[Monster]

Originally Posted by martinbo

Props to your post monster. Fundamentals described in plain, easy to understand English.

I ought to have given karma instead of mere thanks...

Thanks mate, no worries.

I was hoping you can read that post to see if I have made any mistakes. I try to explain it as simply as possible but the post was still so long. I really want to hear Porsche Guy's response to my post.

[siko]

A few more pics from the same series that Rev posted @ Autoblo.com here:

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[martinbo]

Originally Posted by monster

Thanks mate, no worries.

I was hoping you can read that post to see if I have made any mistakes. I try to explain it as simply as possible but the post was still so long. I really want to hear Porsche Guy's response to my post.

I think you've surpassed my level of technical know-how by now. Remember, I'm not an engineer - just a long time and dedicated semi-professional. So, like I've always maintained, eventually a discussion will reach my level of technical incompetence.

I found nothing to disagree with in your post. Discussions on engine vibration frequencies and harmonics are very complex. So I'll refrain from commenting on whether a 4.0 L V8 has less vibration than a 6.2 L V8. Of course, logically it stands to reason; the bigger the cylinder capacity the bigger and heavier the reciprocating components need to be in order to cope with the combustive and inertial forces at play. A bigger engine ought to produce a greater magnitude of vibration than a smaller one of the same configuration. I may just drop one of the IEotY award judges an email about this one - I have his address.

Of course, your discussion on the volumetric efficiency of a 500cc capacity per cylinder is a well documented and recognised fact. From Jeff Daniels at EVO to Jake Venter at SA Car... It's fundamentally why we don't see very large capacity engines (from a single cylinder capacity perspective) in true out-and-out super/hypercars.

Even a Pagani Zonda with 7.3 litres of AMG V12 is closer to the optimum than say a familiar 6.208 L V8. Very importantly, when it comes to high revving engines and risk of engine destruction it's not only how an engine behaves under load i.e. full-throttle acceleration but also when it's unloaded (throttle-lift) at very high rpm. Bigger pistons, con-rods, bearings and gudgeon pins carry more inertia and when the throttle is closed these components have much less resistance to keep them in check on the way up to top-dead centre. We've all seen that famous early Topgear episode where they profile Dario Benuzzi as Ferrari's chief test driver and then see how a 456 sets about blowing its engine under extreme testing. When does it blow? When the car screeches to a violent halt...

I think that not enough attention is paid to the relationship between bore & stroke - and hence internal piston speeds - as well as the weight and internal intertia of bigger capacity engines.

[Bartek Sikorski]

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Those spy shots we showed you yesterday of a higher-performance GT-R have been confirmed by inside sources as the Spec V model, which will both shed poundage and gain power compared to its baser sibling. Weight is expected to drop by over 300 pounds thanks to extensive use of carbon fiber, and as for how much power the twin-turbo 3.8L V6 will make in Spec V trim... some are saying 550 - 600 horsepower, though we think that's a bit optimistic as well as just overkill. These shots show the GT-R Spec V attacking a corner at the Nurburgring, and in the German sun we can see the new front splitter below the grille and carbon fiber rear wing much clearer. The current GT-R's performance has already surprised us all, but it's clear that this is just beginning for Nissan's new halo car.


Gallery: Nissan GT-R Spec-V - spy shots
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[Porsche Guy]

Originally Posted by monster

I really want to hear Porsche Guy's response to my post.

I'm sorry I haven't replied to your post quicker. I completely forgot about it and only rediscovered it reading about the GT-R V spec. Obviously, you know a lot more about car mechanics than I do. Let's just get that out of the way before I make a fool of myself.

Originally Posted by monster

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.

Glass in cars is double paned (I believe) and has to be able to withstand debris kicked up by other cars. Think about how thick/strong your front window has to be to withstand pebbles shot at it from cars ahead of you when you're traveling 80mph. Those little pebbles are moving pretty fast on their own and you're running straight into them on top of that. Glass isn't as strong as steel so in order to protect people from debris, the glass is going to have to be thicker than steel, and its heavier by volume to begin with. The biggest reason Ferrari and Porsche use polycarbonate windows that I can think of is that it's cheaper than carbon fiber so they can use more of it and get a greater weight reduction for the same amount of money.

Originally Posted by monster

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.

No doubt, if you have a single piece of CF at your disposal, the roof is the best place to put it, I'm not disputing that. It's merely a waste of monetary resources. Whatever it cost BMW to buy that chunk of CF, could have probably gone towards something that would have had a larger impact upon performance.

Originally Posted by monster

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%.

Great, but the density of steel (on average) is 7700 kg/m^3. For simplicities sake, assume that we use the same volume of CF, aluminum and steel for the body panels. In the real world, you would use less aluminum than steel and even less CF than that latter but let's neglect that fact because it opens things up for a discussion I just don't really care to get into. The transition from steel to aluminum is 285% decrease in weight while the shift from aluminum to carbon fiber is a 159% decrease in weight. The switch to carbon fiber from aluminum is big, don't get me wrong, but the conversion from steel to aluminum is greater and since F430s and Gallardos are completely aluminum (chassis and body panels), the switch to carbon fiber is not worth the added cost. Global demand from CF has jumper drastically in the last few (the new generation of commercial airliners are to thank for that) and the price has risen as a result, which makes the CF on the M3 even more stupid.

Originally Posted by monster

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.

I remembered discussing acceleration during physics in high school and did a quick search online. And I quote:
"Any change in the velocity of an object results in an acceleration: increasing speed (what people usually mean when they say acceleration), decreasing speed (also called deceleration or retardation), or changing direction. Yes, that's right, a change in the direction of motion results in an acceleration even if the speed didn't change."

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Originally Posted by monster

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.

True, but you've quoted me out of context. I was talking about the aluminum hood in reference to the big fat V8 that sits under that aluminum hood. I'm thrilled that BMW has aluminum body panels but it's just there to help with weight distribution because of that elephant of a motor sitting up front.

Originally Posted by monster

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.

But they had enough cash to go for the CF roof? That doesn't make much sense. Typically, high performance cars are the most profitable cars in a manufacturers lineup. I'm not sure about the M3 and BMW but the 911 Turbo gives Porsche the highest profit margin out of any of their cars, but I'm sure that the new GT2 at roughly 200k easily brings in a much bigger profit. You're paying an addition 70K over a Turbo to get essentially the same car without its AWD system. Porsche is pretty smart!

Originally Posted by monster

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.

You're missing my point entirely, I don't care about KW/liter! A higher KW/liter doesn't make my car perform any better than a car with a lower KW/liter and the same amount of power. It only matters if cars have a displacement cap. I care about KW/lb of engine and the M3 is just ugly in that statistical department. This whole discussion is about saving weight.

Originally Posted by monster

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.

Where have you been? That's the direction all cars are going. Another quote:

"[BMW CEO Norbert Reithofer] points to the twin-turbocharged inline-six in the 135i, 335i and 535i as a good indication of what the future might hold, particularly in the case of the M-badged variants that would make more use of forced induction rather than upgraded displacement and higher cylinder counts (not that they could get much higher). We can only dream, but with emissions standards increasing across the globe, it's the next logical evolution of the performance breed."

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Originally Posted by monster

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.

I don't care how they do it. The simple fact remains that the other engines produce more HP/lb and more Torque/lb. We are talking about weight reduction, not engine complexity. I'm not doubting that the M3s engine has some insane tech behind it, Double Vanos and all that goodness, but at what expense?

Originally Posted by monster

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.

Good to know. So why is M3's 4 liter V8 heavier than AMG's 6.2 V8? High revving engines are typically heavier than lower revving engines. F1 cars don't count. I can't find it online but I remember reading about how the S2000s inline 4 block was really heavy because it had to rev so high. Sorry I can't find the link though.

I look forward to your reply. I'm sorry about the really long post.

[martinbo]

Look, I hear your points Porsche Guy and I've always agreed with and appreciated your posts. Both here and back at the old place. I feel that neither you nor monster are incorrect in anyway - sure, basic hp/litre stats are nice for pub-talk bragging rights but if they don't translate to meaningful real world advantages then so what...

However, looking at how much power or torque an engine produces relative to its weight is equally one dimensional. Let me put it to the forum this way: Merc's V8 weighs 199 kg and BMW's weighs - I think - somewhere around 204 kg no? But then what does BMW's manual gearbox weigh and what does Merc's torque convertor 'box weigh? I bet my bottom dollar that the Merc's transmission is a) heavier and b) less energy transfer efficient. Surely if we're going to be so specific why don't we have a statistic for measured output at the wheels (per gear) / total vehicle weight?

I'll tell you why, because even then with all of this statistical information available it will only give us mere mortals an indication of the performance potential. Drivetrain efficiencies, traction, aerodynamics all come in to play to further influence the performance outcome.

I don't doubt for a second that the Merc engine, with its undeniably superior and exemplary power to weight ratio, is one of today's performance icons. Furthermore, let's not forget that it is significantly detuned in its application in the C63. Nonetheless, for an M3 with its appreciablly inferior outputs (on paper at least), to perform quite so closely with the more muscular C63 points to the fact that BMW must know a thing or two about engineering a complete package.

With regard to the use of the CF roof, I believe that there are two benefits, namely the reduction of roof weight and the subsequent lowering of the CofG as well as the increased torsional rigidity that the roof gives the body structure. The stiffer the bodyshell, the more effective the suspension tuning / behaviour becomes under extreme loads.

So economically, sure carbon fibre is an expensive addition and tangible benefits are difficult to quantify in the real world driving experience at best. But, I'd much rather play with a graphite tennis racquet than an aluminium one! Because it's lighter, stronger and stiffer...

Sorry if I've hijacked your very worthwhile debate.

[bmwrules]

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The prototype Nissan GT-R V-Spec, wearing the "Victory Specification" designation reserved for the ultra high-performance Nissan GT-R, has been caught lapping the famed Nürburgring at an incredible, if not simply unbelievable, 7:25 per lap. This, according to bystanders trackside. (For comparison, Walter Röhrl lapped the Ring in 7:28 while driving a Porsche Carrera GT in 2004.)

In contrast to the standard Nissan GT-R, that made the run around the 'Ring in 7:38, the GT-R V-Spec has a new front splitter, modified rear spoiler, and different wheels. A more extensive use of carbon fiber has reportedly reduced the weight by upwards of 330 pounds. Of course, Nissan engineers also tweaked the twin-turbo powerplant for another 70 horses... or so. Thanks for the tip, XeroK00L!

[chonkoa]

Originally Posted by martinbo

Look, I hear your points Porsche Guy and I've always agreed with and appreciated your posts. Both here and back at the old place. I feel that neither you nor monster are incorrect in anyway - sure, basic hp/litre stats are nice for pub-talk bragging rights but if they don't translate to meaningful real world advantages then so what...

Exactly what I always tell myself, what does all the metrics(hp/l, HP, torque etc) translate to- does it translate to performance increase in certain departments or all departments. If there is no improvement/advantage to reflect this metric, then there is an underlying engineering flaw that is yet to be addressed.

Originally Posted by martinbo

However, looking at how much power or torque an engine produces relative to its weight is equally one dimensional. Let me put it to the forum this way: Merc's V8 weighs 199 kg and BMW's weighs - I think - somewhere around 204 kg no? But then what does BMW's manual gearbox weigh and what does Merc's torque convertor 'box weigh? I bet my bottom dollar that the Merc's transmission is a) heavier and b) less energy transfer efficient. Surely if we're going to be so specific why don't we have a statistic for measured output at the wheels (per gear) / total vehicle weight?

This is where most people miss the point. We get so fixated with the numbers that we fail to ask why kind of transmission efficiencies are involved. How the frictional losses vary under different engine speeds. This I believe is where the engineering and science becomes important. A company that fully understands this dynamics will set the gear ratios to maximize this advantage. Sometimes we just look at the numbers without failing to understand the point of inflexion. There is a point in the torque curve where an increment in torque will reduce performance(too much traction). Isn't that what traction control is all about. Weight by itself is not bad it depends on where you are applying it directly.

Originally Posted by martinbo

I'll tell you why, because even then with all of this statistical information available it will only give us mere mortals an indication of the performance potential. Drivetrain efficiencies, traction, aerodynamics all come in to play to further influence the performance outcome.

I don't doubt for a second that the Merc engine, with its undeniably superior and exemplary power to weight ratio, is one of today's performance icons. Furthermore, let's not forget that it is significantly detuned in its application in the C63. Nonetheless, for an M3 with its appreciablly inferior outputs (on paper at least), to perform quite so closely with the more muscular C63 points to the fact that BMW must know a thing or two about engineering a complete package.

That is why I have more regard for the people at M division than the AMG division. They look at the complete package and seem to consistently deliver. It is not about HP, it is about the complete package and that entails looking at problem from multiple dimensions.

Originally Posted by martinbo

With regard to the use of the CF roof, I believe that there are two benefits, namely the reduction of roof weight and the subsequent lowering of the CofG as well as the increased torsional rigidity that the roof gives the body structure. The stiffer the bodyshell, the more effective the suspension tuning / behaviour becomes under extreme loads.

So economically, sure carbon fibre is an expensive addition and tangible benefits are difficult to quantify in the real world driving experience at best. But, I'd much rather play with a graphite tennis racquet than an aluminium one! Because it's lighter, stronger and stiffer...

Sorry if I've hijacked your very worthwhile debate.

[chonkoa]

Originally Posted by bmwrules

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What I like about this is what it will force Porsche and the other German manufacturers to do.
Nissan is basically rewriting the rules IMHO.