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<snips>If I understand correctly, the raison d' etre for turbochargers is for meeting government economy standards.
Turbos are (at least partially) to meet government standards that may or may not be related to economy and the economy testing may not be the same as real world economy.?E.g.--in some countries there are increased taxes as engine capacity rises. I personally don't believe that governments always know what they are doing.

The rest of what you say is perfectly reasonable.?
 

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I did not know that. I had understood the reason for current popularity of turbos was to help meet the government mpg standards. Maybe both reasons apply.
Turbos make total sense in many ways. They allow a very dense air/fuel charge to be packed into the combustion chamber and allow a smaller displacement engine to produce huge amounts of power in the extreme. If you think back to the early days of turbo cars in F1, they were restricted to 1.5L displacement while the non-turbo cars were allowed 3.5L (going by memory here so the numbers could be wrong). The turbo cars ate the NA cars lunch. Porsche was in that feed line and used the turbos to turn their engines into beasts.

There is not a cut and dry reason for anything. Emissions & mpg played a part in turbo usage for most automakers because they allow increased power/torque when active but generally much better mileage when not active. Porsche fits into that category also since they must meet regulations dictated by governments. The difference is Porsche is at heart a performance company so their turbo usage tends more towards benefiting the performance side rather than the mpg side.

MOO
 

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A comment on turbos w.r.t. engine tuning: The biggest, in fact the only real, limitation on power in an engine (until it blows apart, which is a different issue entirely) is how much air you can get into the combustion chambers. Granted you still have to add in the correct amount of petrol and you still have to mix that petrol with the air and somehow get it to burn cleanly, but those are manageable details.

Making a NA engine breathe in more air can be done only by selecting input and exhaust manifolds and pipes of a length such that they resonate just right. You want a max pressure region at the intake vale as it opens and a min pressure region at the exhaust valve as it opens. For any given pipe length that best resonance occurs at only one frequency. You then choose valve and ignition times to take advantage of it. Of course if your timing and your manifold and pipe lengths are such that you get great breathing at 6000rpm then it won't be so good at 3000. That's why performance engines always have a peaky torque curve.

A turbo changes that whole behavior. It lets you literally stuff air down the engine's throat. The intake effectiveness is no longer determined by the manifold length. And to do so it uses energy in the exhaust that would normally be lost, which is why it improves both power and mpg if used carefully.
 

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This has been covered before and yes, it is definitely a space issue. The turbos and ancillary plumbing require a fair amount of additional space and there wasn't room for both. This video by savagegeese shows an under-body view of the engine in the Carrera T.


The underbody part starts around the 6.00 mark and they move to the rear around the 8.00 minute mark. Obviously the layout is flipped around but you can see there is literally zero space there.
I had a 911T for a short while. I loved that motor! Yes it would be spectacular in a Cayman...Now, I know why they didn't try it. Thanks!
 
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