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Am I asking for trouble? 2.93 to 2.76 swap
https://slantsix.org/forum/viewtopic.php?t=20448		 Page 1 of 2
Author:  sixsignet [ Mon Oct 23, 2006 1:47 pm ]
Post subject:  Am I asking for trouble? 2.93 to 2.76 swap
I have a 63 with an old engine and old auto trans. It's a daily driver with OK performance.
I'd like better freeway mileage.
If I pull the 2.93 and put a 2.76 in its place, is that going to put additional strain on the transmission or torque converter? Could that ratio change cause some other part to fail sooner than it normally would?
Is it safer to stay with the current 2.93 ratio?
Author:  SlantSixDan [ Mon Oct 23, 2006 2:03 pm ]
Post subject: 
There wouldn't be any such undue strain, but the difference in highway mileage is not going to be significant enough to warrant the expense and cost of making this swap. You say the engine is "old"—that suggests it may be worn to the point of being the main cause of your poor mileage.
Author:  sixsignet [ Mon Oct 23, 2006 2:11 pm ]
Post subject: 
I forgot to mention I'm forced to replace the rearend because of bad pinion noise. :oops:
Author:  SlantSixDan [ Mon Oct 23, 2006 2:13 pm ]
Post subject: 
Ah, that changes matters, then!

What speeds do you tend to see most frequently on the highway? And have you got a 170 or a 225? And, what size tires are you running?
Author:  sixsignet [ Mon Oct 23, 2006 5:50 pm ]
Post subject: 
Between 55 and 65. 225 automatic Signet. Tires are 195-70-14
Author:  SlantSixDan [ Mon Oct 23, 2006 7:09 pm ]
Post subject: 
H'mmm. Me, personally, my favourite rear axle with a combo like that would be either a 2.93 like you have now, or a 3.23. With 2.76s, the car's comfy cruising speed tends to edge up to the 70-75 mph range. But that's not to say it'll be anything like a nuisancy combination. And a 2.76 rear axle will be the easiest for you to find. Remember to change the speedometer drive pinion!
Author:  Ron Parker [ Tue Oct 24, 2006 6:22 pm ]
Post subject: 
Dans on the button a 3.23 would be sweet. Thanks Ron Parker :D













It Aint Over Until I Win
Author:  64 Convert [ Fri Oct 27, 2006 9:36 am ]
Post subject: 
I bought a new '75 Valiant with 2.7-something gears and hated it. It was more gutless than a 4-cyl Horizon and got about the same mileage as my '68 318 Fury.
Author:  argentina-slantsixer [ Fri Oct 27, 2006 9:43 am ]
Post subject: 
I agree with dan and ron parker, the 2.76 would give you worse mileage and you'd feel like driving a parade car (those who's top speed is 5 mph)

3.23 is my 2 cents too
Author:  sixsignet [ Fri Oct 27, 2006 10:34 am ]
Post subject: 
Say what?
Am I mis-reading Dan's reply?
Dan said "not a nuisancy combination".

'Driving like a parade car' would be a nuisance.

Remember my 63 is very light.

I've been shopping for a 2.76 because they are common.
Should I limit my search to 2.93?
What percentage of 69 and later A-bodies had 2.93s?
Author:  SlantSixDan [ Fri Oct 27, 2006 11:31 am ]
Post subject: 
Quote:
Say what?
Am I mis-reading Dan's reply?
Dan said "not a nuisancy combination".


By which I meant, it wouldn't make the car a total pain in the patoot. This is not an exact science, there is no single right answer. You will likely not be dissatisfied with 2.76s if that's what you swap in (remember to change the speedo drive pinion), but you also will not realise a big mileage gain.

Note that rear axle ratio trends, as installed by the factory, kind of went opposite the way they should've gone. The early A-bodies were smaller and lighter, with higher-torque pre-smog engines and smaller-diameter tires. The 225/automatics would've done fine with 2.76s, but they got 3.23s and 2.93s. Then, as the A-bodies got heavier and the tires got larger and the engines lost torque due to emission controls, they would've been better off with 2.93s and 3.23s, but they got 2.76s.
Quote:
I've been shopping for a 2.76 because they are common.
They certainly are.
Quote:
What percentage of 69 and later A-bodies had 2.93s?
None or almost none. 2.76s with automatic, 3.23s with manual.
Author:  sixsignet [ Fri Oct 27, 2006 12:04 pm ]
Post subject: 
Thanks, Dan. That allays my fear of the 2.76

Initially, I thought I wanted a 2.76 to get better mileage, but now I want one because I will probably be able to do the swap sooner (because they are common).


I read this over at valiant.org:

"
2.76 was the standard rear axle ratio for all slant-6/automatic cars starting in 1969.
2.93 was standard with 225/auto from mid '62 through '68, 3.23 with 170/auto
3.23 was standard with 170/auto and 225/auto from '61 through mid '62.
3.23 was standard with 170 or 225 and manual transmission from 1962 onward.
3.55 was standard with 170/manual for 1960 and 1961.
F- and M-bodies used even taller ratios (2.45) with the advent of the wide-ratio Torqueflite in 1981. "
Author:  SlantSixDan [ Fri Oct 27, 2006 12:07 pm ]
Post subject: 
Quote:
3.23 was standard with 170/auto and 225/auto from '61 through mid '62.
3.55 with 170/auto in '60 and early '61.
Quote:
F- and M-bodies used even taller ratios (2.45)
And 2.26
Author:  440_Magnum [ Fri Nov 03, 2006 9:38 am ]
Post subject: 
Quote:

By which I meant, it wouldn't make the car a total pain in the patoot. This is not an exact science, there is no single right answer. You will likely not be dissatisfied with 2.76s if that's what you swap in (remember to change the speedo drive pinion), but you also will not realise a big mileage gain.
I agree- if you have to change pumpkins anyway, going to a common 2.76 is a "safe" swap with little chance of a surprise.

For what its worth, 2.76 to 2.93 is not a very large gear ratio change at all. I've swapped from 2.76 to 2.93s in my '66 Polara, and to be honest I cannot tell the difference. I'm sure a stopwatch and strip would show a difference, but regular driving sure doesn't. Of course the Polara has a 440, but one thing a /6 and 440 share is a torque curve as wide and flat as the Caprock.
Author:  slantvaliant [ Fri Nov 03, 2006 12:35 pm ]
Post subject: 
Quote:
... as wide and flat as the Caprock.
Wow! I didn't think anyone in Austin knew about the Caprock, it being well West of I-35 and all ... :wink:
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