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Amazing result from mufflerectomy tested on dyno

Discussion in 'Diesel forum' started by viio, Nov 22, 2013.

  1. viio
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    viio New Member

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    To satisfy my own curiousity, here's what happened when I tested a rear silencer delete on my Audi TDI. No remap done here, just removing the restriction in the exhaust by chopping it off.



    I gained 20.1 horsepower, and a little over 30 ft/lb of torque.
    Last edited by a moderator: Aug 15, 2014 at 12:29 PM
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  2. sje00
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    sje00 Member

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    impressive!
    Does the car sound much louder? much more smoke out the back?
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  3. desertstorm
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    desertstorm Member

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    Very impressive, I have a B8 3.0 TDI A4 I am looking to tweak and the exhaust system is one of the main things that seems to be changed invariably for a Milltek which is quite an expensive option.
    Why was it nearly 2 weeks between the 2 runs,Does your car have a DPF there may be some gains there if the car has had a regen in the 2 week period, different fuel also the correction for atmospheric conditions is never 100%.
    There seem to be very big gains at the bottom end, the amount of power difference is even more marked. Do you get any resonance from the exhaust when driving the car, especially when hoofing it.
    Would it be possibe to get the angle grinder out again and whip the top off a silencer and take a picture. I am interested in what actually happens in the silencer as I may just open them up and remove the restrictions. I have chopped open exhausts before such as this middle box off my Passat.

    IMG_0378_zpse7a686a4.jpg

    Karl.
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  4. viio
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    viio New Member

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    sej00 the car is louder, but it sounds better. I've got a little sound comparison video already, and another to come with the sound outside (during a launch). Some of the clip is shared but you'll get the idea.

    Last edited by a moderator: Aug 15, 2014 at 12:29 PM
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  5. viio
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    viio New Member

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    Funny you should mention that Karl. Being a curious man I did the same as you, and videoed it.



    The car doesn't have a DPF (I was very careful to buy one without).
    The two week gap was because I was moving house and the work was done in Scotland, but the dyno in England (same dyno both times).
    Resonance no, but it is louder (pleasantly).

    There is a bit more smoke and the underside of the car is filthy now from the soot, so I will be putting a proper exhaust on. I made sure to make the most of the experiment though!
    Last edited by a moderator: Aug 15, 2014 at 12:29 PM
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  6. adamss24
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    adamss24 Active Member

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    I don't believe it, if anything, it would have given you a few horsepower (3-5 max), 20Bhp is remap teritory ! You can remove the exhaust altogether, what it does is get's it spooling a bit quicker but it also takes a lot of the top end. Exhaust are carefully designed blend between efficiency and noise...going bigger is not always better ! You need to realize an engine is a pump, what goes in must come out, dyno's can be made to show everything...
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  7. viio
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    viio New Member

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    I was surprised too, but I don't believe anyone has ever tested like this before. That's why I spent a hundred quid on dyno runs.

    There's no reason for the dyno owner to fake a result either - nor am I convinced he could. At best he could have done a low-power run first, but the power result doesn't suggest he did. Regardless of what the numbers were, the power went up significantly, and so did the torque graph.

    Same car, same dyno, same driver, same tank of fuel, same temperature - very different results after one mod.
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  8. desertstorm
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    desertstorm Member

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    Top job there and very interesting looking at the insides to see why there could be such a restriction. As you say the exhaust design doesn't make it easy for the exhaust to pass out. The small holes in the baffles get blocked with soot as well which results in a reduced performance over several years. This wouldn't be an issue on my car as it has a DPF but that in itself is a major cause of pressure drop so will be going. Think I may be performing some open can surgery on the exhaust box. My time costs me nothing and I have plenty of Mig wire and gas.

    There is a good video here

    195bhp Seat Leon Cupra TDI - Mufflerectomy and ECU Remap - YouTube

    where the rear silencer on a 150BHP Leon is removed giving 7-8 bhp extra and also demonstrating how good the standard OE filter is and what a rip off these performance air filters are . I have proved the same myself on the dyno with my old Passat a 10K mile OE filter made less than 1bhp difference over no filter at all on a 200bhp car.
    What year is your car and what is the output supposed to be ?. Have you any other mods.
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  9. desertstorm
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    desertstorm Member

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    Well had a bit of a look at the exhaust on my car and it's different to yours. Can believe how clean it is with 75K miles on the clock it looks like new looking down the pipe like the day it came out of the factory. That DPF does do a good job of removing the soot.

    [​IMG]

    The exhaust pipe appears to go down and all the way to the far end of the box. The last 6 inches or so are perforated holes.

    Looking on one of the Audi SSP documents found this for the newer B8 engines.

    [​IMG]

    Think this may be similar to the exhaust on mine as there is a round protrusion in exactly the same place on the exhaust as on mine.

    Karl.
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  10. desertstorm
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    desertstorm Member

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    Having another look at this It seems a gain of 20bhp looks excessive about an 8% increase.
    I linked to this before 195bhp Seat Leon Cupra TDI - Mufflerectomy and ECU Remap - YouTube and on this an exhaust was worth about 4.5% extra and if that improvement was translated to the V6 it would mean an 11bhp increase.As the V6 has 2 silencers each is only flowing half the gas from the engine so gains I think would be smaller than 4.5% maybe 3% , 5 - 7bhp would seem reasonable.
    The thing I can't work out with the pre and post dyno runs is the amount of increase lower down.I have grabbed stills from the video and put them together in a picture.

    [​IMG]

    You can see the shape of the torque and power curve is radically different at lower RPM. AT 2250 RPM the car was making 120bhp after the exhaust mod it was making nearly 160bhp, the whole shape of the map is completely different.
    So something is not quite right as that is a very significant difference.

    Karl.
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  11. rickquattro
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    rickquattro Member

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    Simple one but was there a map printing error... is that the actual map generated by your car, or another customers from the dyno database.... ?
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  12. NotNormal
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    NotNormal Member

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    I've seen this on the 335d, I had a coupe and so was on e90 post, a couple of chaps did this - all had similar results from just the exhaust change
    results ranged from 15bhp to 21bhp
    i cannot recall the torque figures for them though

    if the exhaust on our 3.0 tdi cars are that restrictive I can see the power curves changing that dramatically

    it'd be interesting to feel the difference ..... Recon I'll try and get mine done this week coming
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  13. adamss24
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    adamss24 Active Member

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    335d has a DPF, that's restrictive, OP states his does not have a DPF...also the 335d is twin wastegated turbo, they came on boost much sooner...
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  14. NotNormal
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    NotNormal Member

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    my reference was to the power increase, not to the power curve

    yes the compound charged 35d engine (twin turbo) single waste gate) comes on sooner and lasts longer than the singal turbo set up but removing the restriction in the flow of the exhaust (and the a6 rear silencers are extremely restrcitve) will change the speed of spool and the power curve will alter quite dramatically - as the ecu compensates for the new parameters it'll fuel and boost sooner and faster

    Dpf's are still going to be the most restrictive component yes, but further restriction removal will have an effect the performance

    my A6 is a facelift 3.0, dpf equipped, so it'll be interesting to see the results next week
    sadly I don't have time to have before and after dyno results but I'll see if I can grab my friends v-box and do a before and after run as a marked bhp and torque increase should be noticeable
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  15. adamss24
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    adamss24 Active Member

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    Bhp is just a relationship between torque and rpm's ! You need loads of torque to get Bhp in a diesel...or high revs for petrol engines !
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  16. desertstorm
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    desertstorm Member

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  17. NotNormal
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    NotNormal Member

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    Decided to give this a go on my car today - please note -

    MY CAR IS EQUIPED WITH A DPF

    I am NOT expecting the types of gain as the OP, but I am expecting a noted difference in the power delivery, power band and economy.
    My exhaust, 09 plate facelift 3.0 tdi with dpf, was the same setup as the pre-dpf version :

    [​IMG]


    as you can see, fairly restrictive :

    [​IMG]

    so, removed the two baffle plates along with the two internal pipes, welded in a straight pipe and replaced the top section of the silencer :

    [​IMG]

    refitted the exhaust system back to my car, then struct it up.

    The he car now has alittle bit more if a deeper note on idle, but only very slightly - once warmed up (hot exhaust) you can detect the v6 engine note, again, only slight and not intrusive in the cabin

    PLEASE KEEP IN MIND - audi's and their ecu's need 500 miles to fully adapt

    First impressions when driving - feels allot freer, the effort when moving off is less so the response is improved
    my car being an auto also needs the miles to adapt properly, but in regular town driving the gear changes are alittle smoother

    once my ecu catches up with the new physical peramiters on the car I'll see how things have progressed

    interstingly, in sport it does feel more eager to rev, but I've not done enough miles yet
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  18. desertstorm
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    desertstorm Member

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    Very interesting I will be tackling this in the next few weeks depending on the weather. bought a new CO2 bottle for the MIG today.
    From my experience with my Passat playing with the exhaust what you describe is exactly what I found. I assumed it would be the same with the Audi. The big difference will occur if you remove the DPF, This blocks a lot of the high frequency stuff.
    I had my Passat running with just a straight through downpipe and it wasn't that loud. The turbo takes so much energy out of the exhaust stream that it silences it pretty well.
    The DPF does a great job of keeping it clean in there. I think you probably get 80% of the advantages of a Milltek exhaust performance wise for 5% of the cost.

    Karl.
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  19. NotNormal
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    NotNormal Member

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    Mini update - circa 250 miles covered, mixed driving, my initial impressions are that you need allot less throttle input to achieve speeds where previous throttle inputs have had to be greater

    feels allot less breathless at the top end of the revs too

    fuel econ seems to be slightly better also, but I will be able to confirm this once I've run through two or three full tanks

    you get a deeper exhaust tone on a constant run when steadily cursing about 2000rpm - this is needs several miles to kick in.


    As I drive and try and load up the car so the ecu targets the new load sites on the map - you can feel gradual improvements in the general drive , the gearbox seems to be responding well to the changes too
    #19
  20. viceroy
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    viceroy Member

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    I'm also very interested in doing this before I tackle a full exhaust, DPF delete and chip.
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  21. NotNormal
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    NotNormal Member

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    Well, i've been running this tweak for about 900 or so miles - it's all positive so far
    The car is fully adapted now, the cars exhaust note inside hasn't changed, it's note outside has stabilised - very subtle v6 burble as I have my DPF in place still
    Until the DPF dies it'll remain in place

    I'm still running my DTUK tung box (CRD-T) and with the exhaust tweak the car feels very perky and responsive - feels alittle easier in D around town to drive
    I need to monitor the fuel econ difference - but it SEEMS to be very slightly better
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  22. desertstorm
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    desertstorm Member

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    I attacked my exhaust on Monday.Didn't have time to do both sides so will do the other side at the weekend. Doesn't take very long to get the exhaust off. It did take me a while to get the baffles and existing pipework out of the silencer due to the restrictions on space with the angle grinder. I am going with keeping the car on the quiet side, boring I know, but I will take the performance benefits. I know it will get louder when the DPF comes out.
    So in keeping with this I have turned the restrictive reflection silencer into a nice straight through absorbtion silencer.
    I did a before Video and will do an after one and post them when I have done both sides.

    [​IMG]

    Nice and clean, DPF does a great job but oh so restrictive

    [​IMG]

    [​IMG]

    After removing the gubbins and cleaning up the pipe entry and exits, cut a 250mm length of perforated 57mm stainless pipe and a short length of 60mm pipe to join it to the outlet pipe.

    [​IMG]

    Wrap 1m stainless wire woolaround the pipe and secure with wire.

    [​IMG]

    Then wrap rockwool insulation tightly round the pipe and fill the silencer with finest quality Wickes Rockwool insulation.

    [​IMG]

    [​IMG]

    Weld back up and refit to the car.

    [​IMG]

    I am seeing and getting the same benefits as other people who have done this. The car requires less throttle when pulling away and seems to be a little better on fuel on the trips I have made that I regularly make the trip is looking better. I anticipate the car will be doing more mpg.
    I did some logging of the DPF differntial pressure, RPM, speed , throttle etc before and will be interesting to see if there is any noticeable difference.
    The DPF pressure reading includes the DPF itself and the hole of the exhaust system.

    Another thing I have noticed is that after a five mile trip the exhaust tip on the silencer that has been done was too hot too touch where as the unmodified one was barely warm. I am not sure if this is because a lot more exhaust gas is taking the easy way out or whether it's because the exhaust gas cools a lot when it's bouncing around in the rear silencer. It's probabaly a bit of each.

    I got the bits to do this from MIJ exhausts in Walsall. They have a store on Ebay if anybody fancies tackling this.Fortunately I live just down the road so popped in and picked up the stuff. If you were just bridging the gap with a solid pipe you woulld need a piece about 300mm long for each silencer.

    57mm perforated tube 500mm
    2.25" 57mm 0.5m Half Metre Stainless Steel T304 Exhaust Perforated Tube Pipe | eBay

    250mm 60mm stainless tube

    Universal 2 3/8" 60mm T304 Stainless Steel Exhaust Repair Pipe 250mm 10" Tube | eBay

    And 2m of stainless wire wool

    Stainless Steel Wire Wool Packing Heat Wrapping Kit Car Bike Exhaust x 1 Metre | eBay


    Karl.
    Last edited: Dec 11, 2013
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  23. NotNormal
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    NotNormal Member

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    Karl, the added heat on the modified silencer will be from the extra flow. The modified side will be getting 2/3 of the gasses as the n/s is in effect blocking the gasses so they're taking the easy way out....the o/s freer flowing side.

    Nice neat job btw, looks well done.
    Any reason for choosing the the baffled pipe and wadding over a straight pipe ?
    Presumably its in your quest for stealth - you didn't want any extra noise ?
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  24. desertstorm
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    desertstorm Member

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    Didn't really want a loud exhaust TBH, This is my daily driver, I quite like the noise it makes as standard it's so much nicer than a 4 pot.
    I know that when the DPF goes it will be louder I just don't want to get any resonance issues.
    Hopefully less chance of that happening with the exhaust pointing straight out of the back rather than at the floor. But even less chance with some silencing in place.
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  25. NotNormal
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    NotNormal Member

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    My friend got in my car today, we whet mountain biking at Sherwood pines, he knew that I had planned to to this, but didn't realise I'd done it - we did about 20 miles before I mentioned it !
    quiet as a mouse and that's with my straight pipe version
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  26. viceroy
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    viceroy Member

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    NotNormal, Any drone at all with this mod?
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  27. JimmyH
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    JimmyH Member

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    very tempted to do this my self now :)
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  28. audi2.5tdi
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    audi2.5tdi Member

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    Anybody with a b5 2.5 Tdi Q done this, the exhaust is different to those shown in this thread, I have a pair of cats, that then go into 1 pipe, into a centre box, 1 pipe out and to a rear boxShould this be done to both boxes or is the centre one already straight through?
    #28
  29. adamss24
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    adamss24 Active Member

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    Get rid of your cat and you will see slight spool improvement but not wonders...
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  30. NotNormal
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    NotNormal Member

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    Nope, no drone The only time the tone become slightly more audible is in the regen cycle, not I'm not talking loud, you just get alittle deeper v6 sound during this period As I do about 1000 miles a week I wouldn't want anything that's noises or annoying
    #30
  31. audi2.5tdi
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    audi2.5tdi Member

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    you guys got off lightly.. look what i found in the backbox of a 99 AFB B5.5 A4 Q

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
    #31
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  32. audi2.5tdi
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    audi2.5tdi Member

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    you guys got off lightly.. look what i found in the backbox of a 99 AFB B5.5 A4 Q

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
    #32
  33. desertstorm
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    desertstorm Member

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    Wow very restictive with all those baffles and pipes.
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  34. CHRISTOPHÉ
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    CHRISTOPHÉ Member

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    Hi audi2-5tdi could you post a video of your exhaust sound after you cut the baffles out please, I'm thinking of doing this on my allroad soon and the cats too. :)
    #34
  35. audi2.5tdi
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    audi2.5tdi Member

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    ill try, doesnt sound all that different to be honest, its slightly louder with the cats gutted, but with just the rear box gutted made little if any difference
    #35

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