gas mileage

justinshelton · Post by **justinshelton** » Mon Jul 28, 2008 8:42 am

Hi, Guys:

I took the 411 on a long drive this weekend for a camping trip. Boy, does that car ever handle better with the trunk fully loaded!

I got 22 and 23 MPG at cruising speeds of 65 - 75 on the US131 (basically interstate highway). I have the 3-speed auto and a Pertronix and newish spark plugs.

I was hoping to get over 25 MPG - maybe at 55 or 60 on a long trip I would.

- Justin

raygreenwood · Post by **raygreenwood** » Mon Jul 28, 2008 12:00 pm

All of the type 4's...auto or manual...should get their best milage in teh 70mph range. Its the final drive ratio.

Is this fuel injected?

You should be seeing on an average state of tune about 30-32 highway and about 22-23 city. I have gotten as high as 38-40 with the four speed.

What is the condition of your compression, what is your state of valve adjustment, what plugs are you using and what is your timing set at?

There are a handful of other adjustments that help this....like corrrect TPS adjustment...and possibly some modifications, getting rid of the pcV valve and going to a fixed restriction system.

Timing is best at about 10-12 BTDC at idle ...hoses on....and 27btdc at 3500 rpm with hoses off. To hold the idle setting you will need to tighten up a few things in the dizzy.

If its original injection, its very sensitive to valve adjustment. It must be spot on. I find it best to adjust cold...and recheck and even up to about .003" hot.
Also check for leakage of all hoses, o-ring at TB, runner boots, injector seal, proper fuel pressure and proper resistance at trigger points. Ray

justinshelton · Post by **justinshelton** » Mon Jul 28, 2008 3:09 pm

I just did the valves three weeks ago, gapped cold. I've got new hoses all around on the engine. There's a new, rebuilt distributor with new cap and wires. I forget what plugs are in there . . .

I have a question about best mileage at 70 MPH. Since this is a 3-speed auto, isn't the engine turning the lowest RPMs and lowest gear at about 35 - 37 MPH, just after it shifts from 2 to 3?

justinshelton · Post by **justinshelton** » Mon Jul 28, 2008 3:12 pm

Forgot to add, this is stock from-the-factory FI set up.

raygreenwood · Post by **raygreenwood** » Tue Jul 29, 2008 5:02 am

Who ever said lowest rpms have anything to do with gas milage?....what a load!

The media has been beating that drum since 1974.

By that respect.....you are getting your best gas milage sitting in the garage.

Gas milage is also a combination of loss of efficiency due to rolling resistance, driven gear versus final drive...versus wheel circumference....and also is based for a large part on where the best torque and power is produced by design on any given engine.

State of tune matters, camshaft matters, exhaust matters.
Also many fuel control systems are more accurate a different rpms, velocities and load factors.
Having logged about 1/2 million miles in type 4's....I have found that when properly tuned, with stock wheel circumference, decent gas and the aerodynamics you are stuck with....they get their best milage around 70 mph.

In traffic with rpms down low in third ....like at 40 mph....the positively guzzle gas in comparison.
The combination of how D-jet works and everything else....combine to make keeping rpms up and the tranny in 2nd in the speeds you suggested...necesary for good milage in the city. Ray

Lars S · Post by **Lars S** » Wed Jul 30, 2008 8:04 am

Just happened to read a magazine article from April 1974 where VW412 Variant was rated by EPA as the most fuel economic car in its class (1136 - 1284kg), having a gas milage of 28mpg (0,84 litres per 10km).
Mazda RX2 was worst with 10.6 mpg.

Lars

ubercrap · Post by **ubercrap** » Wed Jul 30, 2008 10:14 am

Lars S wrote:Just happened to read a magazine article from April 1974 where VW412 Variant was rated by EPA as the most fuel economic car in its class (1136 - 1284kg), having a gas milage of 28mpg (0,84 litres per 10km).
Mazda RX2 was worst with 10.6 mpg.

Lars

Which engine/trans. combo was that? AFAIK all '74 Variants in the U.S. were 1800 L-Jet FI/3 speed auto.

Lars S · Post by **Lars S** » Wed Jul 30, 2008 12:12 pm

The article dont thell about the engine/trans but since EPA is an USA authority it ought to be the US version.
Also nothing is mentioned about the driving pattern but anyhow it suprised me that the 412 was best in is class.

Lars

raygreenwood · Post by **raygreenwood** » Wed Jul 30, 2008 1:24 pm

It might be more helpful to know what other cars were in that class.
Not very many American cars of that era would have been in that class....due to weight alone. Ray

Lars S · Post by **Lars S** » Thu Jul 31, 2008 5:40 am

Continuing reading old magazines...maybe the 411/412 gas milage was not so bad after all:
A swedish road test at constant speed with a brand new -73 412LE Coupe Automatic, made in November 1972 gave the following gas milage:

30mph - 36,4mpg
40mph - 33,8mpg
50mph - 29,6mpg
60mph - 24,9mpg
70mph - 22,5mpg
80mph - 18,5mpg

The 412 fuel consumption was told to be "extremely low on the highway to be an automatic, but more normal in town conditions".

The close to 30mpg figures when cruising at 50-60mph are at the same level as i get with my -73 412 (manual).

Lars

raygreenwood · Post by **raygreenwood** » Thu Jul 31, 2008 6:22 am

A lot of this is due to the factory level of tuning of the MPS on these cars...and a few other details like tires....and the exhaust.

The factory MPS tuning was all over the planet. This is due in great part to the level of tuning of a few other details.

(1) If the throttle valve switch is not spot on...or has slop in manufacturing (many did)....you get a flat spot unless you leave it overly rich on MPS settings. This leads to a throttle-on/throttle-off modulation issue at highway speeds...and can lose you about 2-3 mpg.

(2) The wide variation in fuel pressure stability in the factory fuel pump and regulator system. This leads to s more difficult time tuning the MPS under certain conditions....again wasting fuel at certain speeds especially at acceleration.

(3) Wide ranging valve adjustment specs.

(4) poor atance with headwinds due to highfront end and high tire sidewalls. Tire choice and stance alone I have found is good for about another 2-3 mpg.

(5) Fuel quality issues (octane) and ignition issues (mostly timing slop). Especially on the higher compression 1.7L engine...I have never found one that did NOTrequire preium...and good premium at that. Its is listed for a minimum of 98 octane. Even atconversion from poor fuel in those days to now....it still requires 93 octane for best tunability.

(6) The factory PCV loses a couple mpg right off teh bat and decreases tune ability of the MPS.

I have always bee nastounded at how poor the actual fuel milage ratings of these cars were.
In the early days with my firts 411....I got 18-19mpg in the city....but had numerous small performance glitches that many passed off as part of the odd characteristics of the car.
Mind you....everyone who told me this....worked at a dealer....and at no time in my life have I ever found anyone at any dealer who had actually adjusted an MPS. If it was out of spec...they swapped it.

Once I started working on the MPS....performance improved....milage improved. That in turn started pointing out other little glitches as the tuning of the MPS started outstripping other areas of tune....like ignition timing stability....fuel pressure stability ....and TPS issues.

30mpg on the highway should be a loose standard for this car with its excellent torque band, gearing and low weight compared to many other cars. Ray

Lars S · Post by **Lars S** » Thu Jul 31, 2008 6:47 am

Can confirm the bad city milage Ray, in the test they only achieved 16mpg with the 412....
Also the MPS adjustment is wery critical; I had my crankcase flooded by petrol due to a bad MPS in one of my 411:s.
Anyone intrested in the MPS should take part of the excellent info at:
http://members.rennlist.com/pbanders/ma ... sensor.htm

Lars

raygreenwood · Post by **raygreenwood** » Thu Jul 31, 2008 12:15 pm

Yes. Brad has an excellent site. There is alot more more active driving tuning that can be done even than what the factory lists as "possible". It depends on what you are willing to modify...and if you make any other improvemnets to the engine. Examples would be oversized valves, better cam and exhaust, better ignition as well as mods to the TPS and a greatly improved harness and a ballasted or augmented tPS.....each one of these mods allows slightly better and tighter tuning parameters to the MPS. Ray

albert · Post by **albert** » Thu Jul 31, 2008 3:36 pm

hy,,ray,, many persons do error witch the 412 gas millage,,, you see wend we doo the comparaison,,we forget ,, the impérial gallon and the usa gallons are différent,, the usa gallons is 1/2 pint more smaller ,,the best test is witch the litter,, we obtain betther présition,, plus we can have a signifiant différence witch the alltitude degrées in the différent word contry,, plus wend the weather is appx 70 d.f. or 20 cell. we have a betther millage ,,plus all you have geeve beefore ,, durring the year 75 witch my 412 -74 ,,4 spead ,, i have cross the usa in april and for 3 k. milles my adverage was 40.5 milles gall,, ( usa gall. ) or 45 m.g. impérial gall. wend we respect the speed limit ,,and my expenses for all that ride was ( 100.$) if my mémory is good the gas was 25.cents gall.poop what différence witch tooday,,,albert

raygreenwood · Post by **raygreenwood** » Fri Aug 01, 2008 2:16 pm

Yes Albert. In general....if you can do "real" long distance highway driving with constant speed...high 30's up to 40 mpg on a well tuned car was common.

One of the problems I was getting at with the tuning of the car is this: If you have driving that causes you to have to move the gas pedal too much....it will eat gas. Part of this is in the calibration and sensitivity of the throttle valve switch.

When your car has that "bucking syndrome" with D-jet.....it is eating gas. This was common at very small throttle openings on D-jet. This is because the TPS was constantly slipping in and out of either deceleration fuel cut-off or back into acceleration fuel on...but with the switch wiper on no contact that would give you fuel...because of a combination of the factory adjustment and built in slop. It was a dead spot. So to get past the dead spot...you unconciously learn to push the pedal slightly further.

If your car is adjusted well...you should be able to get 38-40 mpg at 70 mph.
Yes..you can get slightly better as Albert notes on some vehicles at lower speeds...say 55-60.
I found that issue went away when i got rid of that nose high issue with the front end. I think most of the losses at 70 mph are drag related. Ray