wolverine

(1) Assuming the 550i weighs 3,914 lbs, its lbs/HP ratio is 10.87. (2) Assuming the M3 coupe weighs 3,415, its lbs/HP ratio is 10.26. The rear-end ratios for cars (1) and (2), in manual form/SMG form, respectively, are: (1) = 2.93 and (2) = 3.64. In automatic form/SMG form, they are, respectively (1) = 3.38 and (2) = 3.64.

The M3 coupe should be the easy global winner over the 550i. If the 550i weighs only 3,814, then its lbs/HP ratio 10.59, but that's not good enough. And, I am assuming the the extra weight for each car over BMW's given values would be about the same. I have ignored the specific transmission gear vales for simplicity.
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Let's put a finer point to those numbers - hopefully I've got these right:

550i Curb weight 3803 lbs.
M3 Curb weight 3415 lbs.
550i HP/Tq 360/360
M3 HP/Tq 333/262

Now let's calculate the actual test weight of the cars based on a 175 lb driver and 100 lbs of options and 'stuff':

550i 3803+175+100=4078 lbs
M3 3415+175+100=3690 lbs.

Weight/HP ratios:

550i 4078/360 = 11.3 lb/HP
M3 3690/333 = 11.1 lb/HP

That's certainly close enough to call this a driver's race, but let's look at the torque to the rear wheels:

You just used the ratio's but forgot to multiply by the engine torque. Using the 545 SMG ratio that you provided, comparing the actual torque to the wheels:

550i 360 x 3.38 = 1217 ft-lbs
M3 262 x 3.64 = 954 ft-lbs

Dividing by the weight of the cars to get torque/lb

550i 1217/4078 = .298 ft-lbs/lb
M3 954/3690 = .259 ft-lbs/lb

Which is a huge torque advantage for the 550i. Based on a closer look, like I said, I'd take the 550i in a street race.

znod

Let's put a finer point to those numbers - hopefully I've got these right:

550i Curb weight 3803 lbs.
M3 Curb weight 3415 lbs.
550i HP/Tq 360/360
M3 HP/Tq 333/262

Now let's calculate the actual test weight of the cars based on a 175 lb driver and 100 lbs of options and 'stuff':

550i 3803+175+100=4078 lbs
M3 3415+175+100=3690 lbs.

Weight/HP ratios:

550i 4078/360 = 11.3 lb/HP
M3 3690/333 = 11.1 lb/HP

That's certainly close enough to call this a driver's race, but let's look at the torque to the rear wheels:

You just used the ratio's but forgot to multiply by the engine torque. Using the 545 SMG ratio that you provided, comparing the actual torque to the wheels:

550i 360 x 3.38 = 1217 ft-lbs
M3 262 x 3.64 = 954 ft-lbs

Dividing by the weight of the cars to get torque/lb

550i 1217/4078 = .298 ft-lbs/lb
M3 954/3690 = .259 ft-lbs/lb

Which is a huge torque advantage for the 550i. Based on a closer look, like I said, I'd take the 550i in a street race.
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Yep, I agree. I was being lazy--actually didn't forget to multiply. I didn't quess the results would get that close. I do know that for a short distance I rolled even with a possibly modded M3 in my slightly modded 545i. As mentioned, you also need to consider the torque in all the gears. I was way too lazy to do those calculations. It also may be true that the 550i's weight is more like 3900--as least that's what the BMW quick fact sheet shows. I also did not factor in the cars CD's and did not check to see about differences in tire diameters. Good calcs thought: I like them. Thanks for taking mine to the next level.

znod

Let's put a finer point to those numbers - hopefully I've got these right:

550i Curb weight 3803 lbs.
M3 Curb weight 3415 lbs.
550i HP/Tq 360/360
M3 HP/Tq 333/262

Now let's calculate the actual test weight of the cars based on a 175 lb driver and 100 lbs of options and 'stuff':

550i 3803+175+100=4078 lbs
But, it might be more like 4178 lbs for the 550i.
M3 3415+175+100=3690 lbs.

Weight/HP ratios:

550i 4078/360 = 11.3 lb/HP
Given what's above, the 550i = 4178/360 = 11.61
M3 3690/333 = 11.1 lb/HP

That's certainly close enough to call this a driver's race (Excellent point--the M3 suffers more from the added weight--but maybe the suffering still does not yield a driver's race???), but let's look at the torque to the rear wheels:

You just used the ratio's but forgot (was just lazy) to multiply by the engine torque. Using the 545 (550i) SMG ratio that you provided, comparing the actual torque to the wheels:

550i 360 x 3.38 = 1217 ft-lbs
I think maybe you would want to use the manual for the 550i (I didn't provide the rear-end ratio for 550i with SMG; it wasn't given by BMW). If so, then the calculation for the 550i is: 360 X 2.93 (unfortunately) = 1,055 ft. lbs.
M3 262 x 3.64 = 954 ft-lbs

Dividing by the weight of the cars to get torque/lb

550i 1217/4078 = .298 ft-lbs/lb
Then, from above, 550i torque/lb would be: 1,055/4078 = .258 ft-lbs/lb. And, it might be worse--1055/4178 =.253 ft-lbs/lb
M3 954/3690 = .259 ft-lbs/lb

Which is a huge torque advantage for the 550i (looks the other way to me). Based on a closer look, like I said, I'd take the 550i in a street race.

I think all the advantages are to the M3. Maybe the 550i automatic would do better than the manual version, but that would be contrary to BMW's claims and the conventional wisdom. We still need to take all the gearing into consideration, including tire diameters. Maybe tomorrow. I think we can safely ignore CD. ~{;^)
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heezy545i

I've done my fair share of highway runs, but overall, I think straight line racing is overrated. Numbers aside, the tactile and sensory feeling of the M3 allows it to feel much faster.

I've had the pleasure of recently breaking in a ZCP m3 and though on paper it may be similar to a 545/550, in the driver's seat, they are world's apart.

znod

I'm a 50's guy. Straight lines rule. ~{;^) I agree with you about the feels of cars and the M3 feel vs the 545i/550i feel. Try a Lotus Elise or a shifter cart. Smaller cars always yield more feel.

znod

The advantages for the M3 coupe keep piling up.

Headings for what's below are: M3--SMG/Manual 550i--Manual 550i--Steptronic

Gears:
1st 4.23 4.06 4.17
2nd 2.53 2.4 2.34
3rd 1.67 1.58 1.52
4th 1.23 1.19 1.14
5th 1 1 1
6th .83 .87 .69
Rear end 3.64 2.93 3.39

Gear X Rear End:
1st 15.4 11.9 14.1
2nd 9.21 7.03 7.91
3rd 6.08 4.63 5.14
4th 4.48 3.49 3.85
5th 3.64 2.93 3.38
6th 3.02 2.55 2.33

I don't know if the cars would get to 5th in the 1/4, but I doubt it. But, to be conservative, assuming they do, the M3 torque-multiplication factors above for the M3 strictly dominate those of the other two cars, and those for the 550i--Steptronic strictly dominate those of the 550i--Manual (Will the 550i--SMG get a lower rear end???) So, more advantage to the M3 and the 550i--Steptronic over the 550i--Manual in the 1/4 (ignoring efficiency losses for the 550i--Steptronic).

Finally, the M3 stock rear tire diameter is 25," while that of the 550i is 25.85." Maybe worse still--550i drivers are likely to have 18" sport package wheels or upgrades from here to 19" wheels. In this regard, I have not checked to see if the tire diameter is held constant given 18's or 19's on the 550i. I assume that it doesn't get smaller though. Advantage again to the M3 in the 1/4 given the above assumption and assuming the stock rear tire diameter on the M3.

530iii

How's about a 550i vs. the new M3 sedan with a V8?

znod

Post #3 updated.

znod

Bump

530iii

Hey Znod, have you tried my new "acceleration assistant" method yet?