Its your cylinder head temps you need to worry about

It appears people just want to have a radical look, but don't realize they are effecting the engineering designes and best cooling practices planned by some of the best in the business...the German designers of the 911.

I think you should read the thread. As the author i have been asking very relevant questions about impacts on performance and other criteria effecting the function and safety of the motor. Did you miss my comments on datalogging IAT, ambient air in the compartment and engine parameters? Did you catch this thread IS ALL ABOUT CONSIDERING THE IMPACT OF THE ALTERNATIVE GRILL?

Porsche did a great job, 40 years ago, designing a car to generically handle a wide range of operating environments. It did not engineer to the performance envelope this specific car will see. This car weighs about 500 kgs less, makes 75hp more and is being built for a specific purpose. This car didnt even come with a ducktail stock. It also has a front-mounted oil cooler. Coilover suspension with asp. Shaved driprails. Flushmounted windows. EFI. Making decisions to take ideas further or going down different avenues is perfectly acceptable when unconstrained by Porsche's market constraints,the passage of time and unit-cost targets.

I am interested to hear your condescending view of anything Porsche didnt do themselves is somehow lesser or misguided. Your fleet of 911s must all be concours winners running nothing but Porsche Classic oil and bosch washer fluids and Stuttgart air in the tires?

:confused: I will log that too, along with knock.

This most likely is true, and the scientific method would require some A & B testing to verify.

Now, if we are talking cooling at idle or releasing radiant heat after shutdown, then an operable flap/vent in that area may help. Or one could simply open the rear engine lid.

JohnJL
It may come down to just trying it to see what you get. Remember early race cars just added power and bigger tires before aero. Now look how low even street cars are. And compare the windshield angle to cars back in the 70's. Auto engineers have a specific task to accomplish. Before computers aviation design was by test and crash!

Good luck with your idea and let us know what you find.

I just walked by the local p-car dealership. I noticed you can look down the back of the new GT3, through the "scoop" on top of the engine bay and all the way through the vent back out the back end vent above the license plate. A pretty interesting view. Like looking "through" the duck.

John, There's also coolant circulating through the engine. Airflow here is more important to circulate ambient air over the intake bits, but secondary for engine cooling. The exhaust system also has comprehensive shielding unlike earlier air-cooled engines.

Sherwood

Yes, I know its not the same, but was still interesting to note on the GT3. I didnt notice the same on the GT3RS on the same showroom floor but across the room. Maybe I want catching the same angle.

My reply probably sounded snarky. Not my intention. Others may confuse the different MYs with your original topic

I have looked into this as well.

Speed holes in the bumper are to help extract hot air from the bottom of the car. This reduces lift and drag.

The ducktail creates a high pressure on the leading face. This forces cool air into the engine bay and slightly changes to airflow across the top of the car. This later effect is usually at higher speeds. I would not add holes in the backside of a ducktail. This would extract the cool air from the engine bay that is needed.

The speed holes in the bumper combined with a spoiler are your best chance at some aerodynamic aids without bolting splitters, extractors and other non-vintage parts on the car. They can be effective. Just consider the car as a whole. What you do with the front end also plays a role with what happens in the back. Keep air out from underneath and the bumper extraction works much better.

I wonder if there is any way to take advantage of the low pressure area removing hot air from the engine compartment out the vents you are considering. Seems like they would of figured that out. I guess it fights against the fan pulling air in as Steve mentions above.

Any low pressure in the engine compartment is generated by the engine cooling fan. During typical operation at speed there is essentially ambient air temperature on top of the engine. Creating another negative pressure zone in the engine compartment can only disturb the designed airflow through the engine. Conduct some tests and confirm your hypothesis then let us know.

Sherwoodn

I think most people would think holes on a ducktail look really bad. Leave it alone.

Some folks believe form follows function. But that may not be the case here.

How could that be of any help? Any air being pulled out of the engine compartment would reduce the amount of pressure in the engine compartment which would lower the density of the air used to cool the engine. Less dense air means less efficient cooling which means a hotter engine.

The Porsche race shop folks were quite smart back in the day of the air-cooled race cars based on the 911. Contrary to what JohnJL said in previous post, Porsche had some lightweight RSR's with high output engines with ducktails. If there was something to be had for free, the Porsche guys would have implement it.

There were no vents of any type on the back side of the ducktail and the engine air inlet grill, if anything, was more open than stock.

Really, the correct answer here from a functional standpoint is to leave the back of ducktail alone and don't use any grill material that will let less air into the engine compartment.

Winders and Mr. Novak are correct. To put holes, vents, whatever in th duck is counterproductive. Yeah you are actually making things worse and pulling air out

If I were you, I would leave the duck as is and work on vent holes in the rear valence. There are some cool shots of those available

One of the guys I race with in the PRC GTL has been to Fontana and Road America with PCA. His car is drag limited to 142 MPH on longer straights. That is with all the normal body work on the car.

Anyway, at Road America he had to run without his rear bumper due to some accident damage. His car went no faster without the rear bumper which really opens up the back of the car. That means all the bodywork below the tail lights was gone. No bumper and no valence of any kind. This leads me to believe that the bumper/valence does not create drag so cutting holes in it will probably provide little to no aerodynamic benefit. If there is no aerodynamic benefit, I see little chance of their being any kind of engine cooling benefit either.

Some folks want it all ;-)

I was thinking that there might be some hot air building up in the engine compartment - with the old hot air rises theory - and the holes would allow the negative pressure behind the duck to "pull" the hot air out possibly allowing for a cooler intake charge. I think you and others are probably correct that if there was any benefit the factory would of done this on the race cars. Since there was no benefit they kept the more pleasing aesthetics. Would be interesting to run some tests.