GM H platform (1971)

The General Motors H platform or H-body is an automobile platform designation used for the 1971–1980 model year rear wheel drive line of subcompact cars. The fourth character in the Vehicle Identification Number (VIN) for an H-body car is "H".[1]

Main article: GM H platform
See also: List of GM platforms
H-platform
Overview
ManufacturerGeneral Motors Corporation
Also calledH-body
AssemblyUnited States: Lordstown, Ohio (Lordstown Assembly)
South Gate, California (South Gate Assembly)
Canada: Quebec, Canada (Sainte-Thérèse Assembly)
Mexico: Ramos Arizpe, Coahuila
Body and chassis
ClassSubcompact
LayoutFR layout
Body style(s)2-door sedan
2-door hatchback
2- door wagon
2- door panel delivery
VehiclesChevrolet Vega, Pontiac Astre, Chevrolet Monza, Pontiac Sunbird, Buick Skyhawk, Oldsmobile Starfire
Powertrain
Engine(s)140 CID 2.3 Liter OHC 1bbl I4
140 CID 2.3 Liter OHC 2bbl I4
122 CID 2.0 Liter DOHC EFI I4
151 cu in (2.5 L) OHV I4
196 cu in (3.2 L) OHV V6
231 cu in (3.8 L) OHV V6
262 cu in (4.3 L) OHV V8
305 cu in (5.0 L) OHV V8
350 cu in (5.7 L) OHV V8
Transmission(s)3-speed manual
4-speed manual
5-speed manual w/overdrive
Torque-Drive clutchless manual
Powerglide 2 spd. automatic
Turbo-Hydramatic 3 spd.automatic
Dimensions
Wheelbase97.0 in (2,464 mm)
Chronology
PredecessorGM Y platform
SuccessorGM J platform (FWD)

H-bodies were available as two-door Notchback, Hatchback, Wagon, and Sedan delivery body-styles, and have 4, 6, and 8-cylinder GM engines, solid rear axle, and unibody construction. The platform was introduced with the 1971 Chevrolet Vega. The Pontiac Astre, a rebadged version of the Vega, was introduced in Canada for the 1973 model year and later added to the U.S. market for 1975. The Chevrolet Monza, Buick Skyhawk, and Oldsmobile Starfire were introduced for the 1975 model year, while the Pontiac Sunbird was introduced a year later as a 1976 model.

The Vega engine is a 140 CID aluminum-block L4. A 1972 GM prototype had an all-aluminum 302 small-block V8,[2] but this was not approved. Chevrolet hand-built 5000 122 CID L4 Cosworth Twin-Cam engines for the 1975 Cosworth Twin-Cam Vega.[3] Only 3508 1975-76 cars were built. The remaining engines were scrapped. The GM-rotary (GMRCA) Wankel engine was destined for the 1975 Monza 2+2 but the engine was canceled.

The Vega and the Astre were discontinued at the end of the 1977 model year, but the Monza, Sunbird, Skyhawk, and Starfire continued through 1980. The GM J platform replaced the GM H platform in 1981. The H platform designation was later used for the unrelated front-wheel drive GM full-size cars in the 1980s.

H platform component arrangement
Vega Sedan
Years Wheelbase Model Previous platform Next platform
1971–197797.0 in (2464 mm)Chevrolet Vega
1973–1977Pontiac Astre
1975–1980Chevrolet Monza
1976–1980Pontiac SunbirdGM J platform
1975–1980Buick SkyhawkGM J platform
1975–1980Oldsmobile Starfire

See also

References
  1. Vega Shop Manual-Chevrolet Motor Division
  2. Hot Rod magazine-July 1972
  3. Chevrolet Cosworth Vega press release-March 1975
  • Gunnel, John, Editor (1987). The Standard Catalog of American Cars 1946-1975. Kraus Publications. ISBN 0-87341-096-3.CS1 maint: multiple names: authors list (link)
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