Anatomy of a Pro Modified

Below is the anatomy of a typcial Pro Modified, however all cars vary.

Specifications
Pro Mod cars are permitted either a nitrous injected motor running on unleaded race fuel or a supercharged engine running on methanol. The complete has to weigh a minimum of 2375lbs for nitrous injected cars of 27000lbs for supercharged methanol cars. Nitrous or blown motors cost approx £50,000 from a recognised engine builder. Connecting rods last from 25 runs on a blown car to 50 runs in a nitrous car and cost around £1,000. Valve springs are consumable items and individual pistons and rings need changing on a regular basis. A blown car would change spark plugs either every run if they wanted to 'read' the plugs or every 2 or 3 runs if not.

Data Logger
Almost all Pro Mod cars have a data logger on board which monitors and records information from sensors all over the car. The data is used to make the fine clutch adjustments which are essential to get the car to run fast. Other sensors monitor exhaust gas temperatures, fuel flow, throttle position and rear suspension travel. A data logger would cost from £3000 (to monitor basics for tuning) upwards.

1. Chassis
Chassis are custom fabricated from 4130 chrome moly tubing according to strict rules. The maximum permitted wheelbase is 115" (2.92m). Features of the chassis include twin chassis rails, strut style front suspension, carbon or aluminium interior panelling, aluminium motor mounting plates, coil over rear suspension and 4 link or swing arm mounted axles. The car has front and rear brakes but relies primarily on twin parachutes to slow it down from speeds of up to 230mph. the bare chassis will range from about £7,500.

2. Body
Pro Mod body shells are highly modified replicas of original car bodies built ion composite materials. The bodies may have been roof chopped, sectioned, stretched in the wheel base, scaled down from the original or otherwise modified to give better aerodynamics and accommodate the huge rear tyres. The maximum front overhang is 4.5" (114cm). A rear wing is added to give down force at the top end of the track. A central driving position is not permitted. Depending on what style, estimate £6,000.

3. Fuel
Nitrous motors use an unleaded high octane race fuel, the blown cars use methanol. The fuel system on a nitrous car can flow up to 8.5 gallon per minute an the blown car fuel system can flow over 15 gallons per minute. In a blown car methanol costs around £1.70 per litre and each run would use up to 25 litres including the burnout. In a nitrous car unleaded race fuel costs around £6 per litre and each run would use approx 5 litres as well as 6lbs of nitrous oxide at £6 per pound.

4. Engine
Engines are restricted to a maximum of 740 cubic inches (12.12 litres) for nitrous assisted motors and 526 cubic inches (8.61 litres) for supercharged methanol engines. In addition, the blown entries are restricted to a maximum valve size of 1.9" exhaust and 2.4" inlet and are restricted to 20% overdrive when using the 14-71 high helix blower. Nitrous motors are producing in the region of 3 horsepower per cubic inch so the difference in engine size, minimum car weight etc. are designed to redress this balance so that both combinations can be competitive.

5. Drivetrain
Pro Mod cars use a multi disc clutch. Nitrous cars can use a maximum of 3 discs and blown cars 2. Most cars use a planetary design transmission - commonly the Lenco or B+J. some cars have also started to experiment with a twin lay shaft transmission such as a Liberty . Nitrous cars generally use a 4 speed transmission and blown cars use a 3 speed. Blown cars are permitted a maximum rear axle gear ratio of 4.56:1. A transmission and clutch set up would cost in the region of £8,000 and a titanium bell housing to safely contain any clutch explosions would cost around £3,500.

6. Driver Safety Equipment
A fire resistant suit including gloves and shoes must be worn by the drivers of nitrous cars. The drivers of blown cars use the same suits, gloves and boots as Top Fuel drivers. Helmets and a 360 degree neck brace must be worn by all drivers. The Hans device as worn by Formula 1 drivers is also permitted and gaining in popularity. A 5 point, 3" wide driver harness must be used in all cars. All cars have to use a shatterproof bell housing to protect the driver in the event of a clutch failure, a blanket around the transmission and an engine 'diaper' to contain any spilt oil.

7. Suspension
Cars are required to have a production style suspension system. Most cars use a purpose built McPherson style strut with rod ended control arms at the front and most use a 4 link rear suspension which allows an almost infinite range of adjustment to compensate for track conditions. Coil over shock absorbers are used on the rear along with anti roll bars.

8. Wheels and Tyres
Rear wheels are 16" in diameter and 16" wide and have to be 'Beadlocks' i.e. have clamping rings to secure the tyre. Rear tyre pressures are from 4.5psi and front tyres run up to 34psi. The tyres are designed to 'crinkle' to assist the launch and will 'grow' by approx 4" in height during the burnout and at the top end of the track. A pair of rear wheels cost in the region of £2,800 and a pair of slicks about £650 - two or three pairs of slicks are needed in a season.

9. Brakes
The cars are equipped with aftermarket disc brakes on all four wheels with some cars using carbon fibre discs and pads. The brakes are used in conjunction with dual parachutes to slow the car down from speeds of up to 230mph. brakes are generally single pot on the front and 4 pot on the rear with the system designed to rear bias through the large rear wheels and tyres.

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