Best exhaust system for an RS4?

[neilparf]

...welfabs all illegal too).

Yeah, but it's great being naughty

[Mani]

Oh gosh was going to buy a milltek for mine after hearing my mates ones sounded totally different to mine but might just look into getting rid of cats now!

[NJMAudiRS4]

...welfabs all illegal too).

Yeah, but it's great being naughty

To right it is went to a birthday party at the weekend and they could here me a mile away (valves open)

[neilparf]

...welfabs all illegal too).

Yeah, but it's great being naughty

To right it is went to a birthday party at the weekend and they could here me a mile away (valves open)

My kinda party arrival - BOOM!

[Sterling]

No probs with MOT. Flew through every time. It still has standard cats so emissions are not an issue just the noise which is at the testers discretion. The police is another matter though. Any modification to make the exhaust noisier than standard us illegal as they keep pointing out to me (which makes the Millteks and welfabs all illegal too).

Five 0 Anyone been booked or fined for fitting one of these then sounds like you`ve had more than a few run ins Mike ?? may just Take the Mrc centre section weld and gutting

[MikeFish]

Been stopped loads and told off about my driving, noisy exhaust & illegally spaced number plate. Picked up a section 59 the first time and then a second one which got the car confiscated (it was all a bit dodgy if you ask me but that's another story). I think the noisy exhaust gets their attention more. Never had any trouble before the exhaust.

[sakimano]

I'm looking at maybe upgrading the cars exhaust system for something a bit louder to really show off the sound of the beautiful V8!

I'd prefer Non-res but would like to keep the valves

Would anyone recommend an upgraded airbox aswell or would it not be worth doing?

Stick with the stock airbox and save your pounds for better modifications. Stock airbox is excellent. Sealed, pressurised and a great filter. Going to an open airbox wouldn't be great because the RS4 engine bay is pretty hot as is...not to mention there is an auxillary radiator right below the airbox which spews heat right into an open design.

Audi developed a GT series light-race version of the RS4 for the ALMS series. They changed the exhaust, changed the ECU tune, upgraded braking, upgraded transmission gearing, changed a bunch of suspension components, took 1000 lbs out of the car...but left the stock airbox in place. That should tell you something. (pic below)





Some details about the RS4 Challenge car:


•The engine is a stock RS4 engine with identical internals to the RS4 available from Audi dealerships – even running a stock airbox and air filter
•The engine management system has been modified
•The exhaust system is comprised of custom built headers and straight pipes; there are no catalytic converters and no mufflers
•Engine output is rated at around 500 hp
•The transmission has been modified with custom gears and has been both reinforced and lightened
•Doors, trunklid, bumpers, b-pillars, door handles, and dash are all carbon fiber
•Front doors weigh 2 kilos (4.4 lbs) each
•The suspension has been modified for race and uses custom Ohlin components
•The braking system has also been race-modified and utilizes Alcon brake components
•The car weighs approximately 2900 lbs

[sakimano]

What people are also forgetting is that the jhm one is 2.75" and all others including the weldfab one are 2.5 or less,

MTM = 2.75" but no crossover
JHM = 2.75" with gentle x-pipe crossover (ideal for a crossplane V8)
Ebwerks = 2.75" with a boxy x (less desirable)


Personally I can't see the point in getting a 2.5" exhaust or downpipes other than sound.

Stock downpipes are 2.61" and taper down to 2.36" right before they mate up to the stock catback
Stock catback is 2.36" with a couple of narrow spots

2.5" isn't going to change much. 2.75" was found to be ideal for the RPMs the RS4 hits and factoring in our displacement. Improves efficiency, and allows the car to make signficant gains as all testing has shown. Definitely a bit louder, but with an x-pipe and good mufflers (allowing flow but controlling sound) you're all set.

[MikeFish]

•Engine output is rated at around 500 hp

Surely they can't make that sort of power unless the had RAM air!?!

But this is interesting about the standard air box. We all said it was very good and this proves it

[sakimano]

I recall having a conversation with Doug @ MRC about exhausts when he did my stage 2. The man said "cat back exhausts on the RS4 are all about what noise you want and there are very little power gains to be had, all the power gains are in the downpipes and the removal of the 400CEL precats" - Personally I think that makes sense.

He sells 2.36" milltek catbacks though...

We've done loads of testing on this over here. Size and design definitely matters with exhaust. One member did acceleration testing with 4 catback exhaust setups on his catless car:

1. stock catback
2. milltek catback
3. JHM catback
4. no catback

-stock and milltek were almost identical. Imperceptible.
-JHM showed good gains over Milltek and stock
-no catback was best

Pretty funny stuff when I hear people talk about 'BUT YOU NEED SMALLER EXHAUST TO MAINTAIN BACKPRESSURE!'. That's a crock. You need volumetric efficiency in the system and you need to be able to exhaust spent gases. You also need to have a sound you like of course, so option 4 'no catback' isn't ideal.

[sakimano]

•Engine output is rated at around 500 hp

Surely they can't make that sort of power unless the had RAM air!?!

But this is interesting about the standard air box. We all said it was very good and this proves it

Hard to say. Assuming it started at 420 hp? I guess picking up 80 hp is a tough one.

I have seen cars do JHM tune + catless 2.75" JHM downpipes and JHM exhaust, and they picked up around 40-45 WHP (which is about 50-55 hp or ps). This left the stock headers in place, and had resonators and mufflers. If you improved the headers (it's not worth much power as the stockers are great but on a race application every hp counts), eliminated resonators and mufflers...I'm sure you could pick up more.

Here's a JHM car on the dyno. 327 WHP before, 365 WHP after. For sound to help support Sar and Danny
http://www.youtube.com/watch?v=uCsKy7stfhs

Here's my car with JHM catted exhaust and a go pro with external microphone on the bumper
http://www.youtube.com/watch?v=p4SGcn2MRMw

Here's the launch video JHM did a few years back with a few different cars and sound clips.
http://www.youtube.com/watch?v=lhDcNObZLpo

[sakimano]

You still have to fit the JHM after that too and the JHM is non-valved so a cost there vs JCWF...

You mean plugging the vacuum lines? It's about 50 pence in vac plugs. Two of them.

[neilparf]

You still have to fit the JHM after that too and the JHM is non-valved so a cost there vs JCWF...

You mean plugging the vacuum lines? It's about 50 pence in vac plugs. Two of them.

No I don't. It was for comparison purposes, from a cost perspective - that's the thread debate... What's plugging lines got to do with a fitting cost of the shipped system? Re-read the thread...

[sakimano]

You still have to fit the JHM after that too and the JHM is non-valved so a cost there vs JCWF...

You mean plugging the vacuum lines? It's about 50 pence in vac plugs. Two of them.

No I don't. It was for comparison purposes, from a cost perspective - that's the thread debate... What's plugging lines got to do with a fitting cost of the shipped system? Re-read the thread...

You were talking about the cost of the JHM exhaust.

You said you have to fit the JHM (which you have to do with every single exhaust out there so I'm not sure why you are adding this cost)

Then you said that JHM is non-valved so "a cost there vs JCWF". What cost? Are you saying that it's better to have the valves? I like the valves but to be honest, my JHM exhaust is very civil when just cruising about. I have thought a couple of times about what it would take to fit valves but the cost is likely prohibitive for something I really don't care about.

If the exhaust was a bit too raspy and awful sounding, I can see why people would want valves. Fortunately with the resonators and the high quality mufflers, it sounds clean and excellent.

[Smithy4655]

I'm looking at maybe upgrading the cars exhaust system for something a bit louder to really show off the sound of the beautiful V8!

I'd prefer Non-res but would like to keep the valves

Would anyone recommend an upgraded airbox aswell or would it not be worth doing?

Stick with the stock airbox and save your pounds for better modifications. Stock airbox is excellent. Sealed, pressurised and a great filter. Going to an open airbox wouldn't be great because the RS4 engine bay is pretty hot as is...not to mention there is an auxillary radiator right below the airbox which spews heat right into an open design.

Audi developed a GT series light-race version of the RS4 for the ALMS series. They changed the exhaust, changed the ECU tune, upgraded braking, upgraded transmission gearing, changed a bunch of suspension components, took 1000 lbs out of the car...but left the stock airbox in place. That should tell you something. (pic below)





Some details about the RS4 Challenge car:


•The engine is a stock RS4 engine with identical internals to the RS4 available from Audi dealerships – even running a stock airbox and air filter
•The engine management system has been modified
•The exhaust system is comprised of custom built headers and straight pipes; there are no catalytic converters and no mufflers
•Engine output is rated at around 500 hp
•The transmission has been modified with custom gears and has been both reinforced and lightened
•Doors, trunklid, bumpers, b-pillars, door handles, and dash are all carbon fiber
•Front doors weigh 2 kilos (4.4 lbs) each
•The suspension has been modified for race and uses custom Ohlin components
•The braking system has also been race-modified and utilizes Alcon brake components
•The car weighs approximately 2900 lbs

Blimey yeah, I think i'll leave the airbox well alone! Performance must be crazy in that with 1000lbs less weight and 500bhp!