28 MPG in a 126

[pmckechnie]

As requested, I am going to give some of the details about how I got over 28 MPG on a trip from NC to FLA in a 84 500SEL. We drove about 2000 miles over a 4 day peroid.
Now, to start out, I have heard of 300SDLs geting over 30 mpg so I was thinking maybe I could do it in a gas car. You have to put up with some things (rough ride, poor idle, poor performance at low speed) which I will explain later. Here are the highlights
1. Service with synthitic oil front to rear including P/S, trans,engine,diff.
2. Tires inflated to max cold pressure listed on the tires. (rough ride).
3. Ignition set as high as possible without spark knock using prem fuel.
4. MSD Ignition with plugs gaped at .60 inch.
5. 2.5 inch exhaust front to rear with free flow exhaust. Some of you have heard it and it is not that bad when inside the car.
6. Fuel trim set lean at 2500 RPM. This engine doesn't have a computer.
7. Engine has Euro heads and cams.
8. Now this is the kicker. I advanced the cams 8* at the crank.
9. I would draft big trucks when ever safe.
10. 195*f thurmostate to keep engine hot.
11. 95 % Interstate driving.
12. NO agressive driving. (that was the really hard partof the trip)

What a lot of the above did was make the engine more efficent at 2500-2700 range but hurt it at low rpm. Idle was rough, high speed was powerful, and mid was efficent.
Did I leave the car like this, No Way. I usually get around 20 MPG on a trip but the car runs so smooth I just love it. The above was just to see if it could be done. I proved to myself that you can move the "Sweet Sopt" around for different conditions but you can't have them all without modifications morethan what was done above. Some of these things are still there but some are not.

OK, let it fly, I am ready to defend myself, and answer any questions if anyone has any.
Paul

[t walgamuth]

1. Have you checked your odo against the mile markers?
2. How many gallons of fuel did you use? INclude all addetives.
3. How many miles did you drive?
4. Will you take a polygraph?

It just does not compute.

Tom W

[Dee8go]

Did you go fishing while in Florida? If so, how large were the fish you caught? How 'bout the ones that got away?

Thank you.

[t walgamuth]

Originally Posted by Dee8go

Did you go fishing while in Florida? If so, how large were the fish you caught? How 'bout the ones that got away?

Thank you.

that is the real question.

Tom W

[Dee8go]

Actually, I was really disputing Paul's claims. I just enjoy being a smartass and I saw my opportunity . . . . .

What do you think IS the best mileage possible in a gas 126?

[t walgamuth]

The best I ever got driving 65 was 19 something. My car was stock. His with the euro heads and so forth if it has the pistons too would do a bit better but would require premium probably negating the advantage.

Actually after thinking it over, I seriously question whether the car would run at all with the "modifications" he lists.

Tom W

[Dee8go]

Okay. Well, how big do you think the fish might have been ?

[gmercoleza]

In my 380SE I consistently get 16mpg around town and have never done better than 19mpg highway. I don't see how this is possible, even with the more powerful engine. My 560SEL never got better than 20mpg highway.

[Dee8go]

You raised a good point. Would a larger-displacement engine actually get better fuel economy cruising at highway speeds that a smaller one if all else was the same?

I would assume not, but it's only an assumption.

[pmckechnie]

I don't fish, but if I did I wouldn't be able to find a truck big enough to haul it back home.
Please tell me which modifications would prevent the car from running. I'll have to go scold my 500 and tell it not to do that again because it is impossible.
Paul

[Benz Mercedes]

My well tuned 420 sel gets 22mpg at 65 mph , I've checked this several times by putting 10 gallons in when the low fuel light goes on and I can go 220 plus miles on highway trips until the light goes on again . I'm happy with this milage.

Ben

[t walgamuth]

Originally Posted by Benz Mercedes

My well tuned 420 sel gets 22mpg at 65 mph , I've checked this several times by putting 10 gallons in when the low fuel light goes on and I can go 220 plus miles on highway trips until the light goes on again . I'm happy with this milage.

Ben

That is not a reliable method of checking mileage.

Tom W

[t walgamuth]

Originally Posted by pmckechnie

I don't fish, but if I did I wouldn't be able to find a truck big enough to haul it back home.
Please tell me which modifications would prevent the car from running. I'll have to go scold my 500 and tell it not to do that again because it is impossible.
Paul

Leaning it enough to affect mileage and advancing cams? Just guessing really.

A gas engine needs from 1/13 to 1/14 parts fuel to air to run. Richer or leaner will result in real problems. Turning 5 liters of air for every other rotation of the motor will result in a very predictable amount of fuel being used. Since I know what a 500 motor will do from personal experience you telling me that you got 40% better fuel economy causes great scepticism. I never assume anybody deliberately tells untruths so I must assume that a mistake was made somewhere.

I don't believe that you have somehow discovered a magical formula for excellent fuel economy in a 500sel.

Tom W

[pmckechnie]

What started the advancing cams idea was the new engines with VCT (variable cam timing). The exhaust cams are advanced much like the ign timing is advanced at higher RPM. It is not practical to just advance the cams and leave them that way because it greatly effects other aspects of the engine operation, mostly idle and low rpm. Plus, I had to advance both intake and exhaust since I only have one cam on each side. I put the cams back at 0* after the trip for this reason. Tires at maximum pressure caused very rough ride and wear problems. I put them back to the recommend pressure shown in the gas cap door. My background is in computers and I have a reasonably good understanding of how the on board computers work and can tell you they run the engines lean under certain conditions, such as high vacuum. I didn't run the engine in an extreme lean condition but adjusted it using an O2 sensor to .3V at 2500 RPM or so under high vacuum conditions. This is a little lower than the .45V which is considered ideal. The euro CIS on this car has no provisions for mixture control so some aspects of performance were compromised by the lean mixture, but not the constant road speed. Remember, all of this was an experiment to see how much mileage I could get. Did it turn out to be a magic means to get more MPG. No. I just used some of the advances designed by the manufacturers. Mine were crude but cheap. The MSD system I already had was used to fire the plugs set at .60 in under these lean conditions. The plugs are set to .40 in now and the engine never misses a lick. Try that with a stock setup. Drafting trucks is not recommended but it does help with mileage. And also remember, most of this 2000 miles or so was on flat ground, no stopping except for fuel and food and nature calls. Did I learn something. Yes, it can be done. Would it be practical, no. Will I do it again, no. The only thing I can say now is if you don't believe it, try it your self and see.

[Dee8go]

So, Ben, your fish were not as big as Paul's fish, eh?