Fuel economy of flat six

[sser2]

I hated to hijack the thread about dual carbs, so decided to start a new one about fuel economy and how it can be improved.

It has been stated by Sharps40 that 30 mpg at 60 mph highway driving is impossible. I have to agree. It is impossible to argue against extensive experience. At the time when there were no EPA mileage ratings, Chrysler advertised that some drivers managed to make 20 mpg in their cars. Realistically, this means an average driver should have been content with 15 mpg.

But did anyone try modifications aiming at economy? I searched extensively, but could not find anything. All the mods I could find were about increasing power.

We can look at how fuel economy of today's cars has been achieved, and whether some steps in those directions can be taken in our cars.

1. Increase compression.  8.5 - 9 is possible in Mopar engines with 78 gasoline.

2. Decrease engine displacement. This improves economy at the expense of performance. The most fuel-efficient non-hybrid car in the USA, Geo Metro, which is capable of 50 mpg highway, has 1 liter 3 cylinder engine. I own 3 of these cars. They are excellent everyday drivers. If my Plymouth had the same dynamics as Metro, I would be very happy. To compensate for the loss of performance of small engines, their rated power is increased by high rpm, 4 valves per cylinder, and variable valve timing. These power tricks come at drastic loss of economy. There is nothing to be gained here for flat six engines, except understanding that 190 and 201 engines are more economical than 230 ones.

3. Manual transmission. Auto transmission is big waste of engine power. Typically, auto car is 20-25% less fuel efficient than stick shift of the same model. However, manual transmissions are not all the same. The most economical are those that have direct drive, like third gear in a 3-speed Mopar transmission. In third gear, friction losses in such transmission are minimal. Unfortunately, with standard rear end and standard wheels, 60 mph in third gear is not where engine works economically. The simplest solution is overdrive, but friction losses in overdrive should be considered. Higher gearing can be also achieved using 3.9 rear end (which I have in my car) and 235/85R16 rear wheels. This combination gives 15% higher final ratio (for comparison, overdrive gives 30%). Taller gearing should be acceptable if engine power is increased.

4. Leaner burn at sustained highway speed. Flat six engines are intrinsically amenable to leaner burn because they have much more turbulence in combustion chambers than OHV engines. Leaner burn requires stronger spark than pathetic 6V ignition can deliver. This is not a problem. Modern transistorized or capacitor discharge ignition should take care of it. Of course, proper jetting will be necessary, guided by output from an oxygen sensor. 

5. Better carburettor. Newer carburettors provide more precise fuel metering than primitive OEM carburettors of 30s - 50s. Substantial savings can also be achieved by fuel cutoff during engine braking, which newer carburettors allow.

6. EGR. Reduces fuel consumption at sustained highway speed. This is an easy add-on.

7. Tuned intake and exhaust. Most modern cars have intake and exhaust resonators that reduce engine pumping losses at engine speeds of steady highway driving.

8. Electric radiator fan. Belt-driven radiator fan without clutch easily robs engine of 2-3 hp at highway speeds.

9. Thinner engine and transmission oil. With tight tolerances in Mopar engines, 0W20 synthetic oil should be OK. Pennzoil Synchromesh is an excellent transmission fluid that is much thinner than regular gear oil. Not much savings here, but everything adds up.

10. Radial tires. These have 20-30% less rolling resistance than OEM bias ply tires. Of course, steering would be more difficult, but I don't think this is insurmountable. Our Nissan truck has no power steering, but my petite 115 lb wife drives it without complaints.

11. Good driving habits. Maintain steady speed, minimize hard braking and acceleration, use pulse-glide where appropriate. There are devices that show instant mileage - they are very helpful in learning how to drive for economy. Unfortunately, they only work with fuel injection. A manifold vacuum gauge on dashboard is acceptable substitute. Economy driving is safe driving.

Critiques? Other suggestions?

[plyroadking]

We went 1790 miles cross country in two days on 107 gallons of fuel, not quite 17mpg . 1955 230 bored 30 over, single barrel carb, od, 3.73 rear and 235/75r15 radials on the rear. Straight 30 wt engine oil. Ran around 65-80 mph and used neutral on the long downhill slopes. 

[55 Fargo]

Good Luck on 30 mph,it can be done.  I do know you can get more if you want, but can not reveal the secrets of this on the forum.

Most are content with 16 to 20 mpg, so no point in divulging the technological secrets for a lot more horsepower and fuel economy.

I will be waiting to see the results of the experiments you will be conducting, please post your hypothesis, data and results as you attain them...Good Luck

щасливого Різдва

Edited January 9, 2017 by Rockwood

[Ricky Luke]

I'm being pedantic, but Porsche, Subaru and Chev have/had flat sixes. 

From personal experience I agree with 1,3,5,7,8 & 10. Some of the old carbs were no better than a can with a hole in the bottom. I replaced the original carby on a Leyland P76 (Rover based) V8 with a Holley 350 and got a 8 MPG open road improvement without doing anything else. I'm thinking of doing the same with my Chrysler.

Cheers

 

Rick

 

[knuckleharley]

" But did anyone try modifications aiming at economy? I searched extensively, but could not find anything. All the mods I could find were about increasing power. "

 

Of course. Look up "Mobile Economy Runs". Look for little tricks those cars used to maximize economy that you would never live with in a daily driver,like skinny 6 or 8 ply tires pumped up to 50+ psi of air pressure,though. Yeah,it works,but no way is any normal person going to be willing to deal with that harsh ride to save a few pennies per tank of gas. Winning the Mobile Economy Run used to be a big advertising deal,though. Lots of bragging rights attached to it. I may be wrong,but it seems to me like it was either Studebaker or Rambler that won in the 50's.

It is also untrue that modifications to increase performance decrease fuel economy. Up to varying points depending on engine design and modifications,when you make an engine more efficient you not only get more gas mileage,but you also get more power. Obviously a Hemi from one of Gartlitz's old Swamp Rat dragsters makes plenty of power and gets next to zero MPG on nitro methane,but there is a sweet spot between a AA blown fueler and a car modified to be more efficient for daily driving.

Don't forget,factory engines prior to today's modern computer controlled engines were designed for the most part to run smoothly and quietly at low RPM's,not for power of gas economy. You can add a more efficient highway or city cam,depending on where you do most of your driving,along with a hotter spark,more compression,and especially on inline 6's,3 single barrel carbs,dual exhausts of the proper ID with a balance tube,and get a big boost in both power and economy.

[BigDaddyO]

12 hours ago, Rockwood said:

Good Luck on 30 mph,it can be done.  I do know you can get more if you want, but can not reveal the secrets of this on the forum.

Most are content with 16 to 20 mpg, so no point in divulging the technological secrets for a lot more horsepower and fuel economy.

I will be waiting to see the results of the experiments you will be conducting, please post your hypothesis, data and results as you attain them...Good Luck

щасливого Різдва

Oh, you want sser2 to post all of his findings but you "can not reveal the secrets of this on the forum", eh?

[dpollo]

I have two Plymouths  on which I have achieved mileage which is in the high 20s  in MPG.  When I was younger, all I could expect was between 18 and 20 with cars like these.    Several things have changed including my driving habits.   The 51 Plymouth is a convertible with a 251 bored .060 single  exhaust and single carb.  2 inch pipe  all the way to the back.  It has 8 to 1 compression and the intake ports have been matched.  Overdrive and 3.9 rear screw . Radial tires.   The other is a 50 sedan with a 230 bored  .040  8.5 to 1 compression, single carb and  exhaust, overdrive, 3.9 and radial tires.   I covered the ground between Boring Oregon and Arlington Washington  240 miles by the speedometer several times each on just over eight gallons  of regular gas.  I did this in a 92 Sundance 2.5 liter on the same amount of fuel.  Map measurements put this trip at 225 miles and it was necessary to get through Seattle without being brought to a halt in traffic.  Where I live, there is less opportunity to cover this distance without stopping.   It would seem, given the comparison with the Sundance that once you get the mass rolling, it takes about the same amount of fuel to keep it rolling.

[55 Fargo]

3 hours ago, BigDaddyO said:

Oh, you want sser2 to post all of his findings but you "can not reveal the secrets of this on the forum", eh?

Sorry Man, sworn to secrecy on this....LOL Get a life brother, I was only joking.

I wish the OP all the best of luck in his endeavors.

[55 Fargo]

42 minutes ago, dpollo said:

I have two Plymouths  on which I have achieved mileage which is in the high 20s  in MPG.  When I was younger, all I could expect was between 18 and 20 with cars like these.    Several things have changed including my driving habits.   The 51 Plymouth is a convertible with a 251 bored .060 single  exhaust and single carb.  2 inch pipe  all the way to the back.  It has 8 to 1 compression and the intake ports have been matched.  Overdrive and 3.9 rear screw . Radial tires.   The other is a 50 sedan with a 230 bored  .040  8.5 to 1 compression, single carb and  exhaust, overdrive, 3.9 and radial tires.   I covered the ground between Boring Oregon and Arlington Washington  240 miles by the speedometer several times each on just over eight gallons  of regular gas.  I did this in a 92 Sundance 2.5 liter on the same amount of fuel.  Map measurements put this trip at 225 miles and it was necessary to get through Seattle without being brought to a halt in traffic.  Where I live, there is less opportunity to cover this distance without stopping.   It would seem, given the comparison with the Sundance that once you get the mass rolling, it takes about the same amount of fuel to keep it rolling.

US gallon or Imperial gallon based on your high 20s which is good.

I think getting 24 or so is achievable

[dpollo]

8.4 US gallons.

[DJ194950]

Well a start would be turbo changer inter cooled, fuel injection, electronic ignition  with variable timing and also one step further --computer controlled valve timing would be good!

Sorry but these old engines were really up to to snuff for high 20's or even 30 MPG. Too many computers and engineers, flow benches are/were required to make it happen.

Remember the Big phony gas shortage? What did Detroit do? 2.08+ rear gear ratios!

Maybe that would work on flat ground with a fluid drive trans setup if your not in a big hurry and did not overheat the fluid!

DJ

[BigDaddyO]

10 hours ago, Rockwood said:

 Get a life brother, I was only joking.

 

 I'm usually pretty good at spotting humor, however well disguised. I musta missed this one, huh?

Edited January 10, 2017 by BigDaddyO

[greg g]

In 1936 a Willy's Four cylinder America Coupe recorded just over 33 mpg in the Economy Run that year 

Their 132 cu in 5.7 to one cr engine made 48 HP.  Had 7.00x17 tires and probably a 4 something rear end.   

[knuckleharley]

1 hour ago, greg g said:

In 1936 a Willy's Four cylinder America Coupe recorded just over 33 mpg in the Economy Run that year 

Their 132 cu in 5.7 to one cr engine made 48 HP.  Had 7.00x17 tires and probably a 4 something rear end.   

That's actually pretty impressive.

[laynrubber]

While I agree with several of your statements on increasing fuel economy, radial tires, standard transmission, electric fan, better carbs, driving habits they are all good and proven. I disagree with your comment on engine size. I know of your Metros and their small engines, but an engine system needs to be matched to the vehicle. If you go with a too small of power output that engine has to work too hard to move the vehicle. Putting a .7L engine in your metro wouldn't improve fuel economy.....that engine would have to work too hard to move the Metro efficiently. Same with our heavy land yachts, too small an engine system and it will work too hard to be efficient. My 5.7 Hemi gets the same gas mileage as the 4.7 Chrysler engine in the same truck.

An EGR valve is designed to recycle nitrous oxide gases and lower charge temps....meaning less exhaust gas emissions. Not necessarily a fuel conservation item.

A resonator doesn't have any effect on "engine pumping losses" at highway speeds.....a resonator is a sound altering device for the exhaust syatem. It changes the tone ...the wave of the exhaust sound with minimal back pressure.

I had a 59 Ford half ton truck, 223, 3 speed, lower rear end....a 50s truck. On the highway it would average 18 to 20 m/gal. I also had a 1990 Ford truck, 302 fuel injected, overdrive trans, maintained and I would beg to see 15 m/gal on the highway. I never figured that one out.

 

[Don Coatney]

1 hour ago, laynrubber said:

 I also had a 1990 Ford truck, 302 fuel injected, overdrive trans, maintained and I would beg to see 15 m/gal on the highway. I never figured that one out.

 

Prior to retirement I had a 60 mile daily commute. 1997 F-150 24 gallon tank. If I set the cruise at 70 MPH I would burn a tank every 4 days. If I set the cruise at 55 MPH and stayed in the truck lane I could get 6 days on a tank of gas. Driving time with normal traffic was about 5 minutes longer at 55 MPH and a lot less stressful.

[Plymouth#43]

At the risk of starting a bush fire here, what does 50s Fords or a 1997 Ford 150 have to due with improving fuel economy of a flathead mopar ?

No reply required. In fact folks this seems to be a regular trend. I totally get why some get their backs up for all this non-mopar stuff.   Advice as I leave the forum for good,  If you cant directly tie it to a flathead mopar I believe guys are just talking to hear themselves talk.

Enough is enough, Id rather go  organize the speaker wires behind my stereo.

Barb

[knuckleharley]

1 minute ago, Plymouth#43 said:

At the risk of starting a bush fire here, what does 50s Fords or a 1997 Ford 150 have to due with improving fuel economy of a flathead mopar ?

No reply required. In fact folks this seems to be a regular trend. I totally get why some get their backs up for all this non-mopar stuff.   Advice as I leave the forum for good,  If you cant directly tie it to a flathead mopar I believe guys are just talking to hear themselves talk.

Enough is enough, Id rather go  organize the speaker wires behind my stereo.

Barb

I can tell you how it relates,fuel economy for Mopars is determined no differently  than it is for any other car. Some things are universal. Driving habits is one. Flathead engines is another. The 51 Ford I sometime write about here is powered by a flathead 6 cylinder engine. Do you think factors involved with fuel consumption in a flathead Ford 6 cylinder engine are different than those with a flathead 6 Mopar engine? Do you think flathead 6 Ford powered cars have to be driven,maintained,or modified differently to obtain the same fuel mileage or power increases? Certain things are basic and apply to all engines.

[T120]

16 hours ago, BigDaddyO said:

 I'm usually pretty good at spotting humor, however well disguised. I musta missed this one, huh?

....Note to self, - Remember this quote.

[laynrubber]

For Plymouth#43's now gone benefit, the tie in is how a 50s engine and at the time modern a engine had NO difference to gas mileage. Even with the advancements such as they were. The main question was how to improve fuel economy.....

Making the engine better at breathing in and out , driving techniques and some modern technology but you can only squeeze so much out of this flat head design. The car itself has limitations to its aerodynamics also. All of these are fun, for some, to challenge and like most of us here....we want to improve things better, stronger faster. Even if it is tidying up the speaker wires behind the stereo  

[Jeff Balazs]

I would think the quickest way to maximize mileage in any vehicle involves the use of a rolling road and an exhaust gas analyzer to tell you when things were set closest to optimum at various speeds. I watched this process done on vehicles equipped with Weber Carbs and it is amazing what can be gained with a set up like this. Beats the heck out of the "seat of the pants" approach.

Jeff

[55 Fargo]

1 hour ago, Plymouth#43 said:

At the risk of starting a bush fire here, what does 50s Fords or a 1997 Ford 150 have to due with improving fuel economy of a flathead mopar ?

No reply required. In fact folks this seems to be a regular trend. I totally get why some get their backs up for all this non-mopar stuff.   Advice as I leave the forum for good,  If you cant directly tie it to a flathead mopar I believe guys are just talking to hear themselves talk.

Enough is enough, Id rather go  organize the speaker wires behind my stereo.

Barb

Yes , Ford F150s or whatever other manufacturers that are off topic vehicles mentioned.

BTW, who the H ever got into this game for major fuel economy anyway, with overdrives transmissions and a well tuned engine, they are respectable, but fine tuning for 30 MPG give me a break.

Some of the trucks are rolling 1950s fridges aerodynamically, as a tombstone.

Hey yall remember the 100 MPG carb, that all the Oil companies and the CIA suppressed.....LOL

Seriously if you can get near 23-25 mpg that would be excellent.

Yes Barb, some folks like to talk a lot a whole lot.....dble LOL

[knuckleharley]

35 minutes ago, Jeff Balazs said:

I would think the quickest way to maximize mileage in any vehicle involves the use of a rolling road and an exhaust gas analyzer to tell you when things were set closest to optimum at various speeds. I watched this process done on vehicles equipped with Weber Carbs and it is amazing what can be gained with a set up like this. Beats the heck out of the "seat of the pants" approach.

Jeff

Yeah,but even that is more for theoretical purposes  than practical use. Probably the biggest factor beyond our control is where and how we have to drive. If you live in a busy city and drive on busy streets with lots of traffic and red lights,the set up that gives maximum fuel economy is irrelevant because that is always listed for highway mileage.

If you live in hilly country instead of flat country,that's another huge factor where steady RPM's at cruising speeds are irrelevant.  Given the output of our flat 6's and how hard they have to work to just get up steep grades,that's probably be biggest MPG killer of all.

BUT......various people here talking about operating different engine,tire,weight,and geared vehicles over various types of roads and conditions gives us all insights into what will GENERALLY work best for all of us. If you expect to get maximum economy under all conditions,your only hope is to buy a new car with computer controlled everything. We,and the cars and trucks we drive operate in a time in space where you are only in a perfect state of tune at idle or wide-open throttle. Which means there is more to fuel economy and drive-ability to us than just a torque curve. We have to make compromises so our vehicles are at least semi-efficient to all our needs. Guys who just take their cars out on weekend highway runs can pretty much dial them in for the majority of the cars use,and so can guys that live in cities and mostly drive to drive-ins or parks for casual shows or meets. The later don't really care about maximum MPG at 60 MPH,but they do care about torque at take off.

People that live in snowy mountain country or cities in the frozen north will be more concerned about fluid drives,torque converters,and outright automatic transmissions than they will overdrive transmissions.

How boring would this and every other board be if we had a focus so narrow there was always one set of answers to any questions asked? Hell,we might as wlll all buy new 4 cylinder Altimas and be done with it. Providing of course we could all agree on the paint and interior colors.

Edited January 10, 2017 by knuckleharley

[Tom Skinner]

I really don't want to hijack this thread, but here goes,

Chrysler owners know Chrysler products like gas. Gas is Cheap by today's standards. Gas is small potatoes. Don't sweat small potatoes.

There now. Drive your big Chrysler's and enjoy them. I really don't give a fat babies behind what my gas mileage is. I hope and pray for you, that you really don't either.

With the inflated prices of everything else in parts for our cars, insurance, etc. does $2.10 a gallon gas scare you? I thought not.

Tom

[Tom Skinner]

By the way I get around 17 - 18m.p.g. a gallon on the highway. Pretty darned good I would say.

Tom

Edited January 10, 2017 by Tom Skinner