Improving MPG

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FWIW. Post 13-16 by BBMopar Memike ff6 67Dart273 are giving you good advice for tuning. A dash mounted vac gage is a decent low buck alternative to Wideband O2 (AFR) gage or logger. Yup. You need to go to Eddy's website and download the tuning manuals. Jetting effects higher rpm and load but you'll need to tune idle and transition for milage gains at 50 mph and below. A spreadbore gets on the mains a little earlier.

I disagree with your assumption that the timing is 'dead on'. If you had a factory cam, a factory dizzy, and set the initial to the factory specs, then it would be dead on. But you don't have any of those. at best you are ballpark. There's also a caveat as emmissions got more important, the factory sometimes compromised milage to keep NOx down. If you de-EGRed the car, then for best milage you may want to use an earlier year as a baseline. If it didn't have EGR, or you kept the EGR, then '74 is probably OK.

In any event, tuning is iterative. After checking engine condition, measure the timing curves, check the spark plug conditions, and then make your changes - one at a time. Carb then timing, timing then carb, whatever, just have a plan and do one change at a time. Vacuum and AFR gages (with rpm) will provide some immediate feedback. They won't tell you if it can pull a load. That you have to judge while driving.
 
To those 'advising' to just get a more modern pos...
There's another thing about properly tuning your engine... With a well tuned and set up engine you get a way more pleasant and fun driving car.
It's not always about the money 'spent'.

When I swapped the 904 in my Dart for an A518 OD tranny I got a much more fun car to drive in return. Which to me was worth far more than the cost of the tranny-swap.
 
C130 Chief said:
The combo you have should be getting 18-20 mpg as is. What cam? What intake? What is the compression ratio? What torque converter?

Start with the basics. Make sure your vacuum advance is working correctly, and your timing is optimized. Then take a look at your carb. The manual has some really helpful charts. BTW, Edelbrock does not make a 650 Performer.
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THIS is exactly what I've been saying. You don't need to change the rear axle, the transmission, or add an expensive ignition. You need to "fix what's there" with the possible exception of the carb.
 
Mattax said:
I disagree with your assumption that the timing is 'dead on'. If you had a factory cam, a factory dizzy, and set the initial to the factory specs, then it would be dead on. But you don't have any of those. at best you are ballpark.
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EXACTLY

And not only that, but the later distributor you have, the worse the curve was for mileage. But at this point you (the OP) doesn't even know if that is working OK. If the dist has been replaced by a "rebuilt" in it's lifetime, anything "could be in there."

"Factory" timing is "not the best" for mileage OR performance!!!!
 
I am no expert by any means but a high stall convertor can destroy fuel economy. A high stall convertor is less efficient. It takes more gas to make the car move. A lot of pickups have whats called a utility convertor so they can pull a trailer or a heavy load. Hope this helps.
 
67Ruda said:
I am no expert by any means but a high stall convertor can destroy fuel economy. A high stall convertor is less efficient. It takes more gas to make the car move. A lot of pickups have whats called a utility convertor so they can pull a trailer or a heavy load. Hope this helps.
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high stall is a relative term... alot of the new converters act stock in most cases. I dont remember if he said what converter was in it or not
 
Your 3.23 and factory torque converter are probably best for your scenario of city and high way driving and getting decent mileage.

I agree with 805's detailed check list. Get all that done first then start thinking about the next step after you have optimized your existing setup.

Maybe if it were I and I wanted a daily driver with a bit of balls but fuel efficient, I would get an after market mild TBI setup and ditch the questionable carb.

Other than simply and cheaply doing what 805 and others suggested about optimizing your existing system, there is really no way to get ROI on expensive mods designed to make better fuel mileage unless your car some how magically transforms to 35 MPG or you are going to drive that vehicle which may end up at a realistic 22 mpg best case scenario, for a quarter million miles. Then you may see ROI on complex mods. But the fantastic benefits of engine longevity and ease of drivability combined with a bit better mileage may be worth switching to an econo TBI.

https://www.affordable-fuel-injection.com/

http://hamiltonfuelinjection.com/category/2-tbi-throttle-body-injection.aspx

Buy an economical daily driver like a 96 2wd 4 cylinder 5 speed ranger or a geo metro 5 speed if you want excellent mileage.
 
I used to work for a torque convertor shop and on a lot of convertors one of the things they do is bend the fins at more of an angle to achieve that high stall takes more RPM to direct the fluid to the front pump. There goes your fuel economy. Just one of many things that could be causing bad MPG
 
Back to basics: What sits on top,inside the actual 318? Camshaft,intake? Manifold vacuum,at idle would help here(so would some engine bay pictures). Camshafts/overlap,kill mileage,so does worn out/retarded timing chains & cam timing.
 
Some one suggested a vacuum gauge putting one in your car will help you drive so you get better MPG helps a lot.
 
You might want to check to see if your brakes are dragging, especially front disc brakes.
 
Here is my go to list, in order, to tune, which inherently will improve MPG, because once it's tuned, it's doing what it should be doing with the fuel, making more power per stroke.

A- Check tire pressure. Give it a square 35psi on all 4 corners. Check cylinder pressure. Don't skip on this. This is the most important part. A good engine should be seeing at least 120psi min. Better numbers are closer to 150-160psi. For good fuel economy, you will need at least 130psi.

If you are not seeing at least 130, your engine isn't going to fetch anything for MPG, no matter what you bolt on to it or how you've adjusted whatever you've bolted on to it.

If you don't see 130psi, check for leakdown. You need to see at least 75% pressure hold. If you do not see this, you've got a sealing issue and again, you will not get good power.

2- Keep that spark plug socket out and check the spark plugs, cap and rotor. Seems simple, but re-gap the plugs and make sure they are clean. You can have a brand new, computerized injection engine run like a 3 legged dog on bad plugs.

D- Don't put the plugs back in yet. Check ignition timing, using a piston stop. If you don't use a piston stop, you could be playing yourself. Check TDC and mark it, with a stop. Once you have measured and actually know where TDC is and it's marked, you're not done. Put a witness mark on the front of the balancer that goes across the rubber isolating layer, from the outer to the inner. Fire it up and hit it with zero on the light. Write it down. Point the light at your witness mark and make note if it has crossed up under motion. see if it moves more under more throttle. If it does, you may want another balancer. If it stays in position, or even crossed up a little, make note of how much it's moved and know that your timing mark is exactly that far off.

Check the advance pot on the dist. with a vac pump and gauge to make sure that it is moving and holding 100% vacuum at a real level of vacuum that your engine sees. I check mine at 14in.

Check total timing with degree tape or a dial back light and make sure it comes in before 3200rpm. If it doesn't, get a spring kit to recurve the distributor.

%- Once everything checks out, adjust idle to 650-700 RPM, in gear. Check throttle response and again under load. Set accelerator appropriately. Double check idle mixture screw setting and be sure that it's set to drop idle by 50 RPM. This is a lean-best idle. reset idle back to 650-700 (the lowest it sounds smooth in gear) with the idle screw, now that it's dropped.

&-Check AFR. If you do not have o2, consider getting a good reader kit and having them installed. If not, take your car to the emissions clinic and have it read. You are looking for as close to 14.7:1 mixture.

6-Check trans fluid level in gear. Check kickdown adjustment. If kickdown isn't set correct, it can inherently hold the lower gear longer and can also eat clutches quickly.

3- Jack the front of the car up and feel for brake resistance.

This is what works for me. Of course, if I notice anything off about the car, like a misfire or something else, I immediately go to diagnostic. If the engine is running ok, I will start tuning.

Never assume that any marking on a part or part that you install is correctly adjusted. Take the time to measure it and know for yourself. You may find yourself looking to degree your cam or other in-depth tuning, if you can't achieve good results with the little things.
 
I honestly think that once you tune what you've got, check the jetting and everything in the above list, maybe degree the cam if you want more cyl. psi, an Overdrive transmission is an improvement. Especially for highway use.
 
DaveBonds said:
... You are looking for as close to 14.7:1 mixture. ...
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I somewhat disagree with that statement.
14.7 is just a number, a reference point, which shows all the (this type of) fuel is burned perfectly with all the available air.
I doesn't say much about mileage.

When an engine isn't 'working' like when idling or just cruising down a level road, you can tune pretty much as lean as you want as long as it's able to maintain the rpm or speed wanted without having to give it more throttle.

I'm running propane in my daily Dart where the stochiometric value is around 15.5-15.7. But I pretty much always cruise and drive around with the mixture in the 16-17.x AFR range.
At idle the AFR is only at 18 AFR most of the time.
 
I don't actually see any need to set AFR at idle. Hell I used to be able to "meet" idle / smog AFR just by ear most of the time, although I'll admit, back then, I've set hundreds of carbs

Besides, idle mixture is not going to have THAT much of a marked affect on MPG. Certainly not all the way from 12 something to over 17
 
A Q-jet or a Dual-jet Rochestor have the double booster design. some other carbs have this feature (yes even some ford carbs). These carbs work better in a situation where fuel mileage is important. the dual boosters break up the fuel into finer droplets so I would recommend one of these type carbs. the good thing is that Chrysler used rochestor carbs on their trucks and vans in the eighties so you can find a quadra-jet with the mopar linkage setup.
The other thing I would recommend is to set up your Duster with an electric fan setup AND make sure you have a good working thermostat and I would recommend a 195 degree one. Warmer engine get better milage, just look at the factory t-stats in newer cars. Also a bit more compression in the engine would be a good thing as 318's are notoriously noted for LOW compression. I would shoot for right at 9 : 1 or slightly under that number. Other ideas: light weight synthetic oil if you can get by with it, Laser straight wheel alignment and some tires that a rated as good MPG tires.
 
The above might be good info to "build on" but should not be necessary until he gets the MPG up to at least reasonable levels. What he's getting now, hell, my old 440-6 RR could beat, and I didn't drive it all that carefully. That thing would "touch" on 14 mpg. This was with an 800 Holley, Edelbrock 180 manifold, headers, 3:54 gear and 4 speed. And THAT was back before the "double nickel"
 
four speed manual with a good clutch.

conversion to newer type tranny with lockup converter.

either one is big $$$.

old style 727 or 904 with old school converter = gas down the pipes.
you could get a 9.5 converter from dynamic, but $600 later and install time/$$$ will not se as much improvement as a swap to manual trans.

carb tweaks, improving comp ratio, lowering the weight all help the car also. fan clutch, nippondenso alternator conversion, etc.

however, your real big gotcha is the old style automatic.

best bet: drive it enjoy it for what it is. if you are wanting a commuter car with high mpg get one of the new darts. i get 34.5mpg even though i have my foot in the turbo a lot of the time lol.
 
Your driving style could have a lot to do with your mileage most cars never see there advertised mileage. It will be hard to increase from you cars stock mileage, there a lot of great ideas on here already, but you want to keep cost down or otherwise its pointless. Unless your looking for performance with mileage. Comparing Civics and Neons is a bit unfair if you look at cars with similar weight and aerodynamics mileage hasn't improved a lot with 40 years and billions of $$$ especially in town cause it just takes a certain amount of fuel to move your car down the road. EFI was mainly an emission move by automotive industry, and overdrives are more of a performance thing cause you can gear a car for mileage or performance or a compromise of both where OD can give you both.

weight(car and/or drivetrain), aero, getting air in and out of the engine easier, less accessories etc..
 
Your 650 cfm carb is on the high side. Look for a Holley Economaster for your car. There were both 2 bbl BBD and 4 bbl (450 cfm) versions, sold in the 1980's when gas went up. You see new ones on ebay occasionally. Your RV cam is a good choice. I used that, plus Rhoads leak-down lifters (no mpg data yet). Advance the spark timing as much as possible without knocking. That is how new cars run - computer continuously advances spark until the knock sensor tells it to back off. An HEI module might give a slight improvement over the stock Mopar box.
 
2 bbl carbs are not an fuel mileage device but a cost cutting same with 6 cylinder engine. I don't buy the smaller carb automatically gets better mileage a certain fuel to air ratio has to be maintained no matter carbs rated cfm. And a very underrated carb would be a restriction on air causing a less efficient engine.
 
273 said:
2 bbl carbs are not an fuel mileage device but a cost cutting same with 6 cylinder engine. I don't buy the smaller carb automatically gets better mileage a certain fuel to air ratio has to be maintained no matter carbs rated cfm. And a very underrated carb would be a restriction on air causing a less efficient engine.
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I kinda think fuel economy is all about efficiency. How well the vehicle uses the energy. An improvement overall would be a switch to synthetic lubes in the motor,power steering pump,trans,diff and wheel bearing.Throwing out any unneeded weight. Aluminum wheels,fibreglass body parts...
 
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