fishy68
Tyr Fryr's Inc.
Thanks for the info John. Sounds like a great setup.
Living with 3.91's
- Thread starter TimDart
- Start date
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69 Valiant Kid
Well-Known Member
i was wondering how those 3.73's were working for guys....you seem to like them huh?
66dartgt
Well-Known Member
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.
A
Ace
Guest
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.
So 3.55's probably the best compromise. But still a compromise.
sublimeswinger
SUBLIME Senior Member
You guys are scaring me, i want 3.91's bad, but i wanna be able to drive on the freeway.
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.
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.
fishy68
Tyr Fryr's Inc.
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.
abodyjoe
Well-Known Member
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.
sublimeswinger
SUBLIME Senior Member
you sound like me Joe, i like to cruise at 70-80 as well
Joe,
I'm calling the NJ state police.... 153??? :thebirdm:
Very nice. :thumblef:
I'm calling the NJ state police.... 153??? :thebirdm:
Very nice. :thumblef:
abodyjoe
Well-Known Member
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.
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.
sublimeswinger
SUBLIME Senior Member
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
abodyjoe
Well-Known Member
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. 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.
abodyjoe
Well-Known Member
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
YoungBlood
Jolt the Squares
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.
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:
I've already started saving for the gas:clock:
Rude72*
Well-Known Member
This is a 16 year old thread so he may not respond .
3.91 26.5 tall tire 80mph 4000 rpm
3.23 26.5 tall tire 80 mph 3000 rpm
2.94. 26.5 Tall tire 80 mph 2750 rpm
Last edited:
Reddart 1966gt
Member
Years ago I bought a '74 Dart Sport with a good running 383, '67 915 closed chamber heads. The car came with 456's which proved to be too much on the street. My intention was to have fun with a street/ strip car, but my trips to Englishtown amounted to only a half dozen times a season, so, ultimately I chose 391's which were a much better fit for my purposes. I felt only a minor difference in grunt. A 200 mile trip to Carlisle in July was stressful, but the car ran 12.40's consistently on street tires. It really depends on your priorities and being honest with yourself about what your plans are for the car. You will get used to the 391's. Good luck!
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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A 30% gear change is sortof like just using the next gear in the trans.
For instance; Say you had 2.76s and went to 3.91s, the road gears with a 727 are
------ 6.76-4.00-2.76 versus
9.58- 5.67-3.91, ---- So you are just trading one gear for another.
IMO,
what you should really do is get rid of the 2400 stall and swap in something like a 3200.
Say at 2400 your 360 was making 300 footpounds, and saddled by 2.76s, the take-off torque is 300 x 6.76 = 2028 footpounds. But
say at 3200 your 360 is making 360 ftlbs, which is then 2433 ftlbs. Which is 20% better. That would take 2.76 plus 20%= 3.31s to equal the 2.76 at 2400.
Now, you can go up half a gear say from 3.23s to 3.73s
Hpwever
This does not take into account, convertor efficiency.
Say your 2400 has an slip-ratio of 1.6, making your 6.76 to be 10.81, but
Say your 3200 has a ratio of 1.9 making it 12.84, which is a further increase of 18.8%, now your roadgear is up 1.20 x 1.188= plus 23.76% .....
All without changing the rear ratio.
If it all goes up in tiresmoke on the starting line, maybe you lose .4 second in the quarter. But not geared right at the traps is not gonna cost you the same amount of time, unless maybe a shift gets in the way. Lots of guys find out that more gear at the traps may not translate to more speed nor a lower ET.
a 360 is gonna blow the tires off,
in first gear, pretty much with any 3series gears anyway.
and Second is gonna get you to way past the speed limit even with 4.10s
On the street, I want Second gear to be my home. I don't want tirespin at WOT at 30/35 mph. and I want the engine to power-peak at around 50/55mph. I will gladly run down the backside of the power curve, all the way to 60/65 in Second gear.
Thus my gear of choice for a 268/110 cam is gonna be about 4.30s, for 5500= 62mph. Thus 2750 will be about 31mph, in Second gear. Thus, this is about as fun as it gets on the street, with an automatic...... and said 268 cam.
But I gotta tell ya, a well built 360 will blow the tires off all the way thru Second gear, with 4.30s. and what this means is; why the heck did you choose a 360, lol, if you can't run to 60 mph with the throttle WFO, without tirespin. Tirespin will get you into trouble real quick.
You could have picked a smaller engine and/or a smaller cam, and/or a smaller carb, and got there very nearly in the same amount of time, without all the tiresmoke............ 4.30s are a game-changer.
I yanked them out and sold them.
I can do the same with less. and not pay the fuel-economy penalty.
For instance; Say you had 2.76s and went to 3.91s, the road gears with a 727 are
------ 6.76-4.00-2.76 versus
9.58- 5.67-3.91, ---- So you are just trading one gear for another.
IMO,
what you should really do is get rid of the 2400 stall and swap in something like a 3200.
Say at 2400 your 360 was making 300 footpounds, and saddled by 2.76s, the take-off torque is 300 x 6.76 = 2028 footpounds. But
say at 3200 your 360 is making 360 ftlbs, which is then 2433 ftlbs. Which is 20% better. That would take 2.76 plus 20%= 3.31s to equal the 2.76 at 2400.
Now, you can go up half a gear say from 3.23s to 3.73s
Hpwever
This does not take into account, convertor efficiency.
Say your 2400 has an slip-ratio of 1.6, making your 6.76 to be 10.81, but
Say your 3200 has a ratio of 1.9 making it 12.84, which is a further increase of 18.8%, now your roadgear is up 1.20 x 1.188= plus 23.76% .....
All without changing the rear ratio.
If it all goes up in tiresmoke on the starting line, maybe you lose .4 second in the quarter. But not geared right at the traps is not gonna cost you the same amount of time, unless maybe a shift gets in the way. Lots of guys find out that more gear at the traps may not translate to more speed nor a lower ET.
To answer your question, on the street , it hardly matters cuz
a 360 is gonna blow the tires off,
in first gear, pretty much with any 3series gears anyway.
and Second is gonna get you to way past the speed limit even with 4.10s
On the street, I want Second gear to be my home. I don't want tirespin at WOT at 30/35 mph. and I want the engine to power-peak at around 50/55mph. I will gladly run down the backside of the power curve, all the way to 60/65 in Second gear.
Thus my gear of choice for a 268/110 cam is gonna be about 4.30s, for 5500= 62mph. Thus 2750 will be about 31mph, in Second gear. Thus, this is about as fun as it gets on the street, with an automatic...... and said 268 cam.
But I gotta tell ya, a well built 360 will blow the tires off all the way thru Second gear, with 4.30s. and what this means is; why the heck did you choose a 360, lol, if you can't run to 60 mph with the throttle WFO, without tirespin. Tirespin will get you into trouble real quick.
You could have picked a smaller engine and/or a smaller cam, and/or a smaller carb, and got there very nearly in the same amount of time, without all the tiresmoke............ 4.30s are a game-changer.
I yanked them out and sold them.
I can do the same with less. and not pay the fuel-economy penalty.
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