Re: Nissan GT-R Spec V Brochure Leaked
As I have said before, weight loss in the car is a good thing, but weight loss in some areas are more important than weight loss in other areas. I am sure you konw, these are the 3 equations, or reasons why the higher the mass reduction takes place, the more beneficial it is.
F= mass x acceleration
Moment = Force x distance (between 2 centre of mass)
Mass Moment of Inertial = Inertia of the object + mass of object x (the offset distance between the centre of mass relative to the reference point)^2
Glass is heavier than steel by volume so replacing the glass windows with polycarbonate is going to produce a relatively substantial weight loss. Glass sits very high in cars, 1 or 2 inches below the roof and there is a substantial amount of it, by area is close to 2x that of the roof alone. Think about how large and thick your front (especially) and rear windows are..
1st of all, what is the density of the glass used in cars ? I seriously doubt the glass used in cars have a higher density than steel, however glass windows can be heavier than steel panels because of the thickness of the glass, and as you have mentioned, the area of the glass. Even though the area of the glass ends at 1 or 2 inches below the roof, the centre of mass of the window is much further down from the roof than that, of course that distance is determined by the shape of the glass window. Also, because the front and rear window is at an angle, the centre of mass relative to the centre of mass of the car is closer than you think.
Ferrari body panels are aluminium so the transition to carbon fiber is not that substantial. CF side mirrors on the 430S are for show. The total weight savings of the M3's CF roof is roughly 11lbs according to BMW. Do you realize how heavy the power seats are in that car alone? They could have skipped the carbon fiber roof and took well over 100lbs out of the car if they just switched seats. The Gallardo SL, GT3 and 430S all replaced their power seats with lightweight manual sports seats. It's simply a much more cost-effective and dramatic weight loss plan.
The CF roof did lower the centre of gravity of the car by 2mm or something close. This might not seem much, but distances are usually squared, like the 3rd equation I have posted, so even 2mm can make a difference.
As for weight reduction between aluminium and carbon fibre, the density of Al is 2700kg/m^3 while the density of carbon fibre is 1750kg/m^3, so there is still a 35% weight reduction if both panels have the exact same dimensions, but as you know, carbon fibre panels doesn't need to be as thick as aluminium panels to achieve better mechanical properties than aluminium, so the actual weight reduction can be more than 35%.
I do realise the weight of the power seats. The light weight seats have more to do with straight line acceleration than improving the dynamics of a car. Once again the centre of mass of the seats are low when compare to the mass centre of the car so the overall dynamic effects aren't as significant as lightening the roof.
Why not make all the body panels out of aluminium the M3? Why only the hood? There in lies a fact BMW doesn't brag about too much. The reason the M3's hood is the only bit of aluminium is help with weight distribution. .
The hood is aluminium, the front and rear bumpers are made from light weight plastics, and the boot is aluminium as well or light weight plastic. The 3 series coupe, which the M3 is based on, is designed to use steel body panels, and it isn't just a matter of switching from steel to aluminium because aluminium is more difficult to stamp into shape or weld together, so the machines have to be changed in the production line.
The M3 is a relatively cheap car, so the cost factor has prevent BMW from using aluminium panels. I am sure BMW will do it if the M3 cost as much as an Audi R8.
You know why the e92 M3's V8 is 15lbs lighter than the e46 M3's inline 6? Because the inline 6 was CAST IRON. BMW never mentions that fact when they talk about how light the new V8 is. The sad part is, it really isn't that light. The M3's 4.0 liter V8 is close in weight to AMG's 6.2 liter V8 and the Z06's LS7 7.0 liter V8 yet those engines are over 50% larger in terms of displacement. The V10 in the M5/M6 is 100lbs heavier than any engine in its class. HP/liter doesn't mean jack. It's just a unit of measure. People seriously need to get that fact into their heads. How about we measure power output in KW/liter? The M3 now makes 78kw/liter. BMW loves to talk about HP/liter but why don't we talk about something that actually affects performance.
KW/liter is all about engine efficiency, and the optimum volume per cylinder is 500cc, hence the displacement of the V8 and V10 engines, 500cc x 8 = 4.0 L, or 500cc x 10 = 5.0 L. This specific cylinder capacity gives engineers the best volumetric efficiency (% volume of fuel and air that actually enters into the cylinder during the intake stroke to the actual capacity of the cylinder) range through out the entire rpm of the engine.
Given the short time period of the intake stroke, the incoming air fuel mixture has very little time to fill up the combustion chamber. At 500cc the cylinders are not too big so there is a relatively high volume of incoming air+fuel mixture compare to the volume of the cylinder. So even at high rpm, when there is even less time for the air fuel mixture to fill up the combustion chamber, there will still be a high % of air fuel mixture inside the cylinder for good combustion.
Of course cylinders with bigger capacity can compensate for their larger volume by improving the mass flow rate of air and exhaust gas to improve their volumetric efficiency, so engines like the 6.2 L V8 can still provide decent power and efficiency, but the fundamentals are right for the BMW engines, this is the reason why their V8 and V10 can rev that high for a road car engine. Also note that the S2000, 2.0L 4 cylinder (500cc x 4 = 2000cc) can rev up to 9000rpm, and other powerful performance engines such as the 6.0L V12 engine in the Mclaren F1 or the 8.0L W16 in the Veryon, they all have 500cc per cylinder.
How much power does the engine produce relative to its weight, since we're so concerned with weight reduction. The V8 in the M3 produces 20% less power than the LS7 and AMG 6.2 and torque is down 40% also yet they all weigh about the same. Ask anybody to choose between two engines that weight the same yet one makes 20% more HP and 40% more torque and no one is going to pick the weaker one.
Using a measurement such as power vs weight might seem logical, so if every engineer use that as the standard, we will all be driving insanely high pressure turbo 4 cylinder engines.
You have to remember, the M3 produce 20% less power than the LS7 but with 43% less capacity, and the push rod engines are generally lighter and less complex than DOHC engines. As for the AMG engine, the M3 has a 35% smaller capacity but only 19% less power than the AMG engine. As for the torque issue, a high torque engine = bigger and heavier drivetrain components so they can withstand the torsional forces, so even both engines weight the same the BMW doesn't need to use heavier components elsewhere in the car.
But someone is sure to scream, "But the weaker one makes over 100hp/liter!!!" Who cares? That doesn't mean anything for performance. High revving engine require heavy blocks so the engine doesn't vibrate uncontrollably and eventually grenade at high RPMs.
It is all about the vibration chrematistics of the engine and how well the engine is balanced. It isn't all about thick and heavy blocks, it is about the strategic location of mass and reinforcement to reduce the frequencies and the amplitude of the vibration of the engine block. You will be surprised how a little bit of weight at a certain position can dramatically reduce the amplitude of the vibrations.
I think it's tacky that they leave the roof unpainted to brag about their weight saving when they could have selected other more effective and less costly weight reduction plans.
So do I.
It is a long post, hope it all makes sense.
Do you happen to know of any site where they have the engine weights of M3 V8/M5 V10, AMG's 6.2-liter V8 and other engines measured using the same exact standard?
