Dear Ford Motor Company, You're rightfully proud of the new engine for the Shelby GT350 Mustang. With 526 horsepower, a new flat plane crankshaft and a redline of 8250 rpm, it's a performance monster, but you seem to be a little confused about who you're appealing to. In recent years you've reintroduced all of the most famous muscle car era names, Shelby, Cobra, GT500, GT350, names that speak directly to motorheads like me who grew up during that era and remember those cars when they were new. We also remember the 260, the 289 and 427, names based on cubic inches, the earlier 406, the later Boss 302 and Boss 429, but I don't recall anyone speaking in liters at the drag strip where we raced for a quarter mile. Hearing about the new 5.2 liter Shelby engine just doesn't sound right.
Show some respect for the original Mustang buyers
Sure, we're in the new global era, world cars and all that, but the Mustang was All American. Those of us who bought and raced them can cite chapter and verse from the book of cubic inches and our mental reference points are based in the measurements we grew up with. That 5.2 liter (or more accurately, 5163 cubic centimeter) V8 is 315 cubic inches. Why not just say so? It sounds a lot more impressive. I know I have to do a quick conversion in my mind to get an idea of the actual size of the engine and to appreciate what a fantastic job you've done, 526 horsepower from a naturally aspirated 315 cubic inches! Wow! From 5.2 liters? Yeah, whatever.
Use the units used in the era you recall with the name
At the same time the rest of the world was busy telling us how superior the metric system supposedly was compared to our crazy system of weights and measures based on things like horses and the width of a man's thumb, the United States was using those inches and pounds and miles and going to the moon. It isn't the unit that's important, it's what you do with it. So, if your PR and marketing departments are going to reference those days when cubic inches were the standard for displacement here in the USA, then use cubic inches, the units we used, when referring to the engines in Cobras and Shelby Mustangs. Put a reference to liters in a footnote for the rest of the world or let them do the conversion themselves. They won't mind. Mustang enthusiasts in the States will appreciate the nod to the American heritage of the car and the muscle car era when it was born.