Buick Skylark / GS Specs and Maintenance: Every Engine, Tune-Up Number, and Brake Part (1968–1972)
The Skylark range runs from the Chevrolet 250 inline-six to the 455 big-block, and the ratings change meaning mid-run: 1971 cut compression to about 8.5:1 for unleaded fuel, and 1972 switched from gross to net horsepower, so a 1972 455 at 250 hp net is not directly comparable to a 1970 455 at 350 hp gross. Every number below comes from the Skylark / GS guide's Stock Specs and Engine Maintenance tabs.
The engines, year by year
| Engine | Years | Output | Notes |
|---|---|---|---|
| Chevrolet 250 I6 | 1968–1971 | 155 hp @ 4200 rpm, 235 lb-ft @ 1600 | Single-barrel Rochester; base engine; dropped for 1972 (V8-only lineup) |
| Buick 350 V8 2bbl (base Skylark) | 1968–1969 | 230 hp | GS got the 4bbl version |
| Buick 350 V8 4bbl (GS 350) | 1968–1969 | 280 hp @ 4600 rpm, 375 lb-ft @ 2800 | 3.80 x 3.85 bore/stroke; 10.25:1; Rochester Quadrajet 4bbl |
| Buick 400 V8 (GS 400) | 1968–1969 | 340 hp @ 5000 rpm, 440 lb-ft @ 3200 | 4.04 x 3.90 bore/stroke; 10.25:1; replaced by the 455 for 1970 |
| Stage 1 400 V8 | 1969 | 345 hp, 440 lb-ft gross (underrated, real output ~390 hp) | Hotter cam, larger valves, HD valve springs, dual exhaust; Positive Traction mandated |
| Buick 350 V8 2bbl | 1970 | 260 hp gross | Peak year for the base 350; up 30 hp over 1969 |
| Buick 350 V8 4bbl (GS) | 1970 | 315 hp gross | GS 350 trim dropped; 350-4v remained as the GS base engine |
| Buick 455 V8 (GS 455) | 1970 | 350 hp, 510 lb-ft @ 2800 | 4.3125 x 3.90 bore/stroke; 10.0:1; highest factory muscle-car torque of its day, a record held 30+ years |
| Stage 1 455 V8 | 1970 | 360 hp, 510 lb-ft gross (underrated) | Larger valves, higher compression, hotter cam; Motor Trend 13.38 @ 105.5 quarter mile |
| Buick 350 V8 4bbl (GS) | 1971 | 260 hp gross | Entry GS engine for 1971 |
| Buick 455 V8 | 1971 | 315 hp gross | Compression cut to ~8.5:1 for unleaded fuel |
| Stage 1 455 V8 | 1971 | 345 hp gross, ~460 lb-ft | 801 hardtops + 81 convertibles built |
| Buick 350 V8 2bbl | 1972 | 145 hp net | Switch to net hp ratings; six-cylinder dropped |
| Buick 350 V8 4bbl | 1972 | 170 hp net | Skylark 350 engine |
| Buick 455 V8 | 1972 | 250 hp net, 375 lb-ft | 8.5:1 compression, AIR pump, retarded timing |
| Stage 1 455 V8 | 1972 | 270 hp net, 390 lb-ft | 728 hardtops + 81 convertibles (809 total); Motor Trend 14.10 @ 97 quarter mile |
Transmissions and rear axles
Three-speed manuals were standard on the GS 350 and GS 400, with a four-speed Muncie (2.20:1 first gear) optional with a Hurst shifter. On the automatic side, the Super Turbine 300 two-speed with its Switch-Pitch converter was the standard automatic for 1968, replaced by the Turbo Hydra-Matic 350 in 1969 as the standard automatic for 350-powered cars through 1972. The Super Turbine 400 / TH400 was the standard automatic for 400 and 455 cars, and the guide rates it the finest GM automatic; manual cars got 3.42 gears minimum.
Factory rear-axle ratios: 2.93 standard with an automatic, 3.42 with manuals, 3.64 on the Stage 1 (3.42 with air conditioning), 3.23 on the 1968 GS 350, and 2.56 economy. Positive Traction was optional and mandated on Stage 1 cars. The standard rear was the 8.2-inch BOP 10-bolt (28-spline axles, cone-type limited slip); the stronger 8.5-inch corporate 10-bolt appeared in 1971–1972 and is the best junkyard upgrade candidate, while the 12-bolt was very rare in Buick A-bodies.
Dimensions and production
Wheelbase is 112 in for the two-door, 116 in for the four-door, and 121 in for the Sportwagon — GM's split-wheelbase policy, new for 1968. Body styles were the two-door coupe, two-door hardtop, two-door convertible, four-door sedan, four-door hardtop, and Sportwagon; the GS came as a coupe, hardtop, or convertible. Curb weight is about 3,515 lb for the two-door (Motor Trend estimated about 3,700 lb for a GS) and about 4,000 lb for the Sportwagon. GS production ran 21,514 in 1968, 19,257 in 1969, about 20,000 in 1970, 9,170 in 1971, and 8,575 in 1972. The GSX package cost $1,100 mid-year 1970 and came only in Saturn Yellow (491 built) or Apollo White (187 built).
The tune-up numbers
- Engine oil: 10W-30 (API SF/SG or better), 5 quarts with filter, every 3,000–5,000 miles, $40–$60 as listed in the guide. Flat-tappet cams benefit from zinc/ZDDP additive oil.
- Spark plugs, 350: AC R45TS, gap .030 in, replace about every 12,000 miles, $2–$4 per plug.
- Spark plugs, 455 4bbl: AC R44S, gap .030 in, replace about every 12,000 miles, $2–$4 per plug. For HEI conversions, widen the gap to about .045 in.
- Spark plugs, 250 I6: AC N12Y, gap .035 in, replace about every 12,000 miles, $2–$4 per plug. 1971 spec; 2.5 degrees BTDC timing.
- Points ignition: dwell 30 degrees, point gap .016 in; check and adjust every 12,000 miles, $10–$20. Replace the condenser with the points.
- Ignition timing: 350 2bbl/4bbl at TDC; 455 4bbl at 8 degrees BTDC; Stage 1 455 at 10 degrees BTDC. Set at tune-up with the vacuum advance disconnected. Compression-test baseline: about 160–180 psi.
- Valve lash: zero lash — hydraulic lifters, no adjustment required. Confirm no collapsed lifters if the valvetrain is noisy.
- Coolant: green ethylene glycol; drain and refill every 2 years, $30–$50. Flush the heater core and block drains on first service.
- Fuel filter: Quadrajet in-carb filter plus inline filter; replace yearly, $5–$15. Check fuel pump pressure at about 5–8 psi at idle.
Brakes, tires, and wheels
Power front discs were optional on the GS and standard on 455 cars. Front 11-inch disc rotors: Raybestos 56325R at about $56 each, or slotted EBC USR7064 at about $90–$110 each. A disc conversion kit for a 1969 GS 400 runs $700–$900 as listed and includes rotors, calipers, brackets, and hardware, clearing most 14/15 in wheels. Rear drums are 11x2 in cast iron at $60–$80 per drum; note the GS front drums were aluminum with cast-iron liners in 1968–69. A power-disc master cylinder runs $50–$90; bench-bleed before install and match the bore to the disc/drum setup.
Factory tires: 7.75-14 whitewalls on 14x6 steel wheels for the 1968–69 GS 400 (15-inch wheels were not offered those years), G70-14 raised-white-letter bias-ply on 14x6 or 14x7 Rallye wheels for 1970 and up, and G60-15 Wide Oval on 15-inch Rallye wheels for the GSX. The bolt pattern is 5x4.75 in across the range, shared with the Chevelle, GTO, and Cutlass. The modern radial swap in the guide is 225/70R15 or 245/60R15 on 15x7 Rallye-style wheels with about 4 in backspace — verify inner-fender clearance at full lock on the 245s.
Where to learn the jobs
The guide's How-To Links tab points to the community sources for the big jobs: the V8Buick "Summary of 455 Power Tips" thread and the "455 main bearing clearances" thread for rebuild specs, the PowerNation "Machine Shop and Shift Kit" episode for 455 assembly, Buicks.net tech reference for the front disc brake and suspension conversion, the Hot Rod "Lose The Slop" A-body front-end rebuild, and the AACA thread on removing a vinyl top without breaking the trim clips. The 455 oiling fix in the Common Fixes tab — a TA Performance front cover and oil pump kit at $300–$600 — is the one repair the guide flags for any 455 that shows low hot-idle oil pressure or noisy rockers.
Open the full interactive Skylark / GS guide for the complete stock specs, engine maintenance table, brakes, tires and wheels, differentials, parts interchange, and how-to links.
Compiled from the Cerch Garage Buick Skylark / GS guide (Stock Specs, Engine Maintenance, Brakes, Tires and Wheels, Differentials, and How-To Links tabs). Prices and costs are as listed in the guide and change; verify before buying anything. What this page does not cover: torque specs for lug nuts, suspension fasteners, and other hardware. The guide does not state those, so they are left out rather than guessed.