Packard Forum Index » Post-War (1946-54)

Question,

What was the rear end ratio for the senior cars with the 5 main bearing 327? I noticed that after I replaced the bias ply tires with radials the speedometer read maybe 10 MPH high. In other words to maintain say an actual speed of 60 MPH the speedometer was indicating say 70 MPH. In itself not a bad thing however the problem is that the engine at 60 thinks it's speeding down the highway at 70. Not necessarily good on the 327 with it's long stroke compared to the 288.

Does anyone know if the the rear end gear ratio can be changed to bring engine RPM back down? I guess I'm asking if there is a Packard swap I could make? If the existing gear ratio is already as high as they came then the answer is probably no.

3.54 was standard on Ultras except those Clippers mentioned at 3.23. 3.07 looks to be as low as it went for that axle. An optional ratio so it would be a matter of finding either a complete rear end or necessary parts.

You should be able to get a speedometer gear for one of the other ratio axles to help that bad reading caused by smaller diameter tires but wouldn't do anything for the overall RPM.

Quote:


Thanks for the response. I am more concerned with the engine RPM ( specifficly the piston velocity ) than I am with the speedometer reading. I like to freeway drive faster than I probably should. I halfway expect to see a rod come flying out through the top of the hood some day. Should probably just slow down.

If your car is a stick then opt for an overdrive or conversion to one of the Ford 5 spd or 6 spd's. If automatic then rear axle ratio is about the only easy way short of converting to stick with OD or to a modern AOD trans. I think someone is making the coversion kit for the modern AOD.

Someone check my formual.
Average piston speed (in ft/second) =
2 x engine stroke x engine rpm /(12 X 60).

327 has stroke of 4.25. V8 3.5 incehes.

At 1000 rpm:

2 x 4.25 x 1000 / 720 = 11.8 ft/sec. (327 engine)
2 x 3.5 x 1000 / 720 = 9.7 ft/sec (packard V8).

So the 327 has an increase of piston speed by about 21% more than the V8.

My 56 Packard V8 at 70 mph is turning 2700 rpm. For EQUAL PISTON SPEED the 327 would have to turn about 2200 rpm. Figure your cars speed based on 2200 rpm. THat mite give some insight on the axle ratio needed.

My gas milage has been in the neighborhood of 13-14 mph, but that is not a good test, I haven't driven on just highway to figure out highway mileage... Neighborhood traffic, idling in the driveway, backroads all combine with my highway driving... I bet starting and stopping 4000 lbs often takes a lot of fuel!

"The guy that had the car before me used premium fuel with no problem so I'm thinking I'll stick with it for now."

Your car may well run better on regular. Premium is made specifically for high compression motors to prevent knock.

On the tire and gearing question. If your speedo now must read 70 when you are doing 60 your tires are undersize. It would be easier and cheaper to install larger diameter tires than to change gearing.

The cheapest brands of radials are taller and narrower than the expensive ones, just what we need for old cars. I have measured a name brand tire more than 2" wider than a cheap tire of the same nominal size. Get 75 aspect ratio if you can. It is taller and narrower than the 60 or 50.

Much easier and cheaper to put the right sized tires on the car. Check the all the literature on this site. It will tell you what you should be running.

My '54 Super Clipper with the Ultramatic has the 3.23 gears. According to the manuals it turns at 2250 rpm at 60 mph. I'm getting 14-16 on daily driving, mostly highway.

I run super in mine because it doesn't contain ethanol, which will destroy the older rubber parts in the fuel system.

ok. So then at 70 mph Blackbeards engine rpm is 2625 rpm.
80 mph = 3000 rpm. What brand/size tyres do u have on your car???