Would you go catless downpipes?

pysical

Sergeant
Jun 16, 2017
345
73
0
Ride
2009 335xi E90
I currently have CPE high flow downpipes. Would I gain anything if I went catless? I kind of wanted it to be a little louder. Or should I keep the downpipes and remove the secondary cats?
 

LessIsMore

Specialist
Aug 21, 2017
56
22
0
Ride
09 535i
Answer might depend on what area you live in, could be a headache or no problem.

Seems like since you already have the cated down pipes, try removing the secondary cats and see if that makes you happy.
 

TheGoose

Lurker
May 5, 2018
23
3
0
Ride
2007 E92 335i
Catless will for sure be louder. As LessIsMore stated depending on where your at can somewhat force your hand. Would you be doing the work yourself?
 

pysical

Sergeant
Jun 16, 2017
345
73
0
Ride
2009 335xi E90
Swapping downpipes would be doing the work myself. Getting rid of the secondary cats or resonator wouldn't be me. I have the downpipes out now while doing some work so thought maybe to change them out. I am living in Maryland atm but my car is licensed in Utah. I don't have to do emissions on my car. I may end up moving to Texas in the next couple years but I am not sure.
 

TheGoose

Lurker
May 5, 2018
23
3
0
Ride
2007 E92 335i
I hear you on looking at stuff to change when it’s apart already. Having changed the DP’s on my car too many times to remember I would say since you have them out if you either have or could get a set up catless for cheap I would do that. Your already going to have to put yours back in. Also if your doing the work yourself in theory I suppose if you don’t like them you could swap back...
 

RSL

Lieutenant
Aug 11, 2017
696
377
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Have Cobb catted on for 4+ years. I finally bought some used Macht Schnell catless a couple months ago just to check if catless claims I figured were mostly bunk all these years, actually were.

Catless with flapper closed are no louder than high flow catted with flapper open for cold start. No sound difference on cruise/normal driving. Catless under boost may be a little louder, but raspy sounding to me.

As you'd guess, no change in spool, boost, etc. It's pretty much dictated by boost control, tuning and turbines. Literally maybe a +2whp difference across the board on VD with hybrids at 20psi.

People buy catless because they're cheap and want to believe they're significantly higher performing than high flow catted. Not on these cars. If you already spent the money high flow catted, I wouldn't bother with catless. I put the Cobb's back on if it's any indication. If you're interested in the Macht Schnells anyway, LMK, they're sitting in storage wait to be sold as soon as I have time lol
 
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pysical

Sergeant
Jun 16, 2017
345
73
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Ride
2009 335xi E90
Have Cobb catted on for 4+ years. I finally bought some used Macht Schnell catless a couple months ago just to check if catless claims I figured were mostly bunk all these years, actually were.

Catless with flapper closed are no louder than high flow catted with flapper open for cold start. No sound difference on cruise/normal driving. Catless under boost may be a little louder, but raspy sounding to me.

As you'd guess, no change in spool, boost, etc. It's pretty much dictated by boost control, tuning and turbines. Literally maybe a +2whp difference across the board on VD with hybrids at 20psi.

People buy catless because they're cheap and want to believe they're significantly higher performing than high flow catted. Not on these cars. If you already spent the money high flow catted, I wouldn't bother with catless. I put the Cobb's back on if it's any indication. If you're interested in the Macht Schnells anyway, LMK, they're sitting in storage wait to be sold as soon as I have time lol

Thanks. I will just keep what I got then.
 

ShocknAwe

Captain
Jan 24, 2018
1,136
531
0
Charleston, SC
Ride
N54/3 1er ///Mutt
Have Cobb catted on for 4+ years. I finally bought some used Macht Schnell catless a couple months ago just to check if catless claims I figured were mostly bunk all these years, actually were.

Catless with flapper closed are no louder than high flow catted with flapper open for cold start. No sound difference on cruise/normal driving. Catless under boost may be a little louder, but raspy sounding to me.

As you'd guess, no change in spool, boost, etc. It's pretty much dictated by boost control, tuning and turbines. Literally maybe a +2whp difference across the board on VD with hybrids at 20psi.

People buy catless because they're cheap and want to believe they're significantly higher performing than high flow catted. Not on these cars. If you already spent the money high flow catted, I wouldn't bother with catless. I put the Cobb's back on if it's any indication. If you're interested in the Macht Schnells anyway, LMK, they're sitting in storage wait to be sold as soon as I have time lol

So you dyno'd the car before after same day? Do you have any logs? There's a lot more to it than just WHP. Especially if you didn't adjust your tune for the change in hardware.

OP: Any mod changing airflow characteristics will only yield tangible benefits when adjusting the tune to account for that. That said, if you're only after power gains, you could probably achieve a similar delta by cutting out the secondary cats.
 

RSL

Lieutenant
Aug 11, 2017
696
377
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So you dyno'd the car before after same day? Do you have any logs? There's a lot more to it than just WHP. Especially if you didn't adjust your tune for the change in hardware.

OP: Any mod changing airflow characteristics will only yield tangible benefits when adjusting the tune to account for that. That said, if you're only after power gains, you could probably achieve a similar delta by cutting out the secondary cats.
Before and after virtual dyno. Log 3-5x a day in the same spot for years, I'm pretty consistent at it.

No changes to make on a tune for high flow catted to catless DPs on a scaled 20psi tune with hybrids on 93, I'm more or less maxed for the fuel. If they were holding anything back, would change WGDC or boost with nothing changed in the tune. In essence, only potential change would be back pressure and possibly EGTs. Change in tune changes power, catless DPs barely do anything over high flow catted. If I changed to catless and boost went up, yes, it would make more power, but I'm maxed for 93 octane. I'll dig up the logs tonight if I have time.
 

ShocknAwe

Captain
Jan 24, 2018
1,136
531
0
Charleston, SC
Ride
N54/3 1er ///Mutt
Before and after virtual dyno. Log 3-5x a day in the same spot for years, I'm pretty consistent at it.

No changes to make on a tune for high flow catted to catless DPs on a scaled 20psi tune with hybrids on 93, I'm more or less maxed for the fuel. If they were holding anything back, would change WGDC or boost with nothing changed in the tune. In essence, only potential change would be back pressure and possibly EGTs. Change in tune changes power, catless DPs barely do anything over high flow catted. If I changed to catless and boost went up, yes, it would make more power, but I'm maxed for 93 octane. I'll dig up the logs tonight if I have time.

OK so you saw no change in WGDC/PWM, that speaks volumes IMO. Wonder if it's related to the headroom on hybrids and a smaller MOE at that flow rate vs stock twins. Probably not.
 

RSL

Lieutenant
Aug 11, 2017
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Yeah, there was little to no difference anywhere on any logged param that I recall, but I'll dig them up tonight and do an overlay.
 
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RSL

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Aug 11, 2017
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Cobb catted is solid line log, Macht Schnell catless is dash line log.

Catless target is about 0.5psi less than the catted log across the board with slightly different IAT, ECT and OCT between the logs. They were a day apart, but tried to get them as close as possible. IATs were 5F different, ECT was 3-4F different and OCT was 10-11F different. Ambient pressure was the same, but ambient temps were a few degrees different.

MAF (WGDC) is correspondingly 10-15 g/s less on the catless log across the board. WGDC base and PID are the same, catless final WGDC is about 1-1.5% lower in spots, but as can be seen, actual boost (boost mean) is also 0.5-1psi lower on the catless log, even though calculated boost (boost psi) is essentially the same on both.

hiflo-vs-catless.png
 
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fmorelli

Major General
Staff member
Aug 11, 2017
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54
Virginia
www.morelliguitars.com
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E89 Z4 35i, F10 535d
I wanted to remove backpressure from the turbos, get more flow out of the system, yet retain post-cat 02 sensors so all falls in the somewhat legit zip code (emissions testing, etc). Here's what we did (btw this is on a N54 Z4):
  • VRSF catless downpipes.
  • Custom exhaust with 49-stat CARB high flow mid-pipe cats
  • Vibrant j bungs for 02 sensors, now behind mid-pipe cats
  • Extended post-cat 02 wiring harness with Deutsch connectors
I feel like we got the best of all worlds.

Filippo

IMG_20161119_160113.jpg
IMG_20161119_160036.jpg
 
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Jeffman

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Jan 7, 2017
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Have Cobb catted on for 4+ years. I finally bought some used Macht Schnell catless a couple months ago just to check if catless claims I figured were mostly bunk all these years, actually were.

Catless with flapper closed are no louder than high flow catted with flapper open for cold start. No sound difference on cruise/normal driving. Catless under boost may be a little louder, but raspy sounding to me.

As you'd guess, no change in spool, boost, etc. It's pretty much dictated by boost control, tuning and turbines. Literally maybe a +2whp difference across the board on VD with hybrids at 20psi.

People buy catless because they're cheap and want to believe they're significantly higher performing than high flow catted. Not on these cars. If you already spent the money high flow catted, I wouldn't bother with catless. I put the Cobb's back on if it's any indication. If you're interested in the Macht Schnells anyway, LMK, they're sitting in storage wait to be sold as soon as I have time lol
Had you compared Cobb catted highflow to stock catted downpipes?
(After 10 years and 64K miles I’m still on my original stock downpipes and turbos, the last 7 years/42K miles being tuned, and the last two years 20+ psi. The car’s still lots of fun to drive. Just wondering how much more fun I’d have after installing high flow catted downpipes and inlets, and weighing the cost/effort of doing so on this ‘08 xi car.)
 

RSL

Lieutenant
Aug 11, 2017
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I had logs between the stock and high flow, but that was 4.5 years ago and pre-MHD. I was on AP at the time and no telling what was logged. I'll look, but can't make any promises I'll be able to dig up logs or how telling they would be, but will say, there weren't noticeable gains on that swap for me either. I still have the stock DPs and would swap from the Cobb back to stock to test now, but my just sold my house, so my wrenching days will be 0 until I get settled elsewhere.

I did the same, ran 19psi+ tune on stock turbos with the stock DPs for a while before making the switch to high flow. I was more concerned about EGTs than anything else at that point. I had no clue what they were and really still don't, but obviously it's not problem if you've been running it that long.