Black & Tan 332iT

[Bry5on]

Well, some disappointing news. The e46 fuel tank lump on the passenger side that I was concerned about is in direct interference. And also the spring perch is a couple inches rearward on the e39.

All is not lost, there are options still. It’s just not easy now.

[YoitsTmac]

Did I miss it? Are you trying to fit an E39 rear subframe on E46 for multi link or otherwise? Couldn't this affect how Ackerman behaves as like, a line between the outer tie rod pivot point & front rotational axis (FCA outer ball joint) need to align with a specific spot of the rear suspension?

[Bry5on]

Did I miss it? Are you trying to fit an E39 rear subframe on E46 for multi link or otherwise? Couldn't this affect how Ackerman behaves as like, a line between the outer tie rod pivot point & front rotational axis (FCA outer ball joint) need to align with a specific spot of the rear suspension?

Yep, I’d like to make an integral link e46 rear suspension to correct for the inherent jacking problem and provide bump compliance without sacrificing toe control.

i don’t expect the rear suspension to have any effect on Ackerman as the rear axle locations and static toe won’t be changing. I do expect toe control will be better, so less unwanted rear steer, particularly to help with on-center steering feel and immediacy.

[Bry5on]

Well I picked up another cold on my way home from overseas, so I decided to pick up another project that I can mostly knock out on my computer.

So we've moved the natural frequency of the exhaust up away from idle speed when we affixed the exhaust to the transmission. This helped greatly with idle smoothness and eliminated some oscillations during shifting and clutch takeup from idle. There's still one very narrow frequency range which presents a small seat of the pants vibration between 1760 - 1800 rpm. Now that the tune is dialed in, I find this to be one of my more common engine speeds to drive in and pass through. The hypothesis is that this is the exhaust's new first mode and its natural frequency.

Practically speaking, we can't raise the natural frequency of the exhaust any higher as the transmission is the last thing to affix it to, and there's no real way to increase its area moment of inertia due to packaging constraints under the car. So we're left with having to apply some different physics, tuned mass dampers. Each of us has at least one tuned mass damper in the car attached to the front of the crankshaft that is preventing your crank from splitting in two at its natural frequency.

The way a natural frequency works is that when something is shaken (linearly in the case of the exhaust, rotationally in the case of the engine) at exactly the right frequency, it will KEEP shaking or even INCREASE shaking until failure.

The way a tuned mass damper works is the opposite. Using a combination of materials, one that is usually heavy, and another that has elasticity and inherent damping (typically rubber), you can create a tuned mass damper. By varying the properties of the damping material and the weight of the mass, you can create a material that will arrest vibration at a specific frequency, but otherwise sit idly at other frequencies.

The engineers who design cars all know this, and the BMW engineers who designed the e46 knew it too. That's why the non-m cars feature a tuned mass damper attached to the front end of the muffler (32Hz as it turns out). Too bad the e36 didn't use one and I'm using an e36 muffler..

Enter the project. So first let's convert that motor rpm into a frequency in Hz = 1780rpm/60 = 29.67 rps = 29.67 Hz. This is very close to the BMW specced 32Hz muffler damper, which shows we're on the right track. Let's just do a quick hand wavy first principles check. My exhaust is attached to the motor and transmission in roughly the same place as the non-m, so we can isolate our analysis to transmission-backward. Well the length of the exhaust-back is the same as the non-m, the pipe diameter is very close, so we should have roughly the same 'spring' stiffness from the pipes, with the M3 exhaust being stiffer, raising the natural frequency a bit higher than a non-m would be, probably a few Hz. Then I've got the e36 M3 muffler, which is about 5/3 the weight of the non-m muffler. This will bring the natural frequency down, likely more than the stiffer pipes brought it up. Cool, so this brings us somewhere below 32Hz. Empirically we've discovered that 29.67 Hz is right, and the math agrees in a hand wavy way.

A few weeks back, as part of a project with heinzboehmer to retrofit the driver's side euro dash cubby to the US cars, I went hunting and found a 30Hz mass damper attached to an e46. Curiously, this value is not specced for the e46 according to realoem, but it's bang on the frequency I need to tune out my remaining vibration. Here's what that looks like covered in a glove to keep my hands clean:



Sweet. Now we need to attach it to the muffler somehow. I have some scans of the underbody of the car from the suspension project, so let's use one of those to design a bracket. And since I only have a MIG for non-stainless steel and the exhaust is stainless, and I'd like to keep it rust-free, let's bolt it on instead of welding it on. Now I know what you're thinking, time for more of my favorite exhaust clamps! Unfortunately, the pipes are so close together that those clamps won't fit. So we'll need to use a few stainless steel hose clamps (bummer) until I can find a local friend with a nice TIG welder setup. Here's what that looks like:



And with the order placed with sendcutsend, we now wait a week or so until install time.

[Bry5on]

I also have a ZHP muffler and another M3 section 2 here that total 18lbs lighter and the muffler has a 32Hz damper attached, but I'd really like to see this project through before swapping mufflers to experience the effect of change. For science

will likely do the ZHP exhaust setup eventually, for the weight savings, ground clearance and power at the expense of some additional exhaust noise in the cabin.

Plus I can re-make the shittily toleranced SS exhaust pipes to center the exhaust while I'm in there. Hell, maybe even replace the shitty SS slip joint with a joint that will actually seal section 1 to section 2 too. If I'd have known better, I would be using SS v2 headers instead of v1, forum 'wisdom' be damned.

[heinzboehmer]

If I'd have known better, I would be using SS v2 cats instead of v1, forum 'wisdom' be damned.

+1

I'll join the "SSV1 slip joint modification" party if you end up doing it. Should also V-Band section 1 -> section 2 and section 2 -> section 3 for even easier removal/reassembly.

Also, I know you already sent the part to be manufactured, but did you consider bolting it to the muffler body by sandwiching it between the nuts for the hangers and the muffler mounting tabs?

[Bry5on]

+1

I'll join the "SSV1 slip joint modification" party if you end up doing it. Should also V-Band section 1 -> section 2 and section 2 -> section 3 for even easier removal/reassembly.

Also, I know you already sent the part to be manufactured, but did you consider bolting it to the muffler body by sandwiching it between the nuts for the hangers and the muffler mounting tabs?

No mounting tabs or bolts on my conversion muffler - I've got metal rod "J" tabs that the stock hangers thread through then the hanger bolts to the chassis floor. I don't think there's room in there either in any case, it kinda had to be where it landed.

[heinzboehmer]

No mounting tabs or bolts on my conversion muffler - I've got metal rod "J" tabs that the stock hangers thread through then the hanger bolts to the chassis floor. I don't think there's room in there either in any case, it kinda had to be where it landed.

Ah, that makes sense.

[George Hill]

I hate slip fit connections, so terrible for working on "used" exhausts. I always smear them with anti seize and that seems to just only kind of help, ugh.

Im kind of surprised you haven't decided to make your own muffler haha.

[Bry5on]

I hate slip fit connections, so terrible for working on "used" exhausts. I always smear them with anti seize and that seems to just only kind of help, ugh.

Im kind of surprised you haven't decided to make your own muffler haha.

I looked into purchasing exhaust modeling software but it’s prohibitively expensive unfortunately. Not worth attempting to guess and check there. Ha!

In the back of my mind however I still want to do a true equal length stepped header that’s equal length at the section 1-2 joint. Just for the noise.

[George Hill]

In the back of my mind however I still want to do a true equal length stepped header that’s equal length at the section 1-2 joint. Just for the noise.

The only reason I initially S54 swapped my wagon was because I had a set of Kromer Kraft headers. They were old and tired but sounded amazing. They needed some repair and were pulled in favor of a "temporary" euro setup. I think that was 4yrs? ago, lol. My spring goal is to get them back on and I'm probably going to make a muffler to quiet everything down as I can't really buy anything I like at least that I can find.

Going from E36 to ZHP, I think there's room on the table to make more power and be similar sound level even if you are guessing at some parts of the design. IIRC we saw a ZHP left 15whp on the table vs a Stromung conversion muffler, Dinan or BMW Performance mufflers (E36 was even more than that).

[fattycharged]

Stromung so underrated in tone. Love mine on the e36


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[George Hill]

Stromung so underrated in tone. Love mine on the e36

Too loud for a nice daily driver IMO

*TBF I talked to Stromung when they first developed them and they said they couldn't make it quieter because there wasn't enough room to make it a bolt on to the factory section 2. If you took that out of the equation they could make it quieter but wasn't really in the scope of what they were trying to offer.

[Bry5on]

Stromung so underrated in tone. Love mine on the e36


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The e36 stromung is way larger than the e46 one unfortunately. Plus even the e36 one is a bit boomier which comes through a lot more with the wagon than a sedan/coupe. Agree that the e36 stromung sounds good on an s54 converted e46 sedan or coupe though

[Bry5on]

The only reason I initially S54 swapped my wagon was because I had a set of Kromer Kraft headers. They were old and tired but sounded amazing. They needed some repair and were pulled in favor of a "temporary" euro setup. I think that was 4yrs? ago, lol. My spring goal is to get them back on and I'm probably going to make a muffler to quiet everything down as I can't really buy anything I like at least that I can find.

Going from E36 to ZHP, I think there's room on the table to make more power and be similar sound level even if you are guessing at some parts of the design. IIRC we saw a ZHP left 15whp on the table vs a Stromung conversion muffler, Dinan or BMW Performance mufflers (E36 was even more than that).

What’s special about the kromer Kraft? Are they true equal length, stepped? The more of those things, the smoother and higher pitched the sound