I've done conversion's for different reasons. Conversions are usually done for more tunable power while others want to improve the drive train's reliability and serviceability (Jags, English, Italian cars) My most recent conversion was done for the modern technology (5 valve/cyl, twin turbo).

The Mercedes are basically reliable, parts are available, and the 6's give good performance so the conversion should be significantly better in performance than a Benz V8. With more power you will need better braking, handling modifications, and likely wider wheels & tires. Be prepared to pay alot for this project unless you have all the skills to do all the work yourself. You could end up spending enough to buy a new Benz if you do the work right. Many backyard mechanics can do a hack job but you're trying to "improve" your Benz, right? If done right you will have a unique car and the experience of creating a car to your liking...

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'88 300TE, 175k, black RENNTech 3.6L Recaro C's AMG 1 SOLD
'92 500E, 110k, Spruce green, stock SOLD
'94 E320 Cabriolet, 130k, E500 wheels, Emerald green SOLD
'94 E320 Cabriolet, 110k, black, stock, SOLD
'88 300TE, 229k, dark grey, SOLD
'90 300CE, 212k, white, new paint, SOLD
'91 300E, 209k, white, rebuilt head SOLD
'74 914-6, grey, 2.7L 325hp twin turbo Audi conversion