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Discussion summary
YOUR RESEARCH997GT3/Cup underbody panel swap
Leading reported evidence
Run car over the weekend in the gt class
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
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0
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1
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Read evidence and context
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Performed · outcome unconfirmed · Original poster
We ran the car over the weekend in the GT class with NASA.
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Suggestion
I welded studs to the underside when i did my rebuild so i could use the factory hardware and I still need to replace the panel under the trans that has the naca ducts.
Leading evidence: 'Run car over the weekend in the gt class' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Replace panel' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed · Original poster
I ran all weekend on two sets of used tires, both carryovers from the last race I ran in 2024.
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Performed · outcome unconfirmed · Original poster
Sheet metal crews in place of bolts can be used but that's a little more ghetto and not quite as durable long term.
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Performed · outcome unconfirmed · Original poster
I ran all weekend on two sets of used tires, both carryovers from the last race I ran in 2024.
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Replace panel
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that contain suggestions
1
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Suggestion
I welded studs to the underside when i did my rebuild so i could use the factory hardware and I still need to replace the panel under the trans that has the naca ducts.
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Suggestion · Original poster
The panels use the existing attachment points in the center but naturally the attachment points are different around the perimeter since the 996 chassis doesn't have any panels there.
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Suggestion
I welded studs to the underside when i did my rebuild so i could use the factory hardware and I still need to replace the panel under the trans that has the naca ducts.
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26 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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I posted this in the 996GT3 forum but the same applies to the standard 996.2 model so I figured some may find it useful here.
I"ve been meaning to do this for a long time but just got around to installing the 997GT3/Cup flat underbody paneling. The panels use the existing attachment points in the center but naturally the attachment points are different around the perimeter since the 996 chassis doesn't have any panels there. You will simply need to install 10 riv-nuts to bolt every thing up at correct locations at the outboard points. I used M5 riv-nuts with M5x16mm flanged bolts. With a lift this is a very easy job for anyone who is moderately handy and knows how to use a rig-nut tool. Sheet metal crews in place of bolts can be used but that's a little more ghetto and not quite as durable long term.
This mod significantly smooths out the airflow under the car. We are in the process of developing strakes for the underside like those used on the later 991 and 992 race cars and also a diffuser which will tie in with the aft-most panel covering the underside of the engine and extending out to the rear bumper.
STOCK 996 PANELS:
997GT3/CUP PANELS:
Man i cant believe i have had a cool mod on my car before powdrhound
. I welded studs to the underside when i did my rebuild so i could use the factory hardware and I still need to replace the panel under the trans that has the naca ducts. All the part numbers can be found in the 7-3 autoatlanta pet page.
His car is set up like a gt-2 so yes it has the correct fender liners and ducts. His front tray is also from a 7-gt so it has naca ducts under the lca that direct air to the lca scoops and the into the rotors. Its all pretty slick.
Correction: his front section is a cf undertray splitter
That's correct. The underside of the front of thecar is fully sealed off with a large carbon splitter bolted to the front subframe. The side radiator air is vented directly to the front brakes via the 996Cup upper air ducts. This is where the majority of brake cooling occurs. The front brake rotors also receive additional cooling airflow from under the car diverted via 997Cup Grand am ducts.
That's awesome. I'd been measuring my car for an undertray + rear diffuser mod because the rear-engined layout makes it just so easy. Now knowing that 997 stuff fits, the only reason I'd still roll my own undertray would be to avoid the Porsche tax.
Part numbers and recent pricing:
997.504.527.02
front $170 (6TT or GT2 version will work in place of this also and compatible with the rest off 997 panels)
997.504.043.00 center $180
997.504.343.03 center left $148
997.504.344.03 center right $148
997.504.629.92 rear $123
997.504.429.01 rear triangle (.91 is Cup version) $110
That fitment looks perfect. Those fins at the front end are interesting. What�s the intended purpose of those?
The underside of your car looks like a complete work of art!
The curved fins are designed to evacuate the air under the car out to the side. This in turn creates a low pressure area under the car. These are commonly used on pretty much all modern race cars including GT4RS, GT3Cup, GT2RS, etc, etc. These fins are actually OEM GT4RS parts.
Thanks, that makes sense. I love how you�re adopting the technology from all the newer cars. I�m looking forward to hearing how your new aero performs!
Maybe my car can be the test bed for the center exhaust version
. Looks great.
Btw i copied all your other panels over the winter. Also addes a naca duct for the trans cooler.
We machined 5 sets of the diffuser fins so we have enough to make 4 more diffusers. One set is already spoken for. We have the flat base panel in CAD so that can be cut whenever. Not sure if we are going to make a "kit" per se.
Quick update on the diffuser. We ran the car over the weekend in the GT class with NASA. Besides qualifying, I did two races on Saturday and one race on Sunday along with an invite to run in a Time trial session Sunday in the Unlimited category. The car performed admirably all weekend winning all races and also the TT session. The car also set the fastest lap of the weekend.
The weather was challenging with pretty cool temperatures in the morning around 45F but warming up to around 70F in the late afternoon but with heavy winds of 25-30mph and gusting to 40 all weekend. Sunday was a little better but still very windy. The diffuser exceeded my expectations. I ran all weekend on two sets of used tires, both carryovers from the last race I ran in 2024. Even with the rather iffy tires, the back end of the car was extremely planted with zero hint of ever wanting to let go. I actually corded one of the rear Michelin slicks and it was still performing great. The areas of the track, particularly the high speed 75-100mph sweepers where last year the rear was a bit loose when pushed hard, was now absolutely buttoned down, even on the mid-life and older tires. I was rather surprised what a huge difference the diffuser made. It's hard to say with absolute certainly, but I would estimate it's producing an additional 100-150 lbs of down force at 80+ mph just based on how planted the rear end felt. There were zero issues with it all weekend. All in all, a resounding success. We will be installing one of these on a friend's 997GT3 race car that we will be running in some 6 and 12hr endurance races later this year. The aero benefit will pay huge dividends over the course of a longer race.
Here are a few pics of the sled at the end of Sunday. The back of the car is definitely due for a good scrubbing......
cheers...
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