Audi V8 differences

[carsounds_dan]

Hi all,

What are the differences between the different petrol v8s?
Theres two that I'm aware of,
the one originally fitted to the A8, 4.2ltr, 300ish bhp.. standard EFi system..
and the one in the RS4 (also turbocharged in the RS6), 4.2ltr, 420bhp.. it's on FSi which might help it though..

I've looked at different pictures of them online and they look very similar, so what are actually the differences, could the older engine match the newer one's power with bolt on parts from the newer block? Any pictures of the inlet/exhaust ports, of the inside of the heads? etc...

Many Thanks

Daniel

[Nobody You Know]

I'm pretty sure the V8 first turned up in the DTM cars in '91 and a few Audi 100 based road cars. Then the A8.
This was a 32 Valve engine (either 3.6l or 4.2l)
This engine also appeared in the S6 Plus for a limited time.

The engine that appearred in the C5 RS6 and the B6 S4 was a 40 Valve FSI engine.

The valve train appears to be the big difference, also the newer engine uses Coil Packs so they are completely different heads.

I don't think you would have much luck cross polinating the two.

Edited by Nobody You Know on Thursday 19th February 00:13

[Dracoro]

carsounds_dan said:

Hi all,

What are the differences between the different petrol v8s?
Theres two that I'm aware of,
the one originally fitted to the A8, 4.2ltr, 300ish bhp.. standard EFi system..

They may be similar engines but there are V8s as follows: (as fitted to the A8, sure same/similar in A6/S6)
3.7 - 230 bhp
3.7 40v - 260 bhp
4.2 - 300 bhp
4.2 40V - 310 bhp
4.2 S8 - 360 bhp

New shape A8
3.7 - 276 bhp
4.2 - 330 bhp

[marctwo]

Nobody You Know said:

The engine that appearred in the C5 RS6 and the B6 S4 was a 40 Valve FSI engine.

I don't know about the RS6 but the B6 S4 has the 40v 4.2 with 340bhp. I don't think it has FSI. The 4.2 in the S5 is the FSI unit which I think is a detuned version of the B7 RS4 engine.

[carsounds_dan]

thanks for the help guys, any more help would be appriciated.
I'll talk to the chaps at the local audi place and see what they say.
Many Thanks

Daniel

[marctwo]

You might find this thread useful too...

http://www.pistonheads.com/GASSING/topic.asp?h=0&a...

[Robatr0n]

To my knowledge, the first V8 was around in the lat 80s in the Audi V8 which later evolved to become the A8.

http://www.carfolio.com/specifications/models/car/...

eta - supercharging the S4 lump could be interesting.

Edited by Robatr0n on Thursday 19th February 14:37

[Mikeyboy]

I'm not very technically minded so bear with me on the finer points but my understanding was...
The RS4 version had not just FSi and the changes that would bring to the heads but also significantly different materials in the pistons and other moving stuff allowing for higher rev limits. So no I do not believe changing the ECU and exhaust would turn it miraculously from an S4 4.2 to a RS4 4.2

[marctwo]

Robatr0n said:

eta - supercharging the S4 lump could be interesting.

http://www.fourtitude.com/news/publish/Features/article_2349.shtml

[Robatr0n]

marctwo said:

Robatr0n said:

eta - supercharging the S4 lump could be interesting.

http://www.fourtitude.com/news/publish/Features/article_2349.shtml

I like!

[Nobody You Know]

marctwo said:

Nobody You Know said:

The engine that appearred in the C5 RS6 and the B6 S4 was a 40 Valve FSI engine.

I don't know about the RS6 but the B6 S4 has the 40v 4.2 with 340bhp. I don't think it has FSI. The 4.2 in the S5 is the FSI unit which I think is a detuned version of the B7 RS4 engine.

B6 S4 4.2 is FSi, it says it on the top of the engine in my car.

According Wikipedia (not always but usually right) the RS6 engine is a 40V, I wasn't sure so I checked

[marctwo]

Well mine looks like this:

[Poverty]

414hp 4.2 fsi v8 in rs4 is drastically diferent to the lesser 4.2 v8's. There is no chance of you turning a lesser v8 into the rs4 one.

[marctwo]

Poverty said:

414hp 4.2 fsi v8 in rs4 is drastically diferent to the lesser 4.2 v8's. There is no chance of you turning a lesser v8 into the rs4 one.

I don't think anyone is trying to do that, just to better understand the differences.

[Fort Jefferson]

Nobody You Know said:

B6 S4 4.2 is FSi, it says it on the top of the engine in my car.

You'd better take a photo and show us, because it sure as don't on mine.

[carsounds_dan]

the idea isn't to turn a bog standard 4.2 into the RS4 one, so much as see where audi optermised things, apply to the old V8 and see what happens, they're cheap now and I need a new engine for my next project.. I've got a 351w ford v8 but it's bloody heavy, and the extra horses don't come cheap with them so...
Anyway thanks for the advice people, keep it coming, I've been doing a lot of reading into turbocharging the v8 etc... may have some fun with that
Cheers
Dan

[Poverty]

gm's v8 is meant to be light.

[Waugh-terfall]

The Bi-Turbo 4.2 in the C5 RS6 was fiddled with by Cosworth

[Tame Technician]

I've changed engines on a B7 S4 and they.re definitely not FSI, you can see the injectors and fuel pressure regulators in the picture.

No FSI on C5 RS6 either.

[Fort Jefferson]

Tame Technician said:

I've changed engines on a B7 S4 and they.re definitely not FSI, you can see the injectors and fuel pressure regulators in the picture.

No FSI on C5 RS6 either.

The FSI is only a 32 valve engine and not 40 valve like the B6 S4 (there isn't enough room in the head to get 5 valves a spark plug and an injector) so they had to leave out a valve.