75PS car specification: power, track, drag?

So it sees the coefficient of drag is 0.28. Any thoughts on the other data?

try this for the full data: http://www.audi.de/etc/medialib/ngw.../pdf.Par.0008.File.pdf/a2_a0_14_55kw_0303.pdf

Track front 1462 rear 1427mm
Stirnfläche -- > frontal area (and that's the best you're going to get IMO) 2.20m2

Bret

bretti_kivi said:

try this for the full data: http://www.audi.de/etc/medialib/ngw.../pdf.Par.0008.File.pdf/a2_a0_14_55kw_0303.pdf

Track front 1462 rear 1427mm
Stirnfläche -- > frontal area (and that's the best you're going to get IMO) 2.20m2

Bret

Click to expand...

Thank you. That's very helpful.

Is the power measured on a rolling road the same as the power at the wheel ie. 75 bhp?

should be, yes.

Bret

Just found an article which shows 1.2L version has a Cd of 0.25, a CdA of 0.554 and confirmed the 0.28Cd for the standard car.
This would give a frontal area of 2.216 m2 which ties in very nicely with Bret's data.

Although already covered, I found a diagram with dimensions of the A2 bodywork

Cheers Spike

PS. 75 hp is measured at the crankshaft so the power at the wheels will be much lower.
Rolling roads use the wheel hp and a 'freewheeling deceleration' figure after the full power run to calculate the engine power.

Thanks chaps, Useful information.

It's linked to the 5th gear ratio thread. I know someone who can calculate from the above data the power required to do 60mph.

From the torque data before/after remap I can then calculate the maximum power at a given rpm. Hence show the reserve power when doing a constant 60mph.

It will be interesting to see if they come up with the same figures I got using the 'cube law'
Based on Audi's data of 75 hp to do 108 mph, 60 mph only requires 13hp and 70mph needs 20 hp

Cheers Spike

When i got my 1.4 TDi remapped it had a HP of 81 (before the map) and Vince said "he's never had one at 75 yet"

Phil

So some results using the above data, from someone I know off a Mercedes forum:

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I've looked into this a bit more, and it seems that cross section is thought to be 2.18-2.20.

In the absence of any at-the-wheel power figures I've guesstimated the transmission loss at 12%.

I've also had a play with rolling resistance coefficients (<0.001 is possible with low resistance tyres).

transmission losses 12%
engine power (at the flywheel) 75 BHP
engine power (at the wheels) 66 BHP
engine power (at the wheels) 49 kW
vehicle track 1.462 m
vehicle height 1.553 m
maximum vehicle cross section 2.18 m*m
vehicle mass (weight) (kg) 1020 kg
air density 1.202 kg/(m*m*m)
drag coefficient 0.28

rolling resistance coefficient 0.015
> Cruise at 60 mph requires 8.3 bhp
> Top speed 108 mph

rolling resistance coefficient 0.010
> Cruise at 60 mph requires 7.3 bhp
> Top speed 110 mph

Taking a few discrete points off rolling road data gives:

rpm, torque (base), power (base), torque (remap), power (remap)
1500, 100, 29, 100, 29
2000, 160, 61, 200, 76
2500, 160, 76, 190, 90
3000, 130, 74, 180, 103
3500, 110, 73, 160, 107
4000, 110, 69, 140, 107

So at 60mph at 2200mph there is maximum of ~160 lbft and ~70bhp.
Say 8bhp is being used to hold that constant speed, which leaves ~60bhp in reserve for accelerating or going up a hill.

By changing the 5th gear ratio and reducing the revs to 2000rpm to hold 60mph the reserve changes to ~50bhp, or a 15% reduction.

But if the a new 5th gear is used in conjunction with a remap then the reserve becomes 68bhp, or a 10% increase over the base vehicle.

I think all of this has taught me that a new 5th gear would need to be combined with a remap to offer the same in-gear flexibility as before.