Catless DPs & Catted Exhaust vs Catted DPs & Catless Exhaust

SFD507 · 10-21-2009, 12:33 PM

I have an inkling that having catless downpipes with a catted exhaust would have less backpressure, and therefore greater power production and throttle response than catted downpipes with a catless exhaust. Assuming catalytic converters have to be in there to pass emissions (which they do), do any of the experts out there have an opinion on this matter?

I've heard some people complaining about a heavy exhaust smell in the cabin associated with catless downpipes. Is this only the case with a catless exhaust as well?

TIA

enrita · 10-21-2009, 12:45 PM

best option is the first. I dont have smell in the cabin even fully catless.

ar design · 10-21-2009, 12:49 PM

Quote:

Originally Posted by enrita

best option is the first. I dont have smell in the cabin even fully catless.

SV Concepts III · 10-21-2009, 01:30 PM

Running catless DPs and cat back exhaust (no cats), the gas smell is not terrible and actually only notice it on cold starts when I stand outside. With that said, if you are worried, leave cats in the exhaust like the rest mentioned.

marcel b · 10-21-2009, 01:36 PM

there are no error messages when installing Catless Downpipes? So just plug and play?

Skywagon · 10-21-2009, 02:02 PM

For what it's worth, I cut the cats off of a little old 328i. Two different dyno's proved I gained 14hp doing it. If one looks inside of a BMW cat one would be surprised how terribly restrictive they are. One thing, the noise from the engine went up dramatically. I had put a BMW performance exhaust on the car, sounded muted but deep and healthy, sound is subjective. After cat removal way too loud for me. Had to put in a resonator to reduce the sound. I'm driving an X6 3.5 right now. Have had a little contact with Andrew from AR Design in Denver. He needs a car for development of down pipes. Trying to figure out how I can get away for over a week. No smell from my car that I ever noticed.

ianthegreat · 10-21-2009, 02:13 PM

Quote:

Originally Posted by marcel b

there are no error messages when installing Catless Downpipes? So just plug and play?

There are errors. You will need simms.

marcel b · 10-21-2009, 02:19 PM

Quote:

Originally Posted by ianthegreat

There are errors. You will need simms.

sorry, in this area I am a lake. What are "simms"?

thanks

ar design · 10-21-2009, 02:30 PM

Quote:

Originally Posted by Skywagon

For what it's worth, I cut the cats off of a little old 328i. Two different dyno's proved I gained 14hp doing it. If one looks inside of a BMW cat one would be surprised how terribly restrictive they are. One thing, the noise from the engine went up dramatically. I had put a BMW performance exhaust on the car, sounded muted but deep and healthy, sound is subjective. After cat removal way too loud for me. Had to put in a resonator to reduce the sound. I'm driving an X6 3.5 right now. Have had a little contact with Andrew from AR Design in Denver. He needs a car for development of down pipes. Trying to figure out how I can get away for over a week. No smell from my car that I ever noticed.

We would LOVE to get your car out here

Skywagon · 10-21-2009, 03:25 PM

Andrew,
I'm working on it. Will call you next week.

enrita · 10-21-2009, 03:29 PM

Quote:

Originally Posted by marcel b

sorry, in this area I am a lake. What are "simms"?

thanks

o2 simulators, you connect a little box in the ECU . like this http://www.n54tuning.com/index.php?_...d&productId=12

marcel b · 10-21-2009, 03:38 PM

Quote:

Originally Posted by enrita

o2 simulators, you connect a little box in the ECU . like this http://www.n54tuning.com/index.php?_...d&productId=12

Thanks

badass1g · 10-21-2009, 05:05 PM

on turboed cars the smell is alot less noticable without cats. i think they burn alot cleaner than NA cars. i had my c6 vette catless and holy crap, choke me out lol. ive had many turboed cars without cats and turboes hate backpressure anyway. go as free flow as possible. no cats FTW

Eyeman · 10-21-2009, 07:27 PM

You definitely get more effect (hp, smell, etc) by going with catless downpipes. Removing any cat might cause you to be hassled by BMW, for sure downpipes will. I love my downpipes but it's been a huge hassle for me to just get them to replace my hpfp so think twice before you do it.

illone · 10-22-2009, 02:14 AM

If you're getting exhaust smell in the car then you might want to double check your gaskets or tighten things down a bit.

645Nm · 10-22-2009, 04:08 AM

My option:
Catless DPs;
Keep second cats in place;
Aftermarket catback exhaust;
(there will be a smell with cold start ups & when you stand outside the car BUT no smell inside cabin)

Alpina_B3_Lux · 10-22-2009, 08:47 AM

Quote:

Originally Posted by 645Nm

My option:
Catless DPs;
Keep second cats in place;
Aftermarket catback exhaust;
(there will be a smell with cold start ups & when you stand outside the car BUT no smell inside cabin)

The problem with this option (which I have been considering as well) is that there is a definite risk that the high exhaust temperatures destroy your secondary OEM cats. This happened to a friend of mine this summer, and he replaced his secondary cats with metal race cats that are much more robust and can resist much higher temps (and, incidentally, release some more hp and have a nicer sound than the OEM cats).

Alpina_B3_Lux

SFD507 · 10-22-2009, 08:50 AM

Quote:

Originally Posted by Alpina_B3_Lux

The problem with this option (which I have been considering as well) is that there is a definite risk that the high exhaust temperatures destroy your secondary OEM cats. This happened to a friend of mine this summer, and he replaced his secondary cats with metal race cats that are much more robust and can resist much higher temps (and, incidentally, release some more hp and have a nicer sound than the OEM cats).

Alpina_B3_Lux

That is really good to know! Thanks!

10-21-2009, 12:33 PM	#1
SFD507 Private 8 Rep 64 Posts Drives: 2018 Panamera ST Turbo Join Date: May 2009 Location: MA iTrader: (0)	Catless DPs & Catted Exhaust vs Catted DPs & Catless Exhaust I have an inkling that having catless downpipes with a catted exhaust would have less backpressure, and therefore greater power production and throttle response than catted downpipes with a catless exhaust. Assuming catalytic converters have to be in there to pass emissions (which they do), do any of the experts out there have an opinion on this matter? I've heard some people complaining about a heavy exhaust smell in the cabin associated with catless downpipes. Is this only the case with a catless exhaust as well? TIA __________________ The pedal on the right makes the things in the mirrors smaller. Current: '16 f32 435xi \| '05 e46 M3 vert Previous: '08 e90 335xi \| '13 Ducati Hyperstrada \| '12 Yamaha FZ6R
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10-21-2009, 12:45 PM	#2
enrita Major General 161 Rep 7,377 Posts Drives: 335i - Big turbos Join Date: Sep 2008 Location: Italian in Sweden iTrader: (0)	best option is the first. I dont have smell in the cabin even fully catless. __________________ 07 335i AT - MOTIV 750 - MHD E85 BMS flash - BMS PI - JB4G5 - Okada Coils - NGK 5992 Plugs - Helix IC - Snow Stg. 3 - Stett CP - Custom midpipes with 100 HJS Cats - Bastuck Quad - PSS10 - QUAIFE LSD - BMS OCC - Forge DVs - AR OC - ALCON BBK - M3 Chassi - Dinan CP - Velocity M rear Toe arms - Advan RZ-DF - LUX H8 - Level 10 AT upgrade
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10-21-2009, 01:30 PM	#4
SV Concepts III Lieutenant General 375 Rep 17,017 Posts Drives: BMW Duh Join Date: Apr 2005 Location: Santa Clara iTrader: (13)	Running catless DPs and cat back exhaust (no cats), the gas smell is not terrible and actually only notice it on cold starts when I stand outside. With that said, if you are worried, leave cats in the exhaust like the rest mentioned.
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10-21-2009, 01:36 PM	#5
marcel b Lieutenant Colonel 132 Rep 1,898 Posts Drives: F31 340i Join Date: Jun 2009 Location: Europe iTrader: (0)	there are no error messages when installing Catless Downpipes? So just plug and play?
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10-21-2009, 02:02 PM	#6
Skywagon Private First Class 15 Rep 176 Posts Drives: X6 3.5 Join Date: Jun 2009 Location: The Old South iTrader: (0)	For what it's worth, I cut the cats off of a little old 328i. Two different dyno's proved I gained 14hp doing it. If one looks inside of a BMW cat one would be surprised how terribly restrictive they are. One thing, the noise from the engine went up dramatically. I had put a BMW performance exhaust on the car, sounded muted but deep and healthy, sound is subjective. After cat removal way too loud for me. Had to put in a resonator to reduce the sound. I'm driving an X6 3.5 right now. Have had a little contact with Andrew from AR Design in Denver. He needs a car for development of down pipes. Trying to figure out how I can get away for over a week. No smell from my car that I ever noticed.
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10-21-2009, 03:25 PM	#10
Skywagon Private First Class 15 Rep 176 Posts Drives: X6 3.5 Join Date: Jun 2009 Location: The Old South iTrader: (0)	Andrew, I'm working on it. Will call you next week.
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10-21-2009, 05:05 PM	#13
badass1g Captain 51 Rep 646 Posts Drives: 07 335i Join Date: Oct 2009 Location: utah iTrader: (7)	on turboed cars the smell is alot less noticable without cats. i think they burn alot cleaner than NA cars. i had my c6 vette catless and holy crap, choke me out lol. ive had many turboed cars without cats and turboes hate backpressure anyway. go as free flow as possible. no cats FTW
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10-21-2009, 07:27 PM	#14
Eyeman Colonel 121 Rep 2,037 Posts Drives: 2008 135 blk, blk, step Join Date: Jan 2009 Location: Atlanta, GA iTrader: (0) Garage List 1994 Porsche 968 Cab [0.00] 2017 AMG GTS [0.00] 1994 Porsche 968 Coupe [0.00] 1977 Mercedes 450SE ... [0.00] 2008 135 [8.00]	You definitely get more effect (hp, smell, etc) by going with catless downpipes. Removing any cat might cause you to be hassled by BMW, for sure downpipes will. I love my downpipes but it's been a huge hassle for me to just get them to replace my hpfp so think twice before you do it. __________________ Injen, RR OCC, MadDad Whisper, donut spare, 19x8.5et43fr 19x9.5et45r Volk LE37's, rear fenders rolled/pulled, PSS4S 225/35fr 255/30r, KW V1's, AR coated catless dps, Cross strutbar, CF grills and license plate holder, iCarbon diffuser, ETS black anodized FMIC, M3 control arms, Quaife, ER chargepipe, ForgeDV's, Topspeed Custom Tune, V3sims, Braille, Andrey_GTA rear hub mod, Ebay Mstyle front bumper and performance style side skirts.
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10-22-2009, 02:14 AM	#15
illone Private 4 Rep 53 Posts Drives: e90 Join Date: Jun 2009 Location: AZ iTrader: (1)	If you're getting exhaust smell in the car then you might want to double check your gaskets or tighten things down a bit.
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10-22-2009, 04:08 AM	#16
645Nm only in it for the torque - awuleth'umshini wami 50 Rep 425 Posts Drives: sapphire black 335i Join Date: Apr 2009 Location: nomad iTrader: (0) Garage List 2009 335i sedan [0.00] 2005 120D [0.00] 2007 335i sedan [0.00]	My option: Catless DPs; Keep second cats in place; Aftermarket catback exhaust; (there will be a smell with cold start ups & when you stand outside the car BUT no smell inside cabin) __________________
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