The forgotten aspect of improving F1 engine efficiency 

It is well known that in order to get power from an engine, one needs to get a lot of air into it and use that air to combust the fuel as well as you can. What’s often less appreciated is that power can be significantly increased if you minimise the many losses involved in running the engine. So let’s examine this, the second side of the equation.

A kilogram of fuel contains around 43 Megajoules of chemical energy and, when we boast that an F1 engine is over 50% efficient, it’s the same as saying that somewhere around 21 MJ of that energy is going to waste. So where does it go and what can we do about it?

Much of the losses are heat losses in the exhaust and the best way to recover this energy is with a turbocharger – which will use some of this energy to drive a compressor and feed more air into the engine, increasing its power. Unfortunately, this doesn’t come totally for free since some losses occur in what’s known as the gas exchange process: the filling of the cylinder with a combustible charge and subsequent emptying of the products of combustion.

To empty it you want nice unobstructed flow and the turbocharger turbine obstructs this flow, increasing back pressure and robbing some performance. But it does provide a net gain and is almost standard on engines today.

Friction is an obvious loss and oil plays a significant role in this. The main sources of friction are the piston skirts and rings, the crank and cam bearings, the cam followers, the cam drives and their bearings, the valves sliding in their guides, and the friction of the many rotating seals. The engine ancillaries such as the oil pressure and scavenge pumps and the alternator are also culprits.

The oil, while reducing friction, also adds to losses both from the shearing of the oil and the parasitic losses of spraying into moving parts, particularly the pistons where it is deliberately aimed at the underside to try and cool the piston. Most people think of oil just as a lubricant, but it has an important cooling function.

Photo by: Andy Hone / Motorsport Images

Ricciardo's late DNF at Monza in 2022 was triggered by an oil leak - but it has an important cooling purpose as well as lubrication

The oil coming out of a main bearing can reach 300℃, so the oil needs a very high temperature shear strength – and as much care needs to be taken in designing an exit path for the oil as is used in ensuring the oil gets into the right places. Keeping it cool is a double hit as, with somewhere around 45kW to dissipate, large coolers are required which in turn adds to drag and a further efficiency loss.

A race engine relies on high piston pressures and these lead to a high side load on the piston, which tends to increase the ring and skirt friction. A neat way to reduce this is to offset the crank slightly from the bore centre line so that at maximum combustion pressure the conrod is more upright, reducing the side load.

The engine designer also needs to minimise distortion, not an easy thing to do when the engine is very hot (which reduces the material stiffness) and when a light engine is also part of the design criteria. Distortion increases friction and is both variable and less predictable.

While it may seem logical that a three-bearing crank for a four-cylinder engine might have less friction than a five-bearing crank, this isn’t necessarily so since the increased bending in a three-bearing crank might lose more than the theoretical gain

Coatings and surface finishes also play a part. Oil relies on hydrodynamics to maintain a thin film between moving parts but, when a piston is at the extremes of its stroke, it is stationary, leading to a breakdown of the oil film. Coatings such as DLC (Diamond Like Carbon) were developed in racing and, while their use is ubiquitous in pistons, the crank and the valve train (where the contact pressures between the cam and the follower are extremely high) of a race engine, they are now in use in several production engines.

As far as surface finishes go, honing has always been used on cylinder bores to produce a surface smooth enough to reduce friction and yet rough enough to retain oil; but today, laser honing is also used where microscopic pockets are created on the bore using a laser beam after a first honing process. A finish hone then removes the melt protrusions arising from the laser process to create an extremely fine but well-defined surface finish.

So what can we do to mitigate these losses? Firstly, we need stiff components. A light crank, for example, will deform more and lose power at the bearing edges. While it may seem logical that a three-bearing crank for a four-cylinder engine might have less friction than a five-bearing crank, this isn’t necessarily so since the increased bending in a three-bearing crank might lose more than the theoretical gain.

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In 1989 Ferrari ran a four-bearing crankshaft to reduce frictional losses but this set up vibrations which regularly caused the new semi-automatic gearbox to fail

Similarly, to increase stiffness in the valve train, the camshaft base diameter should be kept as large as possible, and bearings should be placed either side of each cylinder. Piston ring design needs careful consideration as the combustion pressure behind the ring allows it to seal but too much pressure and the friction goes up, too little and blowby
occurs which again loses power.

The seals on the crank, various pumps, air springs and valve stems all have to be designed to perform their function and no more. Even the negative pressure which is encouraged in the crankcase to minimise windage losses doesn’t come for free. Generating it requires power and that is power not available to drive the car.

Many years ago I was involved in an early five-valve engine which produced exceptional power. This was put down to the five-valve design but analysis showed that the engine breathing was nothing special. All the improved performance came from an exceptionally well-designed bottom end where the parasitic losses had been slashed.

Of course, power comes from combustion but there will always be losses – minimise them and it has as much effect as improving combustion efficiency – it’s just the other side of the equation.

Photo by: Drew Gibson / Motorsport Images

Crankshaft stiffness is crucial in minimising power loss