Gas mileage on a 1977 Newport with a 400

[commando1]

Sigh.... These cars just don't get good gas mileage. You might be able to bring it up a MPG or two with some tuning and keeping your foot out of the carburetor.

Anything that you do that involves throwing money at the car will probably never pay for itself. Just do the math sometime and remember that it's a limited use car that you aren't putting enough miles on to justify anything.

The best thing to do is just not pay attention at the gas pump. Just think about it as money spent on having fun.

You have nailed it on the head.
Penny wise, pound foolish.
Complain about fuel economy.
Install $2,000.00 EFI kit.
Increases fuel economy 1.5 mpg.
Drives vehicle 2,000 miles per year.
Payback: Year 2066....

 

[70bigblockdodge]

You can try advancing the timing. By eliminating the lean burn and if you do not have to pass any smog test your timing should be changed. You want around 35° btdc at 3000 rpm+ you need a dial back light or do the math and mark the dampener. Most timing especially in early smog engine days was retarded to reduce NOx emissions. I believe your thermo quad may not have a ported spark advance port only a manifold vacuum that went to lean burn box, not sure about year specifics but I know some do not have it. A improperly plumbed or operating vacuum advance will hurt mileage.

 

[Snotty]

This is where the poly shines boys! 20.5imp mpg on the last rip but you all know that.

I got 18 on the highway with my 413 powered '62 New Yorker. It was great!

 

[fury fan]

What is your car/engine?

I wouldn't give up on the TQ, if it is the correct one for the car it is calibrated for the engine. Some Eddy carbs are calibrated rich, some lean (you must research the specs to know) and unless you get a WB o2 gauge and a calibration kit, and spend lots of time fiddling with it and watching your MPG in-between, simply 'putting an Eddy on' is shooting blind at mpg vs the TQ. If the car is running smooth leave the TQ alone, it's one of the best-MPG carbs Chrysler ever used (it has a bad reputation due to the plastic fuel bowls, lack of tunability for performance, and non-knowledgable people 'tuning' them).

I have read that LB units suffer issues due to a poor ground path, they ground thru the aircleaner stud and nut. Reportedly adding a separate ground wire helps with intermittent problems.

Most people want to simply find some solitary magic 'fix' that they've overlooked, and then see MPG go up and stay up regardless of all else. Tuning for MPG must be approached scientifically, and methodically, and the resulting changes must be monitored carefully. IMHO most people do not realize what is involved, you can make a change and think you gained soemthign, but there's usually another variable in there also that you don't see. If you don't sort out those variables scientifically (fuel quality, headwind, road speed, and bunches others) it takes forever to figure out a trend, and by that time on an old non-EFI car something else is out of tune and the situation changes anyway. Or 'winter gas' comes in...

But here's a magic fix -
Speed is a huge reducer of MPG. Drop your highway speeds down and your mpg *will* go up.

 

[Ripinator]

But here's a magic fix -
Speed is a huge reducer of MPG. Drop your highway speeds down and your mpg *will* go up.

That is NOT a manly solution. . .

 

[Wildaugust]

Not a Formal, but the best mileage I've been able to get was over 20 MPG (Cdn gallons) with my '71 383-2V at a sustained speed of 60 mph. I had L-78-15s on the back at the time so, my 2.76 was probably effectively more like a 2.53 or something, instant OD, LOL. Now I have 225/70-15s all around, which I believe are equivalent to H-70-15 and therefore permissible according to the manual, my mileage is less, although not terrible, but I've also made other changes to my engine, exhaust, etc. since then.

With my truck, I noticed a gain in mpg after I installed dual exhaust with Turbo mufflers, an Accel Supercoil and an open chrome air breather. Those changes alone netted me 3 mpg on the highway and the engine felt a lot more powerful too! If you want to keep an all original look, you probably wouldn't want to go that route though.

I have never bothered to check or worry about city mpg, there are just too many variables involved.

 

[Snotty]

The 383 was a motor that got good mileage, which is why I'd like to have one instead of the 440 they swapped in on the day my car was sold.

 

[cantflip]

I never did the math...
Don't like to think too much about it...
Anything better than single digit is good for these cars IMO... especially on ethanol fuels you can buy on the road... I may pay attention going to Garlits... probably won't want to think about it too much then either.

 

[celticwarlock]

My '69 NY (last I checked) got about 18 MPG on a trip from Easton, PA to Derry, NH. I got there without having to re-fuel. I kept it at a sensible speed and tried to keep the secondaries closed.

These cars are not meant to be efficient, but you can squeeze out numbers you can live with if your driving habits are kept in check.

 

[jct]

hyper miling in a c-body

 

[Ripinator]

hyper miling in a c-body

Hyper-miling is NOT manly either. . .

 

[1978 NYB]

I just drove 2000 miles in my 78 NYB w/400 from Maryland to Green Bay and back. No Lean Burn, standard Mopar Electronic Ignition. Eddie performer intake and 1406 carb. Rough guess about 160 gallon's. Driving 75-85 mph most of the time and best guess is 12.5 mpg.

 

[70bigblockdodge]

I just drove 2000 miles in my 78 NYB w/400 from Maryland to Green Bay and back. No Lean Burn, standard Mopar Electronic Ignition. Eddie performer intake and 1406 carb. Rough guess about 160 gallon's. Driving 75-85 mph most of the time and best guess is 12.5 mpg.

You need some more timing at cruise Bob, it will keep your rings in better shape also.

 

[commando1]

You need some more timing at cruise Bob, it will keep your rings in better shape also.

What do you suggest for going about getting more timing in the upper RPM band. Just twisting the distributor CW wont work.

 

[70bigblockdodge]

What do you suggest for going about getting more timing in the upper RPM band. Just twisting the distributor CW wont work.

You need all the timing in in the cruise rpm range
First figure out what rpm all the mechanical advance is all in by I'm guessing it is not even in until 80 mph with big tire, tall geared rear that might need a spring change inside dist. to bring it all in earlier. Needs to be all in at your cruise rpm unless that is less than I would guess 2200 rpm. Above 2200 the total timing should be all-in definitely by 2500. 35° btdc for a big block, 33 btdc for a small block are good starting points, in at 2500 and above is a good place to start. Loosen up the spring in the vacuum advance (turn with 3/32 Allen wrench in the nipple, clockwise) to come in very early because throttle is not open very far open with low rpm Venturi air speed/vacuum because of tall rear ratio, this can be done with a hand vacuum pump with canister removed or in place, if it surges or has unsteady cruise rpm after you put it back on, tighten the spring tension in the vac canister till this goes away, perfect. You need a lot of advance with low compression, gotta light it early with not as much thermal energy generated by squeeze, oxygen molecules are further apart. Of course any knocking will necessitate timing being removed but you will have to find some really crappy gas to get a formal to knock. You should end up with upwards of 50-55° of total timing, initial +mechanical + vacuum.

 

[commando1]

You are my hero.

 

[Dobalovr]

You should end up with upwards of 50-55° of total timing, initial +mechanical + vacuum.

This is my thinking as well. At 2500 rpm total advance on my 300-440 with 2:76 is 48• however it is hard to start with anything more than 8• initial

 

[70bigblockdodge]

This is my thinking as well. At 2500 rpm total advance on my 300-440 with 2:76 is 48• however it is hard to start with anything more than 8• initial

You may need to extend.the slots in mechanical advance to you your 35 total and still get back under 8 initial to keep from getting your kickback when trying to start. 35-8= 27° of mechanical advance. The slots will need to be approximately .270+ .240(pin diameter) = .510 long. That's a really big swing but if it gets you where you can have your total and initial where you need them it will be better for mileage and engine life.

 

[70bigblockdodge]

You are my hero.

Careful you will make my head swell up and it will not fit in this tiny Peterbilt cab

 

[1978 NYB]

You need some more timing at cruise Bob, it will keep your rings in better shape also.

I need to do more than that. I believe my valve guides are leaking big time. I need a new oil pan, timing gear set, etc. I'm thinking of stroking the motor, zero deck pistons, aluminum heads, a performance cam (not outrageous), 2500 stall converter.