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While over at Harvey's this morning he pulled out a Packard dealer repair book which contained this interesting table equating engine rpm's with mph for various 8th Series cars. Wonder how many owners got their Packards up to 90mph?

NOTE - I am arranging to borrow the book, once Harvey finds some missing pages, and I'll have it scanned and loaded in the Packard Literature and Manuals section.

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Oh God! I only hope your posting that doesn't bring Twunk Rack back in here for another diatribe and round of bashing over babbitt bearings and rear axle ratios.

I can't imagine running my '47 356 engine up to 4400RPM much less a prewar babbit bearing engine. I don't imagine the bearings would last very long at that speed supposing it could reach that RPM pushing a 5000lb Packard.

This gives me an idea. I may hook-up a tachometer to my 115C and take it for a drive, noting RPM at different speeds. I believe my car has a 4.69:1 differential ratio.

John, It would be an interesting test. I would love to have a tach on my 47 to see what the engine is turning at various speeds.

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Yes, it would - in and out of overdrive.

Guys, if you know your differential ratio and measure your tire circumference or know the diameter (published data in most tire catalogs), you can very simply calculate the rpm in high gear for any speed. And if you have OD and know the gear reduction, it's equally simple. The only aspect of the calculation subject to a bit of error is the fact that the tires under load deform a bit and the circumference measurement made under a static condition may not be the same as under a dynamic condition.

Wade told me that some years ago he had a tacho on Old Blue, '37 120, and that at about 50mph it was turning at just under 2,000rpm.

John, It would be an interesting test. I would love to have a tach on my 47 to see what the engine is turning at various speeds.

Dave, if I remember correctly, my 48 Custom 8 with OD and G-78x15 tires turned either just over or just under 2000 rpm at 65 mph. Same driveline as your car. I have no reason to believe my speedometer had any greater or lesser accuracy than typical (+/- 3-6%).

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If I could get it to rev to 4000 It would be doing 130MPH!
Dave, I had G78's on my car and because the wheel diameter was smaller than the 700-15's which the car originaly came with by about 2" I figured that at 60 mph the speedo was optimistic by about 10-15%.