Naturally aspirated inline 6, and turbo inline 4's with manual transmissions, modest dimensions (less width, less height, less bulk). Don't make them look like fat old people. Greater visibility all around looking out, analog gauges, oil pressure gauge...For the diesels...Inline 6 engine...Single turbo VNT (dual at most with low pressure/high pressure variance) with CGI cylinder block, or simply regular cast iron if necessary. High pressure common rail...But with high redline...If not possible, go back to IDI, and refine that. I don't know how just do it. Make it work for fun. GET RID OF PARTICULATE FILTERS! REFINE PCV SYSTEMS. Improve build quality. Charge more, give more. Throw out all the useless junk. Lose weight and get closer to 3100 lbs for the C-Class and 3400 lbs for the E-Class. Make them handle. More aluminum suspension bits. Keep that heavy electrical junky stuff for the S-Class.

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)