Roush Propane Racer - Clean Power
Susan Roush Mcclenaghan's 2010 Drag Race Program Burns On Liquid Propane
From the July, 2010 issue of 5.0 Mustang & Super Fords
By Dale Amy
Photography by Dale Amy
Yup, that's just your run-of-the-mill,...
Yup, that's just your run-of-the-mill, all-aluminum 5.4-liter Four-Valve modular being lowered for the first time into a brand-new '10 'Stang race car, but the really interesting part is that it's gonna be fueled by liquid propane.
With crude oil being a finite and mostly imported resource, the search is well and truly on these days for alternative fuels to serve our energy needs. While some take an environmentally zealous, politically pious, or unrealistically utopian view about the preferred types of alternatives to gasoline, the more levelheaded amongst us would surely rank availability, viability, and affordability at the top of the criteria list when considering any such alternatives.
Those three pragmatic criteria have made propane pretty popular not just for heating our homes and cooking our steaks, but also as a transportation fuel, where it ranks third behind only gasoline and diesel. That said, we've never before seen propane used to fuel a drag car, but that's about to change.
For the 2010 NMCA and NMRA season, Susan Roush McClenaghan's She-Devil Motorsports-part of the Roush Drag Team-is fielding a freshly constructed '10 Mustang powered by a naturally aspirated Four-Valve modular fueled by liquid propane.
Why propane? "I was trying to find a way," Susan explains, "to tie our drag racing into the other parts of the [Roush] business, and this project demonstrates a number of those pieces-our engine build services, our liquid propane technology, paint and body services... The other reason for looking at propane is I want to take our race program and really have it stand out in terms of current events, so to speak, with emphasis on alternative fuels and concern for being ecologically responsible."
In the foregoing quote, Susan is referring to Roush Industries' recent forays into the business of engineering and supplying liquid-propane fuel-injection systems for the conversion of fleet vehicles (currently various Ford pickup and van platforms). The research and development invested in that fleet conversion program were harnessed in building her new race car.
The use of propane-more formally, liquified propane gas, or LPG-as a motor fuel has been around for decades, but Roush's fleet and race programs harness the efficiencies and drivability of liquid propane injection systems (older-technology agricultural and fleet propane conversions were vapor-based systems saddled with vaporizers/mixers and carburetors). Check out our sidebar The Science of Propane for more on the fuel itself.
The development engine for...
The development engine for the Roush propane racer is a stock-displacement 5.4-liter Ford GT supercar long-block, modified for wet-sump oiling and bumped to 12.5:1 compression. Its internal specs are otherwise unimportant because, in race form, the project will run a larger displacement variant, as detailed a bit further on. When plumbed for gasoline, it produced around 635 hp on C14 fuel. With the liquid-propane fuel rails and injectors in place, power was about 625 hp even, though for baseline testing purposes, about 3 degrees less ignition timing was used.
Our mid-winter visit to the Roush race shops coincided with the first trial merging of the project's development engine and chassis, the latter having started off as a '10 Mustang body-in-white, now constructed to NHRA Super Stock specs. By comparison, Susan's previous two New Edge drag 'Stangs were simply converted production cars, so this purpose-built racer is a serious step up. Expect to see it in the NMRA's Modular Muscle class and some NMCA events.
The complete development engine in our photos is based upon a stock-displacement Ford GT aluminum block and heads, and is essentially an R&D tool used to develop, package, and test the propane fuel system. This engine has been run on the Roush brake dynos in two forms: initially with a normal gasoline fuel system in place; then, otherwise unaltered aside from recalibration of its FAST XFI processor, with the new liquid-propane injection hardware onboard.
Showing the viability of propane as a gasoline substitute, the engine produced similar power figures when fed either fuel-between 625 and 635 hp. By the time you read this, a second engine will be in place-the real race engine. It will have a similar aluminum 5.4-liter basis, but will be bored and stroked to about 374 cubes, with a target horsepower in naturally aspirated form of somewhere around 700. If the program proves successful, supercharging may be added for next season.
Our captions contain much more detail, but overall, the only real challenges to adaptation of a liquid-propane injection system for race purposes were in
the specifics of the fuel system itself. That's to say that the engine internals-crank, rods, piston, compression, cams, and so on-are no different than if the modular were built to run on gasoline. Of course, the Roush team also needed to develop an efficient means of fueling (and de-fueling) the car at the racetrack, and even for fueling the engine on the dyno stand, as our photos show.
Will we ever see widespread use of propane in the Ford drag racing scene? We would guess it unlikely at least in the near term, but racing, like hot-rodding, is all about experimentation, so who knows?
Horse Sense: Roush Industries reports that propane combustion produces roughly 20 percent less nitrogen oxides and 60 percent less carbon monoxide than gasoline combustion.
The liquid-propane injectors...
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...
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...
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,...
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...
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...
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...
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...
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...
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.
The Science of Propane
At normal room temperatures, propane is in a gaseous state, since its boiling point is a chilly minus 44 degrees (boiling point simply being the temp at which any given liquid changes "phase" to vapor). But much as automotive cooling systems are pressurized to raise the boiling point of their water/antifreeze mix, so is propane pressurized to keep it in a liquid state at typical ambient temperatures. Release it from that pressure and propane immediately vaporizes, expanding and cooling in the process. (Think of what happens when you open the valve to see what's left in your barbecue's propane tank.)
On older propane conversions for carbureted vehicles, that phase change to a gaseous state had to occur at the mouth of the carburetor, after which the mix of air and propane gas had to travel the length of the intake manifold runners and cylinder-head ports before reaching the combustion chamber. Without getting too buried in the science, these systems could be hampered by cold-start issues and had other inefficiencies.
Today's liquid propane injection systems, as employed by Roush, keep the propane in a liquid state right up until it exits the tip of the (specialized) fuel injector, immediately upstream of the intake valve. Like any form of fuel injection, this improves fuel efficiency but also helps make propane cold-start issues a thing of the past.
More propane tidbits:
- Propane holds only about 86 percent of the energy per volume of gasoline, but this is partially compensated by its higher stoichiometric air/fuel ratio of 15.6:1 versus 14.7:1 for gasoline.
- About 90 percent of U.S. propane is domestically produced; most of the balance comes from Canada.
- Propane is a byproduct of both the processing of natural gas and petroleum refining.
- Propane in gaseous form is heavier than air (about 1.5 times as dense) and therefore sinks and pools at the ground. However, liquid propane is significantly lighter than gasoline.
- Propane has an octane rating of roughly 105 to 110, so will theoretically support higher compression ratios and more spark timing.
- Propane burns cleaner than gasoline, meaning both fewer emissions-especially carbon monoxide-and cleaner engine internals.
- Government incentives/tax credits help defray the cost of vehicular propane conversion.