bk_911

One can hope. I'll try and remain positive.

997s07

Burning cleaner because of efficiency? Not exactly. Turbos are in fact less efficient because of an added step in the engine processes. There a few academic papers (and even Andreas saying so) showing that turbos are not what people think they are.

Low end torque comes from more fuel burning not efficiency.

I could go on, but this won't be the first time you doubted me and were wrong.

fxz

So why Porsche have just switched all the Carreras to Turbo?

997s07

To decrease displacement but keep total power up. The turbos are a bimodal engine. For the 991.2, it's a 3.0 liter for testing purposes in government regulations, and a 3.8 liter for power and torque figures. A 3.0 liter acts like a 3.0 liter, it doesn't have much power or torque until the turbos kick in and more fuel needs to be injected to take advantage of more oxygen present in the cylinder (stoichiometric equivalence). That's why Porsche needs turbos, to lower displacement - helps with the testing that governments require.

The 991 turbo has a combined 20 mpg here in Der USA, where the 991 GT3 has a better combined fuel economy. Both 3.8 liter. No surprise that a more powerful engine needs more fuel.

997rs4.0

Not when you drive.... Or me.


When they drive it in the euro test cycle the turbos get very impressive mpg.

997s07

If you drive them both hard the 991.2 will be worse off since it generates more power. If you drive them in such a way wherein the turbos hardly kick in the 991.2 will be better off.

Given the consumption testing conditions, I'm willing to bet the EPA will rate the 991.2 1-2 mpg higher.

MM3.9GT3

Because no one drives at full throttle 100% of the time. Under light/partial engine loads, the downsized engine with turbos is more efficient.

doubleurx

Yes, more efficient means less fuel burned. FI is not an added step. It is an additional component. But the fuel burning process is still the same, just more O2 in the ignition. I'd love to see any engineer producing any data showing the inefficiency of turbo motors. Maybe you have some resources that are on to something, that is escaping the engineers at BMW, Audi, Porsche, Ford......etc.

This is the first I've heard of a turbo engine burning fuel inefficiently. Isn't that the whole basis of forced induction?

As for what I hope for, I'm NA all the way, but there seems to be a big drive for turbos and hybrids, and none of the manufactures are quoting they are less efficient. All state exactly the opposite.

BTW, when was the last time I doubted you? I've been wrong before, but I don't remember questioning you in particular....then again, getting older, it is entirely possible.

CAlexio

Id really like to hear more of fxz's insider information, (all strictly Level 1&2 of course), they make for good laughs.

997rs4.0

It would be interesting to see a fuel consumption test on track with 991.1 and 991.2.

The difficulty is that we use these cars so differently.

On the Autobahn turbo cars are not very fuel efficient. WOT between 70-140mph all the time. You are spooling up the turbos all the time.

At constant throttle the smaller displacement engine has a mpg advantage because turbos are not used.

Obviously this is a very simple explanation. But it basically explains the advantage of turbo.

997s07

But the turbos are not combusting the fuel mixture more efficiently. High pressure doesn't necessarily mean more efficient combustion. Compressing the air into the cylinder is another step. There is a price for compressing air, it's not paid by the heat exchange of gases, it's paid by exhaust strokes of cylinders that push the exhaust that spins the turbine that compresses the air. What are the consequences? High back pressure that the combusting cylinders have to compensate.

I'm not by any means privy to the information that I've given you. All engineers know this. The marketers and advertisers tell us otherwise.

Here is a non technical article: http://www.greencarreports.com/news/1082165_do-small-turbo-engines-really-give-better-gas-mileage. In it you'll find a consumer reports article saying the same thing. If you want the academic stuff you'll have to wait until I get back home Tuesday.

You asked me about the 9A1 problems in the GT3. I told you I can't disclose anything. Then I read a few posts from you doubting any engine issues and essentially disqualifying any ominous reports that we're starting to surface. I don't blame you, but I'm not the type to BS in forums. This was all before Macca spilled his beans.

doubleurx

Ah yes, I do remember that. Of course I was skeptical, since you couldn't provide any info. Hopefully those issues will be resolved, but clearly you knew something ahead of the curve. I can't argue that at all. As for turbo efficiencies, the cost is hotter burn. EGT's are considerably higher. But that is typically the byproduct of a more efficient burn of the fuel.

I'm just a dumb architect though. What do I know?

997s07

I doubt you're dumb. But there's a lot misinformation here. There is no hotter burn, I can get technical but I won't. The best way I can summarize the high pressure process (and in fact any engine thermodynamic process) is that you will only get what you put in. You want power you need fuel and oxygen. More power? More fuel and oxygen. The 'power' (heat, or enthalpy to be exact) in a molecule of, let's say, n-octane is unchanged no matter what the conditions. Fuel isn't burned more efficiently in turbo charged engine cylinders. In fact it is less efficient given that there is so much more to do on so little space. Couple that with having to compress the air and subsequently cooling it down, and you've got a mess on your hands.

Just read the article I've posted.

usctrojanGT3

My question will be this....will either be a free option or will Porsche charge for either transmission.

usctrojanGT3

Well it's not coming in the .2GT cars so we should see some of the "latest NA RS" froth come out of the .1RSs soon.