RS4 Exhaust

[MarkB]

All looks good to me and as to be expected, more flow at the top end.

More importantly, how does it feel to drive and how much change in sound ?

[GrahamS4]

It does feel better and again most notably top end.

Sound, well it is just perfect for me. At idle it has a little more rumble to it externally and a blip of the throttle sounds great with a nice dash of turbo noise.

Internally, it's the peaceful refinement I had before, in fact maybe better! It just sounds so refined and smooth I wonder if it is quieter than before at times. Under load it is just so effortless in the noise dept. I'd say no louder and the noise that is there is nicer in a more refined way. There is a harshness that has gone. Could not tell you the precats are gutted and airbox cut (like sportec box) no change at all.

Doug tells me it sounds deep from the outside though.

Oh - my slight heatshield rattle I had at cold under certain rpm is now gone, another plus.

[ChrisS2]

Its all good then Just gotta find time to do mine now.

[GrahamS4]

Its all good then Just gotta find time to do mine now.

Yeah, all good, top job.

Let me know if the standing around watching you inflict pain on yourself helped the process at all, I can always come back when you do yours LOL.

I will be interested to see what you do to join the S4 Milltek to the RS4 downpipes. Make sure it is tig welded!

Will make a good comparison afterwards.

[ChrisS2]

LOL yeah it was great fun. Should fit straight on

[CliveH]

Nice one Graham I thought that was the way you would go.

I was totally happy with my RS4 setup, it felt a lot freer flowing, and the sound was spot on. As you mention, it does sound a lot meaner under load from the outside without making the cabin rumble.

Your logs look good, and exactly as would be expected.

Look forward to seeing (and hearing) it at the RR

[GrahamS4]

more flow at the top end.

Been thinking about this and various quotes from Dippy in a few ancient threads I found saying that the full Milltek system and cats saw his peak power hold better to the redline.

While it definately does feel better top end, I've also been looking at the logs to see if there is any suggestion this is not imagination.

Peak power on my dyno plots with just the remap is about 5200rpm. Now at about 5200rpm the maf reading is not at it's max. Peak maf is much higher up where power has actually fallen (due to rapidly falling boost I guess).

However from around 4500rpm through to ~6800rpm, my maf reading varies up to 6-8 g/s more now. Also, previously peak MAF was starting to tail off and fall at just past 6000rpm where as now it continues to climb to a new peak at nearer 7000rpm, with the extra timing advance notable in the higher rpms too.

I would guess there could be something like ~10BHP more from about 4500rpm onwards and it would look like there could be a new peak power a little higher rpm than before hence not the obvious tail off previously felt when driving.

A plot of the MAF readings alone shows the difference quite well I think. What we don't know is the affect on perhaps quicker spooling turbos and the extra timing at the top end (or would those factors have ALREADY affected the maf reading??), but hopefully a dyno power plot would follow this trend in terms of change:



In this confused state, I am now on the reserves list for the dyno day in a few weeks! Hopefully I can run and see if any of this waffle comes to anything.

[GrahamS4]

Can you tell it's a wet Sunday?

[CliveH]

Graham - it's sunny here (believe it or not ), but this is a very interesting thread

I wish I could have been arsed to log and plot all my data before and after so meticulously

[Harper--D]

Glad you got it all going in the end!! I think this exhaust would have been better: http://www.rs246.com/index.php?name=PNp ... ic&t=65433 LOL only joking!!! Those logs are very interesting and it will be good to see what it reaches at the RR day!!!

[Doug_S2]

you can run a lot more timing but it does not really affect the maf reading - if you can run more timing you are using the air and fuel a lot more efficiently so you get extra power! Numbers look good Graham - next step is to get rid of the middle box - but that is defintely louder and you will get a drone.

[GrahamS4]

Already posted in the precat gutting discussion thread, but I think the conclusion from my dyno run needs to be here to keep all this exhaust upgrade documentation complete:

Before (Stock S4 exhaust):

Torque curve flat lining at: 3200rpm
Peak Torque: 360FtLb @ 4000rpm
Torque at 6200rpm (where torque is tailing): 240ftlb
Peak BHP (249 @the wheels) reached at: 5120rpm
BHP @ 5900rpm: ~235BHP (tailed ~14BHP)


After (RS4 exhaust gutted precats):

Torque curve flat lining at: 2880rpm (320rpm earlier)
Peak Torque: 380FtLb @ 4000rpm (+20 ftlb or 27nm)

In fact from the point the torque starts to level off at the rpm above, the torque is consistantly always at least 20ftlb more than before.

Torque at 6200rpm (where torque is tailing): 270ftlb (+30ftlb or 40nm)
Peak BHP (249 @the wheels) reached at: 4800rpm
BHP @ 5900rpm: 249BHP (held power)

So the facts show it has made a difference, slighly earlier torque, slightly earlier peak power, good increase in torque accross the range and peak power holds well where as it peaked and started to dive before.