Just put in a 3.5 engine, how to I quiet loud exhaust?

Hogzip · Post by **Hogzip** » Thu Jul 20, 2017 2:37 pm

I've got an '81 528i. Just had my trusted BMW mechanic put in a 3.5 engine, and now the exhaust is too loud for my taste. What are my options for quieting? Right now there is a new catalytic converter (the work was done in California - so I had to include that even though I don't live in California), new long pipes, and the stock muffler. My mechanic suggested a "pre-muffler" - not exactly sure what that is.

I'm not a tech guy - I love driving the car and have others do the work - so my tech understanding is limited.

I would appreciate any suggestions,
Brian Younger
262-672-0733
brian@youngersolutions.com

Either respond via post, or e-mail or call. THANKS!!!

T.Hanson · Post by **T.Hanson** » Thu Jul 20, 2017 7:49 pm

Only posting thoughts anticipating my future exhaust plans. Strange if the car was not scheduled to pass smog to be driven in California the cat was required.

My cars have them with the O2 sensor. When the time comes I will review the local green requirements and technical advice. I have heard the cat and O2 sensor are no longer needed locally if the engine is properly tuned.

The factory 528i exploded parts drawings show the exhaust system if the stock parts are available to get the factory stock sound. If not I expect any local exhaust shop, recommended by vintage enthusiast friends, will be happy to review my show and tell wishes and install a system.

This is not brain surgery and many aftermarket exhaust components are available.

Mike W. · Post by **Mike W.** » Thu Jul 20, 2017 8:55 pm

Hard to say what was done, but a little odd since the stock system isn't very restrictive and will bolt right up. I would guess a pre muffler is a resonator, which is stock on pretty much every M30 car I can think of from '68 to the end of the run in '93.

A lot of muffler shops just weld stuff up and throw it in there. I had an '80 633 many years ago, exact same exhaust as E12 528i. PO had taken it to a shop where an exhaust was cobbed together, single pipe, no resonator, near 90 degree kinked bend near the axle. It had a horrible drone around 2-2.5K, right where you drive a lot, but hit a wall at 5K. I pieced together a more or less stock system and it was quieter and would rev better.

O2 sensor is preferred with or without a cat or emissions testing. It fine tunes the mixture under most conditions, defaults to open loop for maximum power at wide open throttle but helps minimize fuel consumption and emissions with or without a cat.

RonDwyer · Post by **RonDwyer** » Fri Jul 21, 2017 8:28 pm

I have my stock E12 530i muffler behind my conversion. Running the stock cats back to it with matching pipes to the muffler. I run a cat because it needs to be there, besides, making the eyes water of folks behind me isn't really fair. I remember LA in the 60's, it wasn't pretty.

Mike W. · Post by **Mike W.** » Sat Jul 22, 2017 11:54 am

RonDwyer wrote:I remember LA in the 60's, it wasn't pretty.

Ah, another oldtimer. You didn't think that lovely shade of brown was attractive? It wasn't even easy to see with your eyes watering all the time. Yes, I was there too.

tlake · Post by **tlake** » Sat Jul 22, 2017 3:27 pm

RonDwyer wrote:I have my stock E12 530i muffler behind my conversion. Running the stock cats back to it with matching pipes to the muffler. I run a cat because it needs to be there, besides, making the eyes water of folks behind me isn't really fair. I remember LA in the 60's, it wasn't pretty.

Wouldn't a 1977 530i be smog exempt by now

Mike W. · Post by **Mike W.** » Sun Jul 23, 2017 12:17 pm

tlake wrote:
RonDwyer wrote:I have my stock E12 530i muffler behind my conversion. Running the stock cats back to it with matching pipes to the muffler. I run a cat because it needs to be there, besides, making the eyes water of folks behind me isn't really fair. I remember LA in the 60's, it wasn't pretty.
Wouldn't a 1977 530i be smog exempt by now

Not in California. '75 and older is exempt, but not 76 and newer. But they make up for it by ratcheting up the standards every few years so they have to be cleaner at 40 years than they were at 15 or 20.

tlake · Post by **tlake** » Sun Jul 23, 2017 12:39 pm

Mike W. wrote:
tlake wrote:
RonDwyer wrote:I have my stock E12 530i muffler behind my conversion. Running the stock cats back to it with matching pipes to the muffler. I run a cat because it needs to be there, besides, making the eyes water of folks behind me isn't really fair. I remember LA in the 60's, it wasn't pretty.
Wouldn't a 1977 530i be smog exempt by now
Not in California. '75 and older is exempt, but not 76 and newer. But they make up for it by ratcheting up the standards every few years so they have to be cleaner at 40 years than they were at 15 or 20.

That is so stupid, so if I find a 1975 530i I can put a 3.5 with triple DCOE Webers and no one will bother me? But a '76 530i is treated more severely than a 2002 model year car. This is why I luv government...NOT

RonDwyer · Post by **RonDwyer** » Sun Jul 23, 2017 12:51 pm

It really isn't all that bad to put a properly running and outfitted engine from an 89 into a 77. One lead runs a check engine light I rigged up inside the EGR display, looks stock. Other than that, heated O2 sensor, stock cats, replaced all fuel system hoses and vent lines. I did get rid of thermal reactors, smog pump, prehistoric fuel injection and a poor running engine. The conversion was not that bad. Failed smog the first time because of high NoX, got that down and it passed. Also have a 179 ECU that works well in it.

And it has E28 hydraulic power assist brakes now. A pleasure to access the engine. I did the same conversion on my 74 CS. That got a motronic conversion after I said enough to trying to tune carbs.