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My wife and I are planning to attend the first Packardinfo meet. We can drive or we can trailer but I do prefer to drive if we can get new side curtains. My main concern is a good safe sustained cruising that will not damage the engine. I think I heard the gear ratio is around 4:13 but can't find it in my owners manual. If it is then at 65 mph we are looking at about a sustained 2800 rpm. I was going to put a self imposed 50 mph max but if we do caravan with other P-car owners from So Cal, I don't want to hold them up. Opinions please?

Paul, I don't have a lot of experience with a 6th Series Packard but personally with that low gearing, long stroke engine and babbitt bearings I would limit the speed to no more than 50MPH for a sustained cruising speed. Consider also that the brakes, steering and suspension were not designed for 65MPH cruising either given the condition of roads during the era this car was engineered and made. I would err on the side of safety and take it easy on the old gal.

I don't know how a 645 compares to other models but here are some ratios given in the 626-633 book for those series.

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740 and 745 ratios were 4.07, 4.38 and 4.69 and I believe the 640-645 had the same. Typically the 4.07 was in the lightest bodied cars and the 4.69 in the closed cars. My own 34 sedan which shares babbitt bearings and a 5 inch stroke with you has the 4.69 driving thru 17 inch wheels are I try to make 50 mph my maximum, though if forced I'll occasionally go up to 55 or 60 for momentary needs.

I would follow Clipper47 and Owen Dyneto advice on the 50 mph. At least until u get a feel for how the car is running for many long trips.

One thing i would recommend is to check the oil periodicaly during the first long trip. I wouldn't try to run more than 400 miles at a sustained 50 mph without checking the oil. Once u get a feel for the oil consumption, if any, then u'll know what u can get away with. Sometimes oil consumption can occur or increase greatly at the higher engine rpm. Doesn't mean it will increase. Just check it to be on the safe side for the first 400 miles or less if stops are convenient.

So my many years of self a imposed speed restriction of 50 MPH on the old girl was wise and prudent after all. Why change now? One for the fat old guy.

One comment I have is you are running 19" wheels vs 17" wheels which means are RPMs would be lower then OD's. Also there's a good chance that your open car ratio end ratio is lower than OD's closed car.

I don't know what my rear end is, but I tend to limit my speed at 55 mph, but most of the time try to keep it at 50. Also I have 19" wheels.

The good think about doing 50 is you always have plenty of room in front of you for stopping with those meachnaical brakes...that's until those idiots cut you off trying to get in front of you.

7.00 20 tires on our car.