M6 gran coupe vs coupe power

[AstonMartian777]

I got the gran coupe because i was stunned how aggressive it looked especially with those standard wheels, but my moto was always to go after power sacrificing everything else, this time I just fell for the pretty girl. So the question is, if anyone familiar in terms of straight line performance, am I losing a lot vs the f13 ? Thanks !

[MattUK]

I believe they are all fairly similar.. if you want exact details check the tech specs on the BMW USA site.

[RichardP]

Both M6 and M6 Gran Coupe have official 0-60 times of 4.2 seconds.

The M6 Coupe weighs 1925Kg, the M6 Gran Coupe 1950Kg, so only a 25Kg difference, a little over 1% difference. You could save nearly half that by specifying the 343M wheels over the 433M or 601M (Competition Pack) wheels. You can save another 20Kg or so by specking the Carbon Ceramic Brakes.

I think overall the performance difference would be totally insignificant.

[MattUK]

and when doing your high speed runs.. dont fill the tank full Official figures are taken from a 75% full tank i believe and probably a super skinny driver

[Twitch Massacre]

Originally Posted by AstonMartian777

I got the gran coupe because i was stunned how aggressive it looked especially with those standard wheels, but my moto was always to go after power sacrificing everything else, this time I just fell for the pretty girl. So the question is, if anyone familiar in terms of straight line performance, am I losing a lot vs the f13 ? Thanks !

From what I can gather the difference isn't huge. Best numbers I could find for the non-CP GC by any reliable publication were:
0-60 in 3.8
1/4 mile in 12.0
0-150 in 18.5

For non-CP M6 Coupe they were:
0-60 in 3.7
1/4 mile in 11.8
And 0-150 in 18.0

Mind you they were different publications so I would take those with a grain of salt until someone can do a side by side on identical road conditions with the same driver.

[RichardP]

Yep, that 25Kg difference equates to about 30L of fuel, less than 1/2 a tank full.

[Twitch Massacre]

Also keep in mind that most of us won't be hitting 0-60 in 3.7 or 3.8 consistently ourselves. That would require a near perfect, clean launch and that's very hard to do on less than perfect roads in a car that has so much trouble with traction at low gears. I don't care how good a driver anyone is, it's just very tricky.

[M6-Coupe]

According to BMWNA, for US spec there is 175lb difference between them (4255 lb vs 4430 lb). I couldn't find any spec for stock M6, bot @Boss330 reported the CP the other day :

Originally Posted by Boss330

I don't have any Autocar Magazines, but I have looked up in my Auto Bild Sportscars issues and found these test results:

M6 CP GC:

0-100km/h in 3,9s
0-200km/h in 11,7s
0-250km/h in 18,4s

0-402,34m in 11,93s (1/4 mile)

M6 CP:

0-100km/h in 3,9s
0-200km/h in 11,2s
0-250km/h in 17,4s

0-402,34m in 11,81s (1/4 mile)

...

So the difference is in higher speed because of weights

[RichardP]

I can't see those figures being correct if tested under the same conditions.

The weight difference would have more effect at lower speed, but the 0-62mph (0-100 kph)times are identical. The drag differences are very small, but there is a 0.5 second difference in 62-124mph (100-200kph) and a whole second between 62-155mph (100-250kph), that's a very big difference and would indicate that the power in the Coupe was significantly up on the Gran Coupe (0-62 mph being traction limited anyway).

[AstonMartian777]

Oh Thank you guys for some reason I thought i'm 600lb's over LOL ok

[M6-Coupe]

Originally Posted by RichardP

I can't see those figures being correct if tested under the same conditions.

The weight difference would have more effect at lower speed, but the 0-62mph (0-100 kph)times are identical. The drag differences are very small, but there is a 0.5 second difference in 62-124mph (100-200kph) and a whole second between 62-155mph (100-250kph), that's a very big difference and would indicate that the power in the Coupe was significantly up on the Gran Coupe (0-62 mph being traction limited anyway).

You have good point about the relation between weight and 0-60 mph but is not in this particular case! The huge amount of torque and power cause the traction issue for both of them no matter which one is slightly heavier than the other one if both have similar chassis.Actually the car with more weight on rear has slightly better traction, but then power/weight ratio takes the place and you can see the effect when they speed up

[RichardP]

It's the 100-200 and 100-250 (kph) times I don't buy.

Given that the drag is pretty much the same and do is rolling resistance (as the tires are the same), the Coupe is doing 100-200 in 7.3 seconds, the GC in 7.8 seconds. 0.5 seconds is about 7% longer. Given that F=mA (assuming friction and drag are the same), 7% greater acceleration means either 7% less mass or 7% more force. 7% of 1925Kg would be 135Kg, but the difference is only 25Kg (or 80Kg if you take the US figures - must be an equipment difference if those figures are correct).

Given the relatively large differences in measured engine power by different testers, I think it's more likely that at least some of this difference is due to either engine power or the test conditions (temperature, humidity etc.).

[Twitch Massacre]

Originally Posted by RichardP

I can't see those figures being correct if tested under the same conditions.

The weight difference would have more effect at lower speed, but the 0-62mph (0-100 kph)times are identical. The drag differences are very small, but there is a 0.5 second difference in 62-124mph (100-200kph) and a whole second between 62-155mph (100-250kph), that's a very big difference and would indicate that the power in the Coupe was significantly up on the Gran Coupe (0-62 mph being traction limited anyway).

Actually that looks very much correct. In the original Road & Track side by side comparison back in 2006 the E63 M6 had the same performance figures as the much heavier E60 M5 up to 80mph where the M6 started pulling away. I know in the case of these two drag may have come into play a bit but I think we are underestimating the amount of impact a weight difference can make, even if it is very small.

[M6-Coupe]

Originally Posted by RichardP

It's the 100-200 and 100-250 (kph) times I don't buy.

Given that the drag is pretty much the same and do is rolling resistance (as the tires are the same), the Coupe is doing 100-200 in 7.3 seconds, the GC in 7.8 seconds. 0.5 seconds is about 7% longer. Given that F=mA (assuming friction and drag are the same), 7% greater acceleration means either 7% less mass or 7% more force. 7% of 1925Kg would be 135Kg, but the difference is only 25Kg (or 80Kg if you take the US figures - must be an equipment difference if those figures are correct).

Given the relatively large differences in measured engine power by different testers, I think it's more likely that at least some of this difference is due to either engine power or the test conditions (temperature, humidity etc.).

Well you are assuming everything more simple than they are!
The Force in "F=ma" is the net force which is not equal in both cars; however they have the same engine produce the same amount of power/force.
The net Force can be calculated as F(net) = F - Fd - Frr =ma!
where Fd is drag force and Frr is friction force due to rolling resistance.
M6 Coupe and M6 GC have different weight and different coefficient of drag and rolling resistance due to their shape since GC is a bit longer. Manufactures report coefficient of drag but not the coefficient of rolling resistance, so it would be difficult to calculate the rolling resistance. According to the following link, they estimate the coefficient to be 0.03.

http://www.engineeringtoolbox.com/ro...ce-d_1303.html

and this link explains the Fd
http://en.wikipedia.org/wiki/Drag_equation

Hopefully it makes a bit clear. BTW I asked my colleague ( who is mechanical engineer) to explain these to me since I'm not expert in mechanical stuff

[RichardP]

I was trying to keep things simple and as much in favour of those figures as possible!

The rolling resistance should be identical. From what I can find, the GC has a Cd of 0.33, the coupe 0.32, so there is a very small advantage to the Coupe there.

Taking drag and rolling resistance into account make the figures even more unbelievable as they skew the power even further. If you subtract the power required to overcome drag and rolling resistance the 7% figure will become much bigger as the power remaining for acceleration of the mass becomes smaller. For example, lets say (and this is just for example, it's not based on fact at all) that 50% of the power was required to overcome drag and rolling resistance. That means that the remaining 50% would have to be 14% more for the Coupe to achieve those results, or the mass 14% less.

[Twitch Massacre]

Originally Posted by RichardP

I was trying to keep things simple and as much in favour of those figures as possible!

The rolling resistance should be identical. From what I can find, the GC has a Cd of 0.33, the coupe 0.32, so there is a very small advantage to the Coupe there.

Taking drag and rolling resistance into account make the figures even more unbelievable as they skew the power even further. If you subtract the power required to overcome drag and rolling resistance the 7% figure will become much bigger as the power remaining for acceleration of the mass becomes smaller. For example, lets say (and this is just for example, it's not based on fact at all) that 50% of the power was required to overcome drag and rolling resistance. That means that the remaining 50% would have to be 14% more for the Coupe to achieve those results, or the mass 14% less.

Ok so I'm not sure how accurate this information is but I've found the drag coefficients for the E63 M6 and the E60 M5. Seems to be accurate as various sources show the same information. For the E63 M6 it's was 0.32 vs a 0.31 for the E60 M5, why this source claims the old M5 had a lower coefficient than the M6, I don't know, but that's what I found. Assuming that is correct, then there must be some other explanation to this conundrum for the F13 M6 being stated to be faster at higher intervals than the F06 M6 as this too was the case for the E63 M6 and the E60 M5 and that I can confirm with absolute certainty to be true. The old M6 would pull substantially on the old M5 from 80 onwards and they too shared the same powerplant and transmission.

[M6-Coupe]

Originally Posted by RichardP

The rolling resistance should be identical. From what I can find, the GC has a Cd of 0.33, the coupe 0.32, so there is a very small advantage to the Coupe there.

The rolling resistances are not identical since they don't have the same weight!
Are you saying Cd is 0.33 for CG and 0.32 for Coupe?
If yes then I can show you the difference between the time from 100-200 km/h can be close to 0.5 second, but we need to simplify the calculation since the drag force is an exponential equation !

Originally Posted by RichardP

Taking drag and rolling resistance into account make the figures even more unbelievable as they skew the power even further. If you subtract the power required to overcome drag and rolling resistance the 7% figure will become much bigger as the power remaining for acceleration of the mass becomes smaller. For example, lets say (and this is just for example, it's not based on fact at all) that 50% of the power was required to overcome drag and rolling resistance. That means that the remaining 50% would have to be 14% more for the Coupe to achieve those results, or the mass 14% less.

I think I'm lost here

[michel lane]

There is an easy solution to questionable topic... Get both cars side by side and just race each other ! .. Do it the fast and furious way !...lol on a serious note ,i am sure I read somewhere that the gc map is different from the coupe on its torque curve , but I may be wrong .

[M6-Coupe]

Originally Posted by michel lane

There is an easy solution to questionable topic... Get both cars side by side and just race each other ! .. Do it the fast and furious way !...lol on a serious note ,i am sure I read somewhere that the gc map is different from the coupe on its torque curve , but I may be wrong .

The issue is that I live in USA and he lives in UK! so it's not possible unless he waits for me about 2 years when I want to get my next ED M6 Coupe then we can meet somewhere in Europe

[RichardP]

I also have the CP, so not a like for like comparison.

I think at speeds above 100kph drag will massively out weigh rolling resistance, but I don't know for sure. Yes, the extra few Kg will increase rolling resistance slightly, but it would be such a small amount compared with drag. Put the two cars on a gentle slope and release the hand brake, would you see a significant difference in the rate they free wheeled? There would probably be more variation due to the individual tyre variations and differences in tyre pressure.

I believe a Cd comparison of 0.33 and 0.32 is pretty small too, I had a car with a claimed Cd of 0.22 in the 80's and with similar power and weight to cars with Cd in the 0.3 range it was only slightly faster at the top end.

My bottom line, without careful back to back tests in identical conditions or a very accurate simulation that takes everything into account, would be that the Coupe would be slightly faster then the GC, but in all probability, differences in engine output, driver weight and skill etc. would make them all but indistinguishable in day to day use.

[Kenny G15]

I have a M6coupe comp and My pal has a M6GC non comp. My car is much quicker by far, easily noticeable. I don't know if that helps

[Twitch Massacre]

Originally Posted by Kenny G15

I have a M6coupe comp and My pal has a M6GC non comp. My car is much quicker by far, easily noticeable. I don't know if that helps

Comp package adds 15hp so it's not a very even comparison. It would be best of you could compare to a GC with Comp Pack.