Equal length retaining cats

[thump604]

Hi All,
I have found a local guy willing to do the work to add the 18 inches on my BMW M4 to make the exhaust EL.

I have read about this on https://f80.bimmerpost.com/forums/sh....php?t=1675268

I would prefer to retain the secondary cats and OEM emissions system. Can this still be accomplished with the same outcome by going through the oem crossover section with the secondary cats? I wrote TG and they suggested leaving the secondary cats affects the sound too much. Can anyone elaborate on that, why is that?

In short I'm considering having my exhaust fabbed to be EL, but retain the OEM emissions systems. Good idea, bad idea? Will I get the nice sound without rasp and drone?

[andrei.m4]

I tested my car with el, config was downpipe, secondary cats replaced with resonators(resonators are design for max flow and remove raspy sound) and el and I can say i don t like, car was very raspy.

[ntg44]

The reason top gear told you it affects the sound too much is because you're removing the only resonator the car has from the factory by implementing equal length. If you keep secondary cats, you might have trouble placing resonators someplace else. Believe it or not the stock tone hides the rasp very well due to how nasty the tone is overall. Equal length exposes the rasp more due to how it cleans up the tone.

But you're still losing a resonator so you need to find a place to replace it with 2 resonators, one on each side, if you want it to sound any good. Usually that place is where the secondary cats are, but if you can manage to find a spot, by all means go for it.

Also, the length difference is not just 18 inches. It depends where you merge, and the passenger side needs to be 14 inches longer than driver's side measured from downpipe connection to merge point. It's not necessarily 18 inches longer. The only right way is to measure.

[TheMaster1971NL]

Originally Posted by andrei.m4

I tested my car with el, config was downpipe, secondary cats replaced with resonators(resonators are design for max flow and remove raspy sound) and el and I can say i don t like, car was very raspy.

If you want to sell it

[FlyingLow78]

If I end up keeping my TGM system I’m going to look at replacing the resonator section with cats to see if it makes the deep tones a little more mild and bring down the dBs a bit. The upside is that I can just drop them off at an exhaust shop and pick them up when they’re done - I don’t need to leave the whole car. TBH my motivation to sell it is pretty low because I have ideas for making it more to my liking. It def has a smoothness the stock exhaust lacks.

[ntg44]

Originally Posted by FlyingLow78

If I end up keeping my TGM system I’m going to look at replacing the resonator section with cats to see if it makes the deep tones a little more mild and bring down the dBs a bit. The upside is that I can just drop them off at an exhaust shop and pick them up when they’re done - I don’t need to leave the whole car. TBH my motivation to sell it is pretty low because I have ideas for making it more to my liking. It def has a smoothness the stock exhaust lacks.

Just trying to help, because I've been there already. You won't be satisfied by taking the current ones out and replacing with secondaries.

You're better off adding the secondaries to the exhaust rather than replacing the resonators that are already there. Either add the secondaries back in somewhere, add a second set of resonators, or remove and replace the existing resonators with longer ones.

[FlyingLow78]

Originally Posted by ntg44

Just trying to help, because I've been there already. You won't be satisfied by taking the current ones out and replacing with secondaries.

You're better off adding the secondaries to the exhaust rather than replacing the resonators that are already there. Either add the secondaries back in somewhere, add a second set of resonators, or remove and replace the existing resonators with longer ones.

That is helpful. Thank you.

[thump604]

Originally Posted by ntg44

Just trying to help, because I've been there already. You won't be satisfied by taking the current ones out and replacing with secondaries.

You're better off adding the secondaries to the exhaust rather than replacing the resonators that are already there. Either add the secondaries back in somewhere, add a second set of resonators, or remove and replace the existing resonators with longer ones.

So ideally we need to add the additional section going into the OEMM crossover and then add additional resonators down the line. I'm pretty ignorant on this, is it not possible due to space to add the additional length connecting to the oem crossover with the secondaries?

[MJ6]

Originally Posted by thump604

So ideally we need to add the additional section going into the OEMM crossover and then add additional resonators down the line. I'm pretty ignorant on this, is it not possible due to space to add the additional length connecting to the oem crossover with the secondaries?

I actually just posted up some rough figures involving resonance volume and measurements for different/additional resonators in ntg44 's TGM Exhaust review.
Link to the post is here if you wanted to take a look:
https://f80.bimmerpost.com/forums/sh...&postcount=157

[thump604]

Originally Posted by MJ6

I actually just posted up some rough figures involving resonance volume and measurements for different/additional resonators in ntg44 's TGM Exhaust review.
Link to the post is here if you wanted to take a look:
https://f80.bimmerpost.com/forums/sh...&postcount=157

ty

[thump604]

Originally Posted by MJ6

I actually just posted up some rough figures involving resonance volume and measurements for different/additional resonators in ntg44 's TGM Exhaust review.
Link to the post is here if you wanted to take a look:
https://f80.bimmerpost.com/forums/sh...&postcount=157

Aren't you still removing the secondary cats?

[MJ6]

Originally Posted by thump604

Aren't you still removing the secondary cats?

In my particular case yes. The system I have now has resonators in place of the secondary cats, but I'll be swapping them out to a larger size.

[RMDZidane]

[IMG][/IMG]


You mean something like this? This is my first EL exhaust back in 2017. I built this and installed it on my wife's first M3. It didn't sound that great, but it has resonators and the stock secondary cats there. I believe I made the path a little too long. I've thought about shortening it and seeing how it sounds.....but