peterp

I haven't really followed this thread carefully as I have no intention of making this mod. I do recall the video below that talks about what the creator claims is a bit of an aerodynamic miracle of the 996 design directing radiator air exit to under the wheels using the air deflector in font of the wheel wells. This reduces the radiator air drag from the typical 10 or so percent to less than 1%. I'm not sure whether this has any bearing on this discussion, but posting just in case.

rs10

Thanks for the Turbo PET tip!

As per my first post yesterday (and my previous posts), the goal is purely aerodynamic. The aftermarket bumpers are copies of the Porsche C4S bumper and if installed the same way, you get the same result (to the extent they are good copies). At least, I haven't found any aftermarket C4S copies that come with matching ducts, etc. - if you know of any, please do let us know! Cutting holes is easy. As per my previous post, I want the air to enter the wheel wells directed outwards, exactly like on a C4S, 40AE, Turbo, etc. That is not easy. I have found no solution other than using the original wheel well part. (But if you know of any ... .)

And yes, as per my previous post, I know there are many more parts, having put together a "much longer" list. I was inspired to write the last post after starting to check prices of more of the items on the list. I had thought this project would be affordable because I knew the parts that I expected to be among the most expensive - the bumper, radiators, condensers - were affordable. I figured that something like an a/c hose ("line") couldn't be more than, say, 1/3 the price of a condenser. Turns out they may be more than 3 times the price of a condenser. And there are many of them :- ( (With luck, the C4S only needs different lines to go around the 4wd hardware and the differently shaped trunk. But the PET doesn't specify which the 40AE uses, so I don't know.)

GC996

Good video.

Most folks just aren't fast enough for any aero to benefit them on the track. Mechanical grip with a proper suspension set-up, sticky tires, dureable brakes and lsd is much more important.

No question aero looks damn good, but its irrelevent on the street unless you are looking for aesthetics. But who isnt?

rs10

True. Except on streets where it's even more relevant than on track. Like an Autobahn. Sometimes the car feels almost locked down no matter how fast I go. Sometimes the front gets light and nervous above 200 kpm (124 mph). Previous cars (not P cars) didn't. Seems most likely due to cross winds, but I suppose it could be due to poor road surfaces, or something else. Anyway, I don't like it, and hope to change it.

rs10

Hmm, seems I must have been mistaken about this. If this were true, the C4 would also use different lines from the C2, but it doesn't. So it would seems that if you have something else specific to the C4S (ducts? radiators?). then you need the C4S lines. Probably not condensors, b/c I replaced condensers on a C2 I briefly owned, and if I recall correctly, I was annoyed to learn I paid too much b/c my local specialist accidentally ordered C4S condensers. And they seemed to work fine ... .

pdxmotorhead

My c4 narrow body 2003 only vents downward,

I have CSF radiators, and I have the center rad. (Got a deal and couldn't pass it up)
With the low temp thermostat I run dead on 180 F all the time now even in traffic.
I also did the fan resistor change out and used 100W heat sync'd resistors.
I found 1 dead resister while swapping the radiators so just replaced both.

Interesting bit I found while working on the car, I have a piece on the belly pan thats right at the the rear cross member,
it wasn't in my shop manual, its got louvers in it that seem to guid air up around the bell housing, I assume to help keep the clutch cooler.
It attaches between the under-tray large sections and the cross bar.. I went to the dealer and had them look up the number and its a GT3 part.

GC996

Check out Demons dive planes. Heck of alot cheaper than reworking the front bumper.

https://www.demonspeedmotorsports.co...ords=Dive+plan

As a side note, if you don't like the idea of dive plans, check into the multiple front spoilers they have for just about every bumper. I have one of their GT3 front spoilers. Haven't put it on yet but probably will this spring.

Here is the point, aero is nice, but mechanical set up is better before you play with aero. If you are going to drive at 125, you better have a solid, well balanced set-up first. I have done over 1200 laps at Road America on the straights between 130 and 145 without aero. Sure, at 145 in a cross wind the front gets a little light but its predictable.

Tire pressures and tires are also very important. Over inflated tires at that speed are traveling on a very narrow patch.

parris

In my opinion, is not just a question of aero benefit on the track. The aero management in these and any high performance car (and in almost every car) has a lot of engineering behind it and direct impact in thermal management of the engine, drag reduction, stability even fuel economy

Maybe small modifications like opening some vents doesn't have a big impact, but others, like removing the whole air duct behind the fans can mess totally with the way the air is managed around and under the car and have really implications that you can notice (more difficult to cool the engine under high demand, vibration in the wheels, brake fading appearing sooner due to a poorer cooling)

GC996

Bingo. Our cars slice thru the air at speed. Well designed. Quite frankly, I didn't want to mess with aero after I got the right mechanical grip. Didn't want to mess up.

pdxmotorhead

Just soemthing I noticed when I did the 3rd radiator ,,, when you cut the hole for the ductwork it actually creates a pretty fail sized area to push down on the nose.
Not ginormous but I'd say a 18" x 10 inch area of new surface area.. the rearward flow is limited by the size of the air reliefs that are already there..

And I kinda like the new silver area the radiator gives the slot across the bumper. Looks more functional.

rs10

My views are similar. So I'm reluctant to go with a solution that was not designed by Porsche or someone else whom I'd trust to design and test it well, e.g. Manthey, Ruf, ... am I missing someone?

And I fear that if you have a C4S bumper and Carrera radiator and somehow cut/twist/modify the ducts (whether C4S or Carrera) to direct air from one to the other, you are playing with the aero almost as much as if you cut/twisted/modified the bumper itself. On the other hand, I haven't had a good look at either kind of ducts or radiators or their position in the car, and while I understand a good bodyshop can work miracles with a metal fender, I have no idea what they can do with a plastic duct ... .

wdb

I resurrected this thread a while back and rambled a bit about 40AE vents and 997 vents and so on. I finally got to a point where I wanted to have a go at venting into the wheel wells on my own car.

The first iteration was a bit of a bollux. I didn't just want holes in the liner because I didn't like the idea of the wheels heaving who-knows-what into the radiator fans and who-knows-where else. The 997 and 40AE have vents that direct air outwards, so that's what I did. The problem was that I bent the vent tabs outwards, into the wheel well. I had a rude surprise when I installed the liners and the wheel, and realized that the clearance is very tight! The tire hit the tabs. Ugh. Doh. All that.

So then. On to wheel well vents V.2 I bought another pair of liners, laid out vent cutouts, and this time bent them inwards towards the radiator fans. I'm pleased with the result. I took the car for a run which included a brief high speed section, and the front end did not get that floaty feel. It was too short to be a definitive result but I am encouraged.

With the car hot and the fans running I could feel air coming through the newly cut vents. But there was still more air coming out the bottom. I plan to work on that area next but I want to wait until I can test in warm weather, which it definitely ain't where I am.


Radiator frame and fan shroud showing the chunk I cut out


The two pieces together showing the resulting hole into the wheel well


I laid out the vent cutouts on the radiator side of the liner


Head-on shot of the finished product -- what the tire sees


View from the side showing how the air should be directed outwards

circuit.heart

Doesn't really work like that. The flows in the wheel well area are dictated much more by pressure gradients and turbulence than anything else. The guided vents make a minimal amount of aero difference vs just having holes in the liner; like you said, the "tire view" is good to prevent rocks and such from hitting the cooling stack.

If you want to increase the exit flow from the rear vs the factory bottom exit, add a spat on the edge of the bumper a la later GT3's. No matter if you use a crude flap protruding from the fender liner, or a sculpted flick like an OEM solution, you're squirting air outward away from the car right before the wheel well, which lowers wheel well pressure and will aid extraction from the radiator.

hatchetf15

Like this, perhaps?

Tarett dive planes with homemade ABS wheel well deflectors and Demon Speed cup lip

Formerly996fried

I own a 996-01 Cab and have purchased new CFS radiators and a center radiator. One rather rainy afternoon, I began to scour the net and various part vendors for the mounting brackets, I came across part #11, which is the back panel ( Porsche 99657515101 ) that mounts behind the center rad which sends the center radiator airflow under the car, into the existing slots in the under pan. Since I am not going to track the car, and most of my driving consists of driving in local two-lane curvy roads from Shades of Death Road to back roads of the Poconos, although I did experience a light front end while driving at 120, I do not think that the venting wouldn't be much of a hindrance to affect my driving as most of my top speed never gets past eighty-five to ninety, to begin with. If one notices the top of the back panel, several plastic bungs slip into the #2 bracket.....although I riveted on some metal brackets to #2 bracket as there are some lower side mounts on #11 that use bolts to further fasten it. .

Sometimes, I wonder just how many other obscure Porsche parts are available?,