I have been thinking about adding a large rear wing. Racing outside PCA allows them and for open track time it could benefit. GT Racing just came out with a "predator" wing that looks pretty hot. Question is if I increase the rear downforce by 200% (or whatever) what happens to the load on the front? Think this is an issue or not? I am not to crazy about adding any low front splitter. Seems that short cuts across the curbing are required to co exist and stay with the pack.

 

Being a 944 guy, I can only share what I heard from the 'real Porsche' drivers:
Basic rule of thumb: if you increase downforce in the back as you describe, you should also increase downforce in the front: IIRC, I've heard of something like a front RSR or RS spoiler that would do the trick.

I've heard people who increased rear downforce withoout increasing rear downforce felt the car was very unstable, and adding a front spoiler helped this greatly.

HTH,
-Zoltan.

 

You're quite right, it must be in balance! Too much rear downforce, you'll lighten up the front end and understeer at speed. Too much front downforce, the car will oversteer and become unstable. Of course, cars may or may not be balanced with stock bodywork - that's the fun part you get to figure out on track!

Basic principle is as follows; springs and bars to balance the car at lower speeds, in lower speed corners (using Mid-O as an example, think Madness, Carousel, or Keyhole). Then the car must be balanced using only aero on the high-speed corners, such as Turn 1. The most common mistake is to slap on a wing, thereby unbalancing the car, and changing springs and bars to compensate. The net result will usually be a car that handles worse in more corners, and will only have net aero and mechanical balance only at a given speed/corner! <img border="0" title="" alt="[Frown]" src="frown.gif" />

 

I hear the 80's 911's are sensitive to adding a spoiler to either end of the car and not both. Many people have noticed the instability.

Typically passenger cars dont generate downforce (negative pressure), even at higher speeds. Most rear spoilers are used to counteract rear lift, adding rear stability. The rake of the car makes a huge difference in high speed stability, especially with the 993 having a REALLY flat underside. But, in theory, adding aero tweeks to both ends of the car would be best.
This would be interesting to test someday.

I do know on a ground effect racecar, aero balance is EVERYTHING to on-track performance.(and driver confidence and comfort)

 

Bill,

If you read the RS/CS manual regarding the aerokit you'll notice the balance between the front and rear. Most cars that add a wing up in the air flow near or at the roof of the car need something up front to help counteract the rear downforce. Of cars I have seen or have close knowledge of a higher rear wing requires an RSR front splitter with a rather extended front lip to create the downforce needed to balance the rear wing.

Hope this helps.

 

Bill:

What you are talking about adding would be like the wing on my blue race car.

The downforce must be in balance. In fact, on my car, I had an extra front splitter made because if I break the one on the car, its basically undrivable over 80-90mph.

BUT - at VIR your times would fall by 2 seconds or so with proper aero.

Chris Brown

 

Hi Bill,

We added a Fabcar wing to my 914 several years ago. With no other changes (spring rates or shocks) I was almost 2 seconds faster at Roebling Road. Adding a splitter on the front made the car slightly faster. I am looking into installing a diffuser now.

924racr is right. I set my car to oversteer in the slow stuff, and understeer at high speed.

Andy

 

A column in the latest copy of C+D has a very nice interview with Jack Roush. Talking about one uptight new NASCAR driver, he recounted how the guy compained to the crew chief that the car was too loose (in a practice session). The crew chief's response was to take the rear spoiler off and send the driver back out. "That'll teach him what a loose car is!"

 

Thanks for the input! I will hang the wing and drive a test and tune to see what effects I get. The tracks with short straights like Summit, Roebling, CMP and Lime Rock should work fine. VIR and Watkins Glen may be another story. I am sure it will be a fun exercise.

Does PCA rule allow a larger wing in the stock classes. I thought I read that as long as you do not exceed the roof line you could increase the wing size. Maybe I was dreaming.

Andy: You are the king of co-existers. When you lapped us at CMP (during the sprint race) I figured you were my ticket around the car I was stuck behind. He rolled to the right and let you by so I tried to fall in behind you and make it to turn 12 while he was off line. He let you by and chopped me off.

 

You need to balance downforce front and rear, but it's not as simple as a lot of guys see it. Your front hood already functions as a huge wing. I tip-toed with rear wings -- ducktail, 964 tail, IROC tail, RS 3.8, RS 3.8 with extenders, RS 3.8 with extenders and a big honkin' 50+" wing -- and never reached a point where I was outdoing a pretty straightforward front spoiler/splitter combination in front.

The only real way to work it out is to try different combinations on a track you're familiar with and take a lot of notes. Fast and slow sections are going to behave differently. The benfits from aero mods -- especially in back -- are hard to overestimate.

My .02

 

Remember, most turns on a road course are 2nd or 3rd gear and at speeds of less than 70mph. becuase youre turning, the air flow is not even going over the wing as it would in a straight line, and you dont want the extra drag down the straights, if you dont have the power to get beyond it, for negligeble downforce anyway. Unless you plan on using a GT3 speedGT wing, dont plan on getting any more than 20lbs of down force.

Now, nascar is a differnt story, at 190mph, the forces have gone up by the square of the speed.

our fairly big 928 wing puts out 80lbs of downforce at 120mph ,and the 928 has a pretty clean rear deck for air flow. even still, not really a big deal. I remember seeing the Speed touring car leader , smack a wall in the rear , take off teh rear wing and the hatch popped up. the speeds at the track werent even fast enough to push the spring loaded HATCH back down !!

MK

 

I guess it depends on the track. At Willow Springs, only one of the nine turns is less than 70 mph. Six of the turns are 4th or 5th gear turns. At a track like that, the rear wing can mean 3 seconds or more.

 

PCA Stock

6. Body/chassis/interior

I. The addition of any rear wing (not spoiler) to any stock vehicle which could not be added to that year and model as optional equipment (not special order) will cause the vehicle to be classed as "Prepared" and it will progress up one stock class if it has not already done so due to other prepared modifications. Wings added to "prepared" vehicles in the stock classes may not be any higher, realitive to the roofline, than a factory (non-extended) 3.8 RSR wing.

 

The wing that I am considering is not PCA legal. 60" long and raised 6-8" above the club sport wing. I would re install my stock wing for PCA races.

What I am gathering from this input is that a wing of this style will reduce lap time particularly faster through the high speed corners. Little benefit on the slower corners.

I'll take it!

 

Yes, that is true for willow, but interesting enough, one of the POCs best racers and friend of mine, Mark Anderson, was running 1:24s without the wings and splitters. added the BIG SpeedGT wing,and no improvement. Added a big adjustable splitter, and still no improvement. I think the gains are very very subtle. I remember the M3 guys saying their little kick tail wing on the back of the trunk lid , was giving 3 seconds a lap. I had to laugh. I dont think on an old e30, any air gets down that low below the roofline.

anyway, I think willow is the best place to experiement with wings, however, all the turns at the northern tracks are very very slow. 30-70mph at the apexes, with the exception of thunderhill and buttonwillows kink or sweeper,which can be around 90+

as far as Willow, i know turn 1,2,6,8 and 9 are all 70+ turns, but 3,4,5 are pretty slow. so, for 8,9 and 1,2, the wings could have some benifit. also depends on the times.

most of the time, folks get in more hot water trying to guesstimate the down force and wing requirements of a car, than they would if they left things alone. on of the speedvision Vets showed up in canada for a wind tunnel test. Before the tests, the had 10lbs of lift in front and 300lbs of down force in the rear. (after a whole season of toying with them both) after the $30,000 test session, they ended up with 300lbs of down force in the front and 600lbs of down force in the rear, with lower drag overall.
Now, the speeds were probably tremendous,in the tests, and the car made very little improvement in the season as far as times.

without a wind tunnel, its just guess work.
they sure look cool though!!
MK

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by JackOlsen:
<strong>I guess it depends on the track. At Willow Springs, only one of the nine turns is less than 70 mph. Six of the turns are 4th or 5th gear turns. At a track like that, the rear wing can mean 3 seconds or more.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">