Venting the ducktail

[JohnJL]

I recall seeing some pics out there of speedholes and vents people have put on their reflector panels and in the backside of their ducks and IROC tails. I am contemplating the same but cant put my finger on those pics to judge them...

I have chosen a fairly closed pattern for my standard grill opening as it fits the look of the car and what I am going for. Is it perforated aluminum 1mm thick with ~2.5mm holes. I suspect it will allow much less air to freely flow into the engine compartment than the standard grill.



As I am now finishing up all the bodywork, now would be the best time to cut and mount the grill inserts if I was going to do that. THis is a crude Paint version of what I mean: Perf aluminum where its black here:




I am going to paint the perm material body colored (dark charcoal.)

If anyone can share pics of having done something similar, and if anyone has measures of enginge compartment temps with and without vents that would be awesome data. I swear there was a thread on that some time back but I cant find it.

Thanks!

[rywats]

A friends car:

RWB AYU Diffuser by ryan.watson, on Flickr

[winders]

Why would you want to vent the back of a ducktail? What do you think you will gain?

[RSTarga]

That is way to tight a pattern in our grill to cool the car properly. The vents in the back of the ducktail will not help either.

[Winter]

RSTarga has a very good point.

In that regard, there's an old thread that I remember where someone did some airflow comparisons with different decklids in regards to cooling.

You might want to search and see if you can find it. (I'm too lazy to look right now).

Unless, of course, cooling isn't your motivation with this mod and looking "cool" is what you're all about.

Regardless, good luck with your project.

[-Levi-]

Not mine but pretty cool

[JohnJL]

Originally Posted by winders

Why would you want to vent the back of a ducktail? What do you think you will gain?

I am trying to give my engine fan as much air as it wants. The back of the duck is an area of turbulent, lower-pressure air, I am thinking a place that wont mess with the function of the duck and give the fan another supply path.

[JohnJL]

Originally Posted by RSTarga

That is way to tight a pattern in our grill to cool the car properly. The vents in the back of the ducktail will not help either.

Could you expand on that? I am interested?

[JohnJL]

Originally Posted by Winter

RSTarga has a very good point.

In that regard, there's an old thread that I remember where someone did some airflow comparisons with different decklids in regards to cooling.

You might want to search and see if you can find it. (I'm too lazy to look right now).

Unless, of course, cooling isn't your motivation with this mod and looking "cool" is what you're all about.

Regardless, good luck with your project.

I remember that thread too but I cant find it.. My motivation is to achieve both the aesthetic and the engine/aero needs.

[JohnJL]

Originally Posted by -Levi-

Not mine but pretty cool

That pic looks like the leading edge of the duck is also drilled. I dont want to mess with teh front of the tail, that seems like a very functional aero area. I am just talking about the backside.

[911pcars]

To reduce any suspected turbulence under the ducktail area, merely add some material to block air flow into that area (replicate the factory underside). Not sure how the addition of holes on the backside reduces any tubulence inside the lid. But that's just me.

Sherwood

[winders]

Originally Posted by JohnJL

I am trying to give my engine fan as much air as it wants. The back of the duck is an area of turbulent, lower-pressure air, I am thinking a place that wont mess with the function of the duck and give the fan another supply path.

If you want more cooling, leave the ducktail alone. It creates a high pressure area right where the engine decklid grill is and that should improve the amount of cool air getting to the engine intake and engine fan.

Also, you do not want to put a more restrictive engine grill in place. That is the opposite of what you are trying to accomplish. You want that area open.

See here:

Cut slot into ducktail to increase airflow into engine

[Uwon]

+1
Well said winders.
Cheers
Johan

[JohnJL]

Originally Posted by 911pcars

To reduce any suspected turbulence under the ducktail area, merely add some material to block air flow into that area (replicate the factory underside). Not sure how the addition of holes on the backside reduces any tubulence inside the lid. But that's just me.

Sherwood

Hi Sherwood,
THanks for the reply. I am not specifically trying to manage the airflow patterns, just to see if there is collective tribe logic on if vents at the back of the duck can supplement the engine's need for air if indeed the perforated patters is too restrictive. And pics of what people have done.

[JohnJL]

Originally Posted by winders

If you want more cooling, leave the ducktail alone. It creates a high pressure area right where the engine decklid grill is and that should improve the amount of cool air getting to the engine intake and engine fan.

Also, you do not want to put a more restrictive engine grill in place. That is the opposite of what you are trying to accomplish. You want that area open.

See here:

Cut slot into ducktail to increase airflow into engine

I agree thats what I meant in my earlier reply regarding the green car. I dont want to mess with the front and top of the ducktail. Call it a wing, spoiler or whatever, I dont want to mess with the main function of the duck. But if if there is any real-world experience with venting that backside of the duck without significantly impacting the function and if it indeed allows more cool air in then that's what I'd like to hear about some experiences.

[winders]

Originally Posted by JohnJL

I agree thats what I meant in my earlier reply regarding the green car. I dont want to mess with the front and top of the ducktail. Call it a wing, spoiler or whatever, I dont want to mess with the main function of the duck. But if if there is any real-world experience with venting that backside of the duck without significantly impacting the function and if it indeed allows more cool air in then that's what I'd like to hear about some experiences.

There is a low pressure area on the back side of the ducktail (it's a spoiler). Putting holes there would, if anything, pull air out of the engine compartment. Again, not what you are trying to accomplish.

Really, leave it alone and don't use that grill material you showed anywhere. It will restrict air flow into the engine compartment.

[JohnJL]

Originally Posted by winders

There is a low pressure area on the back side of the ducktail (it's a spoiler). Putting holes there would, if anything, pull air out of the engine compartment. Again, not what you are trying to accomplish.

Really, leave it alone and don't use that grill material you showed anywhere. It will restrict air flow into the engine compartment.

I think I am going to leave the duck alone and see what intake temps are like with and without the grill. I can log the IAT and oil temps, and come to think of it I have a few spare channels in MS, maybe I will hook up an air temp sensor in the engine compartment and see what happens with and without the grill...

Still would like to see pics of grills on the backsides of ducktails if anyone has some. Just out of curiousity.

[Mick_D]

Venting the ducktail is useless in terms of feeding air to the fan. In fact it may actually rob the fan of air, given Bernoulli's principal of path of least resistance: air will flow in from the big grill and right back out the slots under the tail. While this could improve airflow coming up from the road into the engine bay by dropping air pressure within it, that air would be a lot dirtier than the air coming from the grill.
Just a guess.

[Steve@Rennsport]

Originally Posted by winders

There is a low pressure area on the back side of the ducktail (it's a spoiler). Putting holes there would, if anything, pull air out of the engine compartment. Again, not what you are trying to accomplish.

Really, leave it alone and don't use that grill material you showed anywhere. It will restrict air flow into the engine compartment.

True wisdom right here!!

[911pcars]

Why not then question the airflow characteristics using the factory engine lid?

I have measured ambient air temps at the carb inlet. At speed, it's the same as engine compartment air temp. as well as the ambient air temp. However, at rest, intake and cooling air is also subject to heated air from the road surface and the exhaust system.