By Dean Larson

It’s plain to see that a mad man constructed this vehicle. We regular Joes understand relish the thought of a simple Ford Windsor small block or FE big block under the clamshell in a GT40 replica. But what sort of lunatic wakes up in the morning as says “ I think I’ll power my ’70s fiberglass car with a 500-ci Cadillac engine instead. And also, it should really be turbocharged and run on propane in this application.” No one does, that’s maniacal.

Yet here we are, looking at a Kellison GT40 with, not one, but two turbochargers and a damn propane cylinder under the front clamshell. Cramming this strange assortment of parts into a ’70s fiberglass car feels a bit like strapping a rocket to your back and lighting the fuse. Altogether, it’s one of the most frightening and impressive pieces of backyard engineering we’ve seen in a long time. To get all these parts to fit in the car and function correctly (all while running on propane mind you) would take a level of expertise higher than ours no doubt.

It’s tough to comment on the rationale and what this completed powertrain would actually drive like, but we can provide a few thoughts. While the hottest version of the 500-ci Cadillac engine produced 400 hp and 550 lb-ft of torque, it was only available in the 1970 model year. Afterwards, the compression ratio dropped dramatically, and engine made just 190 hp in its farewell 1976 appearance.

With twin turbos installed, we’d be willing to bet this engine is a later model sporting a more boost-friendly 8.5:1 compression ratio. That being said, it wouldn’t take a ton of boost to restore the Cadillac powertrain to its former horsepower glory and beyond.

It’s anyone’s guess how the propane effects the whole equation, as it can match the performance of gasoline, exceed it, or be tuned for absolute efficiency. Sources report that when used in a liquid phase injection system, propane will actually increase air density in the intake and improve power output. However, these systems are considered cutting edge, and it would be surprising to see one in this application.

For all its unexplained lunacy, this GT40 is a pretty impressive achievement. I wouldn’t know the first thing about making these systems work together, and you have to commend the builder for that. A dealer has the car listed on eBay without a buy-it-now option, but a quick search finds their website and an $18,000 price tag. Assigning a value to this propane performance machine would be tough, and it's equally as difficult to imagine anyone other than the builder confidently mashing the fast pedal. 

Are you a propane professional? Give us your take on this machine in the comments below.