[Misty]

just got my headers out today to gut my primaries got all the crap out of the cats. going to pick up gasket and a exhaust clamp tm and i should be good to go.

secondaries are deleted too. cant wait to hear these burbles. posting this now cause when ever i do something tedious someone always chimes in and tells me too take care of this while ur at it so if you have any suggestions pls lmk

[Misty]

Originally Posted by BimmerGeeks

Suggestions:

- Be sure you reinstall right.
- Be sure phone is charged.
- Be sure to record an awesome clip.
- Be sure to give feedback whether it's good or bad!

For sure I'll be updating this post Bmw PE + Secondary cat delete on n51 ( Video ) http://www.e90post.com/forums/showthread.php?t=1336678

[Misty]

sounds pretty good

[Misty]

Originally Posted by BimmerGeeks

I'm assuming your throwing Cat codes now? Or do you have other underlying issues? I see a SES on the dash.

Cats but also had a misfire on coil 2

[Misty]

Originally Posted by Misty

Cats but also had a misfire on coil 2

Ses went away? Not sure how or why I got no cats

[boro92]

Is this on the stock muffler?

[Misty]

Originally Posted by boro92

Is this on the stock muffler?

No it's a pe with secondary's deeted

[Noir]

Originally Posted by Misty

just got my headers out today to gut my primaries got all the crap out of the cats. going to pick up gasket and a exhaust clamp tm and i should be good to go.

secondaries are deleted too. cant wait to hear these burbles. posting this now cause when ever i do something tedious someone always chimes in and tells me too take care of this while ur at it so if you have any suggestions pls lmk

I was told somewhere (I can't recall what thread) that it would be best to weld in a pipe to eliminate turbulence...
Digging the raw sound.

[hassmaschine]

Yes its true. When the exhaust gasses hit the large void where the cats used to be, they expand - this causes the gasses to cool which also makes them slow down. This hurts exhaust gas velocity (which already isn't that great with stock manifolds).

Reduced velocity means reduced torque. The common misconception is that reduced backpressure reduces torque but it's often confused with what is really poor exhaust velocity (otherwise stick a potato in your exhaust and see what happens).

So while gutting cats sounds like an obvious answer for cheap performance, it actually does the opposite.

[Noir]

Originally Posted by hassmaschine

Yes its true. When the exhaust gasses hit the large void where the cats used to be, they expand - this causes the gasses to cool which also makes them slow down. This hurts exhaust gas velocity (which already isn't that great with stock manifolds).

Reduced velocity means reduced torque. The common misconception is that reduced backpressure reduces torque but it's often confused with what is really poor exhaust velocity (otherwise stick a potato in your exhaust and see what happens).

So while gutting cats sounds like an obvious answer for cheap performance, it actually does the opposite.

Thank you for reiterating and giving an actual explanation as to why.
Now I know a lil' more not just "you should..."

[Misty]

Originally Posted by hassmaschine

Yes its true. When the exhaust gasses hit the large void where the cats used to be, they expand - this causes the gasses to cool which also makes them slow down. This hurts exhaust gas velocity (which already isn't that great with stock manifolds).

Reduced velocity means reduced torque. The common misconception is that reduced backpressure reduces torque but it's often confused with what is really poor exhaust velocity (otherwise stick a potato in your exhaust and see what happens).

So while gutting cats sounds like an obvious answer for cheap performance, it actually does the opposite.

To be honest it's a 328 it isn't going anywhere lol . I like the way my rice mobile sounds now

As long as I'm reading right I'm not gaining any performance I'm losing correct?


Edit #2 or I read completely wrong and you guys are telling me to weld and not use a clamp?


Ahh took a minute. You guys are saying not to gut but replace the cat with 3" pipe

[Noir]

Originally Posted by Misty

To be honest it's a 328 it isn't going anywhere lol . I like the way my rice mobile sounds now

As long as I'm reading right I'm not gaining any performance I'm losing correct?


Edit #2 or I read completely wrong and you guys are telling me to weld and not use a clamp?

Ah.
So what we are saying (and I'm trying to word this as best as I can.)
You need to weld in a pipe inside of the cat from opening (exhaust manifold to cat) to opening (cat to downpipe).
I tend to overword complicate my sentences... I hope this is sufficient.

[Misty]

Originally Posted by Noir

Ah.
So what we are saying (and I'm trying to word this as best as I can.)
You need to weld in a pipe inside of the cat from opening (exhaust manifold to cat) to opening (cat to downpipe).
I tend to overword complicate my sentences... I hope this is sufficient.

Got it . Pipe in the cat straight through .. wish I did it before hand . Will take a look at it again when the weather gets nice again. Going to pick up mtech bumpers today or I would have pulled em today

[Noir]

Originally Posted by Misty

Got it . Pipe in the cat straight through .. wish I did it before hand . Will take a look at it again when the weather gets nice again. Going to pick up mtech bumpers today or I would have pulled em today

You're good.. I mean having a catless setup is dandy and all. But as hass stated, its degrading your performance in its current state.. it is a 328 and you may think it doesnt go, but going from it to a family members car when I fly home on leave, or my girlfriend's car, they are gutless compared to it.

Best of luck!

[Misty]

Originally Posted by Noir

You're good.. I mean having a catless setup is dandy and all. But as hass stated, its degrading your performance in its current state.. it is a 328 and you may think it doesnt go, but going from it to a family members car when I fly home on leave, or my girlfriend's car, they are gutless compared to it.

Best of luck!

Ok cool . Ya true lol even going from my sisters e90 to my e92 is a huge difference. Thank you appreciate it !

[STR8-6IX]

these are a catless manifold, not headers haha.

how much did you pay to have your cats gutted? is it worth the sound and performance?

headers are better because the tubing provides better exhaust scavenging. do you think this is worth it?

[Misty]

Originally Posted by 6IX-F10-N52

these are a catless manifold, not headers haha.

how much did you pay to have your cats gutted? is it worth the sound and performance?

headers are better because the tubing provides better exhaust scavenging. do you think this is worth it?

Didn't pay much had a friend help me was supposed to pay for welding but didn't end up opening the cat

[Noir]

Originally Posted by 6IX-F10-N52

these are a catless manifold, not headers haha.

how much did you pay to have your cats gutted? is it worth the sound and performance?

headers are better because the tubing provides better exhaust scavenging. do you think this is worth it?

The performance aspect you're asking about is degraded by the turbulence in the hollowed space where the cat used to be.
Not worth the aggressive sound IMO.

[STR8-6IX]

Originally Posted by Noir

The performance aspect you're asking about is degraded by the turbulence in the hollowed space where the cat used to be.
Not worth the aggressive sound IMO.

agreed.. maybe if the hollow space had a straight pipe instead it would be ok, but its best to just install headers.

[STR8-6IX]

Originally Posted by Noir

Performance degradation for sound is....
Whatever.
Do it!

never. it's either headers or I keep my cats. I'm not hacking apart my manifold and making barely any power for more sound.

[Misty]

Originally Posted by Noir

The performance aspect you're asking about is degraded by the turbulence in the hollowed space where the cat used to be.
Not worth the aggressive sound IMO.

Would this also be true for my secondary's cause I gutted those too . @hassmachine

[hassmaschine]

Yes. Void spaces and sudden volume transitions in an exhaust are a bad thing.

IMO, either leave it alone or replace it with a pipe or resonator.