M&M

OK lt's do CSL (or even stock M3)

cD = 0.32
frontal area A = 2.08 square metres
V = 180 mph = 288 km/h = 80 m/s

P = 0.5 * (rho) * Cd * A * v^3
= 0.5 * 1.3 * 0.32 * 2.08 * (80) ^ 3
= 221 kW
== 300 RWHP

So an M3 needs 300 rwhp to do 180mph.

CSL's dyno 310-315.
Stock M3's dyno 275-285.

CSL should top out at 182-183mph
Stock M3 at 177mph.

ZAF

ok can anyone confirm which speedo is more accurate? Digital or analog? I am talking about the CSL video.
If the digital is accurate then the analog is 8.5% off WHICH IS ALOT.

Vomit

M&M: Are your dyno figures for the M3 and CSL in top gear? Also, based on the formula that you just employed, what would a stock C32 top out at, assuming taller gearing? Any chance of my modded C32 (guesstimate of 350 RWHP; best run: 12.8@112) hitting 200 MPH with ideal gearing?

blando

The M3/CSL has a Cd of 0.33, not 0.32. That 1/10 has a significant impact on the formula. Also, where are you getting the 2.08 for frontal area? I've seen 2.09 published. That 1/100th doesn't have as much impact on the formula.

Based on those numbers, the M3 or CSL needs just over 312hp to make 180. That 1/10 on Cd takes the M3 out of the picture and significantly reduces its top end relative to the C32. It would also require the CSL to be making maximum power at that point.

And I was curious where you got the 2.21 for the C32? I had seen 22.5 sq ft published, which equates to just over 2.09 using sq ft * 0.0929.

SLK55_AMG

SMG II seems pretty well!

M&M

OK, messed up the conversion to square metres for the C32's frontal area. It's actually 2.09 sq m. So it needs a few less hp to reach 175. Problem with the C32 is gearing. Once you past 6000rpm at around 175 mph, its game over due to the power drop off. If you could make the 5th gear longer it would make a difference.

M3/CSL with 2.09 frontal area makes almost no difference to the calculation. According to BMW.com the drag co-efficient is indeed 0.32:

http://www.bmw.com/generic/com/en/pr.../m3/index.html

So it needs 302 instead of 300hp to do 180. However, gearing is not an issue 'cos at 175 the M3 is wll in the powerband with no power drop-of. Also having shorter gears & final drive (Torque & hp multiplier) means the M3 is getting more power to the wheels at high rpm than the C32.

blando

That's the first time I have ever seen 0.32 for the M3. All the mags I have seen publish 0.33. BMW's site here in the US publishes 0.33. But since we're talking the CSL, I looked the CSL up on BMW's site (in South Africa no less) and it is also 0.33. Here's the link:

http://www.bmw.co.za/Products/Automo...l/default.html

Thanks for clearing up the conversion issue on the C32. I think it supports the 190 top end with the "optional" final drive they talk about. Wonder how you get that option...

steve s

new v10 m5 tranny is too complicated to be shifted by a human.. so in come smg again (smg 3??)

EKaru

I guess it's safe to assume that the C55 will hit a higher top speed given that the C55 is running at only 5300 revs vesus 5650 @ 155mph?

C32 data:
redline 6220
Transmission: 5-speed automatic
Gear Ratio Overall ratio (Rpm) Mph
1st 3.59:1 10.99:1 (6000) 38
2nd 2.19:1 6.70:1 (6200) 64
3rd 1.41:1 4.31:1 (6200) 100
4th 1.00:1 3.06:1 (6200) 141
5th 0.83:1 2.54:1 (5650) 155*
Final drive ratio...3.06:1
Engine rpm @ 60 mph in top gear..2100

C55 Data:
redline 6250
5-speed automatic
3.59/10.99/(6250) 42
2.19/6.70/(6250) 69
1.41/4.31/(6250) 107
1.00/3.06/(6250) 151
0.83/2.54/est (5300) 155*
3.06:1

Vomit

I'm confused. Why does the C55 turn lower RPMs than the C32 at the same speed in 5th gear when the transmission and final drive ratios which you have cited are identical?

EKaru

Good question... by the way my source is Road & Track..

http://www.roadandtrack.com/article....&page_number=1

http://www.roadandtrack.com/article....rticle_id=1602

Jon200

LMAO, M&M, I have an accounting test next week, can ya show us some formulas for solvency ratio

Jon200

That CSL is amazing, listen to the sound of it.

The CSL will walk a stock C32/C55

Unless the the C32/C55 is are trimmed down to around 1300kg

EKaru

Can anyone shed any light on the difference in Revs despite the same gear/final drive ratios?
Eric...

reggid

i noticed that to. The tyre sizes may be different or it could simply be a misprint

i assume you were talking about why the c55 reaches 151 mph in 4th and the c32 141 mph in 4th with only a 50rpm difference in rpm!

doofoo

I believe it is a misprint, from what I have read online it seems the C32 changes to fifth at 149mph.
http://www.carsource.co.uk/guide3?ID...cle_id=7000040 is a page I found when quickly searching. But I have see it on countless webpages.

-Mike

Vomit

Actually, I was focusing on top speed. At 155 MPH, the C32 is turning 5650 RPMs, while the C55 is turning 5300 (according to Eric's data). If the two cars have identical transmission ratios and final drive ratios, then the only possible explanation is mistake, or that the diameter of the tires is larger on the C55. Any thoughts?

doofoo

That is where I am going with it. I think it is off on 4th gear (149 on C32), so what I am thinking is with the stock 18's on the C55 (they are 18's correct?), and the mis-information, we get to the bottom of it.

So it's a little of both.

-Mike

EKaru

I thought that C32 owners were able to do a simple swap with C55 wheels w/out any calibration...
Eric...

doofoo

Possibly because it is a very small size difference. Only apparent at 100+mph.

-Mike

ZAF

My guess if they have same gear ratio then the C55 must have larger (wider or bigger) rims.

99bmw740il

for comparrison my clk55 went 155 and was at 4100rpms (i think) throttle was half way still felt like it was good for another 20mph atleast. Wouldnt try it without better aero though.

Sometimes cars have higher cd because of aerodynamics, such as wings, splitters, spoilers and so on. all designed to keep the car on the pavement at those high speeds

NORTH 44 C63

I have done a backward swap with my C55 winter wheels. Dropped to 225/45/17 without any recalibration. Everything runs true all the way to 250klm/hr

ProjectC55

Gabri343

www.e39.de
top 100 nations Italy look Gabri and Michele