pretty much a post World War II term. It refers to engine speeds high enough to cause valve float interference in overhead valve engines. That is, redline is the zone above which the valves begin smashing into the pistons. So when you are in the redline zone you are at the limit before engine damage will occur. However, those prewar motors don't spin fast enough. For example, if you try to over rev the Caddy V-12/16s the valve silencers slide on the rockers and you lose power. As well, point ignition systems begin to saturate and ignition breaks down.

Now in aeroplanes with superchargers redline zones can also mean those points where engine revs combined with excessive manifold pressures can cause detonation sufficient enough to cause engine explosion. So the first use of redlines was in aviation during World War II.

Technically a flathead motor does not have a redline because side valve engines can't smash the pistons.

David's observation of driving 45-50 mph in those old Packards is absolutely correct. I knew people who patched old babbitt bearings together with glue and drove for years that way because they adhered to 45-50. Old Packards will run many thousands of trouble free miles that way.

When the manufacturer claims 100 bhp at 3600 rpm, that is the peak of the horsepower curve. After that power falls off rather sharply. If the power output is more than sufficient to move the vehicle above that speed then top speed may be at a higher rpm. With cars like the Packard Speedster they increased the gearing to match peak horsepower at the expense of low speed acceleration.