Strange MPG figures

I'd have said that the MPG figures were extremely optimistic. In all the SD1's I ever owned, I never got 37MPG out of any of them despite owning everything from a 2300 to V8.

It's at a constant 56 mph - not used today. The 75 mph figure seems about right though.

so you never had a 2 litre one ? You haven't lived, they were really gutless, despite a 4.6 to one diff (the useful bit I needed them for)

Mrcheerful

In news: snipped-for-privacy@news.individual.net, Conor wittered on forthwith;

I got somewhere around 35 mpg out of my SD1 Vitesse (manual) on a long run quite regularly.

As for auto vs manual transmission mpg in town it's not that unusual for old autos to be slightly better on fuel. The Mk2 Granada 2.8i auto is another example - IIRC the auto did something like 18.5 mpg (urban) and the manual was 17.8 or summat.

I drove one at a scrappies once. The motor was liberated and put in a Sherpa recovery truck where I swear it went quicker.

The message from Conor contains these words:

My uncle used to make glider winches with V12 jag engines with auto boxes.

I don't remember them being that bad. A mate used to sell for Henleys and often brought their hire one home at a weekend. Auto too. It was nothing like as slow off the mark as you'd think - but I never drove it out of town.

Larger engined autos tend to change up at more economical revs while in a manual there's a tendancy to rev a bit more? In any case what was the procedure for arriving at the results?

You're missing the point, though: that's a snapshot at a constant 56 mph. You would have to drive at a constant 56 mph on a level road to obtain this. Most machines obtain somewhere between the 56 and 75 mph on a run.

Hmm. Gearing maybe: wasn't the old Urban figure achieved by accelerating up to 30 mph (or close) as quickly as possible and then coasting down? Perhaps the automatic reaches 30 in first and then it'll effectively be idling on the way down. The manual perhaps needs second... and isn't as economical on the way down?

Also, these are test bench figures; in town the automatic may have chewed more fuel, just, it's urban figure is flattering.

Whether a manual transmission has a better mpg figure than an auto hinges on how often there are gear shifts in the test. In a run of constant speed, the power interrupt in gear shifting is non-existent. Here, an automatic is unaffected but it lags behind by virtue of its unavoidable power slippage. In an urban cycle, however, the disparaging effect of the accumulative power interrupts in a manual drive, if the number of gear shifts is high enough, overwhelms its superiority of non-existent or minimal power slippage.

A hint of this power play afforded by a manual and an automatic is in this article where the design philosophy of an automated manual transmission is explained.