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Discussion Starter #1
This season I'll be racing in a new club series. Summing up the major things that are being done to my car in preparation - full bolted FIA rollcage, JRZ RS Pro coilovers, GT3 LCA w/ spherical bearings, bigger brakes, 18 inch Apex wheels + medium compound slicks.

Here's a question that I can't figure out - does it make sense to add a GT4 style wing on the back or not. Will it make the car actually faster.

Obviously some of that depends on the nature of the track. If it was mostly straight lines into slow corners then I'd guess a big rear wing isn't going to particularly beneficial. The tracks I will run are more medium speed, not too many very fast corners but some and with the odd straight line in there. I did in fact buy a wing, it's just that now that I've actually received it the quality of the piece and the mounting isn't really filling me with a lot of confidence.

Now, with my old stock-ish setup I certainly felt I could have used some more stability at the back in high speed corners but I'll be starting pretty much from scratch with a new and quite superior suspension set so it may not be very relevant. I'm also thinking that adding a GT4 rear wing without a GT4 front bumper is going to be off one way or the other.

But if anyone has added a rear wing to their track/race car without doing anything to the front aero and has any feedback it would be much appreciated. I know the car will look meaner with the rear wing, but if it slows me down then it's not really the way I'd want to go. If it gains me even a tenth then I'm all for it.
 

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You will need canards or other front end down force modifications to balance the car. When I added the Techart wing, years ago, TechArt would not sell the wing without their front spoiler. I remember reading a while ago that the GT4 wing had up to 200 lbs down force. The following link talks about the 991.2 GT3 wing and total down force of 155 kgs.

https://www.thedrive.com/flat-six-society/8149/everything-you-need-to-know-about-porsches-new-gt3

The problem is the nose may lift at speed if the wing pushes down too much. Canards or more aggressive front splitter mods (or GT4 nose) would be required to keep the car on the track. Lowering the car to reduce air from flowing underneath will help reduce lift. The wing can increase drag, but the additional down force may allow you to accelerate faster out of turns. The wing angle factors into the drag/down force equation decision matrix. Canards by themselves can increase grip in the front tires enabling sharper or higher speed in turns.

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what wing did you get? I purchased an Amazon.com GT4 replica wing and had it mounted already.
 

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Cayman The Destroyer!
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Having done a CFD study on my Cayman race car I can tell you that it is a rather complicated and sometimes counter intuitive science. Standard advice like lowering the car to reduce lift is in fact incorrect or at least misleading. Ride height is important, rake even more so. Dive planes may increase DF in the front or may not! LOL As I see it adding a modest amount of rear DF with a wing is most likely a good thing even with no front aero mods. 200 Lbs on the rear isn't going to lift the front end much and I vastly prefer high speed push to oversteer! It will also help shift bake bias to make the rears work harder at high speed. Of course adding front DF to keep the center of pressure where you want it is best. However it is not easy to get front DF.
 

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Discussion Starter #5
what wing did you get? I purchased an Amazon.com GT4 replica wing and had it mounted already.
I am still in touch with the seller who has promised me a resolution so I'm not going to name and shame. Mine is also a GT4 clone, but one of the mounting points is 5mm closer to the trailing edge of the wing and they are offset a little more than that to one side to boot. The endplates were drilled wrong and both pointing in very different directions.

I don't believe a GT4 wing is going to provide huge gobs of downforce at modest angles of attack and at the speeds that we will be doing. Max downforce at 175 MPH top speed is somewhat irrelevant but I do wonder how much drag is will cause vs the benefits.

Having done a CFD study on my Cayman race car I can tell you that it is a rather complicated and sometimes counter intuitive science.
Isn't that the truth...reality is that for most of us who aren't involved in professional racing teams (and even then...) it's a matter of fitting it blindly, see how it feels and try not to fall victim to the placebo effect. No windtunnels, obvs. My understanding is that front canards could provide a few lbs of downforce especially that there isn't much of a splitter on a GTS that would interfere with them. Might be worth trying in due time.

Getty also makes a 2-pc splitter that I could fit to my GTS bumper but it looks weird to me with the center part "missing" and not available like it is for the regular 981/S bumper.

GT4 bumper I am trying to avoid as I don't generally like Frankenstein cars with bits of bodywork from superior models fitted to them.
 

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Cayman The Destroyer!
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I agree that adding the dive planes in a worthwhile thing to do along with the rear wing. Very inexpensive and in the absence of other front aero mods they will provide some DF. Remember that the rear spoiler on a Cayman cancels lift more than providing DF. Try it and see how it feels. The base line for my CFD wasn't a stock CS. The car has a splitter, rear diffuser and rear wing. The seat of the pants engineering produced a 40/60 center of pressure and some decent DF. We are still massaging the final design but right now the CFD model shows DF at + 250% with a 33% increase in drag with the same 40% F 60% R center of pressure. Super efficient and as my car has 700 hp to play with I'll take all the DF I can get! I can't wait for it to be done as we have some very high speed turns at tracks I drive.
 

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Cayman The Destroyer!
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Caution your mileage may differ! LOL Some additional analysis showed that the angle my dive planes where mounted caused a reduction of 16 lbs of front DF and 3lb rear DF as compared to no dive planes. Optimizing the angle resulted in a 2 lb front and rear DF gain compared to no dive planes. Go figure??
 

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Discussion Starter #8
Caution your mileage may differ! LOL Some additional analysis showed that the angle my dive planes where mounted caused a reduction of 16 lbs of front DF and 3lb rear DF as compared to no dive planes. Optimizing the angle resulted in a 2 lb front and rear DF gain compared to no dive planes. Go figure??
Yeah good call, thanks. Guess the most reliable solution is to just put on a GT4 bumper eventually if I feel the front is lacking. Probably a little easier to put a rear wing on as it's at the back of the car so not having any downstream knock-on effects.
 

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Cayman The Destroyer!
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I think it's worth trying the canards. It's cheap and could be more effective on a car without the extensive aero mods I have. Use the "seat of the pants" dyno to check it out. After all if it feels like an improvement to you it's worth doing.
 

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what wing did you get? I purchased an Amazon.com GT4 replica wing and had it mounted already.
How did you mount the wing to the car? I have an oem wing and am having a hard time finding mounts without either buying a full replica kit or use oem mounts and figure how to slot my hatch.


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If the rules allow a wing, run a wing. No question. However, run a proper race wing (e.g., GT3 Cup or similar) at full roof height and not a street car wing like that on the GT4.

Also, the referenced article states 155kg of total downforce at top speed, not DF from the wing only. From the calculations I did on the 997 Cup and RSR wings it appears the estimates are optimistic and being made at higher than practical speeds for road racing.

Cheers,
 

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Discussion Starter #12
The season's nearly over so I'll follow up with what I ended up doing.

The first 2 races were sans any wing. Best lap time at my reference track - 1:54.5

Race 3 I added a decent size front splitter to my car. It was custom made at a local shop but more importantly it was 1/10th the cost of a GT4 bumper. Still no rear wing though.
Running only the front splitter did make the car quicker, and didn't really make the car too oversteered. Certainly towards the loose end of things, but manageable. Best lap - 1:53.0 but with slightly better tires than the previous best lap.

Race 4 and 5 I put the knockoff GT4 rear wing on (ditched the weak looking supports though and went for custom alu ones) but also added CMS sway bars. I'd been using my X73 bars up to this point with my fairly stiff springs (750/950 or so) doing most of the keeping-the-car-flat job. Huge, huge difference. In fast corners I was going much, much quicker and the car was planted as hell. 7 to 10 mph increase in minimum corner speeds in some places. Slow corners however did become more difficult and a bit understeer-y. Still, big gains. Best time - 1:51.7. Some mistakes in there worth half a sec but the track was QUICK at that weekend. Overall the car felt maybe just under a second a lap quicker.

My last quali effort was 1.1s off the quickest (modified, more power) GT4 Clubsport - whichwas gaining 1.5s+ just on the straights. A stock-ish Clubsport beat me by a mere 0.3s.

Though not a proper racing wing, I do feel the carbon GT4 wing helps quite a bit. It's actually shaped a bit differently from a GT4 wing if you look at it, with a steeper rear part of the wing. Drag is increased a bit but top speeds haven't suffered massively. Planning a 3.8 X51 swap this winter to make up for that and then some..


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Cayman The Destroyer!
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Love the look and sound of your car. Nice driving using the whole track and getting on the throttle quickly at apex. Glad to hear the aero mods are working well for you. Tuning the suspension and aero to allow easy rotation in low speed corners and a bit of push in high speed corners is a seat of the pants thing that will come as you drive it more.
 
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