Exhaust Cam choices

[Mark Halligan]

Good evening fellow S2’ers.

OK here we go,
I am hopefully fitting a new cylinder head very soon, this will be gas flowed, the one bolted to the block at the moment is leaking oil through the valve stems quicker than my bank account is leaking money!(I have done a compression check and the pressures are within tolerances).

I am trying to decide what exhaust cam to go with, the 7A or RS2/ADU. Obviously the 7A has the advantage of being cheaper and more readily available second hand.
I have been looking through some data and through the lists and files on Kruemmer, and the RS2/ADU has 9.5mm max lift compared to the 7A that has more lift at 10.5mm with longer duration. This I am lead to believe will give more power at the higher revs and boost pressures but possibly at the expense of low end torque.
So the question is which way should I go, whilst more power is obviously the goal, it has to be useable, and also any effect on emissions taken into account too as I have removed the cats and they can’t go back on the new downpipe.
And to add to that I’ve discovered that there is another cam from the NM designation engine that has roughly the same lift (9.6mm) as the RS2/ADU but with more duration……choices, choices.

Would have been a question for the more dedicated engine forums once, but we are going more that way now, and advice or opinions will be greatly accepted.

Cheers, Mark.

P.S. Its Friday night and I should be down the pub and here I am writing about camshafts, whats wrong with me?

[Pisobiker]

Re: Exhaust Cam choices

Originally posted by Mark Halligan

.....
P.S. Its Friday night and I should be down the pub and here I am writing about camshafts, whats wrong with me?

Nothing, m8 !
Or at least nothing worst than me !

Marco

[Pisobiker]

Apart from kidding....

I really think this is a question for tuners only. What I mean is that theory say that expecially on a very high output turbo engine, exhaust cam duration shouldn't be too high (or at least overlap should be very small) because of "reverse scavenging" of intake ducts.
But putting this down into numbers is really a too big task, and a well aknowladge tuner will probably know in practical terms (which in this case is the only thing needed) what's the limit at which improvements start to turn into worsening.

Marco

[Mark Halligan]

Marco,
your right, I was wondering if the 7A is really suitable for a turbo engine, after all it comes off of a naturally aspirated car. If it was really that suitable would'nt Audi/Porsche have used it in the turbo'ed ADU?
Just wondering if anyone is using or knows someone that is using the 7A cam for a practical view of its effect on the engines characteristics, I think maybe I am looking too deeply into this

Mark.

[Pisobiker]

Around the Audi IL5 groups (if I remember correctly the Kruemmer list as well) I think I've heard of many people using the 7A exhaust cam even in some "monster HP" cars. But I actually don't know if this is a really pondered choice or it just comes out of the simplicistic way of thinking that "the higher the lift and the longer the duration the better the performances".
I also think there is a balance between intake cam profile and exhaust one, as well as valve area ratio between intake and exhaust. It can of course well be that on ported heads (intake and exhaust) and highly tuned engines with big turbo compresson ratios, an exhaust cam profile with higher lift could give some benefits; maybe more than the ones achievable by using a higher lift intake cam.
As I said... in this case experience is the best source.

Marco

[Audi Parts Guru]

It's one thing to think about the cam duration and lift guys,but you must need to consider the cam timing as well, as good gains can be made with the right cam timing

[Pisobiker]

Cam timing is directly affected by duration.
You can modify lift without affecting timing but each mod to the duration will automatically change timing (more advance on opening only, or some advance and some retard on closing, or only more retarding on closing)

Marco

[martinjs]

Mark,
i wont really know properly till ive got the ecu optimised for my setup, and due to not driving the car for the past 2 months,
ill keep you posted.

martin

[Greg_S]

Originally posted by Pisobiker
Cam timing is directly affected by duration.
You can modify lift without affecting timing but each mod to the duration will automatically change timing (more advance on opening only, or some advance and some retard on closing, or only more retarding on closing)

Marco

The cam timing on the S2 is going to be quite difficult to adjust becuase you want to be able adjust the exhaust and intake cams but they are both connected via a chain drive inside the cam cover?

Greg

[Audi Parts Guru]

Originally posted by Greg_S
The cam timing on the S2 is going to be quite difficult to adjust becuase you want to be able adjust the exhaust and intake cams but they are both connected via a chain drive inside the cam cover?

Greg

This is when you install adjustable cam pulley wheels from someone like Piper cams www.pipercams.co.uk

[Audi Parts Guru]

Originally posted by Pisobiker
Cam timing is directly affected by duration.
You can modify lift without affecting timing but each mod to the duration will automatically change timing (more advance on opening only, or some advance and some retard on closing, or only more retarding on closing)

Marco

Cam duration refers to how long a valve is opened in relation to crankshaft rotation.

Cam timing refers to when a valve opens and closes in relation to crankshaft rotation

[Mihnea]

Mark, my friend with the black MTM S4 (420HP) is using both 7A cams with the S1 EM and K26/27 turbo. I'd suggest you to use the 7A exhaust one, IMHO on an S4 with all RS2 parts on it, it goes better than the RS2 (better top end with similar tuning).


HTH,

Mihnea

[Mark Halligan]

Mihnea,

thanks, I think I'll start looking for one .

Mark.

P.S. What model Audi uses the 7A Engine?

[Audi Parts Guru]

Originally posted by Mark Halligan
What model Audi uses the 7A Engine?

Mark,the 7A engine was fitted to the Audi Coupe and 90 and it was in production from 1989 untill 1991.It's a 2.3 20 valve engine

[Mihnea]

Audi coupe 2.3l 20v quattro or FWD and same for the Audi 90. Both are typ 89.


Cheers,


Mihnea