New exhaust... lower boost

[VERN]

Nige - sorry had forgotton my own question I
Hi Vern . Arse. The real question then is what do I do? Been thinking about getting Blueflame to make me something customer - not as loud as GTT please, but just as free flowing

I think it's only the manifold that MTM supply - don't know about the downpipe - as far as I know it's the OEM kit, which runs into Milltek sports cats.

You have your answer then clive, get the apr d/pipe 3" bolts via link suppiled to your apr system, and inc sports cat race cat 100 cell,( you can then sell your miltek twin cats with standard y piece d/pipe ) very FREE flowing couple of peeps have em on lcr's, but very expensive, i know martin was looking into a cheaper alternative on the TT forum, did it come to anything? Blue flame could be a runner mate full system eh? inc d/pipe, just a shame to get rid of apr zorst so soon, this modding can be expensive/frustrating @ times best of luck mate
vern

[clived]

Isn't the downpipe K04 fitment only though Vern?

[VERN]

Isn't the downpipe K04 fitment only though Vern?

DOh yeah it is mate although jbs can weld a flange to mate to your k24/26) seems a waste though/hassle................ blumeflame full custom sounds like a plan then, bear in mind they will make to your spec d/pipe size (recommend 3") sound/tailpipe style etc , they cannot be bad as make them for forge, and make jabba's ihi bits to mate up to turbo's/systems

vern

[clived]

You know those things you find out about hours too late

Cheers, Clive

[Dippy]

I'm no expert, but I thought boost was on the inlet side and changing the exhaust would have little or no impact on this. Spool up would obviously be impacted by increasing the back pressure. I'm wondering if you have an O2 sensor on it's way out?? I would say the APR exhaust would be less restrictive than the Miltek. Apart from that I'm struggling to suggest anything apart from putting your old exhaust back on and see if your power is restored.

Hey Nige, the whole point of a turbo is that the exhaust gasses spin the turbine which is connected to the impeller, sucking in the air and forcing it into the inlet manifold. So indeed there is very much a direct link between the two!

I have only speed-read this thread, but seems to me that the cause of boost loss must clearly be that the APR exhaust is more restrictive. The car in question is obviously at an extreme level of tuning (not far off 200 bhp per litre for **** sake!) and this can only be done by taking airflow to it's limit. Clearly any any all changes in the breathing system are going to affect performance.

[Nige_RS4]

Hey Nige, the whole point of a turbo is that the exhaust gasses spin the turbine which is connected to the impeller, sucking in the air and forcing it into the inlet manifold. So indeed there is very much a direct link between the two!

Dave, you are quite right, but I can't see how the turbos RPM will be affected by changing the cat-back - spool up time yes, but max RPM??? I would put it down to EGT's being higher (due to a more restrictive exhaust) and the ECU controlling boost to protect the engine?

Think about it this way - when you add sports cats/DPs - does your boost increase? I doubt it, but you do get improved performance through quicker spool up and better breathing at the top end - it should *in theory* be the opposite in reverse.

[clived]

Nige, my money is also on increased EGT...

[clived]

Vern, apparently I do have an MTM downpipe. Don't you hate it when other people know more about your car than you do? (Hello Steve ).

[DuncS3]

I thought MTM didnt make a RHD kit, if correct then it wouldnt be there downpipe right? Isnt it a Miltek downpipe?

Dunc

[Dippy]

Hey Nige, the whole point of a turbo is that the exhaust gasses spin the turbine which is connected to the impeller, sucking in the air and forcing it into the inlet manifold. So indeed there is very much a direct link between the two!

Dave, you are quite right, but I can't see how the turbos RPM will be affected by changing the cat-back - spool up time yes, but max RPM??? I would put it down to EGT's being higher (due to a more restrictive exhaust) and the ECU controlling boost to protect the engine?

Think about it this way - when you add sports cats/DPs - does your boost increase? I doubt it, but you do get improved performance through quicker spool up and better breathing at the top end - it should *in theory* be the opposite in reverse.

Because turbo RPM and airflow are related (I don't know enough to say if they are proportional). So if exhaust gas maximum airflow is reduced as a result of a change in the system, then so too must max turbo RPM and therefore boost will be affected.

Unfortunately I don't believe the ECU has such a subtle approach to high EGT. Yes it will control boost - it's called limp mode!

P.S. Yes max boost can be increased with the addition of sports cats.

[S2tuner]

Sorry for chiming in so late here, been away on business for more than a week...

IMHO, the problem is the increase in back pressure because of the more restrictive exhaust, which will cause 2 things: higher EGTs, and a mixture more likely to detonate, or at least the knock limits of the engine itself are a lot closer now... The car has been remapped by Peter LInk on the previous exhaust as I understand it, so he has mapped it to run full boost at whatever knock control values there were before... if now the ECU is retarding the ignition more, it is going to reduce boost because of the very same reason as stated above, more retarding, as the Motronic ME7.5 adaptive boost control is knock control based as well as intake temps based, on top of all the other parameters that control boost....


HTH,

Mihnea

[VERN]

Vern, apparently I do have an MTM downpipe. Don't you hate it when other people know more about your car than you do? (Hello Steve ).

Clive, minhea knows his stuff, we all seem to agree then, so you need a system with more flow mate, or a new map to match
Let us know what you get up to
vern

[clived]

Dunc - yes, ok, but it's made for Kim by Milltek. Picky

Blueflame exhaust fitted today as an experiment. 1.5 of the missing 2.5 PSI returned straight away. It's amazing that an exhaust that sounds as civilised as it does can flow so well. Returning on the 7th April to have a full custom cat back system made and fitted - obviously aiming for GTT flow with half the noise. Before today (and seeing / hearing the system currently fitted) I wouldn't have thought that possible, but the Blueflame guys seem confident. And given they made the GTT system for GTT, I guess they might have an idea

I'll be getting the whole shooting match remaped at some point in the future anyway once some minor internal work has been done, so hopefully all will be right in Toytown then

Cheers for all comments so far.

Clive

[VERN]

Clive thats amazing, what is more though is that you dont hang around, good on ya, they make GTT then?. even smaller world eh? oh and if you do chip the 535 can you let me know the results for a mate

vern

[clived]

Lol Vern - too many people (not particularly on this forum, but on some others) *talk* a lot about what they are going to do, but very little of it ever seems to happen - I try to avoid that

Yep, Blueflame made the GTT sportlite to Roland's spec... and the Forge TT exhaust... and Mongoose...

Re the 535d I'm *still* waiting on a call to confirm when the demonstrator will be available But will do. I'm obviously expecting the full 0-60 in 5.5s experience that Autocar wrote up!