This might not be the right place to post this (sorry). I would like to hear from owners of basically stock slant six cars. What kind of fuel mileage is normal ( when you keep your foot out of it).
Whats your car/gear/ trans/ carb/etc

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Mostly Old Parts And Rust
1933 Desoto Coupe 426 Hemi
1946 Dodge dumpbed pickup 2.5 Turbo 4cyl
1964 Dodge A100 pickup 273 automatic
2002 PT Cruiser Woody edition

The results will vary by generation and type of vehicle (1985 Dodge Truck vs. 1965 Dart vs. 1976 Feather Duster) and type of driving (all city, all highway, hills/mountains vs. flat land)

Typically I have experienced:
1976 Plymouth Feather Duster Stock 90% flat highway driving 10% light to light city driving 28-30 mpg highway, 20 mpg city 90% light to light 10% on rural beltway. Holley 1945, 2.94 rear gear, manual 4spd w/OD.
Same car, 3.55 rear gear, dual exhaust, 10:1 compression, hyperpak intake Holley 390 cfm 4 barrel 18 city 24 highway.
Same setup above, change to 4.56 rear gearing 17 city, 21 mpg highway.
1974 Plymouth Duster Same drive as above 18 city, 21 highway.
Holley 1945, 2.94 rear gearing, manual 3 spd on floor. Highway mileage improve 1-1.5 mpg with upgrade to Feather Duster exhaust pipe.
1967 Plymouth Valiant Signet 21 highway, 16 city. 2.94 rear gear, Holley 1920. Change to manual 3 spd and later model 225 with Feather Duster exhaust pipe and Mopar EI, 18 city 21 highway.

I have seen a 1965 Dart up to 28 mpg all highway with some supertuning and a recurved points distributor.....3spd manual with 2.94's, Holley 1920.

-D.Idiot

Thank you. good information

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Mostly Old Parts And Rust
1933 Desoto Coupe 426 Hemi
1946 Dodge dumpbed pickup 2.5 Turbo 4cyl
1964 Dodge A100 pickup 273 automatic
2002 PT Cruiser Woody edition

Is the Feather duster exhaust manifold special ?, or just runs a larger pipe size with a standard exhaust manifold ?

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Mostly Old Parts And Rust
1933 Desoto Coupe 426 Hemi
1946 Dodge dumpbed pickup 2.5 Turbo 4cyl
1964 Dodge A100 pickup 273 automatic
2002 PT Cruiser Woody edition

This is correct, a 2.25" pipe vs. the 1 7/8" pipe.
There are other special things that contribute to the mileage increase, that aren't helpful in getting the car out of it's own way in traffic....but they do help mileage.

I think your A-100 is going to bat in the 18 mpg highway range, maybe 20-21 with a lot of engine and drivetrain calcs and planning...the 318 might bat a little more depending on the setup.

-D.Idiot

This is correct, a 2.25" pipe vs. the 1 7/8" pipe.
There are other special things that contribute to the mileage increase, that aren't helpful in getting the car out of it's own way in traffic....but they do help mileage.

I think your A-100 is going to bat in the 18 mpg highway range, maybe 20-21 with a lot of engine and drivetrain calcs and planning...the 318 might bat a little more depending on the setup.

-Dquote]
Yeah I've wondered about that myself. The Slant may have to work harder to get a van moving/ were as the v8 would not feel the strain.

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Mostly Old Parts And Rust
1933 Desoto Coupe 426 Hemi
1946 Dodge dumpbed pickup 2.5 Turbo 4cyl
1964 Dodge A100 pickup 273 automatic
2002 PT Cruiser Woody edition

My D100 gets 20mpg highway with a non-functioning leanburn and non-vacuum advance distributor.... I haven't checked what it does around town. But I've done a couple tanks long distance @ 65-70mph and it got right at 20mpg both times. It is probably geared really high considering that mileage at the speed... my vehicle information sticker is gone, so I have no idea what gear ratio it has. Once I install a tach, I'll try to figure it out.

I can't wait to see what it does with properly functioning ignition timing and carb tuning...

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1985 D100 3.7L Slant 6, 4-speed manual.

In the days before alcohol was added to gasoline, my '63 Valiant got 20-25, while my '75 Brougham was 16-20 with the alcohol, and 18-21 without. The Super Six in my '64 Valiant convertible now gets 18-22, with a best of 24. All my slant cars were automatics.

I've had a number of 225-automatic-2.76 gear A-bodies (1 or 2 bbl). They all got 16-17 in local driving, 20-ish on highway. Numbers went down in colder weather (when it was below freezing, -teens- constantly I got 12-13mpg).

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63 Valiant Wagon
225 - 4 bbl

rustytoolss,
74 Dart Swinger, 3300 pounds, 2.76 gear ratio 8 3/4 sure-grip, 904 automatic, 1920 Holley Economaster style carb with the wagon wheel style throat, #56 jet in the winter #57 in the summer. Local 4 mile trips up to 30 miles 22.5 mpg. Anything over 30 miles on the freeway, 25+ mpg. Tires are 26" tall, and I drive by the vacuum gauge......easy on the foot most of the time.

At the moment the engine is totally stock 1980 barn find for $100. Has a little over 272,000 miles on it now with several intake/exhaust leaks along the head (stock metal gasket).
Some minor modifications are: a little bigger valve lash .012 and .022, recurved distributor for 52 degrees total timing @ 2500 rpm 55 degrees at 3,000 rpm, heat deflector under the carb, two 10" electric cooling fans, Mobil 1 synthetic oil, cold ram air intake, 60,000 volt ignition, 2.5" exhaust using two Flowmaster mufflers in series, FM HP2 in front and a FM70 in back for super quiet ride.

Photos by clicking on the red link below.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG