Backpressure Exhaust Q

jbuds335xi · 12-22-2007, 06:22 PM

I recently got the Reiger rear diffuser and as a result had to cut off the back pieces of my exhaust and had some custom work done to put in new tips and (with some 90 degree bends and what looks like a slightly thinner pipe) to make it fit the diffuser. Now ALL MY POWER IS GONE!!! I feel like a jackass driving around a sick looking car with less power than stock considering the upgrades I have on the thing.

A mechanic told me that by going to some bigger tips, there isn't enough back pressure in the exhaust to spool up the turbos, and that might be what is going on.

Personally I think the opposite. It seems like the custom bends and smaller piping at the end of the exhaust (it was a rush and honestly poorly done job...) is restricting airflow. When I drive above 4k rpms it sounds almost like a hose is loose in the front engine, or that the blow of valve is just constantly venting air. Additionally, there is almost no blow off when I do shift up. Wouldn't these be the symptoms of too much back pressure?

I have considered just lopping off the shitty custom work and driving around in a weird looking and obnoxiously loud car, but at least I'd be able to drive away fast from all the haters... Any suggestions?

Someone PLZ

!!!

Acap14 · 12-22-2007, 06:27 PM

Turbo cars dont need backpressure and you screwed yourself by adding another bend. When it comes to turbos you want the exhaust to get out as quick as possible, thats why you get a bigger exhaust wit as few bends as possible. that will solve your power issue

jbuds335xi · 12-22-2007, 06:35 PM

That's exactly what I was thinking. Think I should just lop the things off until I find a better solution?

Acap14 · 12-22-2007, 06:37 PM

that'll give you your power back, look into a custom catback. can you post pics of the diffuser?

jbuds335xi · 12-22-2007, 06:46 PM

No can do, no camera... Looks real good but I'm not sure what exhausts are supposed to fit it... it's really wide and there are parts of the car that get in the way.

Acap14 · 12-22-2007, 06:59 PM

Probably a reiger system if they make one, if not call them and ask what systems are compatible.

sambonator · 12-22-2007, 08:00 PM

Make sure the vacuum hose that used to go to the left muffler tip is properly plugged and not leaking.

oddjob2021 · 12-22-2007, 08:03 PM

also with exhaust modifications usually you hear the turbo spool a lot more, this could be the "constant venting" sound you hear

Acap14 · 12-22-2007, 08:07 PM

the turbo spooling more usually has to do with the reduction of back pressure, not the addition of back pressure.

O-cha · 12-22-2007, 08:51 PM

Is this the same mechanic that installed/made your exhaust? If so problem found.

12-22-2007, 06:22 PM	#1
jbuds335xi Second Lieutenant 9 Rep 248 Posts Drives: 335xi Manual, Jet Black, Black Join Date: Jul 2007 Location: All over iTrader: (0)	Backpressure Exhaust Q I recently got the Reiger rear diffuser and as a result had to cut off the back pieces of my exhaust and had some custom work done to put in new tips and (with some 90 degree bends and what looks like a slightly thinner pipe) to make it fit the diffuser. Now ALL MY POWER IS GONE!!! I feel like a jackass driving around a sick looking car with less power than stock considering the upgrades I have on the thing. A mechanic told me that by going to some bigger tips, there isn't enough back pressure in the exhaust to spool up the turbos, and that might be what is going on. Personally I think the opposite. It seems like the custom bends and smaller piping at the end of the exhaust (it was a rush and honestly poorly done job...) is restricting airflow. When I drive above 4k rpms it sounds almost like a hose is loose in the front engine, or that the blow of valve is just constantly venting air. Additionally, there is almost no blow off when I do shift up. Wouldn't these be the symptoms of too much back pressure? I have considered just lopping off the shitty custom work and driving around in a weird looking and obnoxiously loud car, but at least I'd be able to drive away fast from all the haters... Any suggestions? Someone PLZ !!! __________________ Modded.
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12-22-2007, 06:27 PM	#2
Acap14 First Lieutenant 104 Rep 315 Posts Drives: E92 M3 Join Date: Apr 2007 Location: Navarre, FL iTrader: (0) Garage List 2008 M3 [0.00]	Turbo cars dont need backpressure and you screwed yourself by adding another bend. When it comes to turbos you want the exhaust to get out as quick as possible, thats why you get a bigger exhaust wit as few bends as possible. that will solve your power issue
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12-22-2007, 06:35 PM	#3
jbuds335xi Second Lieutenant 9 Rep 248 Posts Drives: 335xi Manual, Jet Black, Black Join Date: Jul 2007 Location: All over iTrader: (0)	That's exactly what I was thinking. Think I should just lop the things off until I find a better solution? __________________ Modded.
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12-22-2007, 06:37 PM	#4
Acap14 First Lieutenant 104 Rep 315 Posts Drives: E92 M3 Join Date: Apr 2007 Location: Navarre, FL iTrader: (0) Garage List 2008 M3 [0.00]	that'll give you your power back, look into a custom catback. can you post pics of the diffuser?
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12-22-2007, 06:46 PM	#5
jbuds335xi Second Lieutenant 9 Rep 248 Posts Drives: 335xi Manual, Jet Black, Black Join Date: Jul 2007 Location: All over iTrader: (0)	No can do, no camera... Looks real good but I'm not sure what exhausts are supposed to fit it... it's really wide and there are parts of the car that get in the way. __________________ Modded.
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12-22-2007, 06:59 PM	#6
Acap14 First Lieutenant 104 Rep 315 Posts Drives: E92 M3 Join Date: Apr 2007 Location: Navarre, FL iTrader: (0) Garage List 2008 M3 [0.00]	Probably a reiger system if they make one, if not call them and ask what systems are compatible.
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12-22-2007, 08:00 PM	#7
sambonator Samtaro! 124 Rep 2,601 Posts Drives: 2014 F32 N55 Alpinweiß Join Date: May 2007 Location: Newport Beach, CA, USA iTrader: (7)	Make sure the vacuum hose that used to go to the left muffler tip is properly plugged and not leaking. __________________
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12-22-2007, 08:03 PM	#8
oddjob2021 ASR Turbos+LSD+Meth= :D 73 Rep 1,517 Posts Drives: E92 335i Join Date: May 2007 Location: Miami, FL iTrader: (0) Garage List 2007 E92 335i [0.00]	also with exhaust modifications usually you hear the turbo spool a lot more, this could be the "constant venting" sound you hear __________________ 2007 335i Coupe Mods: Check the Garage
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12-22-2007, 08:07 PM	#9
Acap14 First Lieutenant 104 Rep 315 Posts Drives: E92 M3 Join Date: Apr 2007 Location: Navarre, FL iTrader: (0) Garage List 2008 M3 [0.00]	the turbo spooling more usually has to do with the reduction of back pressure, not the addition of back pressure.
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12-22-2007, 08:51 PM	#10
O-cha Brigadier General 218 Rep 4,726 Posts Drives: Mcoupe Join Date: Oct 2007 Location: In front of you iTrader: (2)	Is this the same mechanic that installed/made your exhaust? If so problem found. __________________
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