Porsche Enthusiasts Club Forum

Great news, after 500 miles since overhaul average mpg is showing 25MPG now

Yep, that's exactly what l got from mine in mixed driving.

Hi
can anyone explain why in the original sales brochures and in the owners handbook the s4 auto returns a better mpg figure than the manual transmission. i have a manual s4 and get around 26 mpg. I have always thought a automatic car used way more fuel than a manual equivalent.
cheers Grahame

I think the mpg figures vary slightly by year (I only have the '84 figures to hand) but the biggest difference is usually in the simulated urban driving. My best guess for this effect would be that the auto is much "smoother" in stop-start conditions - you only have to give it a small amount of accelerator to get it moving whereas the manual has to be revved much higher to pull away cleanly using the clutch and, once moving, the auto is happy to trickle along at low revs but the manual struggles a bit if the revs are too low.

Other factors to consider are that the power loss in the drive train due to the torque converter are probably smaller percentage-wise compared to a smaller car with a less powerful engine so that effect is less noticeable and the fuel consumption at constant speed is affected by the drive ratios in the gearbox - it maybe that at the speeds chosen for the test the engine in the manual is running at a less fuel-efficient part of the curve; the official mpg tests are a very artificial situation and often the real-world figures experienced are quite different.

If that is the case the Porsche gearbox almost certainly has a lock up converter.

IME the lock up converter in any ZF 4HP22 car I have driven is 55MPH (I have one fitted in my Stag, along with previous Jags and Volvos I had coming with the same 'box). With the converter locked up speeds above this make the MPG comparable to moderns. If you do have the ZF 4HP22 you chaps do know that it is not meant to revved in Neutral or Park?

To make things very smart, many modern cars have converter lock up in 3rd, 4th and 5th (My old Mondeo V6 had this) . Now I thought 24MPG around town without trying too hard was good going.