Welcome to the IMSA History unofficial website

This site is aimed at bringing you memories from the glory days of sportscar racing in the US.

Contribute

 Contact


David Hobbs at the wheel of a Porsche 935K3 in 1982.




The GTX were Group 5 cars. It was the home of the turbocharged german nickel rockets, such as Porsche 935s and BMW BMW 320 Tcs, Ferrari 512BBs and then later BMW M1C, Ford Mustang Tcs, Datsun 280ZX Tcs.

Engines:

Proprietary engine block must be used; may be machined so long as camshaft location is not altered.

Cylinder heads are free except that method of cooling must remain as original.

Induction is free, except turbocharging is only permitted on FIA recognized models and is limited to one turbocharger.

Turbocharged engine displacement is 1.4 X actual displacement. Rotary engine displacement is 1.8 X actual displacement.

Engine may be relocated within the standard engine compartment.

Drive Train:

Gearbox or transaxle are free but must remain in standard location.

Rear axle must remain live or independent as appropriate.

Chassis:

Free. Standard wheelbase must be retained.

Brakes, suspension and steering are free.

Coachwork:

The outside surfaces shape and material of the original coachwork must be retained and must remain identical, except for the additions, modifications and substitutions permitted in these rules. Overall length of the coachwork is regulated by the FIA recognition form.

Maximum overall width is 79" for cars under 5.0L and 83" for those over 5.0L. Material of engine and luggage compartment covers, doors and fenders is free provided their original shape is retained. Doors must remain functional. Front engine cars may add an air scoop to accommodate the induction system. Fenders are free in shape and material but are limited as follows: Original wheel arch must be retained and must effectively cover the full width of wheel and tire for 1/3 of their circumference; any rearward opening must be closed by screens or louvers.

Bumpers and external decorative trim may be removed; door sills may extend to the full width of the bodywork. Any additional bodywork must not confuse the make and model identity of the car.

Wheels and Tires:

Wheel and tire section width (maximum width at widest point of tire) may not exceed: 5.0L - 16", over 5.0L - 18"; diameter free.

Track dimension is limited by inner tire clearance and the permitted maximum car width.

Aerodynamic devices:

Front spoiler may not exceed 10% of the wheelbase or protrude a maximum of 20cm (7.87") beyond the front extremity of the coachwork, and must be located below the centerline of the front wheels. Rear spoiler chord may not exceed 20% of the wheelbase or extend beyond the rearmost bodywork more than 40cm (15.75").

Official weight, measured without fuel & driver, absolute minimum weight: 1879 lbs

Engines with overhead cams, 10% less than FIA Group 5 weight: up to 3.8L = 1879 lbs 4.0L = 1924 lbs 4.5L = 2034 lbs 5.0L = 2113 lbs 5.5L = 2212 lbs 6.0L = 2291 lbs

Engines with 4 valves per cylinder, 5% less than FIA Group 5 weight: 3.0L = 1879 lbs 3.5L = 1916 lbs 4.0L = 2031 lbs 4.5L = 2147 lbs 5.0L = 2231 lbs 6.0L = 2418 lbs

Turbocharged Engines Multiply displacement by 1.4 3.0L = 1968 lbs 3.2L = 2025 lbs 3.4L = 2083 lbs 3.6L = 2133 lbs

Specifically allowed:

Crank-fire ignition Polycarbonate windscreen and windows

Quick-change rear axle

Items allowed under FIA Group 5 regulations when contrary to the above are permitted on documented FIA Group 5 cars.