Cut slot into ducktail to increase airflow into engine

[axl911]

Aerodynamicists...

From the picture below, it looks like there is a high pressure area toward the end of the ducktail.

Soooo...if I want to increase airflow into the engine, I can cut a hole as drawn in blue?

Am I thinking correctly here?



thanks,
anthony

[Geronimo '74]

If it's a high pressure area, I would say you would get more air into the engine compartiment.
But sacrificing some downwards pressure on the tail, so more lift at the rear axle?

No expert, just some logical (?) reasoning?

[dipso]

I'm sure the designers of the tail knew what they were doing. If it is an area of higher pressure, I would think that it is there to force lower pressure air in front of it into the existing grill cover.

I wouldn't mess with it. Besides a big hole there would look silly.

[Porchcar guy]

Cut the hole, cover it with a grill and put a rubber surround and you have a whale tail :=)

[Kidasters]

I think it's a really bad idea. You want more air why? Cooling? Then install another oil cooler or duct your current one. If you really really wanted to get air to the engine, build a snorkle out of fiberglass that goes over the roof.

Carving the duck is a bad idea.

[kach22i]

I've seen several photos of slots cut into ducktails, and this was after I drew some sketches of it for another thread about six years ago.

I do not know the outcome of such slots, but they were well done and looked pretty cool.

To me it looks like you give up the down force in trade for air flow into the engine compartment (or route directly into airbox).

EDIT: found the old thread.
Cooling fans and ideas.

[DanielDudley]

Early whale tails have a hole about 1/3 the size of the one in your drawing in terms of length and are about as wide. I would start from there.

[Walter_Middie]

I'm an aerodynamic engineer and I usually stay out of these discussions because they deteriorate quickly. I'll just say no - cutting slots in the spoiler will not help.

The spoiler works completely differently than a wing. The spoiler spoils and separates the airflow coming off the roof, creating a high pressure area on the back window and top of engine lid where the engine airflow intake is (as shown in your picture). Engine cooling air is increased because the intake is now in a high pressure region, and air is forced into the engine compartment. Cutting the hole shown in blue will decrease the effectiveness of the spoiler and decrease the amount of pressure pushing air into the engine compartment.

[axl911]

Originally Posted by Walter_Middie

I'm an aerodynamic engineer and I usually stay out of these discussions because they deteriorate quickly. I'll just say no - cutting slots in the spoiler will not help.

The spoiler works completely differently than a wing. The spoiler spoils and separates the airflow coming off the roof, creating a high pressure area on the back window and top of engine lid where the engine airflow intake is (as shown in your picture). Engine cooling air is increased because the intake is now in a high pressure region, and air is forced into the engine compartment. Cutting the hole shown in blue will decrease the effectiveness of the spoiler and decrease the amount of pressure pushing air into the engine compartment.

Thanks Walter.

But I also have a question, would enlarging the existing opening on the ducktail lid cause more airflow into the engine?

--anthony

[kach22i]

Originally Posted by axl911

existing opening on the ducktail lid

Just to clarify, you mean the stock/standard grill opening, right?

[axl911]

Originally Posted by kach22i

Just to clarify, you mean the stock/standard grill opening, right?

Yes, stock/standard grill openging on my ducktail. Want to get more air into the engine compartment.

If the idea pans out, I'll just cut a hole out just behind the standard grill opening.

[dhagood]

Originally Posted by axl911

Want to get more air into the engine compartment.

why do you think this is important? what will it accomplish?

[axl911]

Originally Posted by dhagood

why do you think this is important? what will it accomplish?

I am looking for ways to lower my air intake temperature. It's hot here in Texas. Engine compartment is at least 10-20 degrees hotter than outside air.

[Geronimo '74]

Did you measure that?
Did you measure during idling and driving?
Do you have the readings to post, that would be interesting.
Maybe there are other alternatives to solve the problem. (have you heard abojt the cool collar ))

[Joeaksa]

Are you checking cylinder head temps? If not then why all this hassle before checking the CHT temps to even see if this is needed.

Frankly if Porsche did not see the need for it, I would not do it. Yes, parts of America are warmer than what we usually saw in Germany but not that much warmer and well within the safe range for operating the flat six engine family. First thing I would do should I find the temps getting warm is to put a second or larger oil cooler on the car. This is a "air/oil" cooled engine, not just an air-cooled engine.

If you are really concerned about getting more air in the engine compartment might look at putting a whale tail on the car in summer months. Personally I would leave it alone.

[kach22i]

Originally Posted by axl911

I am looking for ways to lower my air intake temperature. It's hot here in Texas. Engine compartment is at least 10-20 degrees hotter than outside air.

Have you seen this thread yet?
Cool Air Intake - Plywood

[Flieger]

At the rate that air is sucked in with the fan, I do not think a larger opening will make any difference in air intake temperatures. If the air is warming up that quickly that the high mass air flow from the fan is heating up 10 degrees you would need some nitrous oxide or other compressed/liquified gas to take advantage of a drop in pressure or a phase change. Maybe put an intercooler on it and spray water on it?

How are you measuring those temperatures? You are most concerned about the temperatures at speed (both road speed and engine speed) at the butterflies.

[axl911]

It's a 993 with a slightly modded engine.

I've measured the temperatures with a hand held laser temp gun. I also have AIT, EGT, and multiple CHT temperature sensors.

When this engine had its aluminum vram intake, the engine bay temp is about ambient temp. With the SC producing heat, it is about 10-15F higher. Car runs great, but always looking to improve things so I am looking for way to lower the engine temp and or AIT.

Instead of cutting my lovely painted ducktail, I am now thinking of putting electric 8" fans on the grill opening to suck in more air. Also thinking of sheets to direct air around the engine bay. Right now it's just going in from the grill and taking the shortest path to the engine fan.

If I can direct the air from the grill to the back of the engine, then into the engine fan, this may help lower the engine bay temp a bit.

What do you think?

[axl911]

I have to admit that the ducktail DOES cool the engine very well. As mentioned before, even after driving in Texas rush hour traffic in the middle of 110F summer, I put my hands on the vram aluminum intake, it doesn't feel hot or warm.....just ambient temperature!!!!

[Flieger]

You cannot get the air below ambient temperature without a refrigeration heat exhanger system (A/C) or using the phase change of liquid water to water vapor by misting an intercooler with water or packing it with ice.

Hand-held temp gun- you mean an infra red thing? Those only measure surface temperature and only if the surface has the right range of emissivity. The worst part is that the laser dot is really a gimmick. There is a little camera in the gun that has a cone of vision and it takes the average surface temperature of that surface based on infra red radiation given off by that surface. You need to be almost touching the surface for it to be accurate in regards to the dot.

Is your main goal cylinder head temperature reduction or intake air temperature reduction?

It looks like you have a water/air intercooler. What is the air temperature? The Aluminum intake will be a lot warmer than the air flowing through it.