daves66valiant
68 Dart 340/727:66 Signet Vert 340/5spd: 68 D100
I’m thinking I’ll have a happy medium with my 340. 3.23 gears with 235/70/15 steelies.
2786 rpm at 70mph
2786 rpm at 70mph
Gear ratios and driveability
- Thread starter Go Mango
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Go Mango
Never enough beer...
I think that may be a little low, but it's not far off.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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I have run a lot of different gears in behind my street 360, and my favorites are 3.55s
But it is often said that whatever percentage you slow your cruise rpm down, your mpgs will increase by half that same percentage.3.55s will slow your cruise rpm by ~10%, netting you a possible 5% increase in mpgs. If that matters to you. I much prefer cruising my 360 at 2200. Noise and vibration are much lower. To me, the performance loss,lol, is worth it. My 360 is even happy with 3.23s, and a 3.09 first gear.
Get yourself some Commando gearing; 3.09-1.92-1.40-1.00. and tall 15s(28s), and 3.55s, and your first gear will be about the same;
2.66x3.91x24/25.6= 9.75 Torque Multiplication of the current comboto the road, versus
3.09x 3.55x24/28 = 9.40 the new combo.
But your cruize rpm will drop from 65=3340 to 65=2770, or about 570 rpm lower, a loss of 17.1% and a possible gain of 8.6% fuel economy. Which is like paying 8.6% less for a gallon of gas.
There is only one "down side" to the 3.55/28s; namely 65 =5320 at the top of second, versus 6410 with the 3.91/26.5s. But I bet you weren't spinning it up that high, meaning you would have shifted, to hit 65=4510 in third. My guess is you were spinning 245s most or all the way thru 2 gears, so the new combo with 28s might help to prevent that, and maybe the 3.55/28s will be quicker to 65, than the 3.91/26.5s. Probably. Only one way to know for sure.
3.55s are also probably the right gear to race 1/8th mile; trapping around 5200 in third, about right for the 340 cam.
But it is often said that whatever percentage you slow your cruise rpm down, your mpgs will increase by half that same percentage.3.55s will slow your cruise rpm by ~10%, netting you a possible 5% increase in mpgs. If that matters to you. I much prefer cruising my 360 at 2200. Noise and vibration are much lower. To me, the performance loss,lol, is worth it. My 360 is even happy with 3.23s, and a 3.09 first gear.
Get yourself some Commando gearing; 3.09-1.92-1.40-1.00. and tall 15s(28s), and 3.55s, and your first gear will be about the same;
2.66x3.91x24/25.6= 9.75 Torque Multiplication of the current comboto the road, versus
3.09x 3.55x24/28 = 9.40 the new combo.
But your cruize rpm will drop from 65=3340 to 65=2770, or about 570 rpm lower, a loss of 17.1% and a possible gain of 8.6% fuel economy. Which is like paying 8.6% less for a gallon of gas.
There is only one "down side" to the 3.55/28s; namely 65 =5320 at the top of second, versus 6410 with the 3.91/26.5s. But I bet you weren't spinning it up that high, meaning you would have shifted, to hit 65=4510 in third. My guess is you were spinning 245s most or all the way thru 2 gears, so the new combo with 28s might help to prevent that, and maybe the 3.55/28s will be quicker to 65, than the 3.91/26.5s. Probably. Only one way to know for sure.
3.55s are also probably the right gear to race 1/8th mile; trapping around 5200 in third, about right for the 340 cam.
I ran 4:56 with 275 15’s most of my time with the car and street/strip! It got very tiring. Now run 3:55 and much happier! If I want some spin I will air up to 30psi but generally stay at 12 to 15 for bite and acceleration, boring for some but surprising for others!
That with MT drag radials.
That with MT drag radials.
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It depends on the height of the tire. That tire could be as short or shorter than yours in which case it could turn the engine as hard or harder. The wheel diameter has nothing to do with it.
3.91 out, 2.94s in, done d
eal and everybody is happy !
4spd. 355's, Auto 323's with a factory 3000 stall converter. Not a junk low stall 2200 10.5 truck slug-omatic converter that most use Because they are free. A performance converter for a Diesel is 2000. And I know your 340 isn't making that kind of torque that low.
Ditch the 391's install 323's with a factory stall 3000-3500 . You will be one happy camper with your tiny little tires. and even happier if you increase your tire diameter.
I see your car came with 391's so I am assuming it is 4spd. they went to 355's in 72 for a reason. again increase your tire diameter . I would put as tall of a tire under the back as you can fit.
Ditch the 391's install 323's with a factory stall 3000-3500 . You will be one happy camper with your tiny little tires. and even happier if you increase your tire diameter.
I see your car came with 391's so I am assuming it is 4spd. they went to 355's in 72 for a reason. again increase your tire diameter . I would put as tall of a tire under the back as you can fit.
For me, I can't go down the road over 5 miles if my engine is turning 3000 rpm's to do 55 mph. I can't listen to it. Mine are automatics and people think your in 2nd gear "hey, you need to go to drive"......
I absolutely agree. My first overdrive was around 1984, and I wouldn't even consider owning a car without one since. I get a good laugh every weekend passing all the cars going to Island Dragway. 55mph, getting honked at, passed on both sides, and sounding like they are going to throw a rod. Honestly being a muscle car guy, I find it quite embarrassing. I fail to see the fun in driving a badass car that can't keep up with traffic.
QuickDart360
Well-Known Member
I just went to 3.91's from 3.55's. 3.55 gear was ok but will be swapping cam to the old skool 292 mopar cam so i think 3.91's are better suited for this cam.
QuickDart360
Well-Known Member
Some years ago had 14" rallyes and car felt like if it had the 3.91's! But went to 15" rallys all the way around and 3.55's lost some of the quick acceleration. Rear tire diameter is 28".
That's what I'm running, 255/60/15 in the back with 4.10 gears. My little 318 is winding at about 4,000 at 70mph. Commute is 13 miles, soon to become 18 miles each way. That 3 5/16" stroke can handle it just fine.
69_340_GTS
Well-Known Member
With a 340 the "standard" factory gears were almost always 3.23. Tires were around 25.5-26.0". That's a good all around combination. 2700-2800 RPM at 65 mph. Ma Mopar was no dummy.
MrJLR
Built, not bought
A small block Mopar running 2700 - 3000 RPM for and extended period of time is no big deal in my opinion.
As long as she's not over heating and has good oiling.
They're designed to run....
Jeff
As long as she's not over heating and has good oiling.
They're designed to run....
Jeff
Run that 292 in my 383 and very pleased with 3.55 and 28” tall tires. Almost went 3.73 but happy with my choice. Not as fun and exciting as the 4.56 set, but more enjoyable for longer cruises.
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