Ferrari’s blinding race starts during Bahrain testing have highlighted how it’s gone in a very different direction from its Formula 1 power unit manufacturer rivals when making a key 2026 design decision.
Since the introduction of the hybrid F1 regulations in 2014, the engine manufacturers have had to balance the output of the turbocharged internal combustion engine (ICE) and the electrical output. On top of that, they had to balance the electrical output against the electrical harvesting (input).
This is the basic turbo layout F1’s been using. Up until the end of last season, there was an electrical motor on the turbo shaft (the Motor Generator Unit-Heat or MGU-H). This could be used to spin the turbo up to speed, or hold it back, which would generate electrical power. This was dropped for the 2026 regulations.
Before we actually get to the overall turbo sizing, there is a balance between the turbine volume and the compressor volume, which is also very important, as there are some decisions to make with it:
1) You need to find the optimum ICE rpm window for power output relative to gearing for an average circuit, less any losses. That then gives you the exhaust gas flow volume you have to work with.
To explain those losses: if you were to get an exhaust pipe leak, you get a reduction in exhaust gas flow and, in turn, turbo pumping capacity, so in effect a loss of boost pressure and with that a loss of power. The bigger the leakage, the bigger the losses.
2) You can then decide on what turbo rpm you want to achieve maximum boost pressure at. In the regulations, there is a maximum turbo speed of 150,000 rpm, so you need to stay under that, but other than when the car reaches terminal velocity, the ICE rpm will always be increasing, so the exhaust gas flow will be increasing with ICE rpm.
Before you end up with the correct size balance, you will need to go through these calculations or simulations many times as one affects the other.
MGU-H removal has changed the game
To achieve the above, teams had various options. Having the MGU-H, which, as I said above, was simply an electrical motor on the turbo shaft, can be used in two ways:
1) As an electrical motor to spin up the turbo to achieve the required boost pressure to optimise the power output of the ICE, as the driver requested it.
With this, a big turbo is not such a problem when the ICE rpm is lower than the optimum.
2) As a generator to hold the turbo from overspeeding and/or overboosting and, while doing that, charge up the battery pack.
With this option, a small turbo which spins up faster is not such a problem, as you can generate electrical power to either use as instantaneous power or to charge up your battery pack for later.
So by having that MGU-H, the overall turbo sizing was not as critical as it is going to be for 2026. Now the MGU-H is gone, so the turbo’s sole function is to use the exhaust gases to build up plenum boost pressure, which can only be achieved using exhaust gas flow from a 1.6-litre (turbo) engine.
Over the hybrid years, reportedly, Ferrari was the only power unit manufacturer to use what we will call a small-sized turbo; the others used what we will call a large turbo. The actual size is impossible to know, so, in general, I will call them big and small.
Now with the MGU-H gone, all you have at your disposal is exhaust gas flow to create that intake boost pressure.
To control that you can have a pop-off valve. This is a valve on the compressed airflow to or on the plenum (the plenum is a volume of air that is big enough to run the engine efficiently with minimum pressure variation). When the boost pressure gets to or near the allowable maximum it will open and release that extra pressure. This released flow will then go back into the system before the compressor inlet, however when open it will also allow the turbo to increase in speed.
The negative here is that you are wasting the original exhaust gas energy you used to create that boost pressure.
You can also have a wastegate on the exhaust system, to ‘waste’ excess exhaust gases when or if the turbo is going to overspeed or generate too high a boost pressure.
This would be your main solution to control turbo overspeeding or excess boost pressure. If you were using a big turbo which has a higher pumping capacity then that wastegate would have to react fairly quickly; while with a small turbo, which gets up to that maximum speed and/or boost pressure faster, you should have more control over keeping both turbo speed and boost pressure at a optimum level.
For either turbo sizing, the teams will probably use a combination of both.
However, with any of these systems, waste is a dirty word. When we had the MGU-H, nothing was wasted. You got a more consistent boost pressure and when that or the turbo rpm got too high you could hold it back and create electrical energy.
So, where would suit either of these two solutions the best?
A small turbo would be better when using lower ICE rpm, at circuits with lower speed corners like Monaco, or from a standstill, like off the grid (as you may have seen from some of the practice race starts of the Ferrari-powered cars in testing) or leaving a pitstop.
But a bigger turbo? Well, I’m not sure when that will help with the 2026 regulations. If you can achieve the boost pressure and be within the maximum turbo rpm with the smaller turbo, then the response on and off the throttle will be faster and you will have a lot less pop-off valve and wastegate management needed to control the turbo.
We call the turbo big or small; weight-wise there is a small difference but it’s mainly the pumping volume that is big or small, so I’m pretty sure it would be a difference of grams and not kilograms.
If you look at IndyCar, which has been a turbo formula for as long as I can remember, they will use a small turbo on street and road circuits because the engine rpm varies so much. For the big ovals like Indianapolis or Texas, they will use a big turbo because the engine rpm is much more stable.
Has Ferrari outwitted the others here? It might just be so. I’m surprised the other manufacturers with their big turbos didn’t look more closely at how much they had to use the MGU-H to optimise the turbo speed.
From that, they should have realised that the removal of the MGU-H might just cause them problems.