Amazing result from mufflerectomy tested on dyno

[viio]

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.

 

[sje00]

impressive!
Does the car sound much louder? much more smoke out the back?

 

[desertstorm]

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.



Karl.

 

[viio]

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.

 

[viio]

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!

 

[adamss24]

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...

 

[viio]

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.

 

[desertstorm]

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.

 

[desertstorm]

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.

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.

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.

 

[desertstorm]

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.

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.

 

[rickquattro]

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.... ?

 

[NotNormal]

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

 

[adamss24]

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

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...

 

[NotNormal]

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...

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

 

[adamss24]

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 !

 

[desertstorm]

The link I posted earlier regarding the 150bhp Leon where it gained 6bhp by removing the rear box the before and after dyno plots are here

Tuning my Cupra TDI (PD150) - Remap, EGR, DPF and Mufflerectomy - Page 2 - Overclockers UK Forums .

It's what I would expect with smaller gains at lower RPM and bigger gains as the RPM increases. Theres nearly a 30% improvement on that Audi at 2250 rpm which I don't think can be explained away by removing the exhausts.

Karl.

 

[NotNormal]

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 :



as you can see, fairly restrictive :

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 :

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

 

[desertstorm]

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.

 

[NotNormal]

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

 

[viceroy]

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

 

[NotNormal]

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

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

 

[desertstorm]

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.

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

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.

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

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

Weld back up and refit to the car.

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.

 

[NotNormal]

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 ?

 

[desertstorm]

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.

 

[NotNormal]

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

 

[viceroy]

NotNormal, Any drone at all with this mod?

 

[JimmyH]

very tempted to do this my self now

 

[audi2.5tdi]

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?

 

[adamss24]

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

 

[NotNormal]

NotNormal, Any drone at all with this mod?

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

 

[audi2.5tdi]

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

 

[desertstorm]

Wow very restictive with all those baffles and pipes.

 

[CHRISTOPHÉ]

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.

 

[audi2.5tdi]

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

 

[David Hunter]

Hi all, just bought a 2010 3.0 tdi a4 avant a few months ago and am now thinking about a few mods. Was considering the entire exhaust system but milltek at £850 odds seems ridiculous for little extra power. I was thinking of doing Karl (and others) mod of cutting all the restrictions out of the rear box to see if that gives any. From what I have read the main restriction is the DPF but I am not going down that route due to MOT issues etc.

Has anyone else done the mod and is there definitely a good gain to be had? Has anyone RR'd it before and after confirming the mufflerectomy test?

Also Karl the S/S piping etc you bought and the rear boxes, are they easy to weld up. I recently bought a welder to weld a few scaffolding poles together its a non gas MIG? electric one I believe.

Oh after that I will get a REVO remap.

Sorry for resurrecting an old thread.

Any help much appreciated

David

 

[TurboJeff]

This thread is a very interesting read. I had a mk 1 Volvo V70 2.5L straight 5 injection. I removed the stock exhaust that had a massive middle silencer box, never looked inside but I'm sure there was a lot going on in there. I installed a custom cat back system that I made from straight pipe with a cherry bomb straight through rear silencer. It was loud as hell, but the performance increase was outstanding. top speed went from 120 to 135 mph, much quicker to accelerate and more rev range. Tempted to do this exhaust mod on my 3.0tdi now...

 

[David Hunter]

Hi turbojeff if you can wait a few more weeks I have my car booked in with Simons exhausts in East Kilbride on 16th September (thats how busy he is) to either get the boxes gutted and welded up again or new back straight through boxes put on. Before hand I am getting dynatune in east kilbride to do a before power test then give it a few weeks to adapt then do another power run after the box work. That will verify or not the original info from this post about large gains

 

[David Hunter]

OK got the work done, gutted both rear boxes done by Simon at https://www.facebook.com/Simons-Custom-Exhausts-280991942021542/ in East Kilbride. He has done a very neat job and taken pictures etc.

Looks just like the rest of you guys have done. Amazing how clean the inside of that exhaust is considering the 78K on the clock DPF's really do a very good job.

Anyway only driven about 20 miles in it but like others it definitely lifts faster when you first push the accelerator. The S-tronic box definitely goes through the gears faster so it is either producing more bhp / torque or there is a lot less back pressure. It will be interesting to see if this improvement increases even more as it adapts to the new breath ability.

Noise wise absolutely no difference but like someone else said the tailpipes are a lot hotter so I think I will get some tape for above the tailpipe just in case it starts to damage the plastic valance.

I had hoped to get a dyno run before and after but the guy I had booked into turned out to only have a 2 wheel drive dyno. He works on subaru's mainly but they can be put into 2 wheel drive by pulling a fuse it was only when I went to him did he realise you cant do that with this car.

So officially I don't have a dyno print out to prove anything but its not my imagination that its faster. I will be getting a revo remap soon so I will get a before and after at that point so at least I can say it started at 239bhp probably (out of the factory) then I will see the reading before the remap and after.

Well worth the work and I can highly recommend Simons Exhausts his work is very good, welding is very neat and a great guy to talk to.

Will pop back once the map is done with proper graphs.

Cheers

 

[NotNormal]

@David Hunter

What car is it you have ??

You won't need any tape for the cut outs around the rear exhaust there is suitable air flow between the outer edge of the exhaust tip and the bottom edge of the valance for enoug air to pass to cool it

 

[Gazwould]

Nice job , but knowing how glorious these engines sound for a TDI , I think the way to go with these are to chop the silencers off completely and weld on a tail pipe or select a solid pipe and not perforated to make a straight through in the back boxes , I'm sure this would keep them cooler too .