986 aero & cooling mods

[tonichristi]

Originally Posted by woodsman

Porsche forgot the 'form follows function' rule on the Spyder- but not the 918.

Are you some kind of expert in aerodynamics, rear diffusing and aesthetic design? More so than Porsche? I'm sure Porsche would love to hear from you. Just shut up, already.

[j.fro]

Alright, moving to the front of the car I've replaced the destroyed front wheel air dams with ones similar to those in the rear. As well, I've added a small air dam to the middle of the underside. Both sets direct air towards the GT3 brake ducts.


Another bit, while we are under the nose, is that I've closed off the factory air exits for the center radiator. Air is now forced to exit through the vents cut in front of the hood. Theoretically, this should produce some downforce. The less air there is moving under the car, the better off it is, right?

[jaykay]

You might consider front fender liner vents:

Flow Through Front Fender Liners

[j.fro]

Originally Posted by jaykay

You might consider front fender liner vents:

Flow Through Front Fender Liners

Got 'em

[jaykay]

Originally Posted by j.fro

Got 'em

Nice...less hovercraft action! That is a quick and effective way of doing it!

...eventually you could go to mesh and seal the under side...but there has to be the correct amount of the cooling airflow through the liner.

[woodsman]

Originally Posted by jaykay

Nice...less hovercraft action! That is a quick and effective way of doing it!

...eventually you could go to mesh and seal the under side...but there has to be the correct amount of the cooling airflow through the liner.

I agree with the theory about venting the center rad upwards but how does introducing 10X the air volume into the front wheel- well reduce lift? With aero less is more- I think but than it depends on intended velocity. Auto makers spend days in the wind tunnel to make our cars 'work' with as little drag as possible. For instance, why increase flow through the rad by 500% ( my guess on JFRO'S liner) AND THEREFOR DRAG when blocking the bottom and venting the liner with 2 4" .25" slits would probably suffice? The key concern is ability to cool while creating the least amount of drag-right? At 60 mph we're hitting a cement-like wall of air and aero is gently persuading. And ya let's discuss- it's a FORUM so there's no need to get pissy or all-knowing.

[jaykay]

Originally Posted by woodsman

I agree with the theory about venting the center rad upwards but how does introducing 10X the air volume into the front wheel- well reduce lift? With aero less is more- I think but than it depends on intended velocity. Auto makers spend days in the wind tunnel to make our cars 'work' with as little drag as possible. For instance, why increase flow through the rad by 500% ( my guess on JFRO'S liner) AND THEREFOR DRAG when blocking the bottom and venting the liner with 2 4" .25" slits would probably suffice? The key concern is ability to cool while creating the least amount of drag-right? At 60 mph we're hitting a cement-like wall of air and aero is gently persuading. And ya let's discuss- it's a FORUM so there's no need to get pissy or all-knowing.

Any "intake" events interacting with the main airstream will almost certainly increase drag. Let's not get into exhaust vents and blown surfaces etc. The front rad vents we are talking about remain as they are; they will cause drag.

This drag will vary with airspeed and perhaps a little with exhaust/venting; airflow through the radiators. The flow path is so convoluted and restricted that would guess very little effect. You need a wind tunnel to know. As a side note I believe I recall a Mustang (aircraft not car) cooling vent that actually produced thrust and hearing about open car windows giving very little drag due "filling" of the cabin at speed...thereby giving the effect of a "closed" window....dunno without testing.

In this case there no aim to reduce drag. We are considering aero and cooling. Consider that improved cooling might achieved by venting the liner and improved aerodynamic performance by closing the downward rad vent exhaust. How so you might ask....well it is felt by some that this is done to reduce front end lift at speed (hence the hovercraft reference). And yes optimizing cooling may hurt aero.

Now does lift occur in the wheel well? Perhaps there is just enough escape path areas ...

[JayG]

Originally Posted by j.fro

Another bit, while we are under the nose, is that I've closed off the factory air exits for the center radiator. Air is now forced to exit through the vents cut in front of the hood. Theoretically, this should produce some downforce. The less air there is moving under the car, the better off it is, right?

are you an Aeronautical Engineer?

I guess theoretically, you could produce some down-force, but without putting it in a wind tunnel there is no way to actually know what is happening. you are likely to cause other things like drag.

Yes, the GT3 has them. Porsche did aerodynamic design and testing to calculate and design exactly what was needed.

Without that design and testing, who knows what is happening. You could actually cause more lift on the from end by disrupting the aerodynamics.

its kind of like using a butt dyno to calculate HP increase

I'm not trying to pick on you. IIRC, you were asking about making modifications to the spoiler as well to increase MPG. Its just without advanced computer modeling and actual wind tunnel testing ANY modification to the aerodynamics of the car as designed could cause unwanted properties and have a negative effect on handling and efficiency