Need help selecting a 6-speed trans and rear end combo for better mpg.

[KremlinKrusher]

Hello Dodge lovers,

I have a 1970 Challenger with a 440 from a 73' Coronet. The automatic transmission has a slip stick shifter. And that is about as much as I know.

Now my question is this; I need better gas mileage from my Challenger and I wonder what combination of rear ends and 6 speed manual transmissions will give me the best gas mileage?

 This is not to be raced by any means but to be a simple cruising car to take to shows and daily drives. I'm looking to get 20-35 mpg from proper gearing. I know that it is possible as I have a buddy who has a 55' Chevy with a 454, a 6 speed and a matched rear end that get 38 mpg on Highway. I'm looking to get the same. I'm looking for something in the price range of $2500-4500 for transmission and rear end combos. I would still like to have some speed if to it but it's not a priority over fuel economy.

I'm not that technically inclined when it comes to old cars this is the first I've owned and or worked on. I'm just learning the ends and outs of the engine and have NO IDEA how gearing works on these cars, but I do want to learn and I have to start somewhere. However right now I just need it to run at better mpg.

Thanks in advance for ANY help, advise, or tips you can give.

Kremlin K.

[7212Mopar]

Why don't you take a look at the gearing of the new 6spd Challenger. The 392 HEMI fuel injected with cylinder deactivation (AT) or 6 spd manual is rated only at 14 mpg City and 23 mpg HWY. You should patent your setup if your 1970 440 can do better than that.

 

[ChallengerHK]

Yeah, I think I'd ask to go for a few long distance rides with your friend and calculate the actual mileage from a couple of fill-ups. If he can really get 38mpg, he's going to be richer than Bill Gates, and I want in 

[drewcrane]

Yeah, I think I'd ask to go for a few long distance rides with your friend and calculate the actual mileage from a couple of fill-ups. If he can really get 38mpg, he's going to be richer than Bill Gates, and I want in 

Ditto I currently have a 440 3:23 gears and I average 12 mpg, 38mpg seems a bit exaggerated  for a large cube motor over 45o cubes

[KremlinKrusher]

I appreciate the feedback, I mean it's what he said and he's a very straight shooter. But I don't know what is feasible and not realistic. I mean if he said he was getting 50-60 I wouldn't believe it.

[ChallengerHK]

Realistically, if you go with fuel injection that is impeccably tuned, a 6 speed with gearing something like a Viper, and relatively tall rear end I'd bet you could hit 20, maybe even 25, especially if you stay out of the gas pedal. By my standards, though, that's not going to be a very fun car to drive.

As for your friend, maybe he does know something that none of the rest of us knows. If that is true, though, you're going to have to get that info from him 

[7212Mopar]

Your friend must have the very first classic hybrid muscle car in the World or he is doing the Flinestone way. My daily driver is a FI four cylinder 5 spd and I have yet to get more than 30 mpg combined.

[Haddixj]

Mpg lies are crazy. My 10 corolla gets 31 hand calc miles almost every fill up.

[KremlinKrusher]

well thanks for the feedback everyone!

[73EStroker]

3:23 gears and well tuned engine may get you over 20 but this has already been suggested earlier here. Fuel injection is the best bet but a proper port injection system will run you $4000+ with maybe 1 or 2 mpg gain.

Tell your friend to fill the tank then drive the car 150 miles or so then fill again. See if that comes to 38. I only get a little more than that with a new diesel VW in town.

[brads70]

I do believe realistically you could get 20-23 MPG's with the right combo. It's also what's inside your motor, cam heads , headers etc.... also a well tuned carb or well set up FI will get you what your after. I'd gear the car so in 5th at 65 MPH your at about 2200 rpm's , 6th gear will be for in excess of 65 MPH.  In my combo I get 17 MPG's on the hwy with a 4L60, 3:55 rear gears and a 451 stroker. It lugs a bit at 65 in OD and is happier at 75 MPH . I should have went with 3:73. It all depends on your combo.
My old 440 from a motorhome a 727 and 3:55 got 10 MPG on the hwy.  My new 451 has almost 2x the power and almost 2x the fuel economy. I'm sure it would be better with a FI set up too.
Hope that helps!

PS welcome to the site! 

[1970 RT Challenger 1970]

Maybe his 38 MPG was driving down a mountain road with the engine turned off and coasting downhill...

[ToxicWolf]

My wife has a Prius that gets about 45 mpg on the hwy. I just can't see a 440 getting over 25 mpg.

[Killer_Mopar]

I'm looking to get 20-35 mpg from proper gearing. I know that it is possible as I have a buddy who has a 55' Chevy with a 454, a 6 speed and a matched rear end that get 38 mpg on Highway.

Hate to break the news but your buddy is lying, exaggerating, or is terrible at math.

My Challenger which has a 451 w/ efi, 3.55's, and a .73 OD can get 18-20 MPG and thats IF I cruise at highway speed (65-70mph) and take it easy. In the city I get 13 MPG as I tend to lay into it. Keep in mind that I have quite a bit of aluminum on the car and the 400 is a little lighter than the 440 you have. With a big block I simply dont see getting much more than 20mpg without spending tons of money. Even with a LA small block and a 1/2 ton of weight loss, I would be surprised at 25mpg. You might be able to 30-35mpg with a 5.7 w/ MDS, OD, and if get the car to under 3000 lbs. That would basically make it the equivalent of a thousand lbs lighter LX/LY, cars that weighs 4000 lbs & can get 25-28 mpg.

[KremlinKrusher]

Well I got it on the road today and it's running well. I'm pulling about 12-12.5 mpg. I I could even squeeze 15-16  mpg out of it it would technically be an improvement from current mpg from my current daily driver.