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V6 TDi - More or Less Back Pressure? Whats best?

Discussion in 'A4/S4 forum(B5 Chassis)' started by s200rey, Jun 3, 2013.

  1. s200rey
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    s200rey New Member

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    Howdy all, opinions please...

    I have a 2.5 TDi Quattro, and have recently changed the exhaust system. I now have 2.5" stainless steel pipe, from the downpipe to the rear box, no cats, no middle box / silencer etc. Just straight stainless pipe to the back box. For a month I ran it with the original back box, and it was next to no louder than standard, but felt quicker from low down the rev range and also top end of the rev range, and was pretty impressed with the results!

    However, last week, a friend of mine gave me a freeflow stainless back box (new) that he never got round to fitting to his old S4. As you do, I took it, and got it fitted. However, now the car doesn't seem as quick?...its no different low down the rev range, but top end (speed - not revs) it's awfully flat, it seems hard pushed to do much over 100 now, where as before (weeks earlier) 120+ was easily achievable. Its strange, cos in the past with other deisels I have ran Golf GT TDi's - Pug 306 D Turbo's - PD TDi's - all went much better with a freeflow exhaust system, where as this, as nice as it sounds, it seems to have lost its top end speed?? :think:

    Audi A4 B5 2.5TDi V6, Decat, Freeflow Exhaust - YouTube

    Here's a video of the system fitted a few days ago, the car sounds lovely, and with it being a V6 is lovely under drive, its just annoying me a bit as to why it's not as quick top end as it was. Plan is a re-map, but been told my engine / car year (1999 - AFB) has to have a chip? not a re-map. But was thinking due to the modifications I have made, it could just need a re-map, to use these to its best advantage?

    Any opinions / advice, much appreciated.

    Cheers!! :eyebrows:
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  2. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    maybe the backbox is just crap?

    Turbo engines benefit from as little back pressure as possible in the exhaust, as you've found from your other tdi's

    Perhaps whip the backbox off and see if it improves, it might be coincidence and theres some other issue?
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  3. s200rey
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    s200rey New Member

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    Uhm, I think you might be right?...spoke to him today and he said it was just a universal jobby off eBay (glad he 'gave' me it) so might whip it off at the weekend and put the original back on and see whats what! :shrug:
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