Driving (MPG minded)

[MPGmustang]

How do you drive with a vacuum gage to increase MPG?
my setup is IN SIG with added tach and vac gages... 65 mustang
My max vac is 16, 15 most of the time 21 decellerating, and 0 floored...
I like to drive in the 5-6 vacuum area when I accelerate, but I'm not even hitting 20mpg
I've been soft on pedal on purpose, and I still get 17-18 mpg... jack rabbit starts and I get 16mpg... (all street)
Down Hill in AZ I'll get 25, or 20... same speeds, 91 gas, weight, tank filled to brim (I can see gas in filler neck) (highway @80 mph)

never got concurent readings... almost ready to go on a 1 gallon jug of gas and try it that way...

 

[The Plankster Prankster]

your vac readings seem a bit low overall. a healthy engine ideally idles at 20". hows your timing? bumping it up a few degrees (if you can without getting into trouble) will help with both vac readings and economy.
my LTD idles around 18 or in gear thats 16, and decelerating i've seen as high as 26 (closed throttle, 3rd gear at 70-75mph). and at 4200lbs i manage 18-21 mpg depending on conditions (highway or stop and go). note that is with the bent 6 so not a true comparison, but still.
i'm assuming your gage usually/always provides a steady reading? if it were a shaky reading, i'd be more concerned about problems deeper in the engine, but as that isn't the case, timing is the biggest suspect

 

[MPGmustang]

the engine is not stock, the cam is 264/274 with 110* lobe centers. so I don't get stock vac numbers...

timing is as advanced as I can get without ping... atm ~11*

maybe to change timing I can advance the cam...

but i'm mostly trying to find out if i'm to drive with most vac possible or lowest rpm possible, or lowest rpm and highest vac or high vac with higher rpm... i've done some trial and error, but never got the same reading

the gage is very steady, when not idle'n. for deeper problems I hope not, it's a brand new rebuild < 5000 miles.

 

[The Plankster Prankster]

ok, i don't know enough about cams to give any relevent advice on that side of things....

as for driving style, you should get the best results by keeping the RPMs low (within reason) and from there try to keep vac readings high. natually, this is not a practical combination for climbing hills, for which i would be in a gear suitable to get up the hill and always try to increase your vacuum readings (creep off the gas a little) without killing your speed. its a fine balance, but you'll get a feel for it

 

[CZLN6]

Howdy MPG:

I know I've read it, but I can't remember which 1100 you are using and what vacuum signal are you using for vacuum advance to the DUI? Also what rear gear you've got? My guess is that you may be lugging the engine, which creates a very low vacuum signal to the carb and to the vacuum advance; calling for more gas from the carb and less advance from the vacuum advance.

Vacuum guage driving for economy works best at steady speeds. I'd suggust that you start by graphing vacuum readings at steady rpms/speeds in 4th and in 5th gear. Say 55 mph, 65mph and 75mph in 5th gear. Do the same in 4th gear. You may find that you get better mpg in 4th gear, again, depending on your rear gear ratio. A 5th gear OD with a stock 3.00:1 rear gear may be too high for your engine/vehicle combo.

The best mileage is usually achieve at the highest vacuum/lowest rpm. But, if the load at low rpm causes vacuum readings to drop so will mileage.

Keep us posted.

Adios, David

 

[ludwig]

The cars used in the Mobile Economy Run competition of the 1950's were bone stock, taken off lots in LA, and fitted with nothing extra but a vacuum gauge where we would put a tach: right in front of the driver. They drove on open roads and through towns during the daylight hours.

The drivers worked to keep the needle as high as possible and as steady as possible. They practiced this by pre-driving the route with other new, stock equipped cars. HIlls were a special problem, but they did the same thing as on the flats: keep the needle steady and high. That meant that they would have to ease up as they climbed the grade. They could not (legally nor by the rules) take the car out of gear on the down grade. In town, they braked gently, far in advance of signs and lights. Then they feather footed the gas on takeoff. They would also time their approaches to lights so that they did not have to brake or make up much speed.

Naturally, this was unbelievably irritating to the drivers behind them. But hey, how much gas do you want to save?

 

[JackFish]

timing is as advanced as I can get without ping... atm ~11*

That seems very low.

I have the same cam with 112LC. It does seems kind of lumpy under 900rpm.
I'm still tuning it but the vacuum is unsteady at idle too, around 10hg or so.
Anything off idle is pretty smooth though.
14 or 15hg seems to where it sits at running rpms.

 

[rickwrench]

Driving 60mph vs 80mph on the highway will save you -at least- 4-5 mpg. Maybe a lot more, depending on your cruise rpm and torque peak. Cruising at 80mph requires more than twice the hp as 60mph.

Link to handy aero drag calculator:
http://www.assassinracing.com/tech/hors ... calc.shtml

Falcons and Mustangs have horrible aerodynamics. Figure about .45 for cd and about 25 sq. ft. for frontal area. But regardless of drag numbers, cutting your speed 25% (80mph-->60mph) will cut you required cruise hp in half.

I drive like an old man on the highway, usually. When I'm doing the economy highway thing, I stay in the right lane, turn up the tunes, and ignore the people blowing by at 80. Takes some practice to drive slow and steady, but it doesn't take long to get used to not being the fastest guy on the highway. What's the hurry? I just left 10 minutes earlier when I commuted. Saved me about 20 gallons a month.
Rick(wrench)

 

[ludwig]

Takes some practice to drive slow and steady, but it doesn't take long to get used to not being the fastest guy on the highway.

I learned to drive the family car: 1954 9 passenger Packard limousine. My father told me that a chauffeur must not jolt his passengers in any way when driving. I learned to accelerate deliberately but not hastily, to take the turns at a very moderate speed and swing wide to not scrub the rear tires and drive by looking far down the road to avoid having to brake sharply.

Boy was I disappointed when I rode in a "professionally" chauffeured limo in LA. The guy drove like everybody else. His car was just bigger.

 

['68falconohio]

When I trashed my right ankle last summer I noticed my Falcon ran much cooler in stop-go traffic and I'm sure fuel mileage increased as well. When it hurts to lay into the throttle quickly or stop abruptly(no Pwr Brakes) the wallet hurts less.

MPG', are you driving in a lot of elevation changes?

 

[MPGmustang]

Prankster: driving style what's that? jk... I've been taking it easy for the past 3 weeks and still got 16.2mpg (most recent)

David,
1100v... sig is manifold vacuum to DUI, my final gear is 3.27 (according to tag on housing and my own turning/count)
I can only gues taht I am... the power band doesn't start till roughly 1600 rpm, in 5th gear @ 50 i'm 1600-1700 rpm, so maybe if I advance the cam 2* might help bring the power band sooner.
my 5th is the 0.79 ratio, not much but just perffect @ 65-70mph, ~2400rpm
maybe I just need to hold the foot more steady...

Ludwig,
makes sense, i've actually timed my lights to and from work very nicly, drivng the same route 3+ years now I got a feeling on how to keep going with no stopping, maintaining speed is easier and mroe economical than getting back up to speed... but I still hit a red light here or there... not bad for the 20+ lights between work and home IMO. (10 miles)

timing is as advanced as I can get without ping... atm ~11*

That seems very low.

HAHA! yes it's low, cause you have a higher elevation and colder climate, letting you run more timing. heat is a killer here in AZ during the summer, winter here is like your late spring... except more dry
When I was up in flagstaff (@7500 ft) I was able to run 18* and still not ping climbing huge hills... on the way back I started pining and had to pull over to retard it, 11* was the 3rd try (@2100 ft)

Rick:
Thanks for the calculator!! and the numbers on the mustang, i've been looking for them.. that link is awesome! i'm going to have to try that next time i'm on the road, for the the fun of it...
I put in .45 in DC, 25 sq ft, and 2700 lbs, (should be the car only, and if i'm on the road I guess 3000 is more than adequate)

Ludwig: I'm going to have to get a longer shifter handle then (I see my passengers rocking back and forth, most don't notice it until I mention it )

68falcon: My driving is all flat, AZ is really good for older cars as the road is smooth and basically new,

Over all to use lower RPM range I will have to advance my cam 2* more to get a better range for driving, maybe I can do that christmas break, defenetly not in a hurry, but still a good thing to try, will need to get my cam degree kit.

Thanks to all who posted!
Richard

 

[bubba22349]

never got concurent readings... almost ready to go on a 1 gallon jug of gas and try it that way...

Yeah there can be so many variables! To cut down on some I use the same pump each time and also at close to same time of day (fuel expands and contracts with the temp) I set fill at slowest auto setting let shut the pump off and not top off. Drive the same distance loop in the same direct each time and as the old timers used to say drive like you have an egg between your foot and the gas pedal! If you want more accuracy than that than you are right go to separate 1 gal. tank with shut off (start with a dry carb too) and navigator to use a stop watch to time speed and distance

 

[MPGmustang]

so here are some numbers...

4th @ 47mph = 2200rpm & 14hg (accel @ 12hg)
5th @ 47mph = 1600rpm & 11hg (accel @ 8hg)

these maintained speed (and saw what I needed to accel like an 'egg')... which saves more gas?

 

[MPGmustang]

When I trashed my right ankle last summer

here at first i thought you said axel....

 

[bubba22349]

so here are some numbers...

4th @ 47mph = 2200rpm & 14hg (accel @ 12hg)
5th @ 47mph = 1600rpm & 11hg (accel @ 8hg)

these maintained speed (and saw what I needed to accel like an 'egg')... which saves more gas?

With these numbers you may not be set up for the best in MPG!
What is the finale drive ratio i.e. the rear axle gear plus rear tire dia.?

"(saw what I needed to accel like an 'egg')... which saves more gas?"

Just a figure of speech you use the lightest throttle pressure to move the car yet keep the vac. reading at its highest possible reading! As was said in above post it will take a bit of practice

 

[MPGmustang]

tire dia = 25in
rear = 3.27
5th = 0.79
4th = 1
tire circumference = 78.53 inch


tires are 215/65r14
maybe 70... i'll have to confirm...

 

[bubba22349]

tire dia = 25in
rear = 3.27
5th = 0.79

I would say your speedo is way off than! At 1200 RPM in 5th (0.79), a 3.27 with a 25 inch tire = 69.1 MPH

 

[The Plankster Prankster]

I would say your speedo is way off than! At 1200 RPM in 5th (0.79), a 3.27 with a 25 inch tire = 69.1 MPH

i like to check by cruising down a highway, taking note of the odometer reading at a certain milepost, then taking note again at a milepost 10 miles from there (or whatever number is convenient), and doing math from there. i've had them so far off i hardly had a clue how fast i was going

 

[bubba22349]

Yeah that is an excellant way to check it I have done that a few times too

 

[rickwrench]

tire dia = 25in
rear = 3.27
5th = 0.79

I would say your speedo is way off than! At 1200 RPM in 5th (0.79), a 3.27 with a 25 inch tire = 69.1 MPH

Two tens for a five anyone?

3.27 x 0.79 = 2.5833 final ratio.
25"dia. x 3.14 = circumference of 78.5", distance traveled per wheel revolution.
78.5"dia / 2.5833 final ratio = 30.39" traveled per engine rotation.
1200 revolutions x 30.39" = 36,468" traveled per minute.
36,468" x 60 = 2,188,080" traveled per hour.
2,188,080" / 63,360" (one mile) = 34.5mph

1600rpm = 46.05mph in 5th in his vehicle, with a tire exactly 25" diameter.

Rick(wrench)