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Thanks
... Except that these ducts are not configured to feed the engine with air. Note that the air tubes to the air box still connect to the fan shroud. These ducts are 'open' to the engine compartment.
These ducts were the first thing on that GTS I stared at for a while.
These look to me to be positioned to nestle right in front of the airtube OEM inlet ducts. If they were further aft they would sit right on top of the airtubes, as they seem to be near the edge of the hood and not inboard between the tubes. Any further fwd and they'd be in front of the radiator.
Originally Posted by worf928
These ducts *might* serve to extract air from the engine compartment. Except that, IIRC, if that was their intended purpose they need to be flipped 180 degrees.
I'm not about to pull-out and revive my 30-year-old 'book' knowledge of aero... but, I seem to recall that NACA ducts could serve either as low-drag intakes or extractors.
I'm left with the conclusion that these ducts were installed because: Cool (looking.)
Yeah these would be just about the worst heat extractors from an aero point of view. Any time you extract air from within an enclosure you want to introduce it into the boundary layer tangent as possible to the external airflow. As such, yes you are correct, these are 180 degrees from that objective. Additionally NACA ducts are almost never used for this purpose on aircraft. Instead louvers are used as they introduce a low pressure zone behind each fin.
That duct doesn't really "feed" anything either, although it does ostensibly provide air in the vicinity of the exhaust manifold, which does get very hot. Not sure about the pressure at that point on the hood though...
Originally Posted by Shark2626
If anyone absolutely falls in love with the NACAs, you can find them here (I have absolutely no idea if they are what’s on that car though):
These look to me to be positioned to nestle right in front of the airtube OEM inlet ducts. If they were further aft they would sit right on top of the airtubes, as they seem to be near the edge of the hood and not inboard between the tubes. Any further fwd and they'd be in front of the radiator.
Now that you write that and I look again at the first picture, I think you are right.
If we go with that, then these ducts are actually worse than useless since they rob the air tubes of the higher pressure air flow (area 2 on the chart) above the radiator that enters the lower part of the bumper cover. In that case, then I find it dubious that these are factory.
Yeah these would be just about the worst heat extractors from an aero point of view. Any time you extract air from within an enclosure you want to introduce it into the boundary layer tangent as possible to the external airflow. As such, yes you are correct, these are 180 degrees from that objective.
Thinking about momentum transfer the only way that duct might reasonably extract air is if it's reversed. But, ...
Additionally NACA ducts are almost never used for this purpose on aircraft. Instead louvers are used as they introduce a low pressure zone behind each fin.
... yeah. I don't ever recall seeing a NACA duct used for extraction although maybe there's some application where effects from a louver set are unwanted.
Strosek liked placing these on the hood. Same orientation, but with a location delta.
In the 87+ undertrays, the NACA ducts are oriented the same way as the cool GTS ones and the Stroseks, and are used to bring air into the engine compartment and specifically to the motor mounts. The belly pan ones are located on a flat plane, however, with the air trapped between it and the road below it, not a sloping hood with air wanting to separate after encountering the nose.
I don't know the physics here, but I wonder if it would be some sort of tug-of-war between the air wanting to separate from the hood and the hood NACA ducts trying to suck that air in?
You may be surprised to hear then that Porsche installed what seems to me the exact same NACA duct on the passenger side of the 968 turbo S/RS bonnet for an aesthetical reason, as the driver's side duct is purposed to feed fresh air straight into the single entry, front-mounted airbox. The passenger side however feeds air dust straight onto the PS bottle.
Yes, same NACA ducts. This silver 968 Turbo S was in the lobby at PECLA the same time Minerva was on display last May. That 968 and this 928GTS are owned by the same guy.
Yes, same NACA ducts. This silver 968 Turbo S was in the lobby at PECLA the same time Minerva was on display last May. That 968 and this 928GTS are owned by the same guy.
On the 968 the ducts had an actual function though, right?
This car is super unique and obviously near the top of the 928 feeding chain... But I am discovering that there were more than a few spectacular specimens of the 928 built by Porsche.
Thanks for sharing this one with us Rob!
And Rob, how would any of this allow this little sin to go un-noticed?
Rob E: “I wasn't very good about suppressing my enthusiasm about the car with the owner” I’d have loved to have been a fly on the wall... or in this case a slightly wider front fender^^
02-16-2020 | 05:50 PM
