Anyone measured there highway gas mileage before and after a gear swap?
If so, can you post some numbers. Even if it was somewhat steady state rural road driving. I know that city or around town driving won't be hardly effected by gear ratio.
Thank you.

Only vehicle I've measured it on is my GMC Dually. Going from 4.10 to 3.20 picked up 4 mpg years ago, from 7 to 11 highway (65-70 mph). 2500-2800 RPM is where it makes max torque with least throttle opening.

On my 74 Duster360, I took out the 3.55 rear end and swapped in a 2.45 rear end (complete, drum to drum) before going to Carlisle, back in 1999. The RPM at 70mph went down to 2500-2600. Was able to get 23mpg all day long at 70mph. With the 3.55, mileage was 18-19mpg . . . big difference on long trips. The 360 had more than enough torque to spin the right wheel (open rear) with the 2.45 gears.

Great info. Let's here more replies. Keep them coming.

This is over-simplified, but at a steady speed on the highway, just do a little math problem.

For example, if you got 10mpg with 4.10's and you swapped out to 3.23's, the you'd get about (4.10/3.23) x 10mpg = 12.7mpg traveling at the same speed. This should be really darn close.

I have actually found this to be close to a point, you can not keep adding higher ratio and just always keep getting better MPG as your engine will only make enough power to keep you moving at a certain RPM and if its always downshifting to get up the slightest incline you just reach a point of diminishing returns but if you have very deep gears already than this formula is kinda close. I have contemplated throwin a 2.20 rear diff in my daokta with a .69 OD ratio in the trans and really put it to the test but have not had the time or ambition.

I had thought of going from 4.10 to 3.54 in my van but the cost, time and changing the pcm to change mph would not make it worthwhile I'm my opinion. Maybe only change 3-400 rpm and not sure where the optimum efficiency rpm for a 5.9 Magnum is at. Majority of my driving is around 55 mph. 440s can lug, 318s can't.

When I was messing around with the slant in the duster it seemed like everything I did that made it more fun killed the gas mileage. I put super six 2 brl, 2 1/2" free flowing exhaust opened up the manifold, recurved distributor, and then put 3.73. With the 3.73 the mileage tanked. I decided ok I'm getting v8 mpg, time for the slant to go.

LOL! yep I have change gears enough to tell which is which by the mpg

my 85 truck 318/727/2.76 gets about 18 mpgs 3.55 down 15 mpgs

my lumpy whiplash cam 440 with a street dominator intake 750 edelbrock headers/3" pipes/muffs/29x15x15 M/Ts gets a steady

10 mpg with 3.91 or less depending on how long at WOT

10-11 mpg with 3.23

12 mpg/hwy with a 2.76

when I had the 85 truck 318 & NV4500 granny gear 5 speed turning a 3.55 gear/235/75/15 I rolled a steady 20 mpg/hwy @ 60 mph

my 82 iron head sportster 4 speed got 56 mpg with a 2.2 final gear ratio but dropped to a 43 mpg with the 2.5 final gear ratio

BUT! going from a 3.5 fuel tank down to a 1.9 fuel tank = walking sooner the first ride.

I put thousands of miles on two different 1970 A-bodies when I moved here to PA & I was surprised at the mileage difference.

1970 Dart, 225 auto with 2.76 gears 14.5 MPG

1970 Valiant, 318 3-speed manual & 3.23 gears - 21 MPG

Both engines bone stock with under 38K miles.

Gas mileage is difficult to predict at times. Many years ago, I swapped a 2.94 or a 2.76 for a 2.45??? It made virtually no difference. In fact, the highway RPM's did not change much. The fairly loose factory torque converter seemed to be slipping more. Later I swapped in a transmission with a lock up converter. That dropped the RPM's a little bit. It did not make much difference in the mileage though. I suspect it was because there was not much difference in the gear ratios. (I primarily did the swap because the new axle was a sure grip.)

In some cases, swapping in an overdrive transmission is a better option than changing the gears in the axle.

2500-2600 rpm with 2.45 @ 70? that's more like a 2.93 gear.

It's not hard to understand on carbureted cars; remember vacuum gauges? You want the thing running at max vacuum (minimum throttle opening), which is generally at torque peak. That peak on stockish engines is usually in the low-2000-rpm range.
Like Barry experienced, my last 225/6 Dart got no better hwy MPG than my 318 Dart; it had to be flogged a bit where the 318 didn't.

We have no idea what engine, or car, the OP is talking about.

Best answer, held true in the 2 gear changes I've done.

It just depends on the combo. My 11:1 360 with a big roller cam got better MPG at a 3800 rpm cruise than it did at 3000. I did 4 drag weeks with that 360, the first year we had to run down I-40 and I had to run fast to not die in traffic, 3800-4000RPM for 100 miles netted just under 15 MPG, it usually got 13@3000-3500 cruise. Getting close to peak torque and getting to the tighter side of the converter is the reasoning I am sure.

Because tire diameter and 3rd and higher gear ratios
are involved too,
it is better to discuss this in terms of
Miles per Hour per thousand rpm of engine rotation.

For most heavy V8 vehicles maximum fuel economy on LEVEL highways
comes between 40 and 50 MPH per 1000 rpm.
If your tach is showing 2000 rpm at 80 mph you are in the ballpark.

Manifold vacuum should be
under 12 inches Hg but not less than 4
( you do not want to be in fuel enrichment mode of the Fuel Injection or carburetor)

Camshaft specs matter too. Less lift and less duration help.

One MPG was gained at a steady 70 mph on mostly level blacktop pavement
On a 5400 lb 2wd 360 Ram truck with 39.4 square feet of frontal area and a Aero Cd of 0.42
When the diff ratio was reduced from 3.55 to 3.21.

The $139 computer software modelling program from the Performance Trends company called Fuel Economy Calculator correctly predicted this real world result.

If the diff ratio was reduced from 3.21 to 2.96
Or if the engine displacement was reduced from 360 to 318
the program Fuel Economy Calculator predicts a further improvement of 0.7 MPG at 70 mph.

Another interesting prediction of FEC that I confirmed in the real world was that
if this same pickup is climbing a 4% grade hill,
it does not matter whether you are in 0.69 ratio overdrive gear or 1:1 ratio third gear,
in either gear MPG drops down to 13 because of the added power needed to climb the hill.

235/60/14 tire . . . with that 2.45, that was what the rpm was - 2500-2600.

Gotta think that all the other variables (intake, carb, exhaust, cam, convertor, tranny, etc) factor into all this. Of course each engine needs to be in "it's sweet spot" where it is happy . . .

95 5.9 ram 3.55 to 4.10 actually picked up 2-3mpg in most driving, the OD + lockup was too lazy

My Fury 383 commando spec with 727/3.23 and then a500/3.91 the mileage is actually a little worse with the OD because I don't drive fast enough. The 3.23's were no fun @ 80mph commuting but I don't spend enough time at that speed. The 727/3.23's were better at 60-65mph. With a bigger cam I think it'd make even more pronounced difference as you lug the slobbery cam.

It depends entirely on the engine load and the engine's efficiency map. So there's no real answer, but in general as rpm increases, internal friction goes up and economy goes down. So, IN GENERAL, lowering the numerical gear ratio should increase mileage.

But here's a true story of my '64Dog. It's a 318 Poly stocker D100 and it came with 3.91 gears. Rear tires were 32-11.50 15, 636 revolutions per mile. I used to drive long distances and it would get a maximum of 15mpg. Much of that time was spent on Interstates at 80. Calculating that out that's 3320rpm at 80.

Then, I swapped rears as I had a donor truck and the '64 axle was leaking onto the brakes. The donor truck had a 318 and 727, 3.23 gears. New rpm,2740 at 80.It's like overdrive, right? To my dismay the next trip fuel mileage was same as before, 15mpg.

Changing the gear ratio that much really made for a better road truck but around town it lacked the snap it had with the 3.91s.

R.

This is what I've come to realize by staying with the 4.10s. The rpm would go down at speed with the 3.54s, but the gain would be minimal and a trade off at that. Don't know what the rpm is at 70 but it doesn't seem to be taxing the engine (tires are 245/75r16 30" tall)
And the van will scoot.

This.

My 64 300 came with 3.23's stock. It's get a solid 12 mpg regardless. Swapped in 4.10's and started getting 15. The 413 was warmed up a bit and I suspect the mild gears put it out of it's sweet spot whereas the steeper gears was more to it's liking.

This is true Dave. Another factor is that if your cam/engine makes peak torque (best mileage) right in the "sweet spot" of your highway rpm & you drop the gear ratio, then you may not be in that "sweet spot" anymore....but the math is still good for a ballpark idea of mileage, rmp at highway speed, etc.

I like to think more of displacement per mile than RPM per mile. For example you could have a 512 stroker turning 2000 revolutions per mile (a gear/tire combo that gave you 2000 RPM @ 60 MPH for example) and displace the same air and have the same basic internal friction as a 383 turning 2674 revolution per mile (or RPM @ 60MPH). The two should get very similar MPG and put similar TQ to the tires with identicle top ends, cams...

Also the whole thing about keeping the vacuume as high as possible is sort of bologna, yes you want to keep it as high as possible within a given combo but keeping that number down through gearing is not really by it self a bad thing. You will always get higher vacuume in 1st gear than 2nd 3rd 4th... but you will absolutly not get your best MPG driving everywere in 1st gear. The reason you were getting better MPG watching that gauge is because you were not doing as much work accelerating and then slowing down if you keep the gauge steady with a particular load if you were trying to keep the vacuume up. Also it is a good indicator of your engines tune state. I always got my best MPG with my 318 magnum 5 speed dakota by running a much higher gear selection than most would ever consider running and then accelerating with WOT at a low RPM. I could get near 20 MPG in town all the time driving this way, you will not get anywhere in a hurry but it saves a butt load of gas. If I ran it up to 2500-3000 to shift and accelerated at part throttle is would get maybe 12MPG in town.

I've been driving and digitally ignition tuning a 8.6:1cr 318ci in my dailydriven Dart for well over 5 years and hardly got the mileage to improve noticably (10-11mpg).

I've now got a 11.3:1cr 360ci installed in the car which has significant more power more but the mileage is still the same.
The 360ci has a 208-210 cranking psi with its CompCams XE256H cam.
A518OD / 3.55 gears.

Last year I had installed residual pressure valves in the brake system. 10psi for the rear drums and 2psi for the front discs.
The front disc pressure valve was good for 1 mpg loss in mileage. Noticing hard to rotate front tires lately, I removed front res.valves recently and promptly got the lost 1 mpg back.

Somethings not right if you are only getting 10-11 mpg in a 318 Dart. You should be getting a lot better than that.

Tell me about it.
With all the attempts I've done at improving it I could write a book of things that seemingly DON'T work.

Had hopes the high cr 360 engine now in the car would be more efficient, but I'm still not seeing it happening.

I'm currently kinda blaming the transmission (A518) and the perhaps in-efficient / old design(?) '60s stall convertor (non-lockup) I've used in it for the crappy mileage the car is getting.

I have a 42RH (OD+LU) needing to be rebuild. It has a matching '90s convertor which is also 1" smaller in diameter (less weight / more efficient?).
Hope this trans will be able to 'fix' the mileage issue with the car.

Gas mileage is affected by many factors - the largest factor is rolling resistance. I have owned wicked cars that got good gas milage
One is particular: E Body 416 six pak with 4sp OD and 355's
16 mpg going to and from Carlisle, back in forth to Watkins Glen etc. Top speed 140+ ET 12.20 to 12.80 with 11.90 trap speeds 400+hp at the rear wheels

Place car on level pavement in neutral
Can you push it backwards without effort??
Probably not. This is the test, if you can't do this there will be no gas mileage.

Synthetic fluid in the diff, run level 1/4 inch down.
Rear wheel bearings greased with synthetic grease, end play 0.005-0.007
Front wheel bearings in synthetic grease, bearing preload about 50 inch pounds.
Proper wheel alignment
Manual Trans? Passon gear lube
Auto Trans? Mopar ATF4 or better yet Amzoil synthetic

Engine oil, 10-40 or 10-30 synthetic, 5-30 if your engine will tolerate it

Proper engine tune up and distributor curve - here is the other major mileage factor. Lots of timing advance under part throttle needed.

K&N air filter

60% distilled water, 40% antifreeze, bottle of coolant enhancer.

195 degree thermostat

External Trans cooler if AT with internal radiator connection bypassed

In some posts people complain that on their next trip after a mofification the MPG change they were expecting did not happen or went the opposite way.

One thing I learned doing MPG tests from Durham NC to Wilmington over a mostly flat I40 in a Ram was that
side winds,
Air temperature, and especially
pavement changes from blacktop to concrete
changed fuel economy WAY MORE than I first “guesstimated.”

To really do meaningful tests on real world interstate highways to nail down small changes on the order of 5% you need two vehicles travelling convoy style.

As a miner I know there are many miles of big tunnels in Limestone quarries and Salt mines. I once joked with a friend of my father’s who got out of the coal business and into a Limestone quarry that I wanted him to pave ten miles of it for me to do MPG tests.

That's a lot of turd polishing there.

A stock, no polished turds, 318 Dart should have no problem approaching 20 mpg highway.

Oh DO NOT PRELOAD THE BEARINGS use the fsm method.

one time, a million years ago in the mid 70's, i had a 74 dodge 4x4 pickup with a 318/727/3.91 gear 35" tires that got right around 5mpg pulling a super bed load of junk to the scrapper. it was tuned to the max, but to be fair, i had added a "super" bed made entirely of 1/8" plate steel, with 2" oak floor, and a 3" roll bar using 1/4" tube gas pipe. [and that was a real "treat" to bend !] it had 6"&8" C channel cross members, as well as a piece of 6" well casing between the rear frame horns. up front, there was a fabbed 2" push bar on top of some 4" well casing for a front bumper. to say this thing was heavy would be an understatement ! i built a 440 8.5cr with a torque/rv cam, TQ carb/factory hi stall converter, and swapped it for the 318. mileage went instantly to almost 14 ! the 318 was foot to the floor all the time, while the 440 was just loafing. i wished i never sold that truck. it could sure haul the loads, plus push/pull almost anything out of the road !

In town mileage is hurt, cause we are trying to get 4000 ids up to speed, on the highway, it rolling resistance, AND wind resistance. Usually, less filling of each cylinder per mile is the answer, if everything is set up right. If our engines were turbo charged, then lowering the RPM, and increasing the manifold pressure would do the trick. Read what Charles Lindberg did during WWII to help the P-38 guys save fuel.
Two cents.

Dilbert,
I tried the car-push a number of times.
Some of my other cars move real easy, but the Dart takes some effort to get rolling.
I've always found cars are a bit harder to push backwards. Probably because more internal transmission parts are being rotated then I think.
The 3.55 gears make it a tad harder too, but that should work opposite when power is coming from the driveshaft.

Transmission has ATF-4, external cooler in front of radiator. But transmission oil never gets really 'hot' so installing thermostat would be better I think.

I ran with 0w20 synthetic oil in the 318 during the last year or two.
Besides easier acceleration during morning starts it had maybe a very slight noticable effect otherwise.

Thought about putting synthetic oil in the (Auburn SG) diff. Or maybe even a thinner oil, but I that would focussing on .1 of mileage numbers I would think.

Car has cold air intake.

Ignition timing is digital (MegaSquirt) and I have been tuning the timing map for quite a while now. Timing is increasing the moment there is little to no load on the engine.

I guess an app for Android or iOS could now be written
that could generate a BSFC map for a vehicle/engine combo in real time
by driving in different gears at different speeds.

In addition to the data from the OBD-II port,
GPS and accelerometer data could calculate power independent of OBD estimates.
It would be simpler if the roads were level, but GPS could factor in elevation changes and estimate uphill and downhill grades. Google and Apple maps mostly now contain this grade data.

I tried to test the rotating-resistance of two 727 transmissions and a A500/42RH I got laying around by grabbing the inputshaft with 2 fingers and rotate it clockwise;

Both the 727's rotated fairly easy but the A500 took way more effort and required a firm grip to rotate.

Something is not right with the a-500 or the 727s, too tight of clutch clearance or end play or... when a 727 and a500 are properly assembled the a500 shaft is always easier to turn. At the other end of the trans is a different story as you will have an extra set of clutches and more weight on the a500 output shaft but the extra drag there is more than offset by the lower RPM in %99 of cases (for example a 4cyl might not have enough spare power at a low RPM to overcome the extra friction/weight).

All 3 transmissions were used ones. Both 727s are working transmissions and I only know from the previous owner the A500 has 2nd gear 'gone'.
I've also got used A518 (4x4) unit to try out.

Remove the drive shaft and push the car backwards on a level surface.
See how much force it take- put synthetic lube in the rear, reconnect then try it again. You will be so surprised...


The suggestions to correct the tune up & reduce rolling resistance need to be followed...or you are wasting your time.

As far a mpg and rear end ratios...the rpm of the motor at it's cruising rpm [say 70 mph with an automatic] is where the converter's stall speed
should be just below this rpm. If you are always under the stall speed of the converter you are loosing efficiency and gas mileage.

There is an interesting USA Patent for an improved method of estimating the aerodynamic coefficient of drag of a real vehicle out on roads.

Near the end of their description of their aero method, they also describe a neat way to better estimate transmission and differential friction and “stored rotational energy” in driveshafts and wheels.

They jack up and put the vehicle on jackstands, start the engine, engage the 1:1 gear and bring the drivetrain up to a speed. They measure the rpms of the wheels, then take the vehicle out of gear and let the drivetrain coast down to a lower rpm ( but not zero). After gathering this data, they remove the wheels, and re-run the coastdown again without the wheels.

With the two sets of data, they could calculate both drivetrain friction and stored rotational energy if they just knew how much rotational energy the wheel and tires have.

They devised a neat way of measuring this.

Think of Chrysler torsion rod suspension.

These inventors made a “torsional pendulem” by fixing a small diameter steel shaft to a ceiling and welding on a plate to the other lower end of the steel shaft with studs to match the bolt pattern of the wheels.

They attach a wheel/tire to the plate, then twist the tire on the hanging pendulem, and let it go.

The wheel/tire will twist back and forth in a cycle whose twists per minute depends only on the rotational inertia of the wheel/tire/mounting plate, plus the “spring rate” of the steel shaft. It is a easy to build “ I of a wheel” measuring instrument, where I is the symbol scientists use for “Rotation Inertia” of a rotating mass.

Old fashioned mechanical wrist watches have a similar torsional pendulem inside them.

https://patents.google.com/patent/US5686651A/en?oq=5686651

US Patent 5,686,651

They invented a neat way to calculate that a long time ago, F=ma.

I've been thinking awhile back of mounting a simple pull spring weigh and measure how much pull it takes to get the car rolling, and to keep it rolling also.
Forwards and backwards, and with and without the car idling in Neutral, to as closely mimic the transmission's state with oil pressure present.

I have pushed against the rear bumper of my pickup with a common bathroom scale.

It is hard to find perfectly flat pavement so you should repeat such a test in the opposite direction.

My prefered test is to coast down an approximately 4% grade hill and measure the steady terminal velocity due to gravity.
Do this at three or four different vehicle weights and you can estimate the three unknown aero Cd, tire rolling resistance and drivetrain friction loss.

long story here...
my first car was a '79 Grand LeMans when i was 14 in 1991. Nice enough car, factory buckets, and console. 350 chevy from a '73 monte carlo( according to the numbers)
being i had a few years before i could drive it, and being young and dumb, not fully understanding drivetrain " combinations' , i decided to start modifying. i did a comp cams " 268 high energy" cam, dual plane intake/650 holley, and cheap headers, and a custom dual exhaust that my dad paid for as a gift. ( the car was flatbeded to the muffler shop for this, as i still has a few months before i got my license.)
now comes the first drive... should move pretty good with the things i did right? NO.
the thing was a stone. i remember getting passed by a full size dodge conversion van, who looking back now, probably didn't even know i was floored... and it got horrible mileage. BUT it did loaf along at something like 2,000 rpm at 70...
after 1 to many 1 wheel burnouts, the rear exploded. THAT'S when i started to understand it's not just about the engine.... pulling the cover and counting ( what was left) of the teeth, i had to count multiple times to believe what i was seeing.. a 2.29 final drive ratio. being a broke kid going to high school working something like 20 hours a week, for minimum wage, i borrowed money from my father to buy a complete rear from a monte carlo SS. that had 3.73's.
Holy Moly! did it wake that car up! it would burn the tires going into 2nd gear. not only did the performance improve, so did the mileage! i could not go almost 2 weeks before fill up, where as before, it was at least once a week! but hey, premium was only about $1 then!

Those super tall axle ratios were used before the overdrive transmissions became common. I recall Trans Ams with 2.41 and 2.56 diffs. Ma Mopar had 2.21 ratios in their Fifth Avenue cars.

I have got in trouble on forums for writing this, but if you take an engineering class on automotive design, in the sections on transmissions and gearing you will be taught that engineering convention years ago (1930s) developed the term “overdrive ratio” and it did not originally mean a gear or separate unit like a Gearvendors.

Engineers originally had the straightforward thought that:
“Top gear should be set to let the maximum horsepower of the engine get the vehicle up to its top speed on level highways”.

If this was set correctly, the “overdrive ratio” was 1.00
regardless whether the driveshaft was turing at a lower rpm than the engine.

If the the vehicle did not reach its theoretical top speed and its engine was BELOW the rpm of maximum horsepower, then the “overdrive ratio” was less than 1.00 and maybe 0.90.

If the vehicle did not reach its top speed and the engine rpm was ABOVE its rpm of maximum horsepower, the the “overdrive ratio” was a number above 1.00, say 1.1

Books like the Bosch Automotive Handbook have a German engineering slant and still teach it this way in their section on transmissions.

Yes, it is more “word definitions” but one ought to respect the past traditions.
When Watt defined a “horsepower” for his steam engine it became a tradition even if that amount of power would quickly kill even a Cyldesdale sized horse.

Just checked my van rpm to speed, 4.10 2930-50 @ 60 mph for 15 miles on a hand held diagnostic. 5.9 Magnum 2001. Couple of questions, is this a good rpm for that engines "sweet" spot? Also It's got a lock up converter but the rpm, set at 60 mph on cruise, fluctuates from 1888 to 1955 up and down slight grades but the hand held never goes off 60, is this normal for a new lockup?
Take out of overdrive it goes to 2770 rpm @ 60
Thanks

my 2000 dodge van with a 5.9 and 3.92s is close to that fluctuation and it definately locks solid in lock up. It will not hold the speed as precise as my 2011 1500 ram did on the data stream on my scanner or in real life on the freeway running side by side.

I have a set of 3.21s to install, I am positive they will give me better highway MPG.

It has more rpm in overdrive?

"Take out of overdrive"

Interesting, my scanner would stay at 60 then going down a hill would creep to 61 but rpm would go down to 1888. All over the place. I'm thinking the converter is not locking up to well (all new parts, electrical and trans). Will the lockup fluctuate 100 rpm?
I have a set of 3.54 for the Dana that I would like to try. Talked to the Dodge service man, he said no problem reflashing pcm for the ratio change.

I don't know what your combo is, but I have a 2002 Ram 1500 van 5.9 with 3.55's. 255/70/15 tire. The van gets 11mpg. Mine is a high top conversion so I think the limiting factor is the giant sail effect.

It has the Hughes baby cam and EQ heads, magnaflow exhaust and cat. After the rebuild and add ons it still only gets .5 mile per gallon better than the old factory stock all oem van with 155k.

Even switched to electric fan, still no difference. I am about to rebuild the rear end and thinking of switching to 3.92.

Dont waste money taking it to the dodge dealer for a "flash" after a ratio change, the vehicle speed is measured after the gears and will not affect anything computer related changing gears.

I have worked with so many of these I am 100% confident it will improve my MPG.

2001 3500 5.9 4.10 gears 245/75R 16 tires, I get around 13-14 mpg now. 186,000 miles, new chain, fixed the gasket on the bottom of intake.

What about the speed sensor on the trans (where the old speedo cable went)?

ok, i'm still not understanding. " 4.10 2930-50@60 mph."
then you say " take out of overdrive" it goes to 2770@60"
if you take it out of overdrive, the rpm should increase.
or am i reading this wrong?

Sorry I didn't preview the post very well, rpm should of read 1930 in overdrive.

Looking at the manifold pressure on the scanner, or simply hooking up a vacuum gauge, will help you find the “island of best fuel economy” in the sea of engine performance.

Notice that in nearly all BSFC graphs the best spot is at low vacuum but at an engine speed where the pistons are moving less than 1500 feet per minute.

Another way of saying this is:

Gasoline engines get best fuel economy when
the engine is making high torque
without scraping the piston rings against bore walls too fast.

High torque,
Relative 'slow' RPM/speed,
Low vacuum (so, lots of throttle opening).

Not questioning that you know your stuff sir. Just sharing my experience.
Let us know your results.

Thinking EFI on an earlier built car, which ofcourse is lacking EGR;
What would one think of, instead of normally optimizing ignition timing at cruise rpm, now retarding ignition timing instead. Letting the engine get a bit less eficient so more throttle is needed to maintain speed.
More throttle, less vacuum (with same speed).

Would this have a similar effect as an EGR?

Lockup equipped 727, 42/44/46/47/48 are not modulated lockup designs.
You will never get zero slippage as long as you have power coming from the engine and vehicle “resistance”.

When you get too much clutch slippage in lockup you will set a code. 60-100 rom is quite common.

If it takes too long to achieve lockup you’ll set a code too. Once the lockup solenoid is activated a timer starts and it must achieve a certain amount of lockup in a certain amount of time. If you don’t that’s when the code sets.

All part of OBD,

I'm just wondering with all the gear swaps, did everyone install the corrected speedometer pinion.

That's a lot of turd polishing there....no that's a lack of knowledge on your part...and showing it on the internet

The fsm is a poor substitute for proper bearing preload.
Trying to figure out how to make a 1970 automobile go 140 mph without vibration and stopping issues will lead one to figure out how to set up front bearing preload with the proper tool. It does indeed effect gas mileage and proper braking.

Rolling resistance and engine efficiency is the issue here and it does not matter what kind of car it is.

Monday Wall Street Journal has a front page article on getting better MPG from pickup trucks. Author of article seems to believe that simply putting a very small cubic inch engine in a pickup is the majority of the effort. Almost no discussion of gearing and transmissions.

Most authors of articles in the media have a degree in "useless studies" and know virtually nothing about what they write about. What qualifies them as "knowledgeable" is that they know slightly more than the other "journalists" they consort with.

I’d bet a 440 would get better mileage in a fully loaded c-body, than a slant 6 would, all other options being the same.

Absolutely. A small engine working itself to an early junkyard grave is not going to get better mileage than a larger engine that barely has the throttle open to do the same job.

Big engine or little engine, still takes the same hp to go a certain mph, all things equal on the vehicle.

Axle efficiencies come into play. The internals of the transmission [working through a fluid] driveshaft and axle gears [working through a fluid] have to spin at higher rates, consuming more energy.

Lower [numerically] gear sets offer increased efficiencies, this can be seen in the trucking industry by just researching "downspeeding". If you have the torque on-tap, slowing everything down offers a benefit in fuel economy.

By improvement, I am referring to single digit percentages, which may or may not be significant to you. In trucking, it's a big deal. If I turn a 13 or 15 liter engine 200 times less per minute while producing adequate torque, it doesn't take long to realize there is some energy conservation taking place.


For what it's worth, I do work for a Class 8 truck OEM and have spent some time on the subject.

but when the smaller engine makes 1/2 the power the larger engine does, it's going to be working harder at that same hp level.

No, they will be doing the same work, actually the bigger one would as it has to overcome friction from bigger parts or longer strokes or both.

Also the smaller engine has less distance within the chamber for the flame front to travel across. And since the smaller engine will be operating at a lower vacuume leval the air and fuel molecules will be closer together upon ignition and therefore will burn more completly. Goody could probably back this one up as that is the reason why they run engines with just barely enough power to pull the maximum load the maximum desired speed and then gear it to get the load moving.

With my new Holley Sniper EFI setup I can see exactly how much fuel I'm using as I drive down the road. Once you can see exactly how much fuel you are using you can figure out how to improve it.

I have a 5 speed manual transmission in my car and I can see a big difference in fuel use if I cruise down the freeway in 4th rather than 5th. That test is basically the same as changing the rear gear.

I learned a lot about engine performance under different pavement, grade, wind and speeds using this relatively inexpensive add-on trip computer:

http://www.autospeed.com/cms/article.html?&title=The-OzTrip-Car-Computer&A=0639

At the time I bought mine 62 USA pennies equalled a Austrailan Dollar.

After having the Oztrip for awhile I realized I could go beyond the instant MPG and use the trick of first reseting one of the three mileage memory counters,
then watching the Gallons digital readout until it changed by
exactly 1.00 gallons, or 2.00 gallons, etc

As AndyF says above, seeing how fuel consumption changes as you drive is very educational.
Climbing 4% grade hills at the same MPH in different transmission gears is eye opening.

+1
If a bigger engine got better or the same mpg tooling around we'd all have bigger engines in our late model cars...
Throttle open more = better air and less work to overcome pulling air through the tiny straw of cracked throttle blades.

Well there is an argument to be made here.

Generally, cars with smaller engines are lighter - compare a slant 6 to a 318 to a 440. So in this case the "lighter" car would get better milage.

The other piece of this equation is the time to reach a given speed. Generally the smaller, lighter cars will see better economy because they're slower to accelerate whereas the driver of the 440 car probably has a heavier foot - getting into all 4 barrels !!

So the only way to really gauge the economy would be to have all vehicles geared the same, weigh the same and accelerate and maintain the same speed over a given distance.

I strongly suspect the results would be very close.

My car uses 36 lbs/hour at 65 mph in fourth gear and 32 lbs/hour at 65 mph in 5th gear. So that is the difference due to gear ratio.

My rear end ratio is 3.54 and 5th gear is 1:1 while 4th gear is 1.23 so this test is equal to a 3.54 rearend vs. having a 4.30 rear end.

Anyone here on Moparts presently driving a Ford F150 with the 2.7 L twin turbo V6 ?

Does the Ford trip computer allow you to view the MPG at a steady level highway speed?

How many psi of boost is needed to drive in the 60 to 75 mph range on a level highway?

http://www.wardsauto.com/engines/2018-winner-ford-f-150-27l-ecoboost-twin-turbo-v-6

Yes

Yes. There are so many variables but throttle input seems to have the biggest effect on the gauge reading. I can have a wide difference in MPGs at the same speed on a relatively flat highway. I do most of my driving in the city and can get better mileage than I get at times on the highway, if it is not stop and go. If I drive 40-60 MPH on a flat road with no stops I can get MPG readings of near 30 MPG. At 70-75 MPH I generally get low 20s, but at those speeds the road can have more changes which affect the readings. Overall city MPGs average in the upper teens. Cold weather and stop and go traffic can have a large effect on the city readings. I do have 3.73 gears which could affect the highway mileage some and perhaps benefit city driving. Some others have mentioned sustained MPGs in the mid 20s with the 2.7L.

I have an XLT which does not have a boost gauge standard. Higher trim levels have the boost gauge and I'm sure some have added it to their XL/XLT trucks.

Many of the F150 forum members claim lower MPGs with the 5.0, which seems to be the consensus. The 3.5 Ecoboost is between the 5.0 and 2.7 in terms of mileage. The 5.0 with the 10 speed seems to be a better match than it is with the 6 speed.

A factor to consider is where and how you are driving- Long distances at higher speed would be better with lower ratioo
More stop and go low speed- somewhere the higher # ration would be more effiective it would seem

http://www.hotrod.com/articles/1010sr-quick-change-rear-end/

Being able to quickly change diff ratios could answer a lot of questions similar to those in these posts.

In these days of CNC
it would also seems that making
custom planetary gear sets
to go inside Chrysler 46/47/48 OD units
would not be that hard or expensive.

Swapping OD units would just slightly more work than changing
straight cut gears in a Quick Change,
and those extra gears in a Quick change add friction drag, perhaps 2 to 4%.

Thanks, just removed the speed sensor connector on trans checking what you said, speedo still works! It does work off the rearend. 3.54s are going in today!

Update, 3.54 gears are doing fine. Just floats along with very little pedal effort at 50-60 and mph is dead on. Used the state police mile lay off signs on the highway, cruise set at 60, I went 59.96 seconds so that's real close. Filled up today so in about 100 miles I'll check millage, feels like it will be better than 13.5 mpg, hope, hope. Van just feels all around much better, didn't lose any power that I could tell.

Last week I did some very unscientific testing in my '73 Dart (360ci A518, 3.55:1 in a 8-3/4 rear axle).
Tried to measure drivetrain losses with the help of the MegaSquirt ECU and TunerStudio.

Proceded by raising the rear tires just of the ground, put transmission into Drive, throttle it a bit and let it upshift to 3rd and into OD.
Then I let the engine 'idle' with the wheels spinning, making sure the trans stayed in 3rd+OD by looking at the speedometer.

Then I checked the engine-load kPa with TunerStudio.
Did the same with trans in neutral.
Difference in load with transmission in Neutral and in OD was just 5 kPa (30kPa in N, 35kPA in OD).
About 5 kPa drivetrain (transmission & rear axle) loss, at low rpms.

Now I didn't test at higher speeds to see if the difference would be greater.

Interesting test.

Is the kPa that TunerStudio calculates something similar to
“Brake Mean Effective Pressure” BMEP?

With the Oztrip meter one readout is gallons per hour consumption.
When my Magnum 5.9V8 is in warmed-up idle using gasoline without ethanol the Oztrip displays 0.65 GPH.
If I turn the high beam headlights on at idle this will rise to 0.66 or 0.67
If I turn the air conditioning on at idle this rises to 0.71

with such a small change in the numbers one wonders if any of that is voltage drop due to more load?

'kPa' can be seen as an inversed vacuum number.
I could have done the test with a vacuumgauge as well, but the kPa-reading in TunerStudio was more detailed.

100-101 kPa is about barometric pressure = 0 in/hg vacuum = Sealevel airpressure.
50 kPa is about 15 in/hg vacuum
0 kPA is about 29.5 in/hg vacuum

30 kPa = 20.7" vacuum
35 kPa = 19.2" vacuum
So in short, engine vacuum went from 20.7" at idle, to 19.2" with trans in OD.

My MegaSquirt-setup doesn't control fuel yet so I couldn't read any calculated fuel consumption numbers.

Update again, first millage check going from 4.10 to 3.54.
13.1 to 14.6 mpg all around, almost ready for another fill up. I'll average the two this time.

I did 2-hour roundtrip yesterday with my setup (360/A518/3.55); 13.3mpg.
Average engine rpm was 2200-2300rpm between 65-70mph.

Will probably be changing to 3.23 gears soon and try to do a similar test.
I think the small gearchange will be less effective and probably not even "worth it" for mileage.

Last nite fill up, third since change, 14.91. A lot from the 13.1 with 4.10s. 100 miles on interstate at 70-75, rest around town from 25-60. Rpm is about 1700 at 60 iirc (have to use the hand held unit, no stock tack)

Along with the MPG
test how steep a hill you can climb in top gear without a downshift.

Many customers will complain that their vehicle is “gutless” if it will not climb a 4% grade interstate highway hill at 75 mph without downshifting.

Eventhough I live in a super flat country, the previously installed low CR 318 in my daily would have trouble maintaining speed with some gradients in OD with a 3.23 gearing in the axle.
After a swap to a digital ignition with a better curve and 3.55 gears the problem was gone.
Now with the 11.3:1cr 360ci there are no issues at all with changes in road altitude.