7 1/4 with 3:55's or even 3:23's
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1967 Dodge Dart slant 6 (170 cu. In.) with 3 on the tree had the 3.23 rear gears, with the 7 1/4.
1974 Dart with slant 6 auto had the 2.76 rear gears with the 7 1/4.
1974 Dart with slant 6 auto had the 2.76 rear gears with the 7 1/4.
@RustyRatRod
I seen a 7-1/4 1972 valiant slant six rear axle that sold on here two years ago with 3.55 and suregrip. Rusty had one with 3.90 and a sure grip, but I don’t remember what it came out of.
I seen a 7-1/4 1972 valiant slant six rear axle that sold on here two years ago with 3.55 and suregrip. Rusty had one with 3.90 and a sure grip, but I don’t remember what it came out of.
Just say no!
Wayyyy back when….. I’ve seen aftermarket ratios up to 4.10.
You can still get the 3.55 & up gears from the aftermarket, and even some factory ones may be floating around, since Mopar used a 7.25 in the front of the 4×4 Daks early on.
SGs are a bit rare & parts are almost nada.
Nobody last time I checked nobody is making the 3.23's tho', I have (2) sets of OE ones, and (1) NOS set of 3.55's. The SG I have is a later style with a solid carrier, vs the older 2 piece/4-pinion units.
@Charrlie_S has listed the whole range of race gears available back in the day.
SGs are a bit rare & parts are almost nada.
Nobody last time I checked nobody is making the 3.23's tho', I have (2) sets of OE ones, and (1) NOS set of 3.55's. The SG I have is a later style with a solid carrier, vs the older 2 piece/4-pinion units.
@Charrlie_S has listed the whole range of race gears available back in the day.
73-74 he's talkin about would be big bolt pattern. Mine was small bolt pattern. As long as the ratio was factory available, and they were all the way to 4.10, you might find one.....although rare, I'm sure.
I Think that was the one I bought. When I got it home and looked closer, it had 2.76. It was about a year after the sale and I just figured I should have looked closer when I picked it up. Good lesson here.
Just looked it up.It was supposed to have 3.23’s. I bought it from a guy I met on FABO and I picked it up at the Fall Fling in Van Nuys in October, 2019. The guy was supposed to send pictures but never did, and was in a real hurry when I met him, so I didn’t check. Buyer beware.
Member's name??? Was it at least a SG??
It was a SG, just not the ratio I was promised. I don’t want to post the name because I should have been more careful. But you should never let anyone rush you when picking up parts. On the other hand, I bought a SG unit from a FABO user a few years ago, after viewing pictures online, assuming it was used. When it arrived I discovered it was NOS. I should have balked at this last deal when the seller failed to provide pictures as promised. I did look at the ring and pinion for wear, but for some reason didn’t look at the ratio number. Again, my bad.
69moredoor
Well-Known Member
So how is a stock 225 with a 994 and 3:23 compared to 2:9/2.7 whatever rears? Assuming stick tire size.. is it that bad on the highway?
Which stock tire size???? The OP's talking '73-'74 Duster, 3.23's are a great step up if that's rollin' on 205/75-14's, 13's on an early-A would feel more like the 3.55's.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Every one percent change in tire size,and every one percent change in rear gear ratio, each produces the same one % change in rpm at a given speed.
the formula is;
(rpm times TC) divided by ( 1056 x R1 x R2) equals mph. This is for zero-slip
where TC is Tire Circumference, which is the roll-out, or diameter times 3.1416
and R1 is the trans gear, and R2 is the rear gear
For an automatic, you can expect about 3% slip, which at 2500 is 75rpm, sometimes it is more.
example one;
(2500 x 25.7 x 3.1416)/(1056 x 1.00 x 2.94)=65 mph
example two
(2500 x 27.0 x 3.1416)/1056 x 1.00 x 3.23)= 62.2 mph
from 2.76s to 2.94s is an increase of 6.5%.
From 2.94 to 3.23 is +9.9%
from a 25.7 tire to a 27, is +5%
therefore
Going from 2.94s and 25.7s, to 3.23s and 27s, is plus 9.9%ratio and minus 5%TC; for a difference of plus 4.9%.
Plus 4.9% of 2500 is 122 rpm =2622rpm@65mph
or minus 4.9% speed equals 62mph@2500
Whether this is good or is bad, only you can answer that.
For example,
going from 2.76s to 3.23s with the same 25.7s, but at 75 mph is;
If the 2.76s cruise at 2720( zero-slip) then
with 3.23s it will be +6.5% plus 9.9% =+16.9% is 525rpm=~3250zero-slip, plus 3% slip=3340
For a Roadtrip, that's BAD in my books; and is shortening the life of your engine; but for
short hops I could live with it.
With stock height 13" tires, and three speed manual transmission, Vixen turns about 3100 at like 72 MPH. I normally drive her in the 2500-2800 range, though.
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