Only the P1's version of the M838T has a different, bigger turbocharger to make the bigger HP.

McLaren said the M838T E version in the 570 and 540 has 30% of the components redesigned, but didn't say it was 30% vs the P1's version or the 650S's version.

The 570S's power level is not much lower than the initial launch rating of the 12C. But the 650S version has moved on to a much higher level. From a manufacturing point of view, it makes perfect sense to re-use the not up to par engines for the lower output level, like how Intel did to bin their chips, heck sometime Intel just bin everything to the lower spec just to make up the volume needed.

570S's engines have a different intake and less exotic material in the valvetrains, so bolting those on the rejected engines will be much more time and cost effective. 

McLaren is not a big operation, and the 570/540 will be the volume leader, they will need to make more of those M838TE engines than the M838T, converting the rejected M838T engines to E spec will help the production volume.

 


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