Why have two block designs for NA and Turbo 996's?

A comment in a separate thread got me thinking. Why did Porsche use two radically different block designs between the 996 and 996TT cars? I understand the need for the TT's to sustain higher boost in the cylinder walls, but the two designs seem way off. Was the NA M96 designed first or did they really base the TT's off a GT1 design?

They did. The GT3 and TT share, essentially, the same engine. There was an interesting article in one of the last (I think it was) Excellence magazines. Porsche needed an engine that was easier and cheaper to mass produce. That's all it came down to.

Sorry, it was an article in the June (2013) edition of Panorama. Page 77: Pivotal Years. "Did you know the 993 might have had a water-cooled engine and rear-wheel steering..."

Very interesting. Is there any way to view that article online? Not sure how else to read it. Adding to that - what makes the M96 easier to mass produce compared to the TT block? You bring up another question I had. The GT3, GT2 and TT all share the same block with differing turbo sizes (none, K16, K24?)? Is there anything preventing a TT from being converted back to NA assuming you could reprogram the computer accordingly?

As I recall, the M96 design makes more use of cast-in passages for oil and water, requiring less machining and thus being more suited for mass production. This is why the M96 uses a ball bearing instead of an oil-lubricated solid bearing on the transmission end of the intermediate shaft - there is no cast-in oil conduit to supply high-pressure oil to that end of the M96 case.

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Differences such as compression ratio, plumbing, programming, etc., aside, it's conceivable that one could convert it back to NA. Probably a lot of little differences to sort out. Scanned and uploaded the article for you: http://derek.bp6.com/porsche/pivotal...e_june2013.pdf

That is a great article - I'd already read it in Panorama, and I just read it again for good measure. The 996 may currently be the "bargain" 911, but it's also the 911 that Porsche rode into the 21st century.

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Awesome article - and they look all so pretty in guards red!

As much as the M96 is maligned, Porsche likely would not exist today if not for it. Huge production costs, challenging emissions standards, and a tiny market share were crippling Porsche. Metzger design engines were much more expensive than the M96 and the volume numbers and profit margin they achieved with the Boxster and M96 engined 996's saved Porsche's bacon. Porsche is having record sales numbers and great profit margin these days with several great cars and SUV's, but things could have gone a very different way.

Thats what I was thinking. I guess he means why did they use two different NA M96 engines in the 996. There were far more TT Metzger engines than NA Metzger engines and many, many more NA M96.01/04, 03 engines. I think the bottom line is the NA M96 is way cheaper to build than a Metzger engine wether its TT or NA. A common theory that makes sense is this: So I guess we can thank Toyota for our cheap throwaway M96 engines?

KazyK, I wonder where you got that "Quote" My next question for you is ??? "PCNA"? Did "Porsche Cars North America" hire Toyota to tell the Parent company how to build the new engines? I think not. My understanding is (and maybe I am just as misinformed as your Quote) "Dr. Ing. h.c. F. Porsche GmbH" Did contract with Toyota to help control cost by implementing "Just in time parts" systems for production. This has absolutely nothing to do with engine design. Yes the new engines are less costly, yet they are more powerful and Cleaner and more fuel efficient than the old Air Cooled motor. And really Porsche had no choice but to move to new simpler and cleaner engines to remain competitive. I think the Pano Article is far more accurate and informed than your source. I am really sorry you spent good money on a "cheap throwaway - engine". I own a 996 with a very reliable high performance efficient M96 motor I am very happy with.

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wow, on a technicality you are going to beat him up? The bottom line is that mezger engines have a lot of parts and are assembled in a much larger number of steps than an m96. This leads to longer assembly times and higher costs, but a lot more parts are replacable, leading to a more race friendly motor. wait, the m96 is more powerful than the GT3 motor? since when? You seem to be focused on the air cooled cars, but remember that GT3s, GT2s and turbos of the 996/997 generation(997.1) cars are watercooled mezger engines....which all outperform the m96/m97. Your high performance reliable engine will be reliable and high performancfe until the moment it d-chunks a cylinder, frags an IMS bearing, has leaky/cracked heads leading to intermix, etc. Then it becomes a non-performance paperweight.

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Really appreciate you scanning the article. Just got back from a quick vacation and read it right away. Confirms some of my suspicious and has great history. I really enjoyed some of the German engineers quotes. I'm pretty familiar with the M96 design (because I own one) - I'll have to try and find some diagrams of the Mezger.

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That is my understanding of the situation as well that basically the Japanese were brought in to advise Porsche on how to streamline its parts and manufacturing processes. Also, I remember more and that is some Japanese auto makers visited Porsche to learn as much as they could about engine design as the Japanese believed (and I think rightly so) that the Germans and Porsche in particular had a pretty good handle on engine design.