Classing a 992 GT3 RS for NASA TT: A Real Worked Example

This is the actual classing exercise for my car — a 992.1 GT3 RS with the Weissach package, campaigned in NASA Great Lakes. Every number below is the same math the classing formula article teaches, applied to a real build sheet. Use it as the template for classing your own car, whatever it is.

Step 0: the DRS problem

Before any arithmetic: a stock GT3 RS with functioning DRS cannot run TT1–TT6. ST rule 6.1.1 bans active aero — factory systems included — in every numbered class. Options: keep everything live and run TTGT (no form, no dyno, no classing math at all), or disable and fix the DRS system and class the car normally. This one rule surprises more Porsche GT owners than any other line in the book — the GT3 class FAQ covers how it applies across the GT3 family.

Step 1: the baseline numbers

Input	Value	Source
Peak wheel hp (Dynojet)	~470	Typical stock 992.1 RS range 465–480; your certified sheet governs
Average HP (7-point method, 9,000 rpm redline)	~456	High-revving NA engines average near peak
Competition weight (car + 180 lb driver)	~3,440 lb	Weissach curb ~3,260 + driver
Tires	Trofeo RS	Unlisted DOT R-comp = +0.0 factor
Transmission	PDK	−0.2 in TT1/TT2

Step 2: the TT1 math

Base ratio: 3,440 ÷ 456 = 7.54. Factors: weight over 3,400 is +0.2, PDK is −0.2 (they cancel), Trofeo RS +0.0. Adjusted: 7.54 against TT1's 6.00 floor. Comfortably legal, nowhere near TT2's 8.00. With DRS disabled, this car is a TT1 car as delivered — full stop.

Worth knowing: TT2 runs an extra factor TT1 doesn't (printed rear section width over 315 is −0.3 in TT2/TT3), so the same car checked against TT2 lands at 7.24. Not close.

Step 3: every realistic path to another class

Target	Change	Adjusted ratio	Cost	Lap-time price
TTGT	Nothing — keep DRS live	n/a	$0	Fastest config; DRS worth roughly half a second
TT1	Disable DRS only	7.54	~$0–500	The default competition config
TT2	Cup 2 R or R7 + 300 lb ballast	8.10	~$2,850	+0.3–0.6s — sharpest TT2 build
TT2	Michelin Cup 2 (+2.0 factor)	9.24	~$2,000/set	+1.6s — simplest, huge legality margin
TT3	PS4S (+3.0) + ballast	10.4+	~$1,450	+4s — and unlocks TT Street eligibility
TT4–TT6	—	—	—	No path: ratio gap and factory-hp gates exclude the car

The strategic read for Great Lakes specifically: TT1 winning pace at Mid-Ohio ran 1:28.8–1:30.7 in 2024–25, and TT2 was effectively a one-car class running ~1:39. A GT3 RS built to the 8.10 TT2 spec gives up half a second and gains a class where the competition is nine seconds back. That's not cheating — that's reading the rulebook and the entry lists together, which is the whole game.

Step 4: compliance posture

Declare HP with headroom above your dyno sheet (dyno-on-demand plus GPS monitoring means the declared number must survive any test day — dyno protocol here), declare minimum weight you can make with fuel burned, and file the form before the first event. Then stop touching the car: post-first-session changes need TT Director approval.

Run your own car through the same sequence in the TT Engineer tool — it applies the full 2026 factor tables, including the ones people forget. New to all of this? Start with the complete guide and the class structure.

FAQ

Why can't a stock GT3 RS run TT1? Functioning DRS is active aero, illegal in TT1–TT6 even as a factory feature. Disable and fix it, or run TTGT/TTU.

What's the cheapest path to TT2? A +2.0-factor tire (Cup 2, A052, RE71RS) does it in one line item with margin to spare. The fastest TT2 build keeps a +0.0 tire and uses the full 300 lb ballast allowance instead.