s52 engine harmonics

[mtech325]

Hi everyone,

I've recently finished my 318is s52 swap wrapped up and got everything mostly ironed out, but I was curious about the harmonics of the 3.2 as opposed to the 2.5 m50 that was recently in the car.

Around 3000-3500 rpm the engine seems to make a humming/droning noise that's quite tiresome on longer trips with the windows closed (not unlike a wheel bearing). Initially I suspected my driveshaft my be misaligned, but I don't have any strange vibrations. I plan to double check its alignment, but I'm 95% sure I matched up the white alignment marks between to the halves. The CSB is new as well and has been preloaded. With the clutch depressed at speed the noise goes away, so I'm led to believe it's engine and/or exhaust related. My swap was a long block swap, so my driveline components are the same as they were with the m50 for reference.

I do have a generic aftermarket muffler that's on the louder side, but didn't really drone with the m50. However, the exhaust was originally 1 piece from the downpipes through the muffler, but i chopped it after the cats to use a slip joint/clamp to make removal & install easier, so perhaps it leaks enough there, but the clamp is tight as can be.

The motor is essentially stock, including the front crank pulley dampener. My friend has a similarly prepared s52 car and his car doesn't seem to make quite as much noise from the interior. His car is a 325i though, so I wonder if the 325's factory sound deadening hides a lot of noises vs. a 318? I don't expect the car to be quiet like a new car, but it seems a bit buzzier than it needs to be.

I have an appointment at the exhaust shop next week to possibly install a quieter muffler, but if worse comes to worse, I'll add some sound deadening like dynamat or damplifier. Another item I have thought to experiment with is swapping the Condor UMHW 24v motor mounts out for rubber e28 units, but they only seem to make the car vibrate at idle.

I just wanted to check and see if anyone had some pointers or suggestions of items that I may be overlooking. Otherwise the car is a blast to drive and seems to be running strong.


Thanks,

Joey

[haaken675]

sounds like you need resonators or cats...

[bradmer]

What transmission mounts? I just changed from the condor ones to akg with the aluminum cup because it was so loud, I have stock cats and magnaflow muffler. Huge difference in cabin noise.

[digger]

if its exhaust it will be throttle related, check no throttle, part throttle and wot see if it changes. if its purely rpm related it will likely be engine, might be belts, idler pulleys, engine mounts etc etc

[TobyB]

Digger called it.

I do notice more drone on an m54b30 than an m54b25.

Neither like aftermarket cheap exhausts...

[mtech325]

Thanks for the replies everyone. I think my issue is exhaust related as it seems to be exhaust related because it seems to go away if I let off the accelerator.

To answer some of the question, I have the AKG e21 style mounts with cups, but the difference in noise was very minimal with and without the metal enforcer cups.

My exhaust consists of stock OBD1 cast manifolds to dual CA legal e36 cats (I think the brand is Walker), then a generic muffler outback that I had lying around from a 325e.

Interestingly enough, on my s52 e36, the car is pretty pleasant inside, but I have a stock obd2 dual midsection and a Dinan muffler, so it's little fancier setup! I'm hoping a new muffler or the addition of a resonator will make this car good for long drives once again. I'll keep everyone posted.

[mtech325]

Hi everyone,

I wanted to post an update as to my current findings. I'm still waiting for my appointment at the exhaust shop, as it's a week out before the muffler can be replaced with a better unit.

In the meantime, I swapped out my Condor 24v mounts for the cylindrical e28 m5 mounts and the rubber mounts seem to have made the cabin vibrate substantially less upon startup. This allowed me to pinpoint my noise issue to the transmission itself. I have the classic case of gear rattle. I think my e21 trans mount enforcer cups are exaggerating the noise, but I'd like to see if I can quiet things down before uninstalling the cups.

My transmission is a zf310 out of a 95' M3 with a shaved m20 flywheel/clutch combo. The sticker on the transmission reads ATF, so I put the Fuchs Titan ATF Pelican sells in the trans, but I'm thinking I may need to do the UUC "magic mix." Any reason not to do this, or a better fluid to fill the transmission with?

Thanks,

Joey

[mtech325]

Another update: I changed the transmission fluid out from ATF for MTL and the noise is still there at around 3,000 RPM, regardless of gear. I had my friend drive the car and I couldn't hearing the humming from the passenger seat, so it's definitely on the driver's side (where the exhaust routes).

I have to wait until Monday for the car to go to the exhaust shop, but any suggestions on a quieter muffler that doesn't drone? Borla seems to have a variety of mufflers that could be custom fitted. Since my car is a 318, I'd like a single tip muffler as to avoid chopping up the valence. I also have an obd1 m50/s50 midsection that's laying around. Any reason to use that over my custom midsection section aside from weight?

[36brua]

^ it's free:p

[atldohc]

the zf310 is essentially the same as the zf320 no? and you have a single mass flywheel in a tranny originally equipped with a dmf. on any car this will cause more gear rattle noise. it did on my s52 with zf320. can't say if this is the same issue you're describing here though. if i remember correctly my rattling was the most pronounced around 2k rpms under load

[mtech325]

the zf310 is essentially the same as the zf320 no? and you have a single mass flywheel in a tranny originally equipped with a dmf. on any car this will cause more gear rattle noise. it did on my s52 with zf320. can't say if this is the same issue you're describing here though. if i remember correctly my rattling was the most pronounced around 2k rpms under load

I've had both a zf320 and a zf310 in the car with the same m20 flywheel, and they behave the same. Gear rattle is present, but a little less so once I switched over to Redline MTF.

Turns out most of the noise was the e21 enforcer cups. I feel kinda dumb as they made a bunch of noise on my e36 when I used them previously (which is why I removed them). So now the car has rubber e28 m5 cylinder-shaped motor mounts up front and the bare e21 trans mounts, everything is pretty smooth now in the cabin.

I went to the exhaust shop earlier today and they didn't find anything, so for now I'll just accept the car for what it is. I can't believe those trans mount cups transmit so much noise even with a rubber mount...

[atldohc]

i actually experienced the same when i had those cups on my car, although mine were homemade. it drove me crazy so i switched back to the regular ones. coincidentally i also have the same mount setup as you do now as well with the cylinders up front and e21 mounts in back. glad you figured out the issue.

[nrubenstein]

The muffler that you want is the biggest Dynomax Super Turbo available.