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      04-21-2021, 06:29 PM   #174
Brigadier General

Drives: '08 M Roadster
Join Date: Oct 2007
Location: NJ

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Originally Posted by kyrix1st View Post
S54 was never based on M54, or S52 US for that matter. It was based on S50B32 euro engine, and the S50 euro engine was an evolutionary engine to the inline 6 used in M1. S14 of E30 M3 was two cylinders "chopped off" of M1's inline 6 for lighter weight. So S55 was the first M engine based on a regular production engine N55.

With regards to S85 and S65, they become quite reliable M engines with the simple rod bearing swap and can last 200K+ miles with occasional track usage, so I am not sure what the fuss is. You should see how many AMG/Audi/Porsche V8 engines are grenaded simply due to a poor oil lubrication and piston clearance design which are not an issue with M cars.

BMW M never bothered with turbo engines until S55 because engineers perceived them as laggy, cheap and unimaginative way to gain horsepower, as high compression naturally aspirated engines are much harder to build correctly and require significant engineering exercise. That approach provided distinct character, performance and fuel efficiency over its competition. The reason S65 is two cylinders off S85 is not because of cost, more because the F1 inspired engine is well designed it can run competitive races for hours, and so did the S65.
I didn't say S54 was based on M54, but the departure wasn't radical departure or clean-sheet design like the S85 was. You're right that the degree of parts sharing is much higher now obviously.

S65 and S85 are not reliable, period. Throttle actuators, main bearings, rod bearings, S85 vanos... When you have to say "except the rod bearings" you don't have a reliable engine. The main bearings tend to go, too. These are IMO not regular wear items on a street car and this is still a street car.

The fuel efficiency claim is laughable too. There's almost no quicker way to an inefficient engine than to spin it quickly. S85 and S65 get horrific fuel mileage even compared to their contemporaries. I really love S85 and S65, but they are not perfect. Pretending the R&D cost saved by chopping two cylinders off of S85 is not a factor is a bit naive.

Last edited by chris719; 04-21-2021 at 06:34 PM..
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