I have a nice '71 442. It has a th400 and the standard rear end for an a/c car (3.23?). This trans/gearing gets me close to 3000rpm at 70mph. I have been considering some options on reducing the engine operating speed. I have considered a 700r4, a 2004r, a Gear Vendor overdrive unit to try to lower the rpm's (at age 60 I am much more interested in highway cruising than 1/4 mile performance!) I am giving some consideration to going to a higher rear end ratio (actually a lower #) A ratio of 2.72 or 2.56(+/-) would give me the type of cruising rpm's that I want. Will the rear end in this car (all original Olds posi unit) allow the replacement of the existing ring/pinion with the ratio's mentioned?
Thanks for any advice. The engine is the original (but rebuilt) 455. The th400 is the original trans and has been rebuilt 7k miles ago by a prior owner.

 

Why cut the nuts of a classic muscle car with a huge CI motor? Gas milage? I guess I just dont get this thinking..........455 + 3.55-3.73 gears= Street beast with some manners but with enough gear to get out of its own way,I guess a after market overdrive unit would be the way I would go....My .o2.................Jerr

 

How tall are the rear tires? Might be easy enough to just run a taller tire to give you a little less gear. Probably the cheapest route. JKaz

 

The rear tires are 26" high. Running at a lesser engine speed is just a personal thing-something that I want. I have a '69 Camaro that has a 700r4 and it runs at a less high rpm. However, if I can avoid it, I don't want to have to go through the hassle (and expense) of a trans swap (and I know a 2004r would also fit). I think that Olds had a 'Highway Cruiser' Delta 88 back in the early 70's that had this tall gear rig. I plan to go on the Hot Rod Power Tour in June and would like to have a lesser engine speed on this 2k trip. According to one of the rpm/speed calculators I can save close to 500rpm with a 2.56 change.

 

I would suggest 3.08 you would drop rpm on hwy and still have good take off. If you really want 2.56 some one would trade you for your 3.23 I think I have one some where.

 

I believe you would need a different posi carrier to go 2.56 gears. Either swapping out the internals or putting a different rear end and stashing the 3.23 in the corner of the garage would be the simplest. It would be easy to change it back someday if you ever wanted to. Monzaz could answer your questions for sure on what it would take to convert your present rear end.
John

 

Why on a real 442? Leave it be... How fast do you need to go? 3000rpm at 70 isn't that bad. You could cruise at 80 all day long.
If you really want to lower rpms go with an overdrive trans. Make sure you keep ANY AND ALL stock #'s matching parts. (No I'm not a #'s matching perfectionist btw.)

 

Like 2blu said, just get another rear and stash that one.
Then you can have the best of both worlds.

The 2:56 was optional in '71 and called the "Plains Axle Ratio" along with the 2:73's, for cruisin' the Great Plains I guess?

My '71 Vista Cruiser has a 3:08 rear standard w/air and cruises on the freeway pretty nice but no tach to check RPM's, sort of pointless.

With that 2:56 ratio your top speed before you hit redline would probably be about 175 miles per hour.

 

Don't forget drag... And lack of acceleration in 3rd gear 1:1 and 2.56's... It would take him forever to get there...
Take it from someone with 2.14 gears (not a typo), while it may be able to do 150mph+, it will take you forever to get there. It will begin flat lining when power starts falling off...

 

I am having second and third thoughts on this entire deal. The car does cruise at 70 ok without a lot of effort. Back in '71 when I had a new '71 442 with this same setup, I never even thought about engine rpm's. The car was designed to run with this set up. Perhaps I should just leave it alone and go on down the road?

 

Yes.

 

you'll lose 600 rpm changing from 3.23 to 2.56

 

I run 3.91s, and avoid the highway.....

 

In this case I think your right... The cars that have carburetors must have a certain amount of throttle open with the correct size carb to operate at an effective air fuel mixture where as the fuel injected computer controlled vehicles are checked every freakin millisecond through a ton of sensors. It is always DEAD on as long as all the sensors are telling the story correct...lol.

Cars ran between 2500 and 3000 RPMs all day long. That is just where the car and truck ran at in that day. You can not run a carburetor installed motor below 1500 RPM an expect it to get any kind of mileage and throttle response not enough signal and the metering system in the carb goes from idle circuit to main circuit radically.

Your decision but I think the factory was about right on in the day with the stock 2 or 3 speed trans and a stock cam shaft leave it alone.

Good luck. Jim

 

Don't forget the speed limit in those days was 55 mph.

 

Yeah Jamesbo, and back in YOUR day,it was as fast as you could get the "old gray mare" to gallop!

 

Gaaaaaaaaal Deeeeeeeeeern young whipper snappers.
Ya better watch out..............when citcap wakes up he's gonna jump in ere and help me out.

Ya better watch out.

"Youth and enthusiam are no match for Old age and treachery "

 

X2 Kids these days what ya gonna do. They only think with their little brain, big brain on vacation all the time. I have around 500 old gray mares in the old 57 and they can all gallop pretty hard.

 

I don't think the 55mph came in until 1973 after the Arab oil production boycott. Seems like the speed limit in 1971 was about 65 on most Interstates.