Custom exhaust: impressions and results

[Schreier]

I've had to put this on the back-burner for a while, but here it goes. Here's the results of the exhaust build on my 2000 Z3 2.3, from headers all the way back to the muffler. First, here's how it sounds:



Like it says in the video, the exhaust primarily consists of the following components:

Schmiedmann S-Tech SCM3436 M52 "Shorty" Headers (w/ Jet Hot 2,500F coating)
Columbia River Mandrel Bending 2-1 Merge Collector in 304 Stainless Steel (2 x 2.25" in, 1 x 2.5" out)
304 Stainless Steel Pipes (2.25" + 2.5")
Bosal 2.25" CARB Universal Catalytic Converter 522500
Vibrant Performance Streetpower Muffler 2.5"

One of the biggest reasons for this modification was the original exhaust system being so rusty. When I dropped the rear end for new suspension bushings, I had to seek professional help to break it down, and it never quite sealed back up right. So instead of having to replace studs, etc., I just decided to take the plunge sooner than later.

original_header_flange.jpg

original_exhaust_flange.jpg

Prior to installation, I took the headers down to the local Jet Hot coat-ery and got them treated with "titanium" color 2,500F "ultimate" ceramic coating. I firmly believe this was a solid decision, but in retrospect, should have had them coated after installation. I'll tell you why later on.

IMG_20180410_143718588.jpg

coated_headers.jpg

Installation and fabrication was handled by Mick's Automotive of Oklahoma City. The headers bolted on without issue, but this may have been assisted by the M7X39MM exhaust studs (part #11127593376), which come on the Z4, E92, F30, and a whole bunch of other cars, instead of using the standard M7X39MM exhaust studs (part #11127506203). The replacement has a torx head that makes installation easier, while the original stud does not.

The Schmiedmann header came with all manner of gaskets, but the shop advised me that the quality was not great, so we went with the factory gaskets I provided (1 x Victor Reinz 11621732969 and 2 x Vibrant Performance 3-Bolt High Temperature Exhaust Gasket 2.25" I.D. 1461). I did wrap the heat shield of the manifold gasket with Reflect-A-Gold before it was installed. The jury may still be out on whether that was a wise idea.

[Schreier]

The headers did require modification, as a second O2 sensor bung had to be welded to one of the exhaust headers (I can't tell which exhaust ports this half of the header matches up to). The headers were originally designed for the E36, which near as I can tell, package the headers very differently and don't use integrated catalytic converters. When using these headers, the O2 sensor bung comes too close to the engine block, making O2 sensor installation impossible. So the second O2 bung was welded in a better location. This, of course, required removing some ceramic coating, which is why I mentioned it would have been wiser to coat the headers *after* fabrication and installation. The "stock" O2 sensor bung remained capped off as it came from Schmiedmann.

header_from_bottom.jpg


Additionally, one of the bolts used to connect the flanges together needed to be welded to the header flange, because there wasn't enough clearance in there to swing a wrench and tighten everything down. Again, it would have been wiser to coat the headers post-installation. I used Vibrant Performance 3-Bolt Stainless Steel Flange 2.25" I.D. 1481S for the flanges in this application, which ended up mating perfectly with the Schmiedmann headers.


The most difficult part of the whole ordeal, or so I'm told, was navigating around the x-brace. The rest of it was easy-peasy. I originally purchased two of the Bosal catalytic converters (as is required by CARB) but ultimately decided that one would be efficient enough. I couldn't find any ready-made O2 sensor extensions, so I decided to forgo the post-cat O2s and use a custom DME tune that rendered them unnecessary (many thanks to 328 Power 04 for his invaluable assistance and most excellent tune).

exhaust_catalytic_converter_section.jpg


Haven't yet put it on the dyno to assess gains, but I'd be happy as punch even if it didn't free up any horsepower. The pops and burbles are delightful, as is anything above 4K RPM. I haven't weighed anything either, but I weighed the factory exhaust at 75 pounds. I'm confident this shed a few pounds, and with moving the cat to a more central location, helped inch the weight bias rearward. I'll update this thread with any additional info as I obtain it.

under_muffler.jpg


Could there have been a better header with better fitment? I'm guessing there may be, and Schmiedmann even offers a long-tube header for the M52. And maybe there's even an Ebay header out there with better fitment. But the quality seemed very good, and the price was pretty competitive.


Anyways, If you have any similar or different experiences with custom systems, feel free to hop in.

[jrkoupe]

custom set ups are always so appealing....and headers are just plain sexy...but Im not sure they are worth the cost on a stock- ish engine

u made some nice choices.....but Im not sure I woulda done bosal for cats.

[328 Power 04]

Uuu, that looks like very nice work!

[Schreier]

custom set ups are always so appealing....and headers are just plain sexy...but Im not sure they are worth the cost on a stock- ish engine

u made some nice choices.....but Im not sure I woulda done bosal for cats.

It is quite a chunk of change, but it is part of a larger plan. I've got a list of fix-up items I need to get to, but the goal is to swap manifolds, throttle bodies, cams, and stroke the engine out to 3.0L.

Any particular reason why not Bosal cats? I picked it for being CARB compliant, figuring it would be dense enough to last a while.

[jrkoupe]

I also meant to say very nice welds!!!!

w/ what u did and what u plan to do I woulda went hi qual/ hi flow cats......say Burns, etc etc EVEN maGNAFLOW

i did a custom set up on an s50- e30 and did mf cat..........annnnd they are cheap

[Z3 freak]

I can always appreciate it when people can improvise a product and have plans to fabricate their ideas. It also helps if one has a younger mind set, thus newer concepts with the help of a substantial bank roll to materialize their vision. That being said, I did listen to your video, and not to sound mean I thought it sounded more like the kids where I live that like to zip around in their rice burners. I can always detect the tone of a Subaru, Honda.....or take your pick of Japanese vehicles. Well, just remember this is from an old white guy posting that has gone thru a variety of motorcycles and cars/trucks for about 55 years. In the end what matters is that you like it, and it gives you pleasure!

[jrkoupe]

to both op and Z3 freak:




we are here bcause we love our cars and cars in general... and I hope we all have thick skin..lol


I too thought the sound very subpar for the parts used...and the cost!...lol........but when building an exhaust its very hard to know the final sound!

that being said Id like to add that for all your costs and your plans, i woulda went 2.8/3.0 or s52.....its a better value...yet I do understand having stayed true to car, and just modding her

I would guess that exhaust included once you do all as you say , u will be into the set up for 4-5k?

what hp are u hoping for?


stock is like 170?....Im wondering if u would get to 240/250 ish when all is said and done???...crank

[Schreier]

I haven't put it on a dyno yet to see the gains. It currently puts 158 hp to the wheels with a DME tune and normal tune-up, where it made 147 stock. I would think it produces somewhere near 170 now.

I haven't priced the labor and the parts together, but it's in the mid $2K range.

I've considered swapping straight pipe after the v-band to have a better understanding of what the Vibrant muffler is actually doing to the sound. There may be better muffler options out there.

But At 2.5 liters, it is going to sound a lot like similarly-sized engines, no matter what else you do to it. Having said that, I don't think the audio I posted is capturing the low frequencies very well, especially on the cheap action camera used for the testing under load.

[jrkoupe]

u r guessing 12 hp or so from the exhaust?

[jrkoupe]

IM not sure how the 2.3 reacts to a muffler delete...but the 2.8 and even the s52 sounds good IMO....
https://www.youtube.com/watch?v=3stcwoFc-EU

[Schreier]

u r guessing 12 hp or so from the exhaust?

Yep, although that's a conservative estimate. I've heard 20hp gains are possible with headers in similar applications, but I honestly have no idea. The DME tune and new adaptation should help a bit more. It will be fun to put it on a dyno and find out!

i woulda went 2.8/3.0 or s52.....its a better value

For the money I put in, I also could have most of a homebuilt supercharger or turbocharged system. Or maybe an S52 swap. The main thing keeping me from doing something like that is if I should ever have to sell it, I think it would be helpful to have it in a condition to where a person could roll it into any typical independent garage and not be chased out or taken advantage of. With the exhaust, the owner could just source the original system and bolt it right back up. And as nice as an S52 would be, I'm concerned about the wiring mess involved (wouldn't it require swapping the whole wiring harness?), and again, it not being something a shop would want to repair. Maybe some day, though!

So I figured the next best path is to approach it from the bottom-up. Maintenance items first, then gradual improvements that build on each other in a logical way. If finances are good enough next winter, I'm thinking of sourcing another aluminum block M52TU, taking my sweet time to prep it all outside the car, then take it to a lift to drop the original and swap in the new motor.

[328 Power 04]

See me if you ever want to run an S52 in there.

I have made the S52 run perfectly integrated with your DME with the original harness in place, just one tiny little modification to a plug.

Not that I recommend S52 swaps for everyone, as the m52tu is a very nice motor.

[Schreier]

I have made the S52 run perfectly integrated with your DME with the original harness in place, just one tiny little modification to a plug.

Not that I recommend S52 swaps for everyone, as the m52tu is a very nice motor.

Whoa. I should look into this. That would drop the complexity and make the job a whole lot more appealing.

I still do really like my M52TU, if for nothing else than it having an aluminum block. And yet it will never have that extra 200 cc, or the extra aftermarket support.

This one is a toughie...