900 HP On Propane - 1970 Chevrolet Chevelle
Mothers' LPG-Powered '70 Chevelle Gets a Bigger, Stronger Powerplant
writer Brandan Gillogly
photographer Les Bidrawn
Oct 15, 2012
Any Power Tour(tm) or HOT ROD TV aficionado will recognize this '70 Chevelle. It was built at the request of Mothers' Jim Halloway to show off the capabilities of propane and prove that a hot rod can be green. And this was before E-rod crate engines! Jim was active in HOT ROD TV and built the Chevelle to debut at the '07 HOT ROD Power Tour(tm). As with any build with a firm deadline, it came down to the wire, and there was a bit of drama. Jim didn't seem to have any gray hairs after the stress of the first build, so when new propane technology debuted, he chose to update the Chevelle.
When Jim was first planning the car, Mothers' marketing partner, based in New Zealand, suggested going with propane. In Europe, Australia, and New Zealand, propane-powered cars are much more common. After hearing about the benefits of propane, especially its 110 octane rating, Jim was sold. His marketing partner even found him an engine--a 16:1, 430-plus ci small-block Chevy. The catch? It was in New Zealand, between the frame-rails of a sprint car that was in the hunt for the championship, and it was gasoline powered. The sprint-car team won the championship on a Friday, pulled the engine, bolted the propane intake manifold on, put it in a crate, and shipped it to the States. Johnny Omundsun, the chassis and power-train engineer behind the Chevelle, un-crated the engine on Saturday. Despite the challenge of running that big of an engine on propane, four days later the small-block was revving happily in the Chevelle, making somewhere north of 800 hp. That engine, while still propane powered, was far different from the engine in the car now. It was naturally aspirated with a massive cross-ram intake and a vaporous injection system that ran propane gas to the injector at around 15psi. Jim says that compared with a gasoline engine of the same output, that application emitted about 30 percent less hydrocarbons, 87 percent less carbon monoxide, and 10 percent less CO2. That explains why the oil on the Chevelle was always so clean. Nowhere near as much carbon gets past the rings. The engine went through a second iteration with a new intake manifold and a liquid-propane injection system before Jim decided to go really big with the current power-plant.
01] Wheels are one-off six-lug designs from MHT, with 335/30ZR20 Pirelli rubber used in the rear and 235/40ZR18 in the front.
02] Johnny started with a Viper bearing and designed a billet-aluminum spindle around it. Six-piston Baer brakes are used all around. Coil-overs are parallel to the frame and run on a bell-crank. Ride height can be adjusted without pre-loading the springs, and the spring rate can be changed by running a different bell-crank ratio
03] The frame is 21 inches wide to allow for long control arms. The main rails twist and turn and tie themselves together to create a frame that resists twisting. Flat-oval exhaust tubing helps maintain ground clearance.
04] The PPI tank is an aluminum extrusion with robotically welded end caps. It's a modular design that can be made to fit nearly any application. Also seen in this photo is the Speedway quick-change IRS center-section.
05] The IRS also uses custom-machined billet control arms and spindles.
06] Jim Grifn fabricated the aluminum panels that back the upholstery and the custom center console. Katzkin leather was used on the Cobra seats. The Long shifter connects to a T-56 with a dual-disc Centerforce clutch.
07] Despite the swoopy headers and array of injectors, the engine is still recognizable as an LS. Johnny says the engine is stock internally, and he just runs a cooler plug.
11] Hardtop 900 horsepower on propane 1970 Chevy Chevelle
09] The Chevelle had been sitting for 20 years and had begun to rust, so a donor car in Texas gave it a lot of sheetmetal bits and pieces to complete the basic bodywork before the custom work began shaved door handles, rocker skirts, and narrowed bumpers make the heavy Chevelle look downright trim.
To show that an enthusiast could build his own propane-powered muscle car and still be green, Jim and Johnny ditched the high-strung small-block and opted for a Chevrolet Performance LSX 454 topped with a Magnuson 2300 supercharger. They reasoned if their propane-fuel delivery system can feed a blown 7.4L engine, it should be able to handle most resto-mods and performance builds. Starting with a 20-gallon tank marketed by Propane Performance Industries (PPI) that stores propane at about 200 psi, the fuel is moved to the injector as a liquid. This required special, high-impedance Siemens Deka injectors you'd typically find in an industrial refrigeration application. The benefit to liquid injection is that the liquid fuel expands to more than 200 times its volume when injected into the port. Not only is that excellent for atomization, but when a liquid under pressure turns into a gas, it cools--lowering the intake air temperature and preventing pre-ignition. Also, as was discovered in the engine's second version, the rapid expansion can also add a couple of pounds of "free" boost on a naturally aspirated application.
All this talk about the benefits of propane probably has you wondering just what it all means for performance. On an engine dyno, the 454 put down 924 hp and 980 lb-ft. using a 102mm throttle-body. Jim has since moved to a 90mm throttle body that's not so prone to frying the tires, but they're not yet done tuning, either. The mileage is also comparable to gasoline, because while gasoline has a slight edge in energy density (it has more BTUs per gallon), propane runs at much leaner 16:1 air/fuel ratio.
OK, so it's efficient, clean, and it has oodles of octane, what's keeping us all from switching to propane? The infrastructure's not there yet. It is relatively cheap to build a pump that's compatible with the PPI fuel tank, and the guys carry an adapter in the car that lets them fill up almost anywhere that sells propane, but it's just not convenient to run propane until some major fleets make the switch. But that's already happening.
Readers Rank It
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Overall:6.5
Function:6.5
Stance:7
Engine:7
Exterior:6.5
Interior:6
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