bogdan

Some say that automatics are better on fuel than manuals in normal driving conditions. Is it true?

Nicole

Automatic here:

16 mpg around town or short distances
22-23 mpg when traveling with mainly rapid freeway driving

I don't think there is a significant difference to my previous GT - particularly not on the freeway.

Ron_H

Mine is an automatic and exactly mirror's Nicole's experience. 16 in town and 20 - 22 on the highway if I stay below 100 mph and drive it like is about to break. If I drive the way it is intended to be driven on the open road, I get about 18 to 19. And if I get anywhere near the desert, I can almost watch the guage drop........as my face cracks from the grin.

zoltan944

with a manual
17-19 around town (depending on my driving that fill up) and 26mpg my last drive on freeway.

Mike Frye

5 speed here:

17-19 around town. I haven't had a road trip in a while and didn't log mileage when I did, but I'm sure it's in the low 20s.

My new fuel chips are supposed to be more fuel efficient, but I have to say my mileage will suffer if I don't stop winding it up in 2nd and 3rd before shifting.

fraggle

I think it more depends on your final gearing. With my 2.20 I get 19 to 20 around town and 25 if I keep cruising at 70.


23mpg at 90mph. Errr estimated. Yeah that's it.

Ispeed

I got 25 on the highway to SITM, going 75 mph with the 2.20

I wonder how good it would be if the "batch firing" was changed to individual injectors firing when needed...

Lizard928

You wouldnt see much of a difference with sequential.

But if you lean it way out, you can get very impressive numbers.

When I had the setup on my 86 engine with the 2.20 and a 27.1" rear tire I was able to get over 30mpg. Every stop we made with the rest of the group I was always a few GALLONS less in fuel to top up. And we were not going slow either.
But at cruise, I was able to run 17.5-18:1 AFR with no real load on the engine. Having disassembled this engine there is no sign of any detonation or preign. Not in the bearings, rings, pistons, heads, etc.

bogdan

Very interesting...I have also a Alfa Romeo Brera 3.2 (260 bhp) that gets 11-12 mpg around town with ease. Unlike italian performance cars , Porsche makes performance cars with decent consumption.

Mike Frye

Remember, the whole reason they scaled back from a 5L in the first iteration was the gas crisis of the 70s. This may have doomed the 928 from the start (in many people's minds) but even after things freed up, fuel consumption and emissions were a major issue.

Just another example of how these cars were ahead of their time.

dr bob

My mileage is consisten with others-- 17 in combo driving, 20 on the highway. In sustained highway cruise mode, with a gentle foot, I can sometimes squeek 22. This is auto with 2.54 fdr. This is also with Cali gas. Real fuel inproves those numbers by about 8%. I can map the mileage differences between seasonal fuel blend changes here.

Colin, With modern ignition it's possible to run those lean A/F's in low load/steady state operation. You really need to have a drive-by-wire option on the throttle to make all the tailpipe numbers work with that though. On pedal depress or any anticipated or measured load increase, the mixture needs to go closer to ideal -before- the load is actually added. That would do a lot for detonation/pinging, but more importantly it would eliminate the heavy puff of NOx at the same time. This method is what allows decent mileage from the bigger BMW V8's, for instance. The lack of instant throttle response on those cars, at least the early ones, is a fringe benefit of the technology. The newer models, along with those from other mfrs, are a whole lot better than the early ones. I credit a lot of the improvement to faster computers that aren't saddled with Vista...

Giovanni

I averaged 20 MPG going to SITM at 80 mph and 19 MPG with lots of spirited driving while at SITM.

soontobered84

I got 21+ on the way back from California at close to triple digit speed

Lizard928

Dr Bob,

Yes I do agree, and this was with standalone EFI, with EDIS-8. And yes I was richening it very quickly with TPS/MAP blending and from datalogs I was able to completely remove any leaness from when I first stepped on the pedal.

And I hear the comment about Vista it is a pig. And I just love how it randomly put itself into spanish keyboard mode.

edit:
Forgot to add, I am not really worried about what comes out of my tailpipe on that car, I had two maps, one for emissions, one for driving.

oups59

With my AT, I managed to get around 11L /100 Km so roughly 21 MPG