Video: The Weirdest F1 Engine Ever — BRM’s P75 H16 Double Flat-8

In order to both answer the obvious question while intriguing you enough to continue reading, the engine we’re talking about is an H16 — that’s “H” like the letter, not “H” as in short for horizontal (but it is a horizontal engine). The H16 is essentially two flat-eights on top of each other. Why would someone do that, you might ask? Well, read on.

After a successful few seasons in the pinnacle of motor racing, British Racing Motors (BRM) was looking to continue their winning ways in the 1966 season. However, there were some new rules to play by. Instead of the 1.5-liter maximum displacement allowed in the series, the new regulations allowed for a supercharged 1.5-liter engine or a naturally aspirated engine of 3.0 liters of displacement. This left BRM in a quandary; supercharge their successful 1.5-liter offering, or design an all-new, larger engine.

They chose the latter, kind of. The keen-eyed mathematicians reading this might have already figured out that 3.0 liters is exactly twice the displacement of 1.5 liters. So, rather than start with a clean sheet, BRM decided to take two of their proven engines, flatten them out to 180-degree bank angles, stack them on top of one another, join them at the crankshaft, and not only come up with a new 3.0-liter engine for the 1966 season, but an entirely new engine designation.

The H16 sounded simple in it’s concept. Take the championship-winning 1.5-liter V8 engine, lay it flat, and then stack two on top of each other for a championship-winning 3.0-liter engine. Simple as baking a pie, right?

The odd configuration had an even odder crankshaft arrangement. First was the fact that there were two independent crankshafts, which were connected together via gears in a common crankcase (an interesting way around a single-engine rule). Second, was the fact that each crankshaft was a flat-plane design, and the crankshafts themselves were phased 90 degrees apart. That meant that at any given combustion event, there were four of eight pistons at TDC, and combustion was taking place in two of those cylinders simultaneously.

Like its predecessor, the P56, the BRM H16 P75 had a dual overhead camshaft, two-valve-per-cylinder configuration in early versions of the engine. Later, it was converted to a 64-valve setup, giving each cylinder a pair of intake and exhaust valves. The engine’s rating these days seems to hover at 400 horsepower at 10,000 rpm. However, questionable power figures were the least of the H16’s concerns.

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The crazy crankshaft configuration and the subsequent ignition sequence meant the inherent balance of the engine made a paint shaker look smooth. The immediate fix was bolt-on counterweights that turned the engines into centrifugal cannons when the weights inevitably detached from the crankshafts, usually at the most inopportune times. A cross-plane crankshaft was developed to try and fix this, but it was too late, as the engine’s fate was sealed.

However, it wasn’t a total failure, garnering one win in it’s short life, at the U.S. Grand Prix, no less. The additional pair of valves later in it’s three-season lifespan (only two of which were in Formula 1) are purported to have only added somewhere between 5 to 20 peak horsepower, at 10,500 rpm.

So whether you consider it a failure or a success, the engine sure is an interesting design from the annals of race engine history. And, according to the people who worked on the project, was a fun challenge for them to undertake.