E36 M3 Exhaust Modification

[wrs 118]

I've recently finished a engine upgrade, manual conversion and exhaust swap into a E36 325i

http://bimmersport.co.nz/topic/53887-e36-325i-coupe-project/

Now it's been going for a few days a bad rattle has developed in the front section of the exhaust inside the first small muffler. The cats have already bee removed.

The exhaust is also a lot noisier than I'd expected - nice but just a little loud under power. In cruise it's fine.

I'm considering adding 2 resonators backwards where the cats were (1 in each pipe) and removing the first small muffler. If this is done, do I also need to put a joiner between the 2 pipes in the area the small muffler used to be or can they be left separate right through to the rear muffler?

Edited October 7, 2015 by wrs

[Michael. 2312]

Loosing the cats has probably done this, in my opinion they are worth keeping in a stock M3 exhaust.

They tend to act like small resonators and smooth out the flow.

Definitely put some decent resonators in place.

[KwS 2372]

Both of the cats in my old M3 exhaust were replaced with resonators. Had a great sound and was good in terms of volume.

This was my one.

[Michael. 2312]

Haha. The irony is most resonators are bi-directional.

[wrs 118]

If it's the type with holes in the internal tube then it doesn't matter, yup, bi-directional.

For the type with scallops sticking out onto the pipe by putting it in backwards should help with flow and absorb the reflected pressure wave from the muffler end. It's supposed to reduce resonance better in the pipework between the resonator and rear muffler. However, it's not my area of specialty - seems like a sound idea. Maybe it makes bugger-all difference (does anyone here actually know what difference forwards vs backwards will do?).

The local muffler shop has suggested a straight through type of resonator with holes in the tube part and a small expansion chamber at the inlet end. Anyone know if this works/good idea or not?

Am I better with just a straight through type with holes in the tube only or the scalloped type?

[sweetm3 180]

Hi mate

Have you checked out my exhaust build ?

May help

[wrs 118]

Thanks - good info.

Looks like the merge-pipe helped with mid-range torque and quietness.

I was wondering if merging the pipes would help with noise - didn't realise it would also help torque.

Do you think it would matter if the merge was done after the resonators or best left before. I'm guessing putting the merge before doubles the frequency the resonator sees and halves the pulse size/volume each one sees beacuse they're now sharing all the pulses and flow - should be very benefitial to noise. I'm an electronics engineer - there's a similar effect with analogue filters. Maybe I just answered my own question...

I think I'll give this a try. Car's going in for resonators on Monday morning - I'll see if they can knock-up a merge-pipe during the install.

[wrs 118]

If you put the scalloped type ones in backwards it significantly increases the surface drag slowing gasses and causing significant turbulence inside the resonator.

Whilst this may make it quieter it does so by reducing the flow by up to 30% which is a seriously ugly way of doing it.

Thanks - had done this before on a previous car, sounds like I shouldn't have. Unfortunately I never compared turning it round or trying something different. I went from a stock restrictive exhaust to what was supposed to be a free-flow. It was an on-the-spot design at the muffler shop. It lasted the life of the car so never tried anything different.

[sweetm3 180]

Thanks - good info.

Looks like the merge-pipe helped with mid-range torque and quietness.

I was wondering if merging the pipes would help with noise - didn't realise it would also help torque.

Do you think it would matter if the merge was done after the resonators or best left before. I'm guessing putting the merge before doubles the frequency the resonator sees and halves the pulse size/volume each one sees beacuse they're now sharing all the pulses and flow - should be very benefitial to noise. I'm an electronics engineer - there's a similar effect with analogue filters. Maybe I just answered my own question...

I think I'll give this a try. Car's going in for resonators on Monday morning - I'll see if they can knock-up a merge-pipe during the install.

Warren

for the best benefits the merge needs to be placed at the hottest spot along your exhaust pipe.

You can test this with a crayon or infrared thermometer. I found this spot was located where the cats had been.

The merge design and location affects the salvage, torque and noise levels to a point

I had an annoying rasp at which the merge did remove and it did quiet down the exhaust noise when cruising. Not so much when you put your foot down

Mark

[sweetm3 180]

Sorry for leading you a stray Warren

My research lead me to believe that my merge pipe design was to achieve a venturi affect and that placing it at the hottest spot would be most affective.

But I do know that there is difference between a x pipe and designed merge pipe.

Yeee haa

[wrs 118]

No worries.

What you've done certainly seems to have had some positive impact on your car.

Have spend a large part of the weekend trying to find out how to model the exhaust but it appears the only way to do it (which is still a bit hit and miss) is to use some very fancy software. I guess car manufacturers use historic knowledge + fancy modelling software + a bit of trial and error to get it right. We don't have the $$$$ resource for the software or the trials.

Trying to turn up at the muffler shop and guess the best option probably isn't going to work out the best it could.

I went for a bit of a drive today and I'm actually quite happy with most of the exhaust note. It's just the raspiness between 1500-3000PRM that's the problem.

The muffler shop has suggested fitting 2 x 19" resonators where the cats were (no merge-pipe).

I think I'll give this a go to start with and if it suck's will try again. It might take a few goes to get it right - then again might get lucky on the first time. Can always try the merge-pipe later too just to see if it quites things down - I'm just worried it will muck with my current tuning.

I'm hoping the resonators will damp the rasp without affecting the current tuning significantly. Only one way to find out!!

It's going into the shop again 08:00 tomorrow morning - will report back the results.

Edited October 11, 2015 by wrs

[wrs 118]

Today we mucked around with a couple of resonator options - 2 short Coby style resonators near the back of the front section where the centre hanger is and the current/final configuration with a dual in dual out resonator from AdrenalinR.

The Coby option took out some of the rasp but did nothing to get rid of the low frequency resonance which set up a bit of a vibration through the whole exhaust.

It didn't seem to impact power but it's difficult to tell. I did a hill-climb test trial prior and then after each change as some kind of measure. I was just testing I'd reach the same speed from one marker to the next when doing a rolling start at a specific speed from the first marker to the second + accelarating as hard as I could in 3rd to the second marker. Did this three times on each test to ensure consistency. I have no idea if this is a good method or not but would expect any significant power drop would show up using this method.

So, the Coby option didn't do much to shut things up and had no noticable impact on power.

The next resonator trialed was a AdrenalinR ADR021. This couldn't be mounted as far back as I wanted due to clearance to the heat shield. It did quiet things down significantly. The rasp is all gone and the cruise is now very quiet. It still has a good tone and slight bark under power and at high RPM + a small warble under decel.

I'm really happy with the sound. Power wise, it has affected the low RPM torque between 1200-2200 RPM, down a noticable amount but above this there's no noticable difference. The hill-climb accel test still reached the same speed at the second marker. It sounds a bit like Kevin's (KwS) Youtube above.

When I first started the car after putting on the AdrenalineR resonator I couldn't beleive the noise reduction!!

Thanks to Brent @ AdrenalineR for making up a resonator at 0 minutes notice this morning.

[wrs 118]

Yep, a bit limited at what I could get at short notice but happy with the loss of low-end torque for the noise reduction. Check out below though - didn't notice this earlier at the shop:

Have just been under the car looking at an oil-leak from the 6-speed. Appears the reverse switch got a knock at some time and the plastic end was partially dislodged and was leaking quite badly- managed to fix it :-)

While under the car (and while your were probably typing) I noticed the pipes they've used are the wrong size + they've changed the original flanges from the bottom of the headers to something new with a much smaller hole - appears to be 50mm and they've reduced the 57mm pipe down to fit!!!!!!

The pipe is 57mm - should be 63mm as you say.

It's going back to get fixed...

The reduction at the end of the headers is likely to be having some negative impact I'd think.

Edited October 12, 2015 by wrs

[wrs 118]

I also wanted to get a shorter custom-built resonator but that would have taken a few days as AdrenalineR would have to fabricate the shorter internal pipe and outer shell to suit. The total pipe length including the resonator is 1200mm which means the resonator should have been about 300mm max length with likely 200-250mm ideal. I had to go with 350mm because it was all I could get - not ideal but a compromise to get it done.

I just rechecked again and there's some significant crushing of the pipes that are already too small as well. This will be creating multiple compression and expansion points down the length of the pipe.

I suspect I'm going to have to get mandril bends and a tig to stitch together a proper exhaust. I can do this at work one weekend since it will cost a kidney to get this done properly at the shop. I'll talk to the muffler shop first to see if they'll do it properly with only the difference in cost - if not then I'm sure I can do a better DIY...

[handgrenade 189]

i appreciate your intent to get the noise down. I have an aftermarket system and it sounds great. But I've lost the 'luxury-esque' nature of the bmw! But it does sound great on full noise.

[wrs 118]

Yesterday the 63mm mandrill pipe bends and 2.5m of 63mm pipe arrived. It's all 304 stainless - was only $10 more to biuy stainless over mild steel so may as well go for the stainless.

I got my old exhaust back from the muffler shop early in the week and made up a wooden jig to hold the centre hanger and front flanges. The I cut the old pipe off leaving about a 25mm stub sticking out of the flanges to weld to. I completely removed the old pipes from the hanger.

The new pipework is now cut, taped together and ready to be welded. I may get a chance to do this tomorrow.

The resonator is still in the car but fits in the gap between the pipes.

There will be a bit of mucking round with the rear section of the pipework to mate it up to the rear section of the exhaust. Will do this bit when fitting it up to the car.

The pipes coming out of the front flanges are actually 51mm diameter - not sure if this is normal. I'm going to have to get the front part of the 63mm pipe reduced down to fit over the pipe stubs left sticking out...

Edited October 17, 2015 by wrs

[sweetm3 180]

Warren

I'm sure I read after I built mine that the front section to the cats are double skinned.

I reversed a pair of reducers.

Looking good by tbe photo

[wrs 118]

Thanks.

Yeah, I noticed that - looks like the front section to the cats is 63mm outer & about 50mm inner - designed to transfer as much heat into the cats as possible. Hopefully going to a much bigger pipe doesn't upset anything.

I've decided I'm not going to do the tig - I'll get a friend to do it. My welding is functional but not very pretty. John's welding looks like a machine did it...

[hybrid 1039]

do several sleeved sections with retaining springs... youll love yourself later when you can pull sections of the exhaust apart. That or flange everything.

Also, welcome to the thin wall stainless club ... it just sounds better than everything else

[wrs 118]

John picked up the jig and all the pre-cut tubes tonight. He should have it all welded by the weekend. Hawkes Bay has a 4-day weekend due to HB day falling on the Friday + the 3 day Labour weekend. However, the nice long break is also when my work does major system upgrades... So, I'll be working most of the weekend with no chance to fit up the new exhaust.

So, it looks like the weekend after labour weekend will be the big fit-up at this stage...

Will be flanging the new front section but it will esentially just mount up the same as the original exhaust with a front and rear section.

Edited October 20, 2015 by wrs

[wrs 118]

Today my nice new exhaust was fitted. There were a few very minor as-built changes during the fit but overall everything went pretty close to plan.

The stainless tube was welded using the 'purge' method where the tubes are purged of air and filled with low-pressure argon. It stops the weld bubbling into the internal part of the tube to keep the flow undistrubed. The only untidy area was rear of the AdrenalineR resonator to get the pipes through the hanger area and mating up to the original rear exhaust section.

Since putting the new engine in the car only a short time ago I've been chasing a very small exhaust leak - hadn't been able to find it. On Wednesday this week the leak suddenly got much worse which allowed me to finally find it. It was the flexi-joint on the rear headers. Information on this site led me to Autobend to buy a replacement.

This was welded in during the fitting of the new exhaust.

The results are excellent. The car now idles with a very nice sound and is very quiet in the cruise. Under power it has a very deep growl which is very nice. Under decel it has a deep warble a bit like a race car. Overall I'm very happy with the change. The exhaust put in by the local shop resonated and vibrated badly with a lot of odd harmonic frequencies - probably due to all the restrictions and expansions from the crush-bends in the pipes. All these odd sounds are now gone and there's a very regular sound across the whole rev range.

During the change we also move the resonator back about 250mm from the position the local exhaust shop fitted it. The car now feels responsive again at low RPM.

Another good find during the flexi-joint replacement was a big blob of weld where the old flexi was welding in. Whoever fitted it had to be the worlds worst welder - they'd blown a very big hole in the pipe and just poured in more and more weld to fix it. The result was an 8mm deep blob of weld 20mm long protruding into the 51mm diameter exit tube on the headers. This was removed with a rotary file to restore the pipe to it full internal diameter.

New Exhaust:

New Flexi:

[wrs 118]

Yes, I will be fixing the excess bolt length - need to replace them with stainless bolts but didn't know what length I'd actually need. Just bought some cheap set screws for now until I can measure the length required...

Edited October 31, 2015 by wrs

[wrs 118]

Here's links to full-sized images.

It appears replacing the flexi on M3 Evo headers isn't too difficult - you just need someone who can weld in tight spaces and who can do tidy welds. All welds in the new exhaust are tig welds - no mig!!!

http://i64.tinypic.com/15cf1np.jpg

http://i67.tinypic.com/2ij0ya9.jpg

http://i64.tinypic.com/2qjzsj6.jpg

http://i64.tinypic.com/1zdut6g.jpg

Edited October 31, 2015 by wrs

[wrs 118]

Exhaust Update:

Last Friday I spent the day in at Kwik-Fit in Taradale doing some mods to the exhaust. I'd made quite a bad mistake using 2.5" tube in the front section of the previous exhaust design. I'd also made the pipes too long to the new resonator and the new resonator was also too long meaning I'd de-tuned the exhaust from the factory design into something that had reduced the low-end torque and hadn't really added any high rpm torque. Probably the design was also creating out of phase backpressure pulses due to the bad design...

I got 2 new 50.8mm tube diameter louvre resonators made up of 200mm length - Brent at Adrenaline will do custom builds no problem. This was to try to replicate the effect the cats would have and add additional noise reduction. The current exhaust is still quite raspy.

Matt at Kwik-Fit did a pretty good job doing the install - they don't normally do stainless work. We added the 2 new resonators in front of the dual in/out Adrenaline resonator and made up new 50.8mm pipes to connect to the bottom of the headers. The front of the 2 new resonators are in the same position as the original cats and the tube length from them to the headers is within a few mm of the original factory length.

The result is all the mid-range torque is back, there's no apparent loss of high rpm torque and the rasp is totally gone + the exhaust is much quieter. The exhaust note at the rear tailpipe is much deeper at idle too. Overall the result is excellent.

On Saturday I went to Gisborne and didn't hold back on the hills. It was all going really well until the last big hill before Gisborne when I could start to smell something burning. Fearing the worst I pulled over for a check but couldn't find anything. The burning smell was odd too - not like an any something going wrong with your car smell I've ever noticed before. So, I carried on to Gisborne with the windows down a bit to let the smell out... On Sunday I drove back home - the smell was still there but not as bad, this time right from the start of the trip though. The same smell persisted most of the week...

Today I started trying to find the problem. It did not appear to be coming from the engine bay or from under the car - phew!!! It did appear to be coming from inside the cabin - even with the car stopped and engine not running.

After pulling most of the dashboard appart looking for something frying in the wiring I finally tracked it down to the power supply in the original factory radio. Maybe the welding fried it?? It's strange it didn't show up immediately after though and took nearly 2 hours on the road before it bacame a problem. Could have just been coincidence too. I found a big charred section on the power supply board in the radio so into the trash it went. I'd been looking for an excuse to upgrade the radio - now I have it.

Here's some photo's of the exhaust changes.

The angled brackets are to stiffen up the tube to resonator connections. On the old exhaust the front of the double inlet/outlet resonator had started to fracture as all the weight sits between the mid hanger and the headers. We added an additional support just after the headers to take the front part of the exhaust weight but there's nowhere to attach anything in the middle area to help support the weight of the resonators.I'm hoping the stiffening will stop the flexing of the ends of the resonators so they don't crack and the front support will absorb the resulting additional stress the bottom of the headers would have taken as a consequence.

Overall I'm pretty happy with the result. Now I'll just have to see if it lasts without fatigue problems...

Edited October 9, 2016 by wrs
Spelling Mistakes

[Michael. 2312]

The trouble with stainless is it loves to find weak spots and crack.

The weight, driving forces and heat cycling aren't kind. 

I think it's beneficial having more flanged sections, using the BMW style ones, they tend to allow for some movement between the exhaust sections while keeping a good seal. 

More to the point, How does it sound? Post a drive by video!!