Gas mileage

[SomeCarGuy]

I have had 383s get over 20 mpg before. Usually the small cam engines did that. I had 69 numbers matching Bee with auto that got 18 all the time.

This 383 gets 13.3 to 14 and I don't push it hard, at least not yet. Is it the rotted muffler? Maybe it needs a X pipe to do what I have gotten with other cars, most of those had an X pipe.

I mean, it got 12.5 all the time with a 440, the same tranny, the same clutch, the same 3.23 SG rear. The same headers, the same exhaust- even the same electronic dizzy( I had an adaptor in the pile). I know the mechanical advance works, saw it on the timing light. Maybe the vac advance is stuck???

I really don't know what the deal is. Most of this is two lane 50-60 MPH traveling. Pretty steady too.

Stock cam. 70 model HP engine, doesn't seem to burn any oil. It even has slight leaks and I have yet to have to add any just yet. :huh:

I might get around to putting the new mufflers on tommorrow.

 

[Roadcuda]

I'd jump with joy, (if I could jump that is,) if I got that kind of mileage. My car has the 383, auto, with 3.23s in the rear. Even if I baby it, I'm lucky to get 10 mpg with it. I've talked to other guys with the same drivetrain and most of them say they can get up to 13 mpg with their setup. I don't know the history of this car so I wonder if it has a mild cam in it. That might explain why my mileage is so much lower then other cars with the same drivetrain. And I wonder if it could contribute to the tendency to run hot when at an idle.

 

[ACME A12]

I'd jump with joy, (if I could jump that is,) if I got that kind of mileage. My car has the 383, auto, with 3.23s in the rear. Even if I baby it, I'm lucky to get 10 mpg with it. I've talked to other guys with the same drivetrain and most of them say they can get up to 13 mpg with their setup. I don't know the history of this car so I wonder if it has a mild cam in it. That might explain why my mileage is so much lower then other cars with the same drivetrain. And I wonder if it could contribute to the tendency to run hot when at an idle.

Your experiences better mirror my own also, Steve. My Ice Blue Metallic '69 that I had in the early eighties (stock w/ 3.23 SG) got 10-12 pretty much no matter how I drove it - although it saw very little highway usage.

I haven't checked the mileage on Bambi yet, but I'm sure that with a 440, 4.10s, and the throttle having a tendency to stick while wide open it will be simply stellar... :lmao:

Ray

 

[george68hemirr]

wow i get 8.5 mpg with my 572 hemi with those 2 1050 dominators if i just putt around easy then its gallons per mile when i open it up

 

[69hemibeep]

wow i get 8.5 mpg with my 572 hemi with those 2 1050 dominators if i just putt around easy then its gallons per mile when i open it up

Thats pretty good George! Remember guys pump gas aint what it use to be :yesnod:

 

[Big John]

There are so many variables to gas mileage there is no good answer.

The ethanol mix in the gas cuts your mileage down. Just by looking at the numbers of a 10% mix, you can figure to use about 5% more gas.

 

[mac]

last year i drove down to my brothers for a car show. about 60 miles one way. told myself to take it easy to see what kind of mileage i could get. to my suprise i got almost 13 mpg. 440 with a six bbl and 3:54 gears and a 4 speed.

 

[droptop]

Gas milage is one thing I have never worried about with these old cars. When the tank gets empty, I fill it back up. Driving my old cars is one thing that always puts a smile on my face, so it does not matter to me what kind of milage I get. I can honestly say that I never have checked it in any of my old cars.

 

[SomeCarGuy]

You might if you were putting over 500 miles in a week on it.

I discovered this morning that the fan I pulled from the pile appears to be mounted backwards on the clutch. Should pull air INTO the engine bay correct? NOT push it out the front like it is.

Or is that the right way?

 

[69hemibeep]

You might if you were putting over 500 miles in a week on it.

I discovered this morning that the fan I pulled from the pile appears to be mounted backwards on the clutch. Should pull air INTO the engine bay correct? NOT push it out the front like it is.

Or is that the right way?

It should pull I dont know if it would clear the radiator backwards

 

[ACME A12]

Gas milage is one thing I have never worried about with these old cars. When the tank gets empty, I fill it back up. Driving my old cars is one thing that always puts a smile on my face, so it does not matter to me what kind of milage I get. I can honestly say that I never have checked it in any of my old cars.

I'm with you Harold. I was only mildly concerned with the mileage on that bird way back when because it was my daily driver. Even then, I still had pretty much the same approach...

Ray

 

[Basketcase]

Mine gets pretty good milage. I've never figured it out though. There's no tag on the rear, but I figure it's 3.23s. The engine was supposed to been rebuilt, but I have no proof, and the PO that did the most work on the car, must have died or been picked up by alieans. Last year when gas was $4+, I parked my truck, and drove the car to work. 18 miles one way, I could get 5 days from a tank.

 

[SomeCarGuy]

You might if you were putting over 500 miles in a week on it.

I discovered this morning that the fan I pulled from the pile appears to be mounted backwards on the clutch. Should pull air INTO the engine bay correct? NOT push it out the front like it is.

Or is that the right way?

It should pull I dont know if it would clear the radiator backwards

I think I will change the pulleys today and switch it around. No telling who put it on like that, I usually buy a whole collection of parts and it just happen to fit. I bet that makes the clutch lockup on it a lot.

 

[SomeCarGuy]

Gas milage is one thing I have never worried about with these old cars. When the tank gets empty, I fill it back up. Driving my old cars is one thing that always puts a smile on my face, so it does not matter to me what kind of milage I get. I can honestly say that I never have checked it in any of my old cars.

I'm with you Harold. I was only mildly concerned with the mileage on that bird way back when because it was my daily driver. Even then, I still had pretty much the same approach...

Ray

Back around 1999-2000, my 3 season driver was a 70 Challenger w/ 440/727. It got 7 MPG.

 

[george68hemirr]

Gas mileage WHO REALLY CARES ABOUT GAS MILEAGE....mopars were built for speed....you want gas mileage dont start it up or sorry to say drive a jap car

 

[mcmopar]

Back when I owned my current runner the 1st time it would get 10.5 city and 15.5 highway in dead stock condition with the a/c off (383, 4-speed, p/s, factory a/c, 3.55 Sure Grip). In the runner I had before this one I'd get 10 mpg city/14 mpg highway and it was a 383 4-speed with no accessories and a 3.23 open rear. When I put the 440 in it I used the TRW non-hp 4 bbl cam (350 hp 4 bbl cam) and with some aftermarket goodies (Edelbrock Torker intake andHolley 600 carb) it finally touched 10 mpg in town and around 14-15 on the highway. My little brother once got 18+ mpg on a road trip by drafting trucks through the hill country of Tennessee and Kentucky on I-75. All these setups used a 10 degree advance in timing at idle.
Currently my setup yields around 8 mpg city and about 11.5 highway - at least the last time I checked it. It may be better now since I've adjusted the timing a bit. I finally decided not to worry about it anymore since I don't drive it all that much but if I were to do the 'Nats trip again I'd definitely try to nurse more out of it.
As Big John said - there are all kinds of variables at work. Some get decent mileage and some don't. The best advice I can give is for you to keep it in sharp tune and possibly play with the timing a bit to see if any improvements can be had. I think my present setup was hurt on the highways by too much advance so I'll have to check it again since I've backed the advance down a bit.

 

[SomeCarGuy]

Gas mileage WHO REALLY CARES ABOUT GAS MILEAGE....mopars were built for speed....you want gas mileage dont start it up or sorry to say drive a jap car

You must not drive your car much.

 

[SomeCarGuy]

Back when I owned my current runner the 1st time it would get 10.5 city and 15.5 highway in dead stock condition with the a/c off (383, 4-speed, p/s, factory a/c, 3.55 Sure Grip). In the runner I had before this one I'd get 10 mpg city/14 mpg highway and it was a 383 4-speed with no accessories and a 3.23 open rear. When I put the 440 in it I used the TRW non-hp 4 bbl cam (350 hp 4 bbl cam) and with some aftermarket goodies (Edelbrock Torker intake andHolley 600 carb) it finally touched 10 mpg in town and around 14-15 on the highway. My little brother once got 18+ mpg on a road trip by drafting trucks through the hill country of Tennessee and Kentucky on I-75. All these setups used a 10 degree advance in timing at idle.
Currently my setup yields around 8 mpg city and about 11.5 highway - at least the last time I checked it. It may be better now since I've adjusted the timing a bit. I finally decided not to worry about it anymore since I don't drive it all that much but if I were to do the 'Nats trip again I'd definitely try to nurse more out of it.
As Big John said - there are all kinds of variables at work. Some get decent mileage and some don't. The best advice I can give is for you to keep it in sharp tune and possibly play with the timing a bit to see if any improvements can be had. I think my present setup was hurt on the highways by too much advance so I'll have to check it again since I've backed the advance down a bit.

I have it at 10/34. I may go 12/36 and see what happens.

 

[mcmopar]

I have had 383s get over 20 mpg before. Usually the small cam engines did that. I had 69 numbers matching Bee with auto that got 18 all the time.

This 383 gets 13.3 to 14 and I don't push it hard, at least not yet. Is it the rotted muffler? Maybe it needs a X pipe to do what I have gotten with other cars, most of those had an X pipe.

I mean, it got 12.5 all the time with a 440, the same tranny, the same clutch, the same 3.23 SG rear. The same headers, the same exhaust- even the same electronic dizzy( I had an adaptor in the pile). I know the mechanical advance works, saw it on the timing light. Maybe the vac advance is stuck???

I really don't know what the deal is. Most of this is two lane 50-60 MPH traveling. Pretty steady too.

Stock cam. 70 model HP engine, doesn't seem to burn any oil. It even has slight leaks and I have yet to have to add any just yet. :huh:

I might get around to putting the new mufflers on tommorrow.

I wouldn't think a rotted muffler would hurt your mileage - in fact it should probably help it out a bit since there is less back pressure. I blew one out many years ago in my 1st runner on a trip down here to Florida on vacation abd it seemed to help some.

What carb are you running and how is it jetted? If you are running a Holley I'd recommend a quick change secondary vacuum pod so you can experiment with secondary vacuum springs. I've switched to a very stiff spring to keep the secondaries out of the mix as much as possible. If you have a Carter AVS you might want to try adjusting the secondary buttefly spring tension about 1/2 turn clockwise to keep them out until higher rpm's are reached. If you have a 750 Holley on there you'd be better going to a 650 for a stock cammed 383. If you are adventurous and have a bit of coin to spend you may want to try a mild single plane intake and a small Holley (600 or 650). The Holley Street Dominator or Edelbrock Torker are fine intakes and do help with highway mileage. When I had the 440 in my 1st runner I picked up 2 mpg just by switching from my stock iron intake and Carter AVS to the Torker and a Holley 600. I tried a Torker on my 383 when I had this car the 1st time around and it didn't seem to help as much but then again this car was heavier, had the hi-po cam and Carter AVS instead of the little Holley.

Check the plugs to see how they look right now. If they are dark brown to black you are too rich. A light tan color is what you are looking for. You may need to go down 2 jet sizes if you are running a Holley. For an original AVS you are stuck as it is almost impossible to find jets and metering rods for them.

You may also want to investigate dialing in a bit less centrifugal advance (say 28-32) as too much advance can hurt you a bit. Its great for all out performance but hurts a bit for economy.

Gas mileage WHO REALLY CARES ABOUT GAS MILEAGE

I'd kill to get 10.5/15.5 out of mine again but to do that I'd need to ditch the domed TRW pistons in it and that would require a major rebuild which is out of the question at this point. If I could squeeze another 1-3 mpg out of mine you better believe I'd do it if it wasn't too expensive.

 

[SomeCarGuy]

It has a 750 Eddy on it. A crap carb for sure but this one works pretty good in this app. I may rebuild one of my AVS carbs I have laying around and give it a try. You can run the Eddy strip kits as long as you use an AFB "hat" or fill in the AVS ones with JB weld or something.

I haven't pulled the plugs yet, just too much other repairs going on, hard to justify "fixing" the tune when it is running good, but I do like to think ahead on things like this. I might pull a plug tommorrow afternoon.

I may back the timing off a bit and see.

I was thinking that loose baffle might be restricing things somewhat. That muffler looks new but is rotted inside, no doubt.

I beat the crap out of it with a sledge today but it didn't move. I will have to go to a shop and get a blue tip wrench put on it.