Performance Data

[Mark Gordon]

While reviewing the Knowledge Base under Technical and Performace Data, I noticed that the FHC out performs the OTS in the Standing Mile time, 0-60 time and mileage (better aerodynamics?) even though the FHC is slightly heavier than the OTS. Can anyone explain why the FHC is better in acceleration compared to the OTS?

[Heuer]

The drag coefficient of the OTS is higher than the FHC:

OTS Hood up = 0.54
OTS hood down = 0.55
FHC = 0.52

A contemporary Porsche 911 had a CD of about 0.35 and most modern cars are below that figure. Explains the 16 mpg fuel consumption! The D-Type coefficient is even higher at 0.55.

[Mark Gordon]

Understood, but would that slight decrease in the drag coefficient have made much difference, particularly at the lower speeds as the car accelerates to 60 mph?

[christopher storey]

Mark : the difference is largely accounted for by the fact that the different magazines used different techniques . Motor tests of identical cars were usually conspicuously faster than those tested by Autocar , probably because they used very brutal techniques , e.g. dropping the clutch at 4000 rpm. In any event, standing start times are a notoriously poor guide to real performance, the 20 mph increments in e.g. top and 3rd gears being much more representative of what you feel

[PeterCrespin]

Chris is right, plus there are road tests of cars with differing final drive ratios.

You are right too Mark in that the Cd makes no measuralbe difference to acceleration until you get to pretty high speeds. Power required to overcome air resistance increases as the square of the speed, so unil you are going above 50-ish it's not really an issue.

Pete

[Woolfi]

"Power required to overcome air resistance increases as the square of the speed. . . " This is correct.
The power has to rise in the third "potenz" with speed. For the doubble speed a car needs 8 x more power. For a low speed like 60 mph an E-type needs roundabout 17,5 hp. For 120 mph the E-type needs 140 hp. Regards Wolfgang Gatza

[Mark Gordon]

Thanks to everyone for their replies to my trivial question. Here is what I gather from all of the responses: 1. CD is slightly better for the FHC (as expected) 2. CD has little effect on Standing Mile and 0-60 3. Data may have been obtained by "popping the clutch" It is also interesting to note that the two statistics where CD should have mattered, Max Speed (149 for both) and MPG (21.8 for OTS, 18.5 for FHC), CD did not seem to be a factor. Makes me question performance data for cars in general. As Twain once said there are, "lies, damn lies and statistics."