1987–1992 Pontiac Firebird / Trans Am Convertible — The ASC-Built F-Body Drop-Top Worth a Second Look
Historical Context and Development Background
The third-generation Pontiac Firebird (1982–1992) brought a wholesale rethink of the F-body: lower, lighter, and more aerodynamic than its predecessor, with fuel injection and genuine wind tunnel work. Convertibles, however, disappeared from the domestic performance scene in the early 1980s as manufacturers braced for looming rollover regulations that never materialized. By mid-1987, Pontiac joined Chevrolet in reintroducing an open Firebird, contracting American Sunroof Corporation (ASC) to perform the conversions on production coupes.
ASC, operating with Pontiac’s blessing and warranty coverage, received body-in-white Firebirds and Trans Ams and engineered substantial reinforcements: boxed rocker sections, underfloor bracing, reinforced windshield header and A-pillars, plus revised rear bulkhead structure. The result preserved much of the third-gen’s crisp steering and predictable handling while adding the expected weight penalty of a fully integrated soft top assembly. Pontiac’s convertible option ran from 1987 through the end of the third generation in 1992, available across Firebird, Formula, and Trans Am trims in various years, with GTA convertibles among the rarest.
On the corporate front, the convertible’s return helped Pontiac keep pace with Ford’s popular Fox-body Mustang ragtop and Chevrolet’s own Camaro convertible. Motorsport halo remained the Trans Am’s calling card through IMSA and showroom-stock programs, but the convertible’s mission skewed toward grand touring—top-down torque and boulevard stance—rather than outright track work.
Engine and Technical Specifications
Powertrains mirrored the coupe lineup with some constraints: the 5.7-liter L98 TPI V8 remained automatic-only; 5.0-liter TPI and TBI V8s were common; and base Firebird convertibles in later years could be had with the 3.1-liter V6 in some markets. Tuned Port Injection (TPI) defined the car’s character—broad low-end torque and a mid-range swell that suited the added mass and relaxed gearing of many convertible builds.
| Engine | Configuration | Displacement | Horsepower (typical range) | Induction Type | Redline (approx.) | Fuel System | Compression | Bore/Stroke |
|---|---|---|---|---|---|---|---|---|
| L03 5.0 V8 | 90° OHV V8 | 5.0 L / 305 cu in | ~165–170 hp | Naturally aspirated | ~5,000 rpm | TBI (Throttle-Body Injection) | ~9.3:1 | 3.736 in x 3.48 in |
| LB9 5.0 V8 | 90° OHV V8 | 5.0 L / 305 cu in | ~205–225 hp (year/transmission dependent) | Naturally aspirated | ~5,500 rpm | TPI (Tuned Port Injection) | ~9.3:1 | 3.736 in x 3.48 in |
| L98 5.7 V8 | 90° OHV V8 | 5.7 L / 350 cu in | ~210–230 hp (automatic only in F-body) | Naturally aspirated | ~5,250 rpm | TPI (Tuned Port Injection) | ~9.5:1 | 4.00 in x 3.48 in |
| LH0 3.1 V6 (select base Firebird) | 60° OHV V6 | 3.1 L / 191 cu in | ~140 hp | Naturally aspirated | ~5,500 rpm | Multi-point fuel injection | ~9.0:1 | 3.50 in x 3.31 in |
Driving Experience and Handling Dynamics
Even with the ASC surgery, the third-gen Firebird’s fundamentals remain intact. The front MacPherson strut/rear torque-arm live axle layout delivers predictable rotation, strong mid-corner stability, and an honest rear-drive balance. In convertibles, additional structure beneath the floor and in the sills curbs cowl shake to acceptable levels for the era, though sharp impacts can still coax a flutter from the windshield header on rough pavement.
Steering is light but accurate, with a variable-ratio box that quickens around center. WS6 suspension packages (as fitted to Trans Am, Formula, and GTA in period) bring firmer spring and damper rates, larger anti-roll bars, and performance tires that meaningfully sharpen response. Braking varies: many cars retained front discs/rear drums, while higher trims and option packages could be ordered with four-wheel discs. Gearboxes are period-correct: the 700R4/4L60 four-speed automatic leans into the TPI’s torque and relaxed cruising; the Borg-Warner T5 five-speed adds engagement on LB9 cars. Throttle response is classic TPI—eager off-idle, meaty in the mid-range, and done by 5,300–5,500 rpm.
Full Performance Specifications
| Metric | Typical Figure (period tests/period specs) |
|---|---|
| 0–60 mph | ~6.6–7.5 sec (L98/LB9); ~8–9+ sec (L03/V6) |
| Quarter-mile | ~15.0–15.6 sec @ 90–94 mph (V8) |
| Top speed | ~125–135 mph (engine/gearing dependent) |
| Curb weight | ~3,450–3,650 lb (equipment dependent) |
| Layout | Front-engine, rear-wheel drive |
| Brakes | Front disc/rear drum; four-wheel disc available on performance packages |
| Suspension | Front MacPherson struts, coil springs; rear live axle with torque arm, coil springs; anti-roll bars front/rear |
| Gearboxes | 4-speed automatic (700R4/4L60); 5-speed manual (T5 on 5.0) |
Variant Breakdown (Trims and Editions)
ASC conversion was available across multiple trims during 1987–1992. Exact convertible production by trim/year is not consolidated in a single factory-published source; figures below reflect availability and defining features.
| Variant | Years Available as Convertible | Powertrains | Distinguishing Features | Production Numbers (convertible) | Markets |
|---|---|---|---|---|---|
| Firebird (Base) | 1987–1992 (availability varied by market/year) | 3.1 V6 (later years select markets), 5.0 V8 (L03 TBI) | Simpler trim, smaller wheels/tires; convertible specific bracing by ASC | Not separately published by Pontiac | US/Canada |
| Formula | 1987–1992 (rarer as convertible) | 5.0 TPI (LB9), 5.7 TPI (L98, auto only) | Sleeper spec: Trans Am power with reduced aero addenda | Not separately published by Pontiac | US/Canada |
| Trans Am | 1987–1992 | 5.0 TPI (LB9), 5.7 TPI (L98, auto only) | Aero nose, ground effects, WS6 suspension available | Not separately published by Pontiac | US/Canada |
| Trans Am GTA | 1988–1992 (very limited as convertible) | 5.7 TPI (L98, auto only); 5.0 TPI (LB9) | GTA badges, crosslace wheels, upgraded interiors; four-wheel discs common | Not separately published by Pontiac | US/Canada |
Notes: The 1989 20th Anniversary Turbo Trans Am was not offered as a production convertible. Four-wheel-disc and 1LE road-race packages existed on coupes/hatchbacks; convertibles focused on grand touring and were seldom paired with track-intended options.
Ownership Notes: Maintenance, Parts, and Restoration
- Structure and body: ASC reinforcements are robust, but inspect the underfloor braces and rocker boxes for corrosion and prior jack damage. Check the windshield header for stress cracks and the door hinges for sag (heavy third-gen doors).
- Convertible top: Verify top operation, hydraulics (if fitted), and latch alignment. Top fabric, rear window, and weatherstrips are wear items; many soft parts remain available through aftermarket suppliers.
- TPI/TBI specifics: Early cars used MAF-based management; later years moved to speed-density on some engines. Clean grounds, intact vacuum lines, a healthy IAC, and a fresh fuel filter are essential to crisp drivability.
- Transmissions: The 700R4/4L60 benefits from correct TV cable setup; sloppy adjustment quickly shortens its life. The T5 manual prefers gentle shifts and fresh fluid; clutch hydraulics can be a weak link as mileage accumulates.
- Suspension and brakes: Torque-arm bushing, panhard rod bushings, and front control arm bushings are common refresh items. Rear drum adjusters seize from disuse; four-wheel-disc cars can suffer from sticky rear calipers if neglected.
- Electrical and trim: Headlamp motors (’87–’92 pop-ups) wear gears; window motors slow with age. Dash tops crack with UV exposure; proper top seals mitigate wind noise and water ingress.
- Service intervals: Conventional oil changes at ~3,000–5,000 miles, periodic cap/rotor/plugs on V8s, and cooling system service keep temperatures in check, especially in warm climates where convertibles live.
- Parts availability: Mechanical parts are widely supported due to shared GM small-block hardware. ASC-specific trim and top components are obtainable via specialty vendors and enthusiast networks.
Cultural Relevance and Market Perspective
The third-gen Firebird is forever tied to 1980s Americana—Knight Rider cemented the shape, even if KITT wasn’t a convertible. ASC-built drop-tops show up in period advertising, music videos, and dealer promotions as the optimistic return of the American performance convertible. Among collectors, coupes with rare performance packages tend to command the highest premiums; yet clean, low-mile Trans Am and GTA convertibles are increasingly appreciated for their blend of aesthetics, analog V8 character, and relative rarity in open form.
Documented auction sales have ranged from driver-grade V8 convertibles trading in the teens to strong, original-mile GTA convertibles selling notably higher when provenance and condition align. As ever, originality, documentation, and rust-free structure outweigh model badges alone.
FAQs
Was the 5.7-liter (L98) available with a manual in the convertible?
In the third-gen Firebird/Trans Am, the 5.7 TPI (L98) was automatic-only. Manual transmissions were paired to the 5.0-liter V8.
How much heavier is the convertible than a comparable coupe?
Expect roughly 200–300 lb of additional mass due to ASC’s structural reinforcements and the top mechanism, depending on equipment.
What are the common issues unique to the convertible?
Top fabric and seals, header alignment, and cowl shake over sharp impacts. Otherwise, they share typical third-gen F-body needs: suspension bushings, TV cable adjustment (700R4), and pop-up headlamp motors.
Are four-wheel disc brakes standard on GTA convertibles?
Four-wheel discs were common on GTAs but remained equipment-dependent; verify by inspection or build documentation.
Did Pontiac build the convertibles in-house?
No. Pontiac authorized ASC to perform the conversions. Cars were delivered new with full manufacturer backing.
What engines were offered across 1987–1992?
5.0-liter V8s in TBI (L03) and TPI (LB9) forms, 5.7-liter TPI V8 (L98, auto only), and in later years a 3.1-liter V6 on some base Firebirds.
How quick are they?
A healthy 5.7 TPI car runs roughly mid-6s to low-7s to 60 mph, with quarter miles around the mid-15s—period-correct performance blunted slightly by convertible weight and aero.
Any notable special editions offered as convertibles?
GTA convertibles exist and are among the rarer builds. The 1989 20th Anniversary Turbo Trans Am was not offered as a production convertible.
Why This Car Matters
The 1987–1992 Pontiac Firebird/Trans Am Convertible captured the moment Detroit rediscovered the joy of open-air performance. It marries TPI torque, unmistakable styling, and the tactile charm of an analog chassis—now wrapped in the relative scarcity of a factory-authorized ASC conversion. For enthusiasts who value period-correct feel with the top down, it’s a compelling slice of late-’80s/early-’90s Pontiac.
