StormRune

Due to a recent discussion in another thread I did a little research and think I understand the 991.2 intercooler intakes better now. When I initially saw the 991.2, I wondered why the slats on the deck lid were turned 90 degrees from previous designs and made vertical rather than horizontal. I already knew the engine air intake was up there but didn't initially understand how the intercooler intake up there fit into the design.

Apparently the vertical slats help channel air down into the intercooler. Here are a couple of diagrams showing the flow and the intercooler intakes. But I was left trying to understand how this worked with the intakes under the spoiler.





Here is a photo with the wing up, clearly exposing the intercooler intakes below the plastic mesh under the wing. In the 991.2, a collapsable plastic panel rises from the back side of these intakes up to the bottom of the spoiler creating an air dam that forces much of the air in front of the spoiler down into the intercooler. You can see how a lot of air would get rammed into the intercoolers when the spoiler is up.


So then how does any air get back into the intakes when the spoiler is down. You can see in this last photo that the vertical slats guide air down into a gap between the spoiler to the intercooler intakes while helping hide this gap at the same time. The gap is between a inch to an inch and a quarter and runs across the entire bottom edge of the spoiler so a fair amount of air can still flow down there under pressure. Apparently this is plenty of air for normal driving. But you can see why the car will lift the spoiler at lower speeds if it decides the extra intercooler air flow is needed.

Porsche_nuts

Great information here. Thanks for posting.

JustBud

Could a duck be made to work with this intake/intercooler situation if it had an open channel at the base or does the design preclude that? Would the air be so disturbed that it wouldn't make it into the channel at the bottom of the duck to reach the intercooler?

jnolan

StormRune

Thanks guys.

I'm assuming the nature of this design is what kept Porsche from including a duck or true wing of any sort in their offerings for the 991.2 turbo-engined cars. They'd have to adopt a different intercooler intake strategy (like the capital T Turbos) to get the required flow I'd guess.

wareaglescott

great info. Thanks for posting

AlBinVA

Thank you for sharing. These are the kinds of threads that make coming here worthwhile.

Al

worf928

spdracerut

That's the money shot right there. When just cruising, you're not in boost and therefore the air coming out of the turbos is not heated up much. So only a tiny bit of airflow is required to keep the ICs from heat soaking. When launching from a stop, There's obviously no airflow through the ICs, so the system is basically depending on the thermal mass of the ICs to cool the air; basically it's a big chunk of aluminum that pulls heat out of the hot air coming out of the turbos until there's external airflow to cool the ICs down.

As for not having a wing on the Carrera, I think it's strictly due to product differentiation/heircarchy. The Carrera is the very capable street car and bottom of the totem pole. If you want a wing, you want something more track focused, so GT3. A rear wing similar to the GT2RS setup would still work with the IC setup of the Carrera; the scoops would feed the ICs. In this case of the GT2RS, those scoops are feeding air into the turbos inlets. For the Carrera, you'd need 3 scoops essentially. One for each IC and one for the turbo inlets.

StormRune

I don't see it that way. It appears that when the spoiler is up it would create a high pressure area in front of the spoiler and forces much more air down into the intercooler intakes while at the same time increasing downforce (or reducing lift) . This increased flow is aided by the retractable "dam" along the back side of the spoiler steering the air straight into the intercooler intakes.

StormRune

Yeah, I'd agree with you there. I think they want to keep the standard Carrera design as one with a smoothly descended tail, so the tricks they played with hiding the intake under the spoiler during normal use made it so they couldn't block the spoiler's movement to the deployed position without cutting off the extra flow to the intercooler intakes when more aggressive cooling was needed. A significant tail redesign with scoops more similar to what you show in the photo you referenced would likely be needed, and they save that level of showmanship for the higher-end models.

worf928

This is exactly my point. And for the same reason, I'd argue that the spoiler has to be up to maximize air flow to the intercoolers. At high speed, without the spoiler deployed, I'd wager that airflow through the intercoolers would decrease due to the air flow becoming turbulent before the inlet.

Clearly, Porsche could engineer a fixed spoiler for the non-capital-T turbos if they wanted to. He11, all that's required is something that's exactly like the existing spoiler in its raised position.

This -^

jnolan

jimjoe997

This proves nothing, but I was trying to understand the airflow with spoiler up and down, so I did these flow visualizations. Just posting here because I thought they were interesting... maybe a little bit more work on the source image and Reynold's number modification would be useful.

spdracerut

Well, it is the common design concept that has been used on the last few generations of 911 Turbo What I found interesting was on the GT2RS, they also dump the air below the rear bumper in addition to out the side.