Quote:
Originally Posted by bradleyland
My theory on how they decide: They allocate the engines according to demand. There is no implicit requirement that the engines be physically different. The percentage of people who chip tune their cars is so low that it doesn't register on BMW's bottom line.
Put more specifically, BMW's risk in the scenario where the engines are identical (except software) is that some customers will by a '20i car and chip tune to get the extra horsepower. That would represent a loss of top line revenue and profit because '20i vehicles have lower MSRP and thinner margins. However, BMW have differentiated the vehicles by limiting available options, which protects them in the mass market, and only exposes them to the tuner market segment. This segment is tiny in the overall sense.
Regarding the Alpina engine. That's not a matter of production variation, that's a matter of actual output versus claimed output. This is completely unrelated to the kinds of production variations we're talking about. You can't infer statistical significance from a sample size of 1.
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Of course they have to allocate the engines by demand, but they also have a very clear indication as to which gets the U0 with high compression & which gets the low compression U0. BMW fits the high compression U0 to all F30s & F10/11. That is the one with different pistons & hence they have absolute control, barring defects, on how many 320is & 520is they can make according to demand. This is very clear & made explicit in the product specs provided by BMW.
The low compression U0, which has no physical difference to the O0, is only fitted to E84 20i, F25 20i, F20 25i, E89 18i & E89 20i, plus any of the F30's & F10/11 that needs low compression ratio (decided by BMW according to specific market requirements, & it isn't a customer selectable option).
If u compare how many high compression U0s they make vs low compression U0s, u can see the high compression U0 is made in far larger numbers than the low compression version. I don't have the numbers off hand but u only need to compare annual sales of the various platforms plus which market those platforms are popular in (e.g. E84 & F25 are mostly sold with diesel engines in EU).
The limited option packages u talked abt is US-specific. For all other markets all the options are a la carte (as long as it's legal), so someone can spec the car as they wish & then apply aftermarket tuning. Remember for a market such as germany the price delta for a 320i & 328i is 4,000 euros.
The Alpina example shows things that are out of spec do & can happen. If actual output is much less than claimed output then it shows there are major problems somewhere along the line, variation or not. Also consider those Alpina engines are specially built by BMW for their exclusive use.
Quote:
Originally Posted by bradleyland
1) Why can't they "select engines randomly"? Although I wouldn't call it random. Why not just allocate them as they come off the line? Your hypothesis stands upon two assertions:
a) That manufacturing variances in the N20 are significant enough to justify this binning approach. What I cannot wrap my head around is why the N20 would suffer from these variances, but other BMW engines do not. If all engines do suffer from these variances, then it would be considered "acceptable", and BMW would have no reason to go through the extra effort of waiting for a "defect" engine, subjecting their production process to variances in availability based on defect rate and yields.
b) That "it is only logical for them to detune those not so good ones as a U0". Why is that any more logical than simply applying software as allocation is required?
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We do not know the exact power/torque output variances that exist between the engines, as well as the percentage that falls below that range. One thing is certain is that it's very rare to have engines that produce exactly the same power & torque rev for rev, so variance do exist however small it is. This is not exclusive to the N20. We also do not know how tight the standard is used by BMW. It could be that, judging by the dyno plots in this forum on stock O0's, BMW uses an extremely strict set of criterias for their tests. As they dyno every engine made, they can easily identify which engine is a potential candidate to be a U0 if it needed to be. Remember the production numbers for the low compression U0 is much much less than the O0, they can easily select those that give dyno numbers that lie in the lower end of the acceptable range.
As to why it's logical for them to detune the bad ones, that's to protect their bottom line. They don't want a 20i to be tuned to a 28i with no side effects. That's especially true for markets that have very high taxes.
Quote:
Originally Posted by bradleyland
2) I think I have a pretty good understanding of your hypothesis. I disagree that "If they detune the engines randomly then it will introduce problems." What problems will be introduced?
The binning approach flies in the face of everything I know about manufacturing and supply chain management. I build software to manage the procurement process for Fortune 500 companies. I spend a lot of time with executives in charge of supply chain management, because they're often the ones doing the purchasing. Auto makers rely on just-in-time manufacturing. Cars are built as they are ordered. All the parts arrive in the order they are needed. Literally, every sub-contractor has to load the parts in the containers in the order that they will be needed for assembly. The idea is that a part should be manufactured as late in the process as possible in order to reduce the capital required to maintain parts stock.
An engine is one of the most expensive and complex components in an automobile. If BMW uses binning, it means that the availability of '20i engines is subject to defect rates and yields. That means we're dealing with statistical probabilities. When you flip a coin, there is a 50/50 chance that you'll get heads, but anyone who has flipped a coin knows that you can end up with 6 tails in a row. Or 10. Or 20. It's possible!
The question is not why, but *how* could BMW run an efficient production process if they subject their supply to this type of statistical allocation? If the next engine needed is a '20i, and they end up with six '28i capable engines in a row, what do they do with those engines? Surplus is synonymous with waste when it comes to supply chain management. Engines are too expensive to have them simply sitting around.
This is a matter of applying Occam's Razor. There must be some advantage to the binning approach versus straight forward allocation. I can't see it. I understand the idea. I'm open to considering it, but before I can agree, I need to know the reason why.
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Simply speaking their bottom line will be hurt if the engines can be upgraded by a simple & cheap remap. So far nobody has managed to bring a 20i up to 28i levels without major effort.
I understand that JIT manufacturing is a standard implementation nowadays. With BMW engines it's a bit different. The majority of N20s are made in Munich, & they supply exclusively to other plants worldwide. Apart from Munich (& other German plants) it takes at least 1 mth for the engines to reach the respective assembly plants. That's the reason why for a lot of markets it takes many mths from ordering to taking delivery (e.g. production takes place 1-1.5mths after ordering) and also the SA made cars have an extended lead time. In actual fact BMW try their best to dictate demand, hence the existence of dealer & importer sales allocations. With these allocations they have a very good understanding on wht is needed during certain periods of time, as the dealers & importers have a commitment to buy at least the required volume from BMW. The only variable in this case is the equipment spec (not the engine version).
As for randomness, it doesn't matter cos a good one can always be detuned. The surplus good ones won't be sitting idle cos they'll be used to fulfill the lower grade demand. It doesn't cost BMW anything to do things this way as they already dyno every engine.
One thing to note is that the high compression U0s (i.e. those BMW that have complete control in terms of production numbers) are fitted to all BMWs made in German plants, except for the E84. Whereas the low compression (i.e. those binned) ones are fitted to all cars made in Spartanburg (F25 & E89). It's probable that when JIT is needed & achieveable then they won't use the binning approach whereas they'll use this approach when JIT is not achieveable. A related question is why BMW, after spending all these money, do not use the high compression U0 on all the platforms that use that engine, rather than wht they're doing now.