how many rpm's will i drop going from 3.91 to 3.55????????????????

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I just took the 3:73'S out of my Barracuda yesterday and put 3:23'S in because I couldn't stand the lower gears...What a difference in cruising speeds. I guess im getting old.
 
When I got new mufflers on my car last fall, I swear it seem better on the freeway. I look and see 4,000 on the tach and was like wow...and the mufflers are still louder then stock
 
it really depends what you want to do with the car, for long road trips 2.73--2.94's are best, saves on fuel and wear and tear on the engine. But driving around town you will miss the 3.91's.

I'm keeping the 3.91's cause traffic here goes 35--40 mph on most secondary roads. At those speeds the 3.91's feel just right in 3rd gear and 2nd gear comes on strong for passing.

I did find a different rear end with "normal" gears at my local scarp yard but now that fuel prices are not going to $5 a gallon this year don't think I be getting it.
 
Depends on how much your clutch is slipping. Really it is simply the difference in percent of of one ratio to the other, or the ratio of the ratios so to speak if you want to complicate it. It works going to a higher ratio untill the engine can no longer pull, and it works going to a lower ratio untill the engine explodes.
 
Being old enough to have "grown up" when all these cars were new, I find all this quibbling over ratios in the threes laughable. Looking at what was actually used by the factories might provide a little perspective.
Automatics from the general would come with 3.07/.08 and 3.23 usually and strangely enough, their small motor, two speed (powerglide) combo almost always would be coupled to the 3.07. Standard ratios with sticks were usually 3.36, 3.42, and 3.73 with bigger motors tending to have the lower ratios standard. The 3.73s in my 68 Z28 felt just about right with it's 2.20 low gear. Time tends to fog the memory, but I remember the Tripower 421 in my 2+2 running about 2450 at 70 or so, and giving 16 1/2 MPG with 3.42s.
Mopar tended to be a little more conservative with 2.7sand 2.9s behind automatics (although my buddie's 66 Hemi Coronet automatic probably had 2.56s because it wouldn't really start pulling until you were doing 75 or so, about the time you were running out of road) with 2.9s and 3.23s showing up behind sticks.
 
I hated the 3.23 in my duster, with the 4 - speed I felt alot of chuga chuga on take off. My car came with a 3.91 so thats what went back in, to be honest with the small amount of highway driving I do, I don't see a big difference in fuel mileage ( at least thats what I tell myselfe) I would like to try a 3.55 or 3.73 though.
 
Took my ride for a few rides the last 2 days/ man I wish it had MORE gear, like 4.10 or even 4.56's

4.56 would be the "perfect" gear for the 340 it seems, 1st gear is nice with the 3.91's but 2nd gear is lugging a bit till its over 55 mph and 3rd gear seems like a nice cruising gear till over 55 mph.

Now the engine does seem happy around 2200 rpm so I guess it be nice to have that and 70 mph vs 40 mph but when you get on the gas you can feel its being held back just with the 3.91's let alone 2.94's.

So I my 3.91;s and 27 inch tires IS a compromise, going any taller would just make it a nice driver...like the new cars are toady, lol
 
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