Cerbera drag coefficient?

[chaparral]

Has anybody ever put a Cerbera in a wind tunnel? I'm trying to calculate the theoretical maximum speed of this car in order to put together an on-paper "top-10 fastest cars under 100k" list.

[j_s_g]

chaparral said:

Has anybody ever put a Cerbera in a wind tunnel? I'm trying to calculate the theoretical maximum speed of this car in order to put together an on-paper "top-10 fastest cars under 100k" list.

Out of curiosity, how're you going to calculate this? Taking into account red-line in top gear on a standard box, or assuming it's just force vs. drag, etc?

[ocean1]

I seem to remember reading somewhere that it was 0.35

Ocean

[carl_w]

IIRC the Cerbera is in CarTest:

www.jason.fletcher.net/tech/downloads/cartest.zip

A very useful program. A bit of tweaking with the parameters and I can get it very close to the actual figures (0-60 around 4s, 0-100 around 9s, flat out at about 190).

[Boosted LS1]

Whilst your at it take a look at the c5 corvette. I think it's 0.29, shall check later.

[chaparral]

Yep, the C5 coupe's drag coefficient is .29. The Coupe and Z06 have a .31 Cd, and the convertible, top up, has a .32.

[chaparral]

Yep, the C5 coupe's drag coefficient is .29. The Coupe and Z06 have a .31 Cd, and the convertible, top up, has a .32.

[Boosted LS1]

chaparral said:

Yep, the C5 coupe's drag coefficient is .29. The Coupe and Z06 have a .31 Cd, and the convertible, top up, has a .32.

Oh, and very little lift as well

[gazzab]

Boosted LS1 said:

chaparral said: Yep, the C5 coupe's drag coefficient is .29. The Coupe and Z06 have a .31 Cd, and the convertible, top up, has a .32. Oh, and very little lift as well

Particulary with fat americans weighing them down.

[Tam Lin]

gazzab said:

Particulary with fat americans weighing them down.

Hey Gazzab, don't knock it:

Those fabulous 5.7 litre engines, made to Detroit standard tolerances, are said to produce almost 154 SAE Hp (130 Bhp). Gee, with power like that, you need the Cd of a Honda Insight. And the C5 (original name, eh, Mr Sinclair?!) is as good lookin' as an Insate too...

I'm gonna chop the roof off, and paint a Stars and Stripes on the hood. With a coupla Jatos I'll beat the Yanks to the next Darwin awards...

Sorry, what was the thread?!

>> Edited by Tam Lin on Thursday 23 October 23:59

>> Edited by Tam Lin on Friday 24th October 00:01

[chaparral]

Hey! Our SAE horses are stronger than anyone elses! I'm surprised to see this coming from a TVR fan - how is it that the 4.2 has as much power as a 4.5 on a dyno? Not flame-baiting here, just reminding you of this.

350 horsepower out of 5.7l isn't bad for an engine you can buy for the equivalent of 37p and have it run!

>> Edited by chaparral on Friday 24th October 03:28

[ro_butler]

Good point chaparral

You may find that the cdA figure is more useful in trying to calculate top speeds.

Please post your findings as I would be very interested. People are forever saying that the cerbera is a 190+ or even 200mph+ supercar but to the best of my knowledge no one has got anywhere near these numbers under test conditions.

Rob.

[dannylt]

Several of my friends have managed 190mph GPS verified - there are some pictures around to prove it. With 400+ bhp ,the RR might manage over 200, assuming it doesn't run out of revs (which I think it does).

danny

[olly]

I've seen plenty of Cerb pics showing 180+ speedo figures (I think Ben Pike once recorded 200.1mpg on a GPS tracker ?). Whether the speedo is accurate or not at those sorts of speeds could be argued, but they definately get over 180mph.....

[j_s_g]

olly said:

(I think Ben Pike once recorded 200.1mpg on a GPS tracker ?).

Does the tracker run on standard or super?

[chaparral]

I've done some preliminary calculations using the manufacturer's power figures, and assuming a drag coefficient of .35 and a rolling resistance coefficient of .06, and using the manufacturer's dimensions for frontal area and weight. The results:

Cerbera 4.2 and S6 (350 bhp): 300 km/h (186 mph)
Cerbera 4.5 std. (420 bhp): 330 km/h (205 mph)
Cerbera 4.5 Red Rose (440 bhp: 340 km/h (211 mph)

I've heard that the power figures for the 4.5 are overstated- does anyone have accurate crank or wheel horsepower on these cars?

[BCA]

Power figures are overstated. Even so, having checked our power figures against the gearing of a standard 4.5 they are NOT capable of 200mph - although 195 is within reach. Power wise ours is a particularily average 4.5 (standard 17"ers all round).

Worked this out a while back and havent got the figures near me - but I think gearing is limiting it to around 195 (true GPS reading)- the speedo would show a little over 200 at that point

With the right gearing (or right wheels?) im sure a 4.5 Red Rose could crack 200mph - dont think I would want to be in it at that sort of speed though. Not bad for a sports car eh?

[carl_w]

Using the values I have in Cartest.zip (can't remember where I got them from) I get (for the 4.2):
0-60 4.3
0-100 9.5
Standing 1/4 12.5
Top speed 181.4

But this is with a drag coefficient of 0.3! 0.35 seems a bit high for a Cerb.

[j_s_g]

BCA said:

With the right gearing (or right wheels?) im sure a 4.5 Red Rose could crack 200mph - dont think I would want to be in it at that sort of speed though. Not bad for a sports car eh?

Having put 245/40 ZR18s tyres on the rear (whilst switching from 16" wheels), the circumference is up by 3%. Assuming the 17" wheels have the same circumference as 16" ones (albeit with slightly lower profile tyres), and a 4.5 is geared toreach 195, that extra 3% would push it just over 200mph.

[BCA]

Spiders + RR conversion on order asap (when I can afford them, no time soon sadly!!)

The drag co efficient must be under 0.35 thats worse than alot of the older porkers - The Cerbera is a very slippery shape, theres no downforce, but its pretty slippery!!

Im pretty confident most standard Cerberas would crack 190mph real.