Good news everyone! I've finally got around to fixing most, if not nearly all the glitched cars for the 13D spec! G will update the OP as well, but here is the near final list for everyone.

I worked too much on this, spent too much CR on this, and got eventually tired of doing it... But now I've got this far with it, it should improve and make a much more fun, enjoyable, and even racing at the infamous wangan!
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Cars with special specs for 13D class (A-Z)
(All cars that are duplicates, will use that spec, unless the duplicates are proven glitched more than the car used for spec)
- Aston Martin V12 Vantage - 480hp/1500kg
- Audi R8 4.2 FSI R Tronic ‘07 - 460hp/1,320kg
- Audi RS6 Avant ‘08 - 450hp/1,680kg
- BMW 135i Coupe ‘07 - 475hp/1,475kg
- BMW M4 Coupe - 450hp/1,525kg
- BMW M5 ‘08 - 470hp/1,740kg
- Chevrolet Corvette Stingray C7 ‘14 - 405hp/1,530kg
- Chevrolet Corvette ZR-1 C4 ‘90 - 430hp/1,600kg
- Chevrolet Corvette Z06 C5 ‘04 - 415hp/1,415kg
- Chevrolet Corvette Z06 C6 ‘06 - 410hp/1,450kg
- Chevrolet Corvette ZR1 C6 ‘09 - 455hp/1530kg
- Dodge Charger SRT8 ‘11 - 470hp/1,520kg
- Dodge Viper GTS ‘02 - 450hp/1,580kg
- Dodge Viper SRT10 Coupe ‘06 - 500hp/1,430kg
- Dodge Viper '13 - 425hp/1,510kg
- Ferrari 512BB '76 - 430hp/1,600kg
- Ferrari GTO ‘84 - 420hp/1,360kg
- Ford GT40 MK1 '66 - 360hp/1,280kg
- Ford Mustang Mach 1 ‘71 - 450hp/1,500kg
- Ford Mustang SVT Cobra R ‘00 - 440hp/1,600kg
- Ford Mustang V8 GT Coupe Premium ‘07 - 470hp/1,560kg
- Honda NSX Type R '02 - 440hp / 1,370kg
- Hyundai Genesis Coupe 3.8 Track ‘13 - 460hp/1,570kg
- Isuzu 117 Coupe ‘68 - 319hp/882kg
- Isuzu Piazza XE ‘81 - 349hp/996kg
- Jaguar S-Type R ‘02 - 435hp/1,700kg
- Lamborghini Countach LP400 ‘74 - 400hp/1,265kg
- Lamborghini Countach 25th Anniversary '88: 452hp / 1,480kg
- Lamborghini Miura P400 (Proto) ‘67: 300hp/1,180kg
- Lexus LFA ‘10 - 440hp/1,620kg
- Lotus Esprit Turbo HC ‘87 - 380hp/1,340kg
- Lotus Esprit V8 ‘02 - 440hp/1,430kg
- Lotus Evora '09 - 410hp/1,130kg
- Mercedes SL55 AMG R230 ‘02 - 490hp/1,975kg
- Mercedes C63 AMG ‘08 - 490hp/1,560kg
- Mazda Atenza (Speed 6 MPS) ‘05 - 420hp/1,430kg
- Mazda Roadster RS (NC) ‘07 - 397hp/930kg
- Mazda RX7 FC GT-X (FC) ‘90 - 450hp/1,290kg
- Mazda RX7 FD efini '91 - 440hp/1,330kg
- Mazda RX7 FD Type A '02 - 420hp/1,465kg
- Mitsubishi GTO/3000GT ‘98 - 470hp/1,370kg
- Mine's Lancer EVO VI - 470hp/1,115kg
- Mugen S2000 ‘00 - 460hp/1,150kg
- Nissan 200SX/Silvia K's AERO (S14) ‘96 - 452hp/1,350kg
- Nismo 270R ‘94 - 400hp/1,430kg
- Nissan Fairlady Z Version S (Z33) ‘07 - 410hp/1,560kg
- Nissan GTR R35 - 410hp/1,840kg
- Nissan Sileighty ‘98 - 415hp/1,270kg
- Nissan Skyline R32 V-spec II (R32) '94 - 430hp/1,495kg
- Nissan Skyline GTR V-Spec II Nur (R34) ‘02- 470hp/1,265kg
- Nissan 300ZX 2seater (Z32) ‘98 - 450hp/1550kg
- Nissan Z 300ZX Z31 '83 - 435hp /1300kg
- Oullim Spirra Prototype ’04 - 410hp/1,270kg
- Plymouth Superbird ‘70 - 550hp/1,320kg
- Renault R5 Turbo ‘80 - 328hp/848kg
- RUF 3400S ‘00 - 450hp/1,400kg
- RUF RGT ‘00 - 390hp/1,530kg
- RUF Yellowbird/BTR - 470hp/1350kg
- Spoon Civic Type R (EK) ‘00 - 308hp/820kg
- Spoon Integra Type R (DC2) ‘99 - 314hp/1,075kg
- Spyker C8 Laviolette ‘01 - 400hp/1,270kg
- Tommy Kaira ZZ-S ‘00 - 353hp/690kg
- Toyota Aristo 3.0V ‘91 - 430hp/1,680kg
- Toyota Aristo V300 ‘00 - 450hp/1,680kg
- Toyota Soarer 2.5GT-T ‘97 - 415hp/1,650kg
- Toyota Supra 3.0GT Turbo A ‘88 - 450hp/1,650kg
- Toyota Supra RZ '97 - 410hp/1,680kg
- Toyota MR2 GT-S ‘97 - 350hp/1,470kg
- TVR V8S ‘91 - 400hp/1,250kg
- TVR T350C ‘03 - 400hp/1,190kg
- TVR Cerbera Speed 6 ‘97 - 400hp/1,150kg
- TVR Griffith 500 ‘94 - 400hp/1,200kg
- TVR Tamora ‘02 - 400hp/1,200kg
- TVR Tuscan Speed 6 ‘00 - 400hp/1,200kg
- VW Golf VI R ‘10 - 461hp/1,310kg
- VW Scirocco R ‘10 - 461hp/1,240kg
Investigated cars (More specs coming soon)
- Pre-tuned cars that don’t appear in the previous list
- Pretty much every car technically, since I’ve not tested every single car on GT. But most shouldn’t be glitched at least.
Temporary forbidden cars
- Detuned supercars
- Cars with flat floors
- Cars under investigation or known to be glitched, but not fixed
- Concept cars
- Prototype cars
Experimental spec
(These cars are still in progress and are allowed, but may be glitched, use them if you want and report back to @KazaMR2 if they are OP)
- RUF CTR2 ‘96 - 460hp/1,500kg
- Chevrolet Corvette Stingray Racer Concept ‘59 - 310hp/1,350kg
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The new part at the end is pretty much cars that are still being tested, but aren't fully fixed yet. Feel free to test those against yourselves in lobbys to see what you think.
Also... With the 13D spec pretty much complete, I will begin creating the next stage up...
THE ZODIAC
Stay tuned for the new spec details, I'll get onto making them soon, but for now 13D will be the main wangan class.