Tractor turbo brings century-old Ford Model T engine to life

Merlin Johnson, the man behind Merlin's Old School Garage, experimented with a Model T whose 177-cubic-inch, or approximately 2.9-litre, four-cylinder engine follows Ford's original architecture. Ford itself lists the historic Model T powerplant at around 20-22 hp, or 15-16 kW. It is a side-valve engine, with the intake and exhaust on the same side, and a sensible operating speed of around 2,000 rpm.

2.9 litres and just 15 kW leave plenty of room for a turbo

By modern standards, the Model T engine's specific output is almost absurd. Around 15 kW divided by 2.9 litres works out at only slightly more than 5 kW per litre.

For comparison, a typical modern 1.0-litre turbo petrol engine often develops 74-96 kW, meaning its specific output can exceed that of the Model T by more than tenfold. It is not just about the turbo. A modern combustion chamber, higher compression ratio, precise injection, electronic ignition control, better gas exchange and much higher engine speeds use every unit of displacement far more aggressively.

The Model T engine operates in a different world. Large displacement, low revs and low original output mean relatively little air reaches the cylinders for their volume. With an engine like this, even modest boost can make a noticeable difference, without necessarily chasing a three-figure kilowatt output.

A turbo from a small-displacement, low-revving diesel engine has to spool up with a modest exhaust-gas flow. A large sports-car turbo would be a far worse match for the Model T engine, as reaching sufficient turbine speed could take an eternity.

0.4 bar is far from insignificant pressure

During testing, boost eventually rose to around 6 psi, or 0.41 bar.

At first glance, 0.4 bar looks modest alongside modern turbo engines. From a physics perspective, however, it is a significant change. If intake pressure rises in ideal conditions from atmospheric pressure of around 1.0 bar to 1.4 bar, the engine can theoretically ingest approximately 40 per cent more air mass.

That does not automatically mean a 40 per cent power increase. The actual result depends on mixture composition, ignition timing, intake temperature, turbo efficiency, exhaust back pressure and the engine's volumetric efficiency. In the Model T's case, the rather creative tolerances of a century-old design are another factor.

But the principle remains the same. More air makes it possible to burn more fuel and generate greater pressure in the cylinder. That is what the crankshaft feels as additional torque.

This is also where the experiment becomes most interesting. The Model T engine has no knock sensor, lambda sensor, electronic engine management or electronically controlled wastegate. A modern turbo engine constantly corrects fuelling, ignition and boost. In the old Ford, the mechanical components have to cope on their own.

The biggest issue was not cylinder pressure

Mounting the turbo to the exhaust is only half the job. The turbo shaft requires lubrication, and this is where Model T technology immediately conflicts with the demands of a modern turbocharger.

The Model T engine has no conventional pressure-fed oil pump. Instead, the powerplant uses a more primitive splash-lubrication system, while the engine and planetary gearbox share oil.

Johnson therefore had no pressurised oil gallery from which to run a conventional turbo oil feed line.

He solved the issue mechanically. The movement of the flywheel helps direct oil into a copper pipe, from where it travels to the turbocharger before returning to the engine. The solution cannot be compared with the stable pressure lubrication of a modern engine, but it supplied the turbo with the lubrication required for the test.

This detail makes the project technically more interesting than simply bolting on a turbo. When fitting forced induction, attention tends to focus on compressor size and boost pressure, but reliability is often determined instead by lubrication, temperature, mixture and detonation.

Speed increased by around a fifth

Johnson's driving test produced a relatively simple measurement of the turbo's effect. The car reached around 45 km/h, while the same test before forced induction had topped out at approximately 37 km/h. That is a difference of around 8 km/h, or more than 20 per cent.

This cannot be used to calculate the engine's precise power increase, as top speed is influenced not only by power but also by gearing, aerodynamic drag, tyres and test conditions. Johnson did not put the turbocharged engine on a dyno after the conversion.

An earlier measurement nevertheless provides interesting context. Merlin's Old School Garage's 1915 Model T delivered approximately 9.5 kW at the rear wheels and around 121 Nm on a dyno. This means Ford's historic 15 kW rated output is far from unrealistic, even if losses in the century-old drivetrain consume a considerable share of it.

In the Model T's case, torque is even more revealing than power. Its large 2.9-litre displacement delivers force at very low revs, and a small turbo suits that character well. There is no need to force the engine to high revs; it is enough to improve cylinder filling where the powerplant already operates.

Compared with a modern 1.0-litre engine, the difference is brutal

The European-market perspective puts the project into the right scale. A modern roughly 1.0-litre three-cylinder turbo engine, with half the number of cylinders and nearly three times less displacement, can produce five or six times more power than a Model T.

That does not make the old Ford engine bad. On the contrary, it shows what it was designed for.

The Model T powerplant had to run on poor fuel, be cheap, simple to repair and withstand use at a time when a proper road network was far from guaranteed. Ford Racing describes the original engine as a 177-cubic-inch, or 2.9-litre, side-valve four-cylinder with a factory rating of 20-22 hp.

A modern turbo engine extracts as much work as possible from the same quantity of air and fuel. The Model T design prioritised modest loads and mechanical simplicity.

It is therefore no surprise that moderate boost gives it noticeably more life. More surprising is that an engine based on a principle more than a century old tolerates it without immediate mechanical catastrophe.

A turbo Model T does not need huge power to be technically fascinating

Johnson's build does not prove that every Model T should receive a turbocharger. Nor does a drive of a few kilometres prove that the original pistons, connecting rods, bearings and cooling system could operate without concern for tens of thousands of kilometres at 0.4 bar of boost.

A turbo does not care whether an engine comes from 1910 or 2026. If more air is forced into the cylinder, the appropriate amount of fuel is added, and temperature and detonation are kept under control, the engine's ability to do work increases. The Model T simply makes this fundamental principle especially visible.