I was reading an old post a moment ago on the issue of engine rpms at a given speed, which is a topic weighing on my mind of late so I thought I'd ask ya'll about it.

According to my calculations, with 215/75R14 tires, a 2-speed Fordomatic and 3.10 final drive, my Galaxie should be doing 2340 rpm at 60 and 2730 rpm at 70.  I assume the number is actually higher than that, given torque converter slip.  Am I correct in thinking that the rolling tire diameter is smaller than the theoretically calculated one I used to get those numbers as well?

Regardless, I don't feel good about cruising at 2730 rpm (or more).  It just bothers my conscience somehow; I can't help but think of the engine wear and fuel consumption incurred by running at such a high speed.  The engine is smooth and quiet even at 70, and doesn't exactly feel wound out, but even so I know it could move the car along more happily around 2000 rpm.

In order to do anything to change it, I see two options: get a 3-speed and change the rear axle ratio to something more like 2.7, which would bring rpms to 2040 at 60 and 2380 at 70, or put in a 4-speed overdrive auto such as the aod, which would bring rpms down to 1570 at 60 and 1830 at 70 with the stock rear gears (assuming 0.67 overdrive, as per Wikipedia).  Of these two, the overdrive trans is more appealing, because it's probably less work.  Though it may be more expensive.

Option number three is the easiest and the cheapest: don't change anything, and don't worry about it.  I prefer this option, but as I mentioned before, I have a hard time not worrying about it.

What do you guys think?

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

I have option number 4. First change only the rear axle ratio. Drive the car with the 2 speed Ford O Matic just like a million Chebys with a 2 speed PowerGlide. Pete

I'm not a person for automatics. I like T86 overdrives so I can run run 3.89 rears. Y blocks were designed for higher rpm with their short stroke. In fact this was their big advertising campaign in the 50's. I think you will really be disappointed with the low end torque of you get too fast with the rears. I commuted to college 90 miles 1 way for 5 semesters and dated my wife who grew up 85 miles away almost 3 years in a y-block. My tach never got below 3000 and my fuel economy wasn't that bad. Engines lasted 100,000 with the oil of the day. When something broke, it usually happened on the quarter miles we had marked off on the country roads around here.

Kenneth

Fredricksburg, Texas

How about rounding up some taller 15" wheels and tires - and trying them out on the rear axle? Speedometer will be off while you do your test - but you can calculate the difference so you can get in some test miles at "70".

I've got an idea the original final ratio (including the tire size) was a compromise based on highway "gradability", headwind tolerence, etc. - so the tranny wasn't constantly in kickdown mode. Your test might help decide whether a small change is OK. 

 
 Steve Metzger       Tucson, Arizona

 agree with Steve Tire changing is the easiest thing to do.  Here is a web site (in the tech section) that allows you to enter different tire sizes and it calculates revs per mile. I wouldn't worry too much about going up and inch or two in dia although the car might look a bit odd with a rake.

http://www.1010tires.com/TireSizeCalculator

BTW I am not sure when FoMoCo made the Ford O a 2 speed but I thought it was 1960.

Doug T

The Highlands, Louisville, Ky.

Crenwelge is right, nobody looked at the feeble torque that's left with a 2.xx gear.  You did the rpm math, now do the rear wheel torque math.

Your engine efficiency isn't based on low rpm, in fact the Y-Block starts feeling its torque curve oats (and higher efficiency) at 2,500 rpm, then it gets even better with higher rpm.

3,000 rpm is a very comfortable speed for the Y.

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

I agree with most or all above.  Try some larger diameter tires.  As for a high rear end, I have one, 3.00.  70 mph cruise is about 2500 or less.  3.00 is too high unless all you do is freeway driving.  With non freeway cruising of 55 the rpm is only 2000-2100, too low and not efficient.  At 3000 rpm I would probably be over 80 mph in danger of the cab blowing off .  Someday maybe it will be changed to 3.25 limited slip.  That would allow me to increase the tire diameter at 1-2 inches to fill up the wheel wells and give better ride, which cant be done now. 

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.

Wow, such good thoughts!  I like what I'm hearing, because I didn't relish the idea of a trans swap.  Also, I never thought of option 5, namely changing wheel/tire size.  This is probably due in part to the fact that I have 4 new tires on the car.  My speedometer is already about 6 mph fast, so I could probably stand to run something larger.  I selected my tires based on this info: http://www.carnut.com/specs/tires.html  215/75R14 was the closest diameter to original with the best fit to those narrow stock rims.

I never seriously considered lowering the final drive ratio without upgrading to a three speed because I assumed that there would not be enough torque in the 2-speed first gear to cope adequately with much less than a 3.10.  This seems especialy likely if the Y is weak on low end torque.

Does anyone have an idea of how long these engines can last on modern oil?  I have always had the impression that "old" engines in general last about 100k, but have never heard or read a report on how that number changes with modern oil.  I expect at least 200k out of a well-maintained modern engine.

AZ28, I think you're right.  There were probably a lot of compromises involved with having just two forward ratios to cover everything from steep grades to highway cruising.  Seems like the effect of changing tires size on roadability would be comperable to an equivalent rear gear change--just a lot easier to execute.

Doug T, I'm not sure what the range of production was for the 2 speed; I would have guessed it to predate the Cruise-o-matic of '58 but I'm no expert.  Anyway, the data plate on my car calls for a 2-speed and the factory manual covers it, so they were definitely in production for the '59 model year.

simplyconnected, I didn't think about calculating torque produced vs. torque needed.  How do I do that?  I knew there was a tradeoff between rpms and load, but specifics are vague in my mind.  I have noticed that it doesn't feel like I need much throttle to maintain 70, except perhaps up a long grade.

"3,000 rpm is a very comfortable speed for the Y."  This is what I needed to hear!  I wouldn't have guessed it.  I didn't know the Y liked to spin so much!

Well, I suppose I'll feel a lot better about driving my car on the highway now.  Mission accomplished!  I don't get the impression that it's really worth my while to change anything.  Bigger tires (say, 215/75R15, 1" more in diameter) would only save about 100 rpm.

Thank you everyone!

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

My speedometer is 13.2% low.  I decided to get used to it when the speedo shop quoted $200 for a converter.

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.

My 61 F250  Unibody runs @ 2600-2700 @ 60 mph with 32" tires and with 4:56 gears, 4 speed.  When I drive it at 65  its right at 3000-3100 and get 12-15 mph at that speed it there isn't a lot of hill or headwind. But I am going to change it at some point down to tlike 3:73's to get some ore milage out of it and reduce noise/and engine wear.

                                                   

Michael

Sandy Valley, NV