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Finally laded a Sure Grip. Once again, requesting input.

TBass

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I know I am not the first one to entertain this, but I swapped for a 3.91 Sure Grip in a 741 case. All seems well with this gear, but I am almost positive it will be way too low behind my 727 and I am considering swapping in 3.23's or 3.55's. My converter is an 1800 RPM and my cam is best between 1400-5800. I want to drive it, but I also want to possibly do some 1/4-mile stuff from time to time. Nothing insane. Just looking at running in the 13-second range.
 
I found 3:55 works better with the 727,as the 3:91 gets you up in rpm's way too quickly. Your tire size can compensate for that, what is on the rear?
 
I switched up to 15" wheels and went as big as I could safely go with tires on my '66. I just can't remember what size I went with exactly. I know that is the missing numbers from this equation, but once I bring the car home from the shop this weekend I will know more. My dad has a 3.55 open in his '67 and I really like that gear, but I have a cream puff with A/C and all that. I am thinking that 3.23 will be less risky. I think my stock gears are 2.94 or something crazy like that.
 
Is this your daily driver? If so, 3.91's will be a bit harsh on the highway but if your driving is limited and you know you won't be over 60 mph much, then I'd go with the 3.91's and a taller rear tire....something like a 275-60 comes to mind and is what I had on a 71 340 Cuda which also had 4.56's in it at one time. Most of the time the car had 3.55's and it liked the 3.91's a lot. My drive to work was 15 miles one way and part of that was freeway.
 
Noooo! It is definitely not a daily driver. Too many people like to run into the old stuff. Especially that tail light area toward that rear of these ole Chargers. It gets driven very little. I am probably going to throw in these 3.91's. If the 383 likes them, I will keep them. I am installing the heavy duty u-joints and adjustable snubber with it. Already sporting the super stock springs. Seems like itmight be a fun time for awhile. I am thinking the tires I puton it are that exact size actually. I just don't know off the top of my head. A set of ETs might end up on there if it runs well. My buddy had a '66 Coronet built similar with 3.23s and he had a best ET on street tires of 13:23. So I am kinda dancing around that expectation.
 
Throw those 3.91's in there, what do you have to lose? You can always swap em out this winter. I run 4:10's in my not-so-daily driver and love em. Sure, i keep it to 60mph on the highway, but boy do i get there in a hurry. :)
 
Tony...I have 3:91's in my '66 Ply Sat with a 383 T/F and they are really quick gears. I have yet to take it on a highway but I already know I want to change to 3:55's as I get rubber upon acceleration in first and second. 3:23's are great for cruising and give good gas mileage. The 2:94's also get great mileage but I do want a little attitude as they say. 4:10's are just way too tall for me as well. Just go with what you are comfortable with is the best advise. I think 3:55's will make you very happy...cr8crshr/Tuck
 
IMO, with the auto trans, you will be overall happier with the 3.55's if you are on the street at all; your upper PRM limit of 5800 will make the shifts come pretty early with a 3.91. But as said, you have nothing to lose; you can change later.
 
Going from 3.91's to 3.55's is about a 10% change.....10% reducing in rpm too but makes about a 30% change in the fun factor :D I ran 4.10's in my 66 Belvedere /6 for a long time before pulling the motor out.
 
I would love to have 2.94 gears because I spend most of my highway drives well above 60... I had 292 gears and a hoped up 360 4 speed in a truck that would smoke a friend's 400 factory charger.... flat out in 3rd we would just nose to nose at 120 with his 410 gears once I hit 4th it was a steady climb to 150 but it was a dog at lower speeds.... but on long trips I could cruze at 60 at 2000 rpm. An automatic would be limited in gear selection but an overdrive is the best of both worlds....
 
In the big picture I think yanking my 742 case and setting it aside until I buy new gears is the right answer. Deciding between the 3.23s, 3.55s, and 3.91s are what I have to do. I went to 4.11s in one of my Fords once and it was heaven in the 1/4-mile. Just gotta see where my priorities are gonna lie the most with my Mopar. I don't think I have anything to lose in giving this whole chunk a shot. At least until the fun wears off. I still have to install a shift kit in my TF to make it play as hard as everything else as well. Plus my pinion snubber, limited slip additive, and u-joints escorted my diff gasket in from Summit today. Therefore this has shot to the #2 spot on my priority list for the weekend. #1 is to get the car back in my driveway where it belongs.
 
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