Difference between various releases of the 4.2L V8

[Dad_fast]

Does anyone know, or have a reference of, the different components and variations of the Audi 4.2L V8? I'm curious to know what makes the difference between an R8 V8 and an S4, RS4, S5, etc. The power numbers are quite different so it begs the question.

[bluebull]

RS4 = BNS block with forged internals if I’m not mistaken
420 hp/~330awhp factory #s


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[Dad_fast]

I see, so they are not all the same blocks? I didn't realize that. Thanks for the reply.

[roboto_1337]

They’re very similar, however the coolant channels in the BNS block vary from the BHF (S4) as well. There’s a RS4/R8 has direct port injection too so they’re subject to carbon buildup, where the BHF is not... I also believe that there’s a different cam profile and compression. There are also variants of the 4.2 with less power than the S4 BHF block that were found in the Q7/A6/allroad ... can’t remember if there’s one in the A8 or not. These engines have the chains on the front if I’m not mistaken.

I’m not sure if BHF heads can be swapped onto these variants, but my suspicion would be NO as the timing is driven from the other end of the engine which would change the bearing/crank orientation.

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[MugelloB7RS4]

The Non FSI 4.2L V8 are closely related and the FSI 4.2L V8's are closely related. The wider gap is between the Non FSI version vs the FSI version. That transition started with the B7 RS4 and made its way into the S5, RS5, Q7, R8, etc.

[Dad_fast]

Thanks, guys! That helps.

[JohnVZ]

There’s also differences across the years in terms of the PCV system within the valve cover..


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