Roush Propane Racer - Clean Power

The liquid-propane injectors are fairly new technology and differ substantially from a typical gasoline injector. They must maintain the propane in a liquid state-that is, under pressure-until it reaches the injector tip, at which point it changes phase to vapor, expanding and cooling rapidly in the process. Note that the Sullivan intake was substantially modified to accept a pair of injectors for each cylinder. Because propane holds fewer BTUs per pound than gasoline, a higher volume of fuel flow is required to support a given horsepower level, though this is partially offset by the leaner air/fuel mixture required by the more efficient combustion of propane.

The 5.4-liter development engine achieved its 620-plus horsepower on just one injector per cylinder (running at about 85-percent duty cycle), however the propane project's whole fuel system has been sized to support up to 1,000 hp, thus explaining the twin-injector setup. It will all be controlled via the car's FAST XFI processor, obviously having propane-specific calibration.

This is the car's custom-made 10-gallon fuel tank. Notice the thickness of the bolt-on lid sitting beside the tank, indicative of the pressures this vessel must withstand. Internal pressure will rise in relation to ambient temperature, and could reach upward of 300 psi in a mid-summer track environment. Inside the tank is an Aeromotive A1000 fuel pump, along with a Weldon pressure regulator set to maintain 50psi of fuel pressure beyond whatever pressure exists in the tank, meaning the fuel rail and injectors will see pressure that varies with ambient temperature. A pressure/temperature sensor in the fuel rail helps the XFI processor compensate for flow rate changes caused by these pressure fluctuations.

Let's talk safety. First, the pressurized tank is essentially surrounded by tubular cage elements in the trunk to protect both the tank and its fittings. Also, because propane is heavier than air and would therefore sink in the case of leakage, the trunk floor is both vented and has a blower. All elements of the fuel system are spec'd to deal with the necessary high pressures, and all tank orifices have excess-flow valves, which would automatically shut off in the case of a leak. The -10 feed and -8 return lines are made of Teflon, because propane would leak through rubber lines. Even the transporter trailer will have a leak-detection sensor and a means of evacuating any such leakage.

Obviously, fueling a propane race car in the pits is a bit more complicated than its gasoline cousins, so Roush had to fabricate a couple of these carts, from which the car can either be fueled or drained of fuel, if necessary, using the transfer pump. The cart tank holds about 20 gallons of liquid propane-certainly more than enough for a race weekend. Guess they can power the crew's barbecue, too. On a related note, a similar setup had to be created just to fuel the engines while they were undergoing testing on Roush's brake dyno.

This is the new race block under construction, which came to Roush as an aluminum 5.4-liter raw casting. There, the entire cylinder area was machined away and replaced with a Darton Modular Integrated Deck system-basically interlocking ductile-iron cylinder elements that improve strength and cooling, and permit the 3.70-inch bore size. Stroke will be 4.350 (for just over 374 ci) from a Kellogg steel crank, tied by way of Carrillo rods to Diamond pistons configured for 12.5:1 compression. Durability of the cam chain drive system will be assured with Roush-manufactured steel chain guides and manual tensioners to replace the factory-style plastic guides and hydraulic tensioners.

It should be apparent from the aluminum shavings that a little whittling is going on in the Ford GT head castings, no different than would be the case for gasoline race use. Only the valve seats and valve material differ for propane, which lacks the lubricity of gasoline. Custom-ground Comp Cams will be bolted on, along with PAC valvesprings and a Jesel valvetrain (followers and lifters). It's likely that the same Sullivan intake and Wilson throttle body shown on the stock-displacement development engine will be utilized.

Starting life as a '10 Mustang body-in-white, Susan's propane racer was constructed to NHRA Super Stock legality, and its outstanding level of detail, evident here in the graphics-embellished blue and silver paint scheme (all done in-house), is sure to be an attention grabber. This is Susan's first purpose-built race car; her previous two New Edge racers were modified production cars.

Some of the car's Super Stock-style construction is visible here. The engine is secured by rigid tubular engine mounts and a rear motor plate, behind which will be a Powerglide automatic.