318 MAX fuel economy builds?

[Hysteric]

Because fuel is heavier than air,

Isn't that the dilemma? What affects the weight of the fuel? Wouldn't droplet "size" play a major roll in how the fuel is not only vaporized to which extent but how far it travels and whether it ends up on the intake and ort walls and travels down into the cylinder as an accumulated mass that doesn't really burn well. There was a study done sometime where they figured out what size droplet best followed the air path (remained entrained) as mixture. Guess what its a lot smaller than the droplet size a Holley produces.

heavier fuels

Yes the heavies. Funny you should chose to place the lowest part of the piston on the exhaust side.........Oh I noticed the spark plug fires on the exhaust side too

 

[mpgmike]

The exhaust valve is the hottest part of the CC because it was just torched during the exhaust stroke. The charge will thermally ionize within that region. It makes the most sense to capitalize on that ionization by sending the initial spark kernel where it has the best chance of "getting lucky". Conversely, if the spark energy were sent to the intake side, the heavy ions in the exhaust region would tend to start their own combustion event once pressures got high. Can you say detonation??

 

[Hysteric]

The exhaust valve is the hottest part of the CC because it was just torched during the exhaust stroke. The charge will thermally ionize within that region. It makes the most sense to capitalize on that ionization by sending the initial spark kernel where it has the best chance of "getting lucky". Conversely, if the spark energy were sent to the intake side, the heavy ions in the exhaust region would tend to start their own combustion event once pressures got high. Can you say detonation??

You'll like this paper:

https://www.jstor.org/stable/44470833

 

[mpgmike]

I've read numerous such papers. Some are comparing ignition systems, some squish pad clearances, others other aspects. With that type equipment, you can test all sorts of cool stuff and get remarkably accurate data. I wish I had regular access to that caliber lab equipment. (I have had limited access to certain equipment for the duration of the project in the past, but never owned such expensive test equipment.)

 

[Hysteric]

I've read numerous such papers. Some are comparing ignition systems, some squish pad clearances, others other aspects. With that type equipment, you can test all sorts of cool stuff and get remarkably accurate data. I wish I had regular access to that caliber lab equipment. (I have had limited access to certain equipment for the duration of the project in the past, but never owned such expensive test equipment.)

I know where you're coming from but that's how you leverage their knowledge and experience. You would be surprised what you can see with something just as simple as a data logger and monitoring just a few parameters. That paper is especially poignant when you combine that with a good understanding of plug reading.

 

[motorpirate]

I have no idea how some of you guys are getting 20+ mpg on an old carbureted V8. I'm measuring my MPG super closely, and I have to wonder if everyone else is doing the same. I fill up the car, log every mile I drive, fill it up again, and calculate accordingly based on distance driven and fuel used. I have been doing this for every tank for 25+ years, initially because the fuel gauge didn't work and now just out of habit. So I'm darn sure my MPG calculations are as accurate as possible.

My current setup is this:

Stock heads, standard bore 5.9 Magnum. Engine doesn't burn any oil or smoke at all.
Factory EFI, factory tune (1994 OBD1 PCM). Injectors are clean, fuel atomization is perfect.
Mopar M1 EFI intake
Hughes SER0814ALN-14 roller cam with their Magnum springs
Comp roller rockers
46rh transmission with lockup converter.
Doug's long tube headers into 2.5" exhaust.
Electric fan
3.23 gear

With my 26.5 inch tire I'm spinning about 1700 rpm at 60 mph, and the best I have ever gotten on at 80 mile highway trip is 19.6 mpg. Admittedly that was at about 70 mph, and that highway has some hills so it would be better on flat ground, but that was me TRYING to make MPG (careful throttle modulation, don't stomp on it, etc).

Before the 46rh I had a 904 with a ~2200 rpm converter, and the absolute best I ever got was 16 mpg. That was taking it super easy on country roads running around 55 mph. On the highway at 65 mph I would get a little above 15 mpg, so I guess the 46rh giving me +4.5 mpg on the highway is pretty good.

I'm sure the stock cam would be better for MPG, but I don't think a lot better. My cam doesn't have a ton of duration since it's designed to work with the factory tune. Also, I went from the stock kegger intake to the M1 intake back when I still had a 904 trans, and I actually got BETTER highway MPG. The 904 trans + 3.23 gear was turning 2600 - 2700 rpm on the highway. I think going back to the stock intake with the OD would probably be better for MPG; that kegger is a low end torque monster, but dies around 4500 rpm.

Before the EFI 5.9 I was running a slightly warmed over 318, Eddy 1406, 904 trans, factory converter, and 3.23 gears. The absolute best I ever got was 15 mpg on an 80 mile highway trip, running at 60 mph or less the whole way. Usually that setup got me 14 mpg on the highway, 13 mpg around town / mixed driving, and 11 - 12 mpg if I had my foot into it a lot.

Don't forget there's more to gas mileage than just the engine.
Example:
Wife's 00 Durango, 5.9 ,46RE , 9.25/3.92 gears.
Wife is a ledfoot, throttle WOT unless she is braking.
She was a consistent 9 to 10 MPG
I could coax 15 to 18 mpg if i tried.
We put new tires on (Goodyear Duratrac"s an aggressive mud tire) and on it's maiden trip with them over inflated and running only on the skinny row of cleats in the center, 22 MPG loaded with camping gear!!
Bottom line, the whole car has to be optimized not just the engine.

 

[autopar3000]

Don't forget there's more to gas mileage than just the engine.
Example:
Wife's 00 Durango, 5.9 ,46RE , 9.25/3.92 gears.
Wife is a ledfoot, throttle WOT unless she is braking.
She was a consistent 9 to 10 MPG
I could coax 15 to 18 mpg if i tried.
We put new tires on (Goodyear Duratrac"s an aggressive mud tire) and on it's maiden trip with them over inflated and running only on the skinny row of cleats in the center, 22 MPG loaded with camping gear!!
Bottom line, the whole car has to be optimized not just the engine.

Yeah, I totally agree, there's much more to milage. Your wife's 10 mpg is what I would expect from a lead foot driver. And you getting up to 18 doesn't seem impossible under ideal conditions. But 22 MPG??

Some other factors impacting the mileage when I got my best of 19.6 mpg:
☆ As you mentioned, driver. I was driving like there was an egg between my foot and the gas pedal. And with hills and valleys, I didn't try to maintain a constant speed; I let the car speed up going down and slow down going up (i.e. avoid moving the throttle.)
☆ Also as you mentioned, tire pressure. I was running 36 psi in the 215 (f) and 235 (r) tires.
☆ Fluid type and viscosity: I have synthetic 10w-30 in the engine ATF+4 in the transmission, and synthetic 75w-90 in the rear.
☆ Aerodynamics - a 70 Dart has terrible aero, with the flat grill inset into the nose, drip rails, concave rear window, etc. But can it be any worse than a 2000 Durango?
☆ And one of the most important things: WEIGHT. My Dart is about 3150 lbs unloaded, your Durango 4600 lbs. With your truck being loaded up it was probably a solid 1800 lbs more than my car!

Did the 22 mpg calculation come from the Durango's trip computer?

 

[rumblefish360]

You missed a little something. The torque converter.
Under heavier loads, some vehicles of mine and some trucks get better mileage because the converter is working and not slipping. I have found this loaded / unloaded truck example working on my vehicle and others have told me about there experience’s.

22 out of the above ride doesn’t surprise me.

 

[mpgmike]

There is a fuel economy site where the members focus mainly on the rest of the vehicle; aerodynamics, weight, reducing friction, etc.

www.EcoModder.com

 

[motorpirate]

Yeah, I totally agree, there's much more to milage. Your wife's 10 mpg is what I would expect from a lead foot driver. And you getting up to 18 doesn't seem impossible under ideal conditions. But 22 MPG??

Some other factors impacting the mileage when I got my best of 19.6 mpg:
☆ As you mentioned, driver. I was driving like there was an egg between my foot and the gas pedal. And with hills and valleys, I didn't try to maintain a constant speed; I let the car speed up going down and slow down going up (i.e. avoid moving the throttle.)
☆ Also as you mentioned, tire pressure. I was running 36 psi in the 215 (f) and 235 (r) tires.
☆ Fluid type and viscosity: I have synthetic 10w-30 in the engine ATF+4 in the transmission, and synthetic 75w-90 in the rear.
☆ Aerodynamics - a 70 Dart has terrible aero, with the flat grill inset into the nose, drip rails, concave rear window, etc. But can it be any worse than a 2000 Durango?
☆ And one of the most important things: WEIGHT. My Dart is about 3150 lbs unloaded, your Durango 4600 lbs. With your truck being loaded up it was probably a solid 1800 lbs more than my car!

Did the 22 mpg calculation come from the Durango's trip computer?

nope, pen and paper. it only lasted until the high center rib wore down even with the rest of the tread. and with Wifey driving it it never repeated it either.
but it was 22 MPG both ways that trip thru 4 tanks of gas.

 

[autopar3000]

nope, pen and paper. it only lasted until the high center rib wore down even with the rest of the tread. and with Wifey driving it it never repeated it either.
but it was 22 MPG both ways that trip thru 4 tanks of gas.

Well that gives me something to shoot for! Maybe your later OBD2 computer does a better job of controlling the fuel and timing than my 1994 OBD1 computer does. I know it controls the transmission between gears 1, 2, and 3 whereas mine is old school hydraulic control in the first 3 gears, but that won't have any impact on highway drives.

Just to be clear, I didn't build the car for fuel economy. It's just a game I like to sometimes play to see what I can squeeze out of the car since I'm already recording distance driven and fuel used. It has also been fun to see how my fuel economy has changed since I put in the EFI engine, made some modifications to it, then put in the OD transmission, got it dialed right in, etc.

Next mod is to swap out the 3.23 for something more aggressive. I think the shortest gear available for my 741 case is 3.73, so maybe that's the ticket. It should make a big difference on the fuel economy in the wrong direction.

 

[autopar3000]

You missed a little something. The torque converter.
Under heavier loads, some vehicles of mine and some trucks get better mileage because the converter is working and not slipping. I have found this loaded / unloaded truck example working on my vehicle and others have told me about there experience’s.

22 out of the above ride doesn’t surprise me.

Yeah, torque converter can definitely impact mileage. In the case of @motorpirate's Durango any my Dart we're locked up on the highway, but the OP will definitely have to consider TQ.

Years ago my car used to have a 904 (or maybe it was a 998 or 999?) out an 85 5th Avenue. It had the mechanical lockup, where it would lock up as soon as it got into 3rd gear. For @gagembassett's max fuel economy build that would probably be the best transmission that could be easily installed (i.e. doesn't require any modifications.)

I also didn't mention the thermostat. I'm running a 180° but if I really wanted max economy I would go with a 195° stat.

 

[rumblefish360]

I have t found mileage in a thermostat. I do my swapped between the 180 & 195. Or a 160 to a 180. That one was when I realized it during a temp dip. LOL!

 

[Jadaharabi]

Is that a compliment??

Pay no attention to what Rusty Rod Bolt says.
I thank you very much for your post and I appreciate all the work you've done.

 

[Jadaharabi]

There is a fuel economy site where the members focus mainly on the rest of the vehicle; aerodynamics, weight, reducing friction, etc.

www.EcoModder.com

I will try to make this post short as I wouldn't want to offend Rusty Rod Boat.
Back in 1983 I moved to New Mexico. There was an old geezer there that I met and spent quite a bit of time with. He would build these metal boxes, fill them with copper tubing and then route them to the hot water on a motorhome engine and he would cycle that hot water inside the tubing in that box underneath the carburetor. He used to sell this gadget of his to the people with motorhomes because it would improve their fuel mileage almost double. So if they were getting six or eight miles a gallon they were getting 12 to 16. He put it on a few trucks for different guys but he didn't put it on a car because it raised the carburetor up too much and it interfered with the hood an the air cleaner.

A little side note on old Jim, he took some old radios and invented some kind of gizmo that would confuse the radar in the local cop cars. He would fly through town but their Radars never picked up what his speed was.

 

[mpgmike]

Hundreds of inventors did similar things. In fact, here's a 10 minute video showcasing some of the better known guys:

 

[mgoblue9798]

I will try to make this post short as I wouldn't want to offend Rusty Rod Boat.
Back in 1983 I moved to New Mexico. There was an old geezer there that I met and spent quite a bit of time with. He would build these metal boxes, fill them with copper tubing and then route them to the hot water on a motorhome engine and he would cycle that hot water inside the tubing in that box underneath the carburetor. He used to sell this gadget of his to the people with motorhomes because it would improve their fuel mileage almost double. So if they were getting six or eight miles a gallon they were getting 12 to 16. He put it on a few trucks for different guys but he didn't put it on a car because it raised the carburetor up too much and it interfered with the hood an the air cleaner.

A little side note on old Jim, he took some old radios and invented some kind of gizmo that would confuse the radar in the local cop cars. He would fly through town but their Radars never picked up what his speed was.

Couple thoughts. You don't need the hot water system on an RV in order to make this contraption work. Plenty of 180 water available in the cooling system.

I wonder how much of this gain could be realized by just switching from a Holley carb to a Thermoquad? Thermoquad does the best job atomizing fuel of any of the v8 carbs used by the big 3.

Is better atomization the only effect responsible for the increase in mileage with the water heated intake plenum, or is there something else at play? Did the effect of a longer intake runner impact fuel mileage as well?

 

[Jadaharabi]

Couple thoughts. You don't need the hot water system on an RV in order to make this contraption work. Plenty of 180 water available in the cooling system.

I wonder how much of this gain could be realized by just switching from a Holley carb to a Thermoquad? Thermoquad does the best job atomizing fuel of any of the v8 carbs used by the big 3.

Is better atomization the only effect responsible for the increase in mileage with the water heated intake plenum, or is there something else at play? Did the effect of a longer intake runner impact fuel mileage as well?

In effect it was a heated carb spacer.
Everybody else wants to cool the air going into the engine this was heating it up instead.

 

[Dartswinger70]

It’s about equal. Build dependent.

Factory dual plane, Edelbrock Performer & the SP2P for mileage builds.

Any dual plane except the SP2P or the Offenhauser dual port.

The thing here on a mileage build is beating the factory intake in the low rpm range. The SP2P intake would be a disaster for a performance intake. Though it was never built for performance. It was introduced during the gas crunch days.

I had a coworker tell me it was a good help in his van. It is possible but more likely improbable to find a two barrel SP2P.
Crazy hard to find they are.
The one below is a picture gleamed from the web.
AKA - Not mine.

View attachment 1716014565

The below standard Chrysler 4bbl Thermoquad intake is all you really need for a mild performance build or a mileage master searching intake. For its design, it’s hard to beat.

View attachment 1716014564

I have one of those somewhere in my parts stash. I have a TQ somewhere also.

 

[YY1]

@mpgmike

Thanks for that vid.

Only 2 real results that I heard, and no explanation of what happened to the technology or how either actually worked, besides the DIY cylinder deactivation.

 

[rumblefish360]

A small primary TQ I hope.

 

[autopar3000]

I have t found mileage in a thermostat. I do my swapped between the 180 & 195. Or a 160 to a 180. That one was when I realized it during a temp dip. LOL!

Yeah, I'm not sure how much of an impact it would make. Personally I've never tried a hotter stat for economy; only colder ones for power. My car runs a solid 180 even in super hot weather so I could try a 195 thermostat without any issue, but I won't. Something about seeing that gauge at 180 is soothing.

@mpgmike what are your thoughts on engine temperature for fuel economy?

 

[mpgmike]

Higher temperatures vaporize more fuel -- good for fuel economy.
Lower temperatures facilitate slightly higher VE at WOT -- good for WOT.

I tried heating the intake air on carb and PFI engines. I found warmer air helped MPG in wet flow (carb/TBI), but cold air and heated fuel actually worked better on PFI. PFI usually doesn't suffer from vapor lock, so up to engine temps work well and don't kill parts. If you have a return line, you should run a fuel cooler to keep vapors down, and prevent softening a plastic fuel tank. The longer version:

Combustible Caliente (Heating the Fuel) | Ecoceptor

 

[Hysteric]

Is better atomization the only effect responsible for the increase in mileage with the water heated intake plenum, or is there something else at play? Did the effect of a longer intake runner impact fuel mileage as well?

Just to be technical so people can understand the difference the Carb atomizes the fuel from there how much of it is vaporized depends on the manifold, pressure differential at the valve and how much you compress the mixture. And a whole raft of other factors.

I wonder how much of this gain could be realized by just switching from a Holley carb to a Thermoquad? Thermoquad does the best job atomizing fuel of any of the v8 carbs used by the big 3.

I went from a modded edelbrock 600 with Carter boosters to a stock Thermoquad and the difference was very pronounced. The car revved smoother and quicker. I've also had modded 750's and an 800 AVS on it as well but nothing felt and drove like the TQ. It really surprised me.

e used to sell this gadget of his to the people with motorhomes because it would improve their fuel mileage almost double. So if they were getting six or eight miles a gallon they were getting 12 to 16. He put it on a few trucks for different guys but he didn't put it on a car because it raised the carburetor up too much and it interfered with the hood an the air cleaner.

Yeah from memory some one said they had built a plenum with a water heated section inside that would cause the methanol to completely vaporize as it left the carb and hit the plate. Said the car would rpm to 8000k+ during the race while the other competitors in the same class could only manage to get theirs to 6800. they broke all the track records then had their set up banned the following year.....

 

[volaredon]

I agree 1000% on running a TQ.
These are a couple of examples I've had about Holley vs TQ.
At one time I bought a new Holley #1850. My mileage TANKED. This was on my 76 Charger SE. W/a 318.
My brother bought an 80 ram charger w/a 360 around the same time. Someone had replaced the original TQ in that one with a Holley 1850. And for some hair brained stupid reason they subbed in a point distributor in place of the factory electronic. We couldn't get that thing to pass smog for anything. I found a couple of TQs and a factory electric dist for my brother's, tweaked them out, and both his and mine mileage went way up and strangely now his ram charger passed smog with flying colors besides
(He lived a couple of towns away, just across the county line, I still lived at home where we didn't have to deal with smog)