Inline-6 engines are commonly tilted on their sides a bit. Also their intake manifolds can be pretty much on the side of the engine whereas on a V they have to be on top more or less, so I'm not sure I buy the V configuration has the lowest center of gravity. Another advantage of the Inline setup is that in a longitudinally mounted configuration, all of the weight is more or less right on the roll center of the vehicle with minimal weight out towards the sides of the car which will help to improve cornering performance. The Inline-6 setup also has a very short timing chain run rather than the elaborate mechanisms needed for overhead cam V engines, thus minimizing friction. And yes all internal forces cancel each other out in Inline-6 engines which also make them incredibly smooth engines. I can tell the difference vs. a lot of the V-6 powered cars I've owned, and they sound and feel wonderful to drive too.

From a packaging standpoint though they make little sense. They're very long engines, are very difficult to squeeze into transverse mount applications, and are limited in displacement scalability too which is why most of the rest of the world has gone to V-6 engine architectures for their 6-cylinders. Now that the trends are going towards downsized engines with direct injection and turbocharging, I'm wondering if Inline-6 engines will start to make a bit of a comeback.

Anyways I'm super pleased that they have NOT gone with a V-6 here. Not that they're bad, but BMW has always been known for their Inline-6 engines, have said in the past that it would be a cold day in hell before they ever built a V-6, and their I-6 engines have such a wonderful character about them. Plenty of BMW purists could not accept a V-6 too.

 

nothing wrong with it, except the gas mileage

 

How much you average when you had yours, Henry?

 

it was right around 16. quite a bit from isf (for example), but still better than c63. i don't think it's bad at all, but with all the new upcoming regulations i think they need to do better. all the new 63 amg with tt setup they get quite a bit better mpg

 

I can understand the argument for straight 6 > V6, but as a performance car, why doesn't BMW go with a flat 6 for the M3 instead?

There's a reason many (all?) Porsches use the flag 6 design, apparently. Every advantage the straight 6 has, the flat 6 has as well, and in addition it provides further advantages (mostly handling related due to its lowest center of gravity compared to the other 2).

 

To heavy, to thirsty.

 

Wow, I am getting 17 with 70% highway, and my TT V8 is pushing a 4700 pound car. So how much the new M3 trying to achieve? I would say at least 20.

 

keep in mind my car was 4100lb already.

i think 20mpg seems to be the new "norm", given what i see on the new amg

 

Wow, never thought the M3 was that heavy! 3500-3800 is more acceptable for a nimble sports car. Maybe BMW is trying to achieve the weight this time.

 

sorry, to be exact, e90/2 (sedan/coupe) m3 is 3700lb. e93 (vert) which is what i had was 400lb heavier at 4100lb

my car is noticeably heavier even when driving it, and i could feel the rear having the weight

 

thats really heavy... weight saving would do wonders.

 

oh i am sure, the 4gs is a prime example. the isf is also 3700lb. when it comes to convertible it's pretty much inevitable because of the extra hardware and reinforcement. just look at the is350 vs is350c, 360lb increase.

plus with convertible ppl go with the cool more than performance in general. i am interested to see how they do the new m3

 

I don't believe that was ever under consideration, and I can't think of a single reason why they WOULD consider it.

 

Porsche seems to do ok with the 6 turbo....

2012 Porsche 911 Turbo S specs


Cylinders 6
Displacement 3.8 l (3,800 cc)
Horsepower 530 hp
@ rpm 6,250 - 6,750 rpm
Torque 516 lb.-ft.
Compression ratio 9.8 : 1
City (estimate) 17 mpg
Highway (estimate) 25 mpg

 

An M3 or IS-F powered by a big heavyweight V8 will have the best straight line power, the nicest naturally smoothest sound, and perform the best on a circuit with the longest straights, or a fairly straight circuit, or even an oval circuit.
However, this big heavy V8, not only is heavyweight, but its weight is more forward of the front axle, increasing its polar moment of inertia, such that it is slower to change directions, so not as agile.
The extra weight over the front wheels and nose heaviness also promotes understeer.
The big heavyweight V8 will not perform as well on tight circuits, with lots of S-shaped bends.


The in-line six is naturally smooth.
The in-line six also has straight inlet ports for superior breathing, resulting in the best torque and power of all the sixes!
The magnesium alloy BMW in-line six is even lighter than an aluminium alloy in-line six!
Mercedes is dumping its range of coarse 90 degree V6's, in favor of a totally new range of in-line sixes due for release in several years.

The proper 60 degree V6 is smoother, has good natural primary balance, with some secondary vibrations.
However these secondary vibrations can be absorbed by the engine mounts.
All Lexus V6's are 60 degree V6's.
Compared to the in-line 6, the 60 degree V6 isn't quite as smooth, and the 60 degree V6 lacks the in-line six's natural straight ports and bottom end torque.

The 90 degree V6 can be cast from a 90 degree V8 die, saving money by not having to fabricate a proper 60 degree V6 die.
90 degree cost-cutting V6's are commonly employed by Benz.
Unfortunately, the 90 degree V6 has an uneven firing order, but this can be overcome by off-setting the crankshaft pins.
Still, the 90 degree V6 is coarser than the 60 degree V6.
The 90 degree V6 also lacks the 60 degree V6's bottom end torque.
Once you drive a Benz 90 degree V6, you will instantly note the total lack of bottom end punch.

The flat six has the lowest center of gravity, and is the lowest engine.
However, the boxer configuration is not as smooth as the in-line or vee configuration, so it is only used by Porsche and Subaru.

All the sixes don't have quite as much straight line power as the V8.
However, the sixes are smaller and lighter, with more weight behind the front axle for a lighter noses.
Thus, the sixes enjoy faster changes in direction; faster turn in or steering response, or steering sharpness as some call it.
The sixes excel on tighter racing circuits, with more S-bends, and fewer and shorter straights.


The in-line four is the smallest and lightest engine, with the least weight, all potentially fitting behind the front axle.
The four gives the best agility, with the fastest changes in direction.
However, the four lacks cubic capacity, so can't manage to compete with the others in straight line power.
Furthermore, the four is naturally coarse, with lots of vibrations, even at idle.

So, whether the next M3 and IS-F is V8, 90 degree V6, 60 degree V6, boxer flat 6, in-line 6, or in-line 4, it all depends what you want.
Bigger heavier engines will perform better in the straights like the current IS-F V8.
Smaller engines lack the punch, need a turbo to compensate, but then the lighter nose is more agile on tight winding circuits, with fewer and shorter straights.
If we drive a six back to back with a V8, the difference is like night and day; the 8 is substantially heavier in the nose, and much more reluctant to change directions, but the 8 does have the cubic capacity in the straight line.
All depends what you want.
The same rules apply to in-line fours, V10's, V12's and Bugatti V16's.

Some could say a V8 for straight line performance.
An in-line four for agility.
While a six has the best balance; the best of both worlds.


After a while, we end up moving to a new topic, where with the bigger capacity and multi-cylinder engines, the mid-rear engine position becomes superior to the mid-front engine position.
The mid-front engine position is more practical, so that we can have four seats and a big rear boot.
The mid-rear engine position allows much larger capacity multi-cylinder engines to be used in a low waist-line motor car that does not hinder the driver's vision, but it often comes at the expense of forfeiting the rear seats, and the bigger squared off rear boot, for a smaller luggage compartment under the sloping bonnet...