Living with 3.91's

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Personally I like my 323's and relatively short 15" tires. But, I dont race, just cruise around and I like driving on the highway. I had a car with 3.91's and a 4 speed years ago and it was fun, but the highway drove me nuts, too many Rpms and too much engine drone. Its mainly a matter of preference and what you intend to do with the car.
 
The 3.91's are perfect for the 27" Dunlops I have right now - for 1/4 mile, that is. I would not recommend them for ANYTHING else. It's taching around 3500 rpm's at 65 on the highway. The 3.23's I started out with after I first installed the new rear however, seemed too tall for even normal driving. Cruising the highway was good, but seemed to take too much clutch to start out and slower pulling up through the gears.

So 3.55's probably the best compromise. But still a compromise.
 
Man those 340's must have been great to take up to 7000 rpms once the motor was blue printed.
They were!!! Ran 4.89's in my old 340 Swinger on the street back in the early '70s - fun on the street and the track, but couldn't take it on the freeway with those gears.
Currently building another '69 Dart with a 360/727 combo and will have 2 chunks: 1 with a freeway gear for road trip car shows and events and 1 with 3.73's for local cruise nights and some track times.
 
69 Valiant Kid said:
i was wondering how those 3.73's were working for guys....you seem to like them huh?
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I like them. My car had 4:10's in it when I bought it and with 27" tall tires it was really screaming much above 60. I debated on going with 3:55's or 3:73's but I'm too power hungry:snakeman: and went with the 3:73's cause I was afraid I'd loose too much going down to 3:55's. I am glad now I went with the 3:73's. They dropped the 60 mph rpm by 400+ rpm's which is pretty darn good cause now at 60mph it's under 3000. It did loose some on takeoff as could be expected but I believe on street tires it's just as quick cause they don't hook real well and the usefulness of the lower gear is lost time in spinning.
 
sublimeswinger said:
You guys are scaring me, i want 3.91's bad, but i wanna be able to drive on the freeway.
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you'll need overdrive then.. 3.91 with a 28 inch tire and cruise on the highway but if your anything like me you'll be pissed the entire time because at 3000 rpm your only doing about 60 - 65. i need to cruise between 70-80 mph comfortable and 3.91 gear just didn't do it for me. around town they were great but noton the highway. i can honestly say i love the 2.94 gears i just put in the car. 75 mph at just under 3000 rpm. its finally the cruiser i wanted.


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Joe,

I'm calling the NJ state police.... 153??? :thebirdm:

Very nice. :thumblef:
 
crackedback said:
Joe,

I'm calling the NJ state police.... 153??? :thebirdm:

Very nice. :thumblef:
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that was on the PA turn pike...lol.

there is no way i ever got going that fast. only think i could think of is it jumped between two different satilites or something. i was movin but nowhere that fast..lol
 
Well guys, i originally started this thread and it seems to be a good one. I finally fitted the 3.91's yesterday. Its too early to make any real assertions at this point with just 20 miles under my belt. But those 20 miles included town, country and a spot of highway.
The converor really likes the change. The car is straight off and running compared to the 3.23s. The whole motor seems to like the where the power band is.
Regarding cruising at highway speeds, i can't tell as i now need to change the speedomoter drive as its reading way out. First impressions are positive, though.
 
Keep us informed, i have the same 3.23 and want 3.91. What motor are you running? And what car? Im sure its listed in here, just to lazy to look. lol
 
Regarding cruising at highway speeds, i can't tell as i now need to change the speedomoter drive as its reading way out. First impressions are positive, though
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you'll be fine at 55-60. its when your getting passed by every soccer mom in minivans that you'll want to step up the speed some. thats when it sucks. spinning at 3800-4000 sucks.

again it all depends on what you really want to do with the car. i want to get on the highway and cruise and 3.91's were horrible for that without OD. now with the 2.94 gears its awesome for what i want and i will probably never take those gears out unless i do an OD unit down the road.
 
My car is a full weight mild 360 in a Dart Sport.
Joe, I have spare gears if I want to go back, but it wasn't screaming like you say. My peak torque is around 3,200 rpm. I dont mind cruising at that speed. Came back from UK mopar Nats last wek at a steady 70-80mph in the 3.23s, guess a little readjustment will be required.
Then again, i intend to break into the 13s with this car now.
 
Joe, I have spare gears if I want to go back, but it wasn't screaming like you say.
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guess it depends what screaming means to you. i know with 3.91 gears and a 28" tall tire my dart would turn 3800 rpm to cruise at 75-80 mph. and that sucks on two hour rides . at those speeds i was still getting blown by on the turnpike and expressway. now i do those same speeds at 2800 rpm and its heaven.. like i said it all depends how your using the car. if its only gonna see the highway a few times and short distances then it will be fine. but if a road trip is in store for it they suck..lol
 
I have 4:10's in my duster with 275/60/14's in the back. Around town its a blast & seems perfect for crusing but its not too fun on the highway. Its a stoplight screamer in town tho!!
 
The title of this thread cracks me up. Its almost like 3.91's are an ailment.

They would be for me actually. Its all long roads and highway where I live. If you went lower than 3.55's around here and drove regularly, you would be bankrupt. I like driving. I switch between 2.76's and 3.55's.
 
Well, it finally stopped raining today, so i'll take the car out and put some highway miles on it and see how it goes. Got a race/show event in September which involves a 500 mile round trip.
I've already started saving for the gas:clock:
 
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