Motec 964 Turbo

[4WD]

All this lightweight chat is rather interesting. It seems the CTR has an amazing ratio of power, weight and small frontal area = unbeatable performance!

Is there some kind of calculation or eqution which could sum up this relationship, in one number? Similar to how manufacturers quote Cd using a single unit, but to encompass all of the above elements. Would be a handy way to compare various cars at a glance, for pub chat reasons. ie to compare;

a. Skyline, low aerodynamics, 700bhp, 1500kg, verses...
b. Caterham, meadium aero, 300bhp, 400kg, v
c. 911R, high aero, 300bhp, 800kg etc...

If this could be done it would make an interesting addition to the Vmax result charts. Maybe add an extra column so you can give each car a single unit summary.

[johnny senna]

4WD,

I would say that all 3 cars you mention have poor aerodynamics?? The Skyline has a huge frontal area for a start.

One eye opener for me at Vmax was the performance of the 997S that was there versus my own modified 993 RS. My car has 348 BHP (proven on the rolling road), the 997S has 355 BHP. My car weights under approx 1270 kg, the 997S weighs 1420 kg.

And yet, my car did 158 mph and the 997S did 170 mph. Obviously aerodynamic drag was the key factor.

I'm sure that below say 70-80 mph my car would have the edge due to its lower weight, but above that the newer car would walk away. Mind you, I'm not bothered, my car is built for bends, not Vmax!!

[clubsport]

I am suprised you didn't see any more speed at Vmax Johnny...my car has been around 160mph with me driving, I am sure GuyR drove it to about 163mph with Big H on board as well!
That was achieved with a measly 295 horse...maybe they are Stuttgart stallions, to your Warrington pit ponies Sorry 9M...all in jest!

The RSR rear wing has much more drag they my regular RS wing, it has to be worth a few mph....

>> Edited by clubsport on Saturday 16th April 14:58

[iguana]

4WD said:

a. Skyline, low aerodynamics, 700bhp, 1500kg, verses... b. Caterham, meadium aero, 300bhp, 400kg, v c. 911R, high aero, 300bhp, 800kg etc...

b- Caterham cam hardly be descrribed as medium areo, its very bad aerodynamically at high speeds, as even the top dog 450odd kg 250 bhp R500Evo, is only good for 150odd mph & thats with the far more efficent aero screen, not the barn door like windscreen.

c- 911R doenst have 300bhp, =210bhp, the R based later racing S's did have 230- 260bhp tho.

[4WD]

I didn't spend more than a second making up the above a,b,c examples, so please ignore them!

My point was to illustrate the desire to summarise each cars potential in a single figure (derived from an equation covering Cd, power, weight). Any idea how to do this?

[tony.t]

IIRC acceleration is directly proportional to weight ( in a vacumn) for a given force but air resistance increase to the square of the force needed to overcome it. Air resistance at low speed requires a very small portion of the cars power to overcome it but at high speed nearly all theengines power is overcoming air resistance.

Without air resistance a car would accelerate as fast from 100-160 as 0-60.

good info here http://wps.aw.com/wps/media/objects/877/898586/topics/topic02.pdf

[warmfuzzies]

www.pumaracing.co.uk/topspeed.htm

Nice write up and clear explanation of the forces involved.

kevin

[iguana]

4wd said:

300kg sounds like an awful lot to loose. I wonder where it all is? Im guessing an extra 30 on luxury front & rear seats, maybe 10 for aircon compressor etc, 10 for general insulation, maybe 20 on glass rather than perspex. Just made all that up so it's a wild guess... around 70kg there or so. What about the rest?

I know you are guessing but the figs are not that accurate, even basic light VW seats are in the 15kg each bracket, think when I last weighed a leather electric porker seat it was nearer 35kg. Lightweight Recaros are about 4 & a half KG.

Interior soundproofing & standard carpets etc all weighs more than you'd expect (i did have some figs somewhere from when stripping a 964 to a track car but can't find 'em at the mo)

I know a fella with a track Mk1 Golf which are pretty skelital light as standard & no real lardy stuff on board & official VW kerb weight is 840kg, now fully stripped out of absolutely everything & plexi glass & grp hatch & bonnet & even now with a slightly heavier engine by around 20kg & = 650kg on the weighbridge! (don't think hes stripped off the underseal yet either) & he still thinks more to come yet!

[4WD]

Amazing that you can save 60kg just on the front seats!

[tony.t]

4WD said:

Amazing that you can save 60kg just on the front seats!

I agree; 964 leather electric seats weigh 56lbs or 25.5kg each.
Recaro SPGs are 4.5kg but the brackets weigh at least as much. Total saving nearer 30kg. Perhaps he meant lbs

[johnny senna]

clubsport said:

I am suprised you didn't see any more speed at Vmax Johnny...my car has been around 160mph with me driving, I am sure GuyR drove it to about 163mph with Big H on board as well! That was achieved with a measly 295 horse...maybe they are Stuttgart stallions, to your Warrington pit ponies Sorry 9M...all in jest! The RSR rear wing has much more drag they my regular RS wing, it has to be worth a few mph.... >> Edited by clubsport on Saturday 16th April 14:58

Paul,

I'm not that surprised. The top speed of Adam's dad's R Turbo on this Vmax was only 185, it went 200 mph on a previous Vmax, fully 15 mph faster, so this Vmax was probably a slow one. Perhaps if my car had been at the same Vmax as when you went mine might have managed about 163 mph?? Possibly. Really crappy aero though. Only good for downforce.