Will I regret change to 3.55s from 2.76s

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here ya go... this is the approximate rpm you'll be turning with a 27" tire...


2.76 Gear: 87.3 MPH @ 3000rpm
2.94 Gear: 82 MPH @ 3000rpm
3.23 Gear: 74.6 MPH @ 3000rpm
3.55 gear: 67.9 MPH @3000rpm

like i said only you can decide.. for me and how i drive and enjoy the car i will not go anything more then a 3.23 gear. but i also have areal good converter in the car and a low gearset 904 plus i only have a 25.5" tire. i'm only doing about 70 mph at 3000 rpm..
 
1973dust said:
I'm never on a road with a speed limit higher than 55 and never drive over 60-65. I did not change the valve springs yet but I have Comp 901-16's new in the box. I normally drive it 1500-2500 miles a year in nice weather and don't have any intentions of any long trips. Obviously, the hotter than stock cam doesn't make much sense if I leave the 2.76s. While answering you guys questions, the 3.55's seem to be becoming more of a no-brainer.
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I wouldn't overly worry about mileage, how many miles you put on a year ?
Say 2500 miles, going from say 16 to 14 mpg is about 22 gallons more a year.
As long your fine with the highway rpm which sounds like you are, I spend the extra for the performance.
 
harrisonm said:
I don't want this to sound bad, but I don't understand people who get into this hobby, have a nice car with a lot of money invested and then worry about gas mileage. I realize the Op in no way indicated that he was worried about gas mileage. I'm not referring to him. I get about 10 MPG in town and about 14-15 on the highway with my moderately built 340 4 speed and 3.55 gears. I am fine with that. I look at it as 10 Smiles Per Gallon in town Now if the mileage went down to 5 MPG in town, I would worry about what the problem was that caused a drastic reduction in MPG and fix it.
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Especially with most their probably not putting crazy amounts of mileage on anyways. So even makes less difference.
 
Thanks for all the responses, guys. I think you've successfully pushed me towards doing it. I realized this morning driving to work, that 2nd gear with 2.76s equals 4.0 overall gearing so I drove a few miles in 2nd at 55. That was definitely more revs than I would want all the time but it wasn't horrible so I think the 3.55s will be pretty decent. I also measured the rears again and they're closer to 26.5 than 27 so moving to 28 would drop close to 150 rpm if I feel it's needed later. Now I'm getting excited to make the change. From the responses, it sounds like the 3.55s will really wake it up.
 
I have 411 gears with a 27 1/2 inch tall tire currently in my duster. This was part of an 8.75 swap that I did for the motor and trans I’m slowly getting together to replace the 318 that is currently in the car. Our speed limit on the highway in Texas is 75, so I stay off of the highway as much as possible. Not because the motor minds buzzing along at 3400, I just don’t want to get run over from cars going 80-85 miles an hour. All that said, I much prefer the way the 318 runs now with the 4.11’s vs. the 2.94 previously in the 8.25 I took out. It’s one of the quickest 318s I’ve ever had, lol. Do what makes you happy and don’t overthink it!
 
I blew up a rebuilt 360 when I went from 276 gears in my 74 to 355. I had about a 27 inch tall tire. Held it wide open for almost 2 miles.
No idea speed or rpm but floated the valves and when I slowed down it was down on power and top end sounded like a rattle trap.
It is a surprising difference if you only have a small tire.
 
HankRearden said:
I blew up a rebuilt 360 when I went from 276 gears in my 74 to 355. I had about a 27 inch tall tire. Held it wide open for almost 2 miles.
No idea speed or rpm but floated the valves and when I slowed down it was down on power and top end sounded like a rattle trap.
It is a surprising difference if you only have a small tire.
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I wouldn’t blame the 355’s for destroying your engine. You probably could’ve blown it up with the 276 gear doing the same thing.
 
Putting 3:55 gears I. Where you had 2:76 will make it feel like a new car, but crazing at over 70 mph would be marginal deal. As far as gas mileage, I have a 340 six pac with 3:55 gears, it will supposedly get close to 20 mpg if I keep my foot out of the throttle, i have never been able to actually find out, lol!
 
middleagecrisis said:
I wouldn’t blame the 355’s for destroying your engine. You probably could’ve blown it up with the 276 gear doing the same thing.
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Maybe.I had done it before on the same road. It pulled noticeably harder with the 3.55 to the point I was too busy working the wheel and watching the road to pay attention to anything else.
It was a good excuse to swap in the 440.
 
2.76 gears suck. They kill the torque. The car just may get better mileage with 3.55.

Why do you think Chrysler cars with trailer towing had 3.23 gears standard? Also on slant 6 manual trans 3.2 was standard. To get the car moving easier.

Remember you bicycle days? When you left it in gear 7-10 it was impossible to get it moving from a stop without shifting down. Well it's the same in the car.
 
I went from 2.93 to 3.23 and I can see on paper a difference (slightly quicker 1/4 mile) but not on the street.
 
i find 3.45:1 with a manual trans ok in a car that runs 235 70 R14 tyres...

just don't fit a droney exhaust

my car does 99% highway driving at speed
and 1% messing about at the track
it does both things adequately and is "enough fun"....:)

i went from 2.92:1 to 3.45:1 the change was noticeable in a good way and no obvious bad way but went hand in hand with a new (now quite old) Motor build

still get 15 MPG around town and 20+ on the freeway due to way more efficient Motor with this axle and box


dave
 
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I have a 3.55 SG 3rd member for the 8 3/4 in my Duster (~400hp 360, 904, 27" tires), ran it for about a year and it was fun around town and at the drag strip but started to annoy me on the freeway. I put the 2.94 3rd member back in and prefer it this way because I like to be able to keep up with traffic and cruise at 75-80 mph to get where I wanna go. I won't be putting the 3.55s back in until I swap in a TKX 5-speed, at this point who knows when that will be so 2.94s it is.

In your case since you aren't cruising over 60 mph I think the 3.55s will be fine. I just got sick of it because I built my car more for high-speed cruising and handling than straight-line drag runs. With 1.14" torsion bars and 18" wheels my car starts to feel like it's "settling in" once above 70 mph or so and feels "in the zone" around 90 mph.
 
You only drive it 1500-2000 miles a year on nice days? And never over 65mph? First of all, you should buy a Prius, (Kidding) second of all, you should have 4.56:1 gears.
 
junkyardhero said:
the same ones who worry about having to run premium gas.

that whole $5 more per tank is a total deal killer!
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Um.. more like a buck a gallon. $20-ish per tank. If you drive 1000-2000 a year that's one thing. But up that to 10000 miles or more a year and I'm no, I ain't buying premium.
 
volaredon said:
Um.. more like a buck a gallon. $20-ish per tank. If you drive 1000-2000 a year that's one thing. But up that to 10000 miles or more a year and I'm no, I ain't buying premium.
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interesting. out by me the difference between regular and premium is only 30~40 cents

well, you know what they say: pay to play. and it is what it is.
 
The national average difference between premium and regular pump fuel is 30 cents. So @junkyardhero statement holds up. In “most” places a tank of premium vs a tank of regular will average about $6.00 not enough to worry about.
 
TT5.9mag said:
You only drive it 1500-2000 miles a year on nice days? And never over 65mph? First of all, you should buy a Prius, (Kidding) second of all, you should have 4.56:1 gears.
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Now you've gone and hurt my feelings:rolleyes: . In a good year I may do 3000. Believe me, if I was in Southern California, it would be on the road a lot more. Illinois weather can be pretty crummy. I basically will not drive it if there is a chance for rain as I don't want to feed the rust monster and it doesn't get left unattended in a parking lot. There are just too many stupid people around where I live. Took me 12 years to redo and I want it to stay nice as long as it can. I think my insurance actually limits me to 2500 miles, although they've never checked up on me. And no, 4.56 aren't happening.:)
 
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Not everyone needs to cut 1.7 60 ft times at every stop sign. In fact, many (me included) like highway speeds and not that I worry too much about mpg, it is impactive. I pull my car trailer with a classic. I have taken vacations (many) in classics. So to me, it depends on the use of the car. Only the owner will know that.
 
1973dust said:
Now you've gone and hurt my feelings . In a good year I may do 3000. Believe me, if I was in Southern California, it would be on the road a lot more. Illinois weather can be pretty crummy. I basically will not drive it if there is a chance for rain as I don't want to feed the rust monster and it doesn't get left unattended in a parking lot. There are just too many stupid people around where I live. Took me 12 years to redo and I want it to stay nice as long as it can. I think my insurance actually limits me to 2500 miles, although they've never checked up on me. And no, 4.56 aren't happening.
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MopaR&D said:
I have a 3.55 SG 3rd member for the 8 3/4 in my Duster (~400hp 360, 904, 27" tires), ran it for about a year and it was fun around town and at the drag strip but started to annoy me on the freeway. I put the 2.94 3rd member back in and prefer it this way because I like to be able to keep up with traffic and cruise at 75-80 mph to get where I wanna go. I won't be putting the 3.55s back in until I swap in a TKX 5-speed, at this point who knows when that will be so 2.94s it is.

In your case since you aren't cruising over 60 mph I think the 3.55s will be fine. I just got sick of it because I built my car more for high-speed cruising and handling than straight-line drag runs. With 1.14" torsion bars and 18" wheels my car starts to feel like it's "settling in" once above 70 mph or so and feels "in the zone" around 90 mph.
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That is why I put 3:23s in my dart, allows a bit of that type of cruzing (75-80) while still has plenty of get up and go at the stoplight.
 
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