Best rear gears for 383/727?

[SteveSS]

My two B-Bodies have original 383's. Both with 727 automatics. One is a '71, one is a '69. The '71 is not done yet.

The '69 is an SE. Although it was built to be a luxury cruiser I need some more low end torque. It's happy going 75 mph but seems awfully show from the start.

The '71 is a Charger 500 and I suspect the gearing will be the same. Is there a ratio where I can spin the tires and go highway speeds below 3K RPM?

 

[747mopar]

3:23s is about it, 3:55s are a good gear but will put you just over 3,000 rpm at 75mph.

 

[lewtot184]

does the '69 engine have 8:1 pistons?

 

[SteveSS]

I don't know. It had a 2 bbl originally. Now a 4 bbl. We have a 71 Challenger with a 408 (Stroked 360) and 391 gears with a 4 speed. It is NOT happy on the highway.

 

[lewtot184]

2bbl engines were rated at 9:1. they may have had a little less. i've messed with some rebuilt 383's that had 8:1's put in them they are real turds. i remember one with 3.91 gears that wouldn't even spin the tires. the best running one had 3.23's and was far from peppy.

 

[Cranky]

Had a 70 383 4bbl dual exhaust Challenger (factory non RT) that loved the highway with 2.94's. Gas mileage jumped from 12 to 16 when I pulled the 3.23's. It did fine off the line though but that was one car that never saw the drag strip so I have no numbers. I figure it ran high 15's maybe with the 2.94's. Only things that were changed on the car was going in with a dual point Accel dizzy with Accel wires and changing the timing and tuning the AVS carb. I didn't have a limited slip and if I wasn't careful, it would spin em off the line and then light up the right side tire but it did pretty good most of the time with keeping a weight box in the right side trunk loaded with about 50 lbs when it was time to play a bit on the street. What gears are in the car now and how tall are your tires? Can't remember right off what size tires I was using but they were not short by no means.....a size down from a 275-60's or so. Heck, sold that car in 98....

 

[HT413]

I don't know, if you love cruising at 75mph, to me it seems any gain in low end will be offset by a loss in highway cruising fun. Look at the chart below (using 26" tires as a guess), if you go from 2.76's to 3.23's you'll lose about 10mph in cruising speed. Is that worth it?

You'll easily spend $500-800 having a rear end built, so maybe it's worth it to spend that money on cam, intake, what have you, to build more power and keep your cruising rpm.

 

[mopar 3 B]

Your 383 should go better than that. Time to find out what is wrong.

 

[GetX'd]

I'm a 3:91 advocate for your set up. Not bad on the top end - good on the low end. You may not be able to cruise like a luxury car but if you want to take advantage of the muscle of the car you have to give something up. I think the above is the best ratio. Have it for my 440 - stock.

 

[Budnicks]

3.73:1 my preference/compromise between the 3.55:1 & a 3.91:1
runs about 3000-3100 rpm with a 28" tire @ about 70
my 68 RR came with 3.23:1, it was ok I wanted better performance thou,
I live in the Sierra foothills, windy *** rd's & I like to wind the engine a little more...

or 3.91:1 with a 28" tire, works well with a 383 too,
not as open road or freeway friendly thou
but great all around gear for a smaller 383ci B engine or a Small Block

mine is a 4.15" stroker so I was more incline to go with the 3.73:1,
It make gobs of torque, I've had/used everything from 3.23's to 5.13's,
behind a B-Block

I prefer the lower gears I don't have a freeway for 75+ miles from me,
I'd rather have the bottom end, for drivability & the torque multiplier,
taller tire for better roll out & bigger rubber patch/footprint on the ground...
28" tire, Fills the rear wheel wells better too...

try this site it has calculators for a ton of different stuff
http://www.wallaceracing.com/Calculators.html

a good converter, properly spec'd for what you intend to use the car for,
is a really good idea too