CAN YOU GET DECENT GAS MILEAGE OUT OF A 1975 CADILLAC FLEETWOOD BROUGHAM?

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The mid-1970s were not kind to giant cars with an uncontrollable appetite for gasoline.

Gasoline price spikes and shortages made domestic land barges with horrific gas mileage numbers even more impractical from a consumer’s point of view.

Mid-1970s Cadillac Fleetwood Brougham models were ultra luxury cars with an expensive addiction to fossil fuel and very poor MPG numbers. Fortunately, their upscale owners cared little about cost, so the big Caddies continued to enjoy a loyal customer base, despite the gas pump price hikes and intermittent shortages.

Cadillac Fleetwood Broughams were still the high-water mark for automotive luxury in 1975 North America and they were sold to buyers who wanted only the best in their viewpoint. The Cadillac name represented the ultimate in luxury standards and was applied to many products as the “Cadillac in their class”, so to speak.

However, MyStarCollectorCar would like to return to that pesky MPG problem inherent in 1975 Cadillac Fleetwood Broughams because 21st century gasoline costs more and delivers less bang for the buck than its 1970s predecessor. The sad reality is a stock 1975 Cadillac Fleetwood Brougham’s MPG would need to be improved in a big way to make it a regular part of traffic in 2024.

A ’75 Cadillac Fleetwood left the factory with a 500-cubic-inch big block that had an anemic 190 horsepower rating and 360 ft. lbs. of torque to move this mechanical Brontosaurus down the road. Blame the lack of horses on Seventies-era automotive legislation hell-bent on strangling performance out of domestic cars built during that decade.

The grim result provides a challenge to do a 21st century mechanical makeover on an almost-50-year-old car to drastically improve its overall MPG averages. Is it possible? We at MyStarCollectorCar say “Yes” and want to offer our choice of ways to get the most performance out of a giant 1975 Caddy.

Our hypothetical game plan: retain the factory engine and tranny while adding enough improvements to make the car function better and become a born-again gas miser.

Our first order of business would be an upgraded distributor to give the engine a more efficient spark system. The MPG improvements may be nominal with a hotter distributor, but a healthy ignition system would be a cornerstone for better fire in the Caddy big block’s belly.

We would also add an EFI unit to replace the car’s carburation system, even though we believe a well-tuned carb will match an EFI in terms of efficiency. The big problem is very few car guys know how to tweak a carb properly in 2024, so a computer-controlled fuel distribution system is a good idea for the average car guy.

The next area is likely to be controversial for green people because we believe a free-breathing exhaust system will help increase the performance numbers on the big Caddy. The process should include more efficient exhaust flow (possibly headers) without a catalytic converter if the owner can legally eliminate the choking device.

Lightweight intake/exhaust manifolds and cylinder heads, along with an electric fan in conjunction with a lighter, and a more efficient radiator, would also lend a hand in MPG improvement.

The last component on MyStarCollectorCar’s better big boat fuel mileage list will likely provide the largest fuel mileage jump, namely an aftermarket overdrive unit to dramatically lower the big engine’s RPMs on the road. We at MyStarCollectorCar believe an add-on overdrive system will provide the biggest boost in MPG, although their steep price will require lots of driving to justify the cost.

Happily, the idea of a 1975 Cadillac Fleetwood Brougham owner spending many more hours behind the wheel of a large-and-in-charge luxury sedan seems like a great idea to us here at MyStarCollectorCar.

BY: Jim Sutherland

Jim Sutherland is a veteran automotive writer whose work has been published by many major print and online publications. The list includes Calgary Herald, The Truth About Cars, Red Deer Advocate, RPM Magazine, Edmonton Journal, Montreal Gazette, Windsor Star, Vancouver Province, and Post Media Wheels Section. 

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