Will I regret change to 3.55s from 2.76s

[1973dust]

If this is an 8 3/4, just whoop up another chunk with a 3.55 in it. That way you can easily swap it back if you want to.

@1973dust Not sure if you knew or not, but the A999 is basically a beefed up version of your A904 commonly found in Dodge Diplomats & Plymouth Gran Fury's plus others in the 1980's and also with different 1st & 2nd gears.
A904: 1st=2.45, 2nd=1.45 & 3rd=1.00
A999: 1st=2.74, 2nd=1.54 & 3rd=1.00

Thanks for all of the good conversation, everyone. I've been convinced since Tuesday to do the 3.55's but all of this other info should be helpful to others trying to make a decision. I actually feel silly that I was that worried about it.

No Rusty, it's just a 8 1/4. Otherwise, your plan is exactly what I would do. I'm removing a 7 1/4 BBP so there probably won't be any going back, although I will keep the complete rear because you never know what the future will bring. The only thing better than an 8 3/4 would be TT5.9mag's 3.91's with an OD idea. That would be the ultimate but I'm too cheap to spend that much. Compromises, compromises.

Cuprum-74, yes I actually did know about the A999 from an old Mopar Muscle article, but thanks for that info. My 904 is working so well that I don't see doing anything different with the trans. in the near futures because, again, I'm cheap.

 

[TT5.9mag]

I’ve built a bunch of cars, all makes, all levels of performance. The ONE single modification that will always make you drive your car more and enjoy driving it will be an overdrive transmission. I’ve never once regretted the cost. It’s been worth it every single time regardless of rear gear ratio.

 

[1973dust]

I’ve built a bunch of cars, all makes, all levels of performance. The ONE single modification that will always make you drive your car more and enjoy driving it will be an overdrive transmission. I’ve never once regretted the cost. It’s been worth it every single time regardless of rear gear ratio.

It's definitely not a never, but not right now. Out of curiosity, what auto would you use if doing it? 500, 518, or other? I know a lot of guys seem to like the 200r4 as it appears they fit with less structural surgery.

 

[RustyRatRod]

I gotta say, I would just leave it as is. But it's your car.

 

[TT5.9mag]

It's definitely not a never, but not right now. Out of curiosity, what auto would you use if doing it? 500, 518, or other? I know a lot of guys seem to like the 200r4 as it appears they fit with less structural surgery.

I’m right in the middle of doing a 46re in my D100, I have a T56 magnum going in my dart, I’ve used 700r4, 4l80e, 4l60e, and one ford 6r. The “best” one for you will be entirely up to you. I dont care much about sheet metal work, I’ll cut the car to fit the trans. Other guys don’t want to do that, but the cost goes way up if you buy a direct fit 2004r specifically made for your car. So it’s personal preference really.

 

[Chris1974]

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.

I agree 110% with harrisonm were talking about muscle cars here were not doing it for gas mileage I have no idea what I get in my duster and don't care. I have a F450 with a v10 and get about 8 MGP and I only know that because the computer tells me, but I have a guy at home depo that says you must not get very good gas mileage with that truck and my response to him is if you can't afford the gas don't buy the truck. I also agree with rusty if it ant broke don't fix it

 

[Workingdog1]

Ok ok I hope you know I was joking. Kinda. I feel a little differently than you do because I’d never spend a bunch of money to redo a car and not drive it. I don’t see the point. And trust me when I tell you, there are WAY more idiotic drivers here than just about anywhere. But they aren’t going to keep me from enjoying my junk. My recommendation to you is this, and this time I’m very serious, put 3.91s in your car and then put an overdrive trans. It’s that whole “have cake and will eat it” type of deal.

Stuffed an 8 3/4 3.23 sourced from @junkyardhero replacing 2.76 7 1/4 and mucho better.
I'd love to try 3.55 only to want to try 3.73, then 3.91, then 4.11, and then try 4.30 for s...s and giggles.

'64 Dart now 340 904 pushbutton so a bit light.

I believe the motor wants 4.30's but I may start with 3.73, 3.91 and want more , 4.11 be pissed etc.

Thoughts @darto ? BTW finally running and driving plus very happy with everything.

I've yet to deal with convertor issue before gear changes but a fun little grocery runner car that wakes peckerheads up should eventually be fun.

 

[273]

I've yet to deal with convertor issue before gear changes but a fun little grocery runner car that wakes peckerheads up should eventually be fun.

Out of the two the convertor will make the bigger difference.

 

[RLF Cuda]

My 340 came with 3.55's and it ran like a bat out of hell turning 13.55's at 104 MPH. I now live in CO and do longer drives. I have both 3.55's and 2.94's with 255-60x15 BFG's. Truthfully, although much faster with 3.55's, on longer drives I like the 2.94's better. lower engine speed and noise, and cooler operating temp. Yes, I miss the 1-2 chirp, but that is about the only downside. I will put the 3.55's back in if Bandimere ever gets up and running again. Can't beat 3.55's for the strip.

 

[mad mike]

I'm Running a 360 mag. with a cam a little larger than stock 600 cfm carb with 391 gears. It runs as fast as I want and looks great. The last thing on my mind is gas mpg plus the additive I use. If I can't drive there I will trailer it. I love my car and don't worry about price cause it takes what it takes to look cool and go fast. I would stick in the 355 gears and by a pinto for long trips. LOL. Just have fun with it.

 

[Swinger 340]

I'm looking for some experienced opinions as I've searched thoroughly on here and I still can't decide. My car is a 73 Duster with a stock bottom end, stock head 74 318. Engine mods are Performer intake, 600 Edelbrock carb., cheap Summit cam 204/214 278/288 .421 .444 112LS, decent ignition curve, and duals off of the stock manifolds. Drivetrain is stock stall 904 and 2.76 peg-leg 7 1/4 with 27" tall rear tires. The trans. does have the part-throttle downshift valve body and I have modified the kickdown linkage to give me 2nd gear out of low-speed turns with fairly light throttle. I seldom really run my car hard but would say that I always accelerate "briskly". I definitely don't ever hold up traffic. I feel like the car runs really well the way I have it set up now and I get 15-16 mpg with a mix of in-town and 55mph 2-lane roads. I'm sure it would get 18-19 on an extended highway run. I have a 3.55 geared peg-leg 8 1/4" that came from a Jeep Cherokee that I was going to install but I'm starting to wonder if it will be a mistake. Obviously, I'll have to remove the Jeep perches and weld new ones on, shorten a driveshaft, and swap over the brakes. The wider Cherokee rear would fit perfectly with the rims I have as I'm currently using 1 1/2" bolt-on spacers on the 7 1/4. If I had a 8 3/4 where I could just swap the center section I would just try it and see. Certainly, my car would be quicker with the 3.55's but I'm not sure how much gas mileage I'll be sacrificing although I suspect 2-3 mpg. I'm currently running about 2100 rpm at 55 which would increase to about 2700. I do realize that the engine would not have to labor as hard to get up to speed with the deeper gear but I also would be deeper into the throttle. If you've taken the time to read this novel, thanks for any thoughts you can offer.

I think your mileage will suffer more like 3-4 miles per gal. That would be around 20-25%, from what you are getting now. If you do mostly city or around town, then you will on the right path, but if it is mostly highway speeds, I would leave it at is.

 

[Workingdog1]

I think your mileage will suffer more like 3-4 miles per gal. That would be around 20-25%, from what you are getting now. If you do mostly city or around town, then you will on the right path, but if it is mostly highway speeds, I would leave it at is.

Lol as planning estate kind of thing with the only responsible kid.

4.11 or 4.30 for thrill and or die putting it off the Highway or County Road into the lake, river canyon for the grocery getter.

Faak it ! Working on the Trust, Will and making sure one of the kids understands 3 gun cabinets and contents. LMAO