4.2liter V8: A6 vs. S6
 

I've heard that the '03 allroads and the '04 S4s are going to be offered with the new, shortened 4.2l V8 engine. I like that! I've got a '98 A4 2.8l (with a PES G2 s/c), and I'm really considering getting a new allroad (need a little more legroom for rearseat passengers).

Thing is, all indications are that the allroad is going to get the A6 version of the engine (300hp) and the later S4 will get the S6 version of the engine (340hp).

I was just wondering if anyone knows for sure what the difference is between the two engines...I've read that it might be exhaust, or it might be different-lift cams, or it might be something else.

I've noticed, by reading the specs on the two engines, that the A6 engine is rated 300hp @ 6200rpm and the S6 engine is rated 340hp @ 7000rpm. So that means the S6 engine is simply producing the same amount of torque at 7000rpm that the A6 engine produces at 6200rpm (255 ft.lbs.). Is it possible that the A6 just has a shift limiter on the Tip that keeps it from going past 6200rpm, and other than that, it's the same as the S6 engine (meaning, the torque curve is flat from 6200--7000rpm)?

Does anyone have any dyno curves on stock A6 and S6 4.2liter engines?

Just curious!

Hey mr g2!
 

Sign up on my registry for the g2 owners!

FSI technology. One valve is displaced so only 4V per cylinder....
 

Fuel injected directly in the chamber - provides better fuel economy, lower emissions and better low end torque. The intake manifold is designed along with the piston to tumble the air in the cylinder. Higher compression - 12:1 is used and fuel pressures are in the couple of hundreds of psi. What does this all mean? Good luck to future S4, Allroad owners who are thinking of PES. It may not happen. On the good side, the 2002 Lemans R8's are also FSI (direct injection) and run a good amount of boost, so there may be a turbo'd version from Audi offered later (2nd gen RS4?)

The current 4.2 V8's are 5V per cylinder, typical compression ratio engines.<ul><li><a href="http://www.audi.com/com/en/company/company_perspective/technology/fsi/stratified_charge/stratified_charge.jsp">FSI powa!</a></li></ul>

Re: FSI technology. One valve is displaced so only 4V per cylinder....
 

Just a small point.
I don't have the exact number with me right now, but LeMans rules not only impose inlet restrictors, they also limit maximum boost.
The Audi (or any boosted 3.6 L) is limited to only around 7psi boost IIRC.

PES--maybe or maybe not
 

Just got an email from PES yesterday. They can't start working on a supercharger system for an engine that doesn't exist yet (obviously). But they did sound hopeful that if it's a popular engine, they'd find a way to make a s/c kit for it.

My gut feeling is that with the big positive displacement Eaton blowers they use, it would be pretty easy to get an extra 40-50% hp out of the engine with just a few psi of boost. So a high compression engine is not necessarily a death knell...

Also, my gut feeling is that if all the later S4s have this 4.2l engine, somebody is going to find a way to squeeze a lot of power out of it eventually...it always happens.

Also, isn't there a chance that the shortened 4.2l engine will still be a 5V (instead of FSI 4V)? The FSI link you had posted was for the European 1.6l 4-cyl engine (found in the fuel-sipping A2). What makes you think the new 4.2l engine will be like that? I've never read anything about FSI in any of the new allroad articles. The only tech info I've seen on the engine is that it's 37mm shorter than the current A6/S6 motor, and that it's got a timing chain (instead of a toothed belt) that's located at the rear of the engine.<ul><li><a href="https://www.audiworld.com/news/02/geneva/allroad/content.shtml">v8 allroad (with dyno curves)</a></li></ul>

Maybe I spoke too soon ;) Euro articles talk about the 4.2 FSI, to be unveiled in 2003
 

I also read about the Allroad with the FSI engine, but if the Allroad 4.2 is available now, then they most likely have the same 4.2 as the current A6 and A8. They may migrate to the new engine later. Hmmm that sounds familiar - oh yes, my 12V A4 :)

Reason why I linked to the Euro version with the A2 is because I couldn't find one like that talking about the 4.2 yet


No doubt there will always be sources for more power. However, with FSI technology, 30% os so increase in hp will not be around $5k anymore. Perhaps double. Issues to deal with could be numerous:

- timing with fuel injectors that run at 110 bar fuel pressure.
- there's the dreaded 12:1 compression ratio
- intake manifold to piston design is an air-guided combustion process with continuous control of charge movement
- more sophisticated exhaust emission control system with an EGR, NOx storage-type catalytic converter and NOx sensor

For the '2004 S4', I'm going to a wait and see approach

How's the progress on the 3.0 L Eaton? TIA. :)

Don't know...check with PES maybe

Thanks. Hoping you might've heard something. :)