does anyone know exactly what they did with the newer 4.2s that differed from the older 4.2s to bump the power up by 40 horses? i'm just curious because the motor in my 2000 a6 is rated at 300hp, while the motor in a 2004 s4 that i was looking at was rated at 340hp. i've never really gotten a good look at a newer one, but i noticed right off the bat that the newer ones have red coilpacks, but i have no idea what else they changed to get the extra power. just curious because i'm thinking about some chipping stuff, and i was just curious if there were some little thing i could replace off of a newer 4.2 onto mine to get the power up a little more.
-mike

 

Good question!!!!

Personally I don't know the exact differences, but it could be a variety of things. Different intake manifold/exhaust manifold/dps/cats/mufflers/cam duration/valves/pistons(slightly different compression?)for a few examples. Easily the ECU could be different. Difficult to speculate.

If anyone knows the real difference in specs I would like to know too.

 

The only differences that I could readily find involve the changing of the location of front accessories and a redesign of the timing belts to decrease the length of the engine by 52mm or so to get it to fit in the A4 body. They also mentioned that the pistons were lighter, allowing the engine to rev to 7,200rpm and that the overall engine was a bit lighter.

My guess is that the difference in power was related to tuning and the use of lighter weight pistons, freeing up rotational energy. There may be more to it, but we are only talking about 40 crank horsepower, which isn't much.

(If I had to guess, I would say any other changes were probably made to the cam profiles. It would be the easiest way to add power and would be needed to take advantage of the extra RPM's.)

 

Good show mate! That sounds about right to me and I totally agree that with this engine 40 crank HP is nothing in regards to its potential. If this block is anything like (or better than) the American V8s, it has a ways to go yet.

 

I'd like to know also. If I'm not mistaken, the older 4.2 C-5 avants had more HP's as well. The motor was different. I think it may have had timing gears instead of a belt, etc...

 

even the older a8's with this engine had more power.... they detuned it to go in the a6...hopefully someone that knows what they did will chime in

 

As far as the differences between the new chain drive s4 engine and the older belt driven engine, theres alot. They have different compression ratios.11.0 to 10.8. Different blocks and internal componants. Each piston is 70 grams lighter. 66 grams lost in the conecting rods. Theres also a different camshaft adjusting system which is better in the new engine. The camshafts are also going to be radically different, but i can find any infor on them. As for the intake, The older engine has a three stage intake, but the newer one has only two. Probably not much to be gained on the intake side considering they reduced the number of available runner lenths available on the new engine. Also, the newer engine has a slighly smaller displacement, 4163ml vs 4172ml, due to a slightly, .2mm, shorter stroke. Only comes out to one cubic inch thou. Couldnt find any info on exhaust. Hope that helps.

 

ok this is long so I am pasting this from what I wrote on another site.

All the 4.2 A6's were the same from 2001-20042002 has some styling changes but little at best
the 2000 A6's were different asthey had 2 less cats and no ESP no immobilizer some other small stuff

2005 the A6 went to the chain driven timing belt (Shared with the B6 S4 )Also the gear ratio was changed to 3.3 from 2.7...one of the huge issues is the gear. Even the A8 has a better gear ratio 2.9

2006 added the FSI and 12.5.1 compression ratio

there is possible improvement with the A8 camshafts as the motor has less compression but more power. Other than that all is the same.

power break down on the S 6....and 8 4.2
the A6 has better cams not sure on the intake and throttle body and better ECU tuning and TCU tuning (info from Vast)
The S8 has different

intake manifold
MAF
injectors
headers
throttle body
camshafts
tuning
The best gear ratio you can get in a tip trans 3.73
Bigger air box

 

I'm not so sure on the why there are differences but the C5 - S6 was rated 340 hp, the same engined S8 was rated 360 hp. The difference between the two was I belive primarily tuning as a chip is available to gain the 20 hp back.

I know none of that helped answer the question, but I'm just showing my lack of attention currently...

 

Actually The S6 gets its power difference in RPM 7000 as opposed to 6200 3

The difference in the S6 and S8 is the intake manifold,throttle body,exhaust, camshafts (just checked and they are different part #'s) the S8 has a completely different motor code