Hotter BMW M4 coming

M will debut BMW’s all-new water-injection technology in a faster, limited-edition version of the M4 at either the Tokyo or Los Angeles motor shows late this year.

Sources have admitted the M4 will boast at least 500hp (373kW) and will be a lot more track-focused than the standard coupe, which comes with a twin-turbo 3.0-litre inline six.

While still road legal, the limited-edition car will be based on the indirect water-injection technology M has been testing and developing beneath the skin of this season’s M4 MotoGP Safety Car.

While the current M4’s S55B30 six-cylinder engine boasts 317kW of power and 550Nm of torque, the track-focused update will boost that by nearly 60kW, with a target output of 375kW.

It will be the first production BMW – but far from the last – to use water-injection to help it lower combustion chamber temperatures, raise compression ratios, reduce the threat of knocking and lower fuel consumption, all while lifting power and torque.

“Water injection is very important to me,” BMW’s board member for development, Klaus Fröhlich, said at a technical presentation this week.

“We are going to continue with this in all variants in different drive systems, just as variable valve timing eventually came in all variants.”

That’s a big future, which will begin with M, though BMW refuses to confirm whether the limited-edition model will be an E46 M3 CSL-style lighter, sharper version of the M4 or will take its track focus to extremes like the E60 M3 GTS.

The car will use a development of the MotoGP Safety Car’s indirect injection system, which will be the first generation of BMW’s planned water-injection rollout and uses three injectors to deliver atomized water into the inlet manifold, just before the inlet valves.

Unlike diesel engines, petrol-powered turbo motors cannot just accept more and more pressure due to the risk of knocking, or the uncontrolled detonation of fuel in the combustion chamber.

“If you operate a combustion engine under high load, we have to reduce either the pressure or the temperature to reduce knocking,” BMW’s engineer responsible for water-injection development, Werner Mahrle, said this week.

“This also means we lose efficiency, so we need more fuel than we need to use.

“Water-injection is one of the possibilities to get the combustion process back to where we want it.

“On the M4 Safety Car, it physically means cooling the fuel-air mixture before the combustion phase. The water is injected into a very fine spray that cools the mixture but is evaporated completely before the combustion phase.

“The challenge is that we have to get it into the combustion area in a very fine spray, and the ideal ratio is about 30 per cent water for the fuel in there. This is how to get to the optimal point for fuel without knocking.”

However, while the first water-injected BMW production car will come from M, the technology won’t stay exclusive to the hotshop and it won’t stop with indirect injection.

Ultimately, a combination of direct and indirect water-injection technologies will spread across the entire petrol-powered BMW range.