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      07-24-2012, 02:46 AM   #1
flinchy
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Oem exhaust piping size?

As in the title, what is the ID of the stock exhaust? Im guessing 2.25-2.5 somewhere, but i can find google results of aftermarket 2.5" setups, ao possibly less than 2.5" stock?

128i and 130i i'm wondering about
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      07-24-2012, 02:52 AM   #2
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is 2.25" for 135i if that helps

disclaimer** I am not 100% on that
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      07-24-2012, 05:04 AM   #3
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Quote:
Originally Posted by RaihaX View Post
is 2.25" for 135i if that helps

disclaimer** I am not 100% on that
2.25" no shit? that's tiny! going to a 2.75 or even 3" full catback would show absolutely immense gains, 2.25" would be choking the shit out of the engine in even stock form - even evo's and sti's love a 3"

ima need a second opinion on this one, cos even bmw surely can't be that silly!
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      07-24-2012, 06:33 AM   #4
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I will check in the next day or 2

yes 3" is good even in a single pipe like Riss racing mid pipe.
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      07-28-2012, 12:37 AM   #5
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Had my car on a hoist at a shop about an hour ago - looks like (to them) twin 2" pipes from the headers, 2.5" pipes with a crush around the diff (so it's effectively a bit lower than 2.5", around 2.35-2.4 roughly)

On another note, they said they couldn't put an exhaust on my car, no muffler would fit ahahah, worst exhaust shop ever. Was treated like an idiot.
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      07-28-2012, 05:55 AM   #6
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Quote:
Originally Posted by flinchy View Post
2.25" no shit? that's tiny! going to a 2.75 or even 3" full catback would show absolutely immense gains, 2.25" would be choking the shit out of the engine in even stock form - even evo's and sti's love a 3"

ima need a second opinion on this one, cos even bmw surely can't be that silly!
You could actually lose a good bit of power increasing the diameter. Dont forget about scavenging, especially for N/A motors you need to pull all the air out quickly to fill the cylinders fully with the fresh incoming charge. F/I cars like the Evo/Sti easily fill the cylinders through turbo pressure.
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      07-28-2012, 08:14 AM   #7
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Quote:
Originally Posted by NYC6 View Post
You could actually lose a good bit of power increasing the diameter. Dont forget about scavenging, especially for N/A motors you need to pull all the air out quickly to fill the cylinders fully with the fresh incoming charge. F/I cars like the Evo/Sti easily fill the cylinders through turbo pressure.
the difference between being .25" over is still better for power than being .25" under.

the biggest issue is back pressure, you ideally want none, no leftover gases in the cylinder chamber.

regardless of the turbo being able to push in tons of air, it doesn't PUSH out burnt exhaust gases (being the exhaust valve is open when the intake is closed, mostly)
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      07-28-2012, 08:40 AM   #8
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Magnaflow's cat back is 2.5 inch tubing. It is also mandrel bent - smoother bends = less restriction.
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      07-28-2012, 01:34 PM   #9
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Quote:
Originally Posted by flinchy View Post
the difference between being .25" over is still better for power than being .25" under.

the biggest issue is back pressure, you ideally want none, no leftover gases in the cylinder chamber.

regardless of the turbo being able to push in tons of air, it doesn't PUSH out burnt exhaust gases (being the exhaust valve is open when the intake is closed, mostly)
"2.75 or even 3" full catback would show absolutely immense gains"
Your talking up to 1/2" increase and you're talking about immense gains. It aint gonna happen.
BMW is certainly adept at fine balancing its N/A engines. The are damn near close to optimum balance of intake and exhaust to get the most power out of its engines. Going larger in tubing size isnt going to help, it will hinder low end tq certainly and likely hp. IMO.

OK. Let us know how it works out for ya. Dont forget the before after dynos.

Last edited by NYC6; 07-28-2012 at 01:50 PM.
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      07-28-2012, 02:36 PM   #10
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The stock exhaust is not too restrictive. Infact, if you remove the rear cat converters for those who and an N54, and replace the downpipes with catless ones, the stock exhaust is pretty good as is. Where other turbo cars may have a single 3 inch exhaust, the BMW has a double 2.-- midpipe that y-pipes into a 3 inch muffler. The catback can be upgraded, and also converted to all straight 3 inch, but unless you are running 5-- +HP there isnt any point to it IMHO.
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      07-28-2012, 05:45 PM   #11
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Quote:
Originally Posted by JimD
Magnaflow's cat back is 2.5 inch tubing. It is also mandrel bent - smoother bends = less restriction.
The stock one in mine is mandrel except for a single press around the diff, as well as the res/cats/muffler being really restrictive

And of course the stock bends not being as efficient as possible
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      07-28-2012, 05:47 PM   #12
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Quote:
Originally Posted by NYC6
Quote:
Originally Posted by flinchy View Post
the difference between being .25" over is still better for power than being .25" under.

the biggest issue is back pressure, you ideally want none, no leftover gases in the cylinder chamber.

regardless of the turbo being able to push in tons of air, it doesn't PUSH out burnt exhaust gases (being the exhaust valve is open when the intake is closed, mostly)
"2.75 or even 3" full catback would show absolutely immense gains"
Your talking up to 1/2" increase and you're talking about immense gains. It aint gonna happen.
BMW is certainly adept at fine balancing its N/A engines. The are damn near close to optimum balance of intake and exhaust to get the most power out of its engines. Going larger in tubing size isnt going to help, it will hinder low end tq certainly and likely hp. IMO.

OK. Let us know how it works out for ya. Dont forget the before after dynos.
Go check out e90post, then come back to me about it, they all show plenty of gains with bigger piping, especially since stock is a bit under 2.5"

I mean, hondas (like my old prelude) are a 2.2L 200-220hp and they get large gains going up to a 2.5" or 2.75" lol

Most exhaust mods are only a 0.5" increase and that's enough for many performance cars to gain 10 or 20 hp

And i've got a 'before' dyno in about a week or two, and i'd say an after about two after that
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      07-28-2012, 05:51 PM   #13
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Quote:
Originally Posted by 1911A145
The stock exhaust is not too restrictive. Infact, if you remove the rear cat converters for those who and an N54, and replace the downpipes with catless ones, the stock exhaust is pretty good as is. Where other turbo cars may have a single 3 inch exhaust, the BMW has a double 2.-- midpipe that y-pipes into a 3 inch muffler. The catback can be upgraded, and also converted to all straight 3 inch, but unless you are running 5-- +HP there isnt any point to it IMHO.
Actually, in my googling yesterday, a 3" full exhaust is even restrictive at like 400hp - remember even evo/sti's go a 3" exhaust to run stock turbos and just a tune, 3.5" for bigger things

Also, are you sure the 135i has a 3" inlet? From everything i can gather at most it's a 2.75" with a crush

An as said - the 128/130 is a 2.5" with a crush and other inefficiencies so there's plenty of room for upgrades - we aren't talking about the 135i (remembering they still commonly replace their catbacks too for gains..)
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      07-28-2012, 06:47 PM   #14
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135i N55 mid pipes measure 58mm in outer diameter.
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      07-28-2012, 07:41 PM   #15
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135i N55 mid pipes measure 58mm in outer diameter.
that's the twin pipes yeah? that's 2.25" OD, so 2" ID would be right same as 130i
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      07-28-2012, 08:15 PM   #16
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Quote:
Originally Posted by flinchy View Post
Go check out e90post, then come back to me about it, they all show plenty of gains with bigger piping, especially since stock is a bit under 2.5"

I mean, hondas (like my old prelude) are a 2.2L 200-220hp and they get large gains going up to a 2.5" or 2.75" lol

Most exhaust mods are only a 0.5" increase and that's enough for many performance cars to gain 10 or 20 hp

And i've got a 'before' dyno in about a week or two, and i'd say an after about two after that
I did take a look over there. Some talk about gains but like the 128 section, dyno printouts are as rare as hens teeth. Go figure.

If you can find huge gains with just adding a 3" pipe I'd be glad to look at it, besides someones way optomistic butt dyno.

Then I think we need to establish what does "immense" mean to you?

I look forward to see how you do with your up coming mod. What size are you going with?
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      07-28-2012, 08:36 PM   #17
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Quote:
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I did take a look over there. Some talk about gains but like the 128 section, dyno printouts are as rare as hens teeth. Go figure.

If you can find huge gains with just adding a 3" pipe I'd be glad to look at it, besides someones way optomistic butt dyno.

Then I think we need to establish what does "immense" mean to you?

I look forward to see how you do with your up coming mod. What size are you going with?
huh? go back and re-read the context of the post, he's running 3" pipes with a restriction on the end, it'd be the 5 or whatever over stock with what he's done, but if he modifies the rest so that the WHOLE THING is 3" all the way through, there will be further gains to be had lol.

immense on our engines, including headers, no cats primary or secondary, and at least 2.75" piping all the way through with a single res and muffler that are less restrictive than the stock items, or 3", i'd consider 20-25whp to be seen peak, as immense, considering the low down gains as well, i consider that immense overall for a single breathing mod.. and when the total cost is >$2k, it'id want to sound nice too lol... i'm also still waiting for dyno's of MMW headers, though as far as i'm aware, supersprint has shown a 10~hp gain over stock haven't they?

i'm talking to some local shops at the moment, the first one told me they couldn't do it (wankers), but i'm going to some more reputable/prestigious (yet decently priced ones) this week when they're open to have a chat, i've seen on their facebook pages they've done 135/335's and other bmw's, so i'm sure they'll be able to 'fit a muffler' in my space -_-

if i get it custom, it'd be twin 2" pipes into a 3" merge with a res and muffler, no secondary cats
if it turns out that everyone refuses, it'll be a laptorr which is twin 2" into a 2.75" and a fairly high flow res/muffler, not glass pack which is awesome, and no cats, plus it sounds freakin amazing lol - it's just $2.5k shipped, hence why i'd like to try get a shop to mimick it in 3" end piping..

the real gain, in my opinion, isn't the power, it's the throttle response... my first car was a 1997 mitsubishi lancer 1.8, i went to a 2" cat-back, stock cats, with aftermarket headers, and they way the revs instantly went to where you wanted them... well lets say it makes the response in my 130i almost disappointing. - it makes heel-toeing an absolute dream.
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      07-28-2012, 11:09 PM   #18
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You realize SuperSprint makes everything from headers on back for the 130i right?

http://www.supersprint.com/en/prod-2...093E280BA.aspx
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      07-29-2012, 06:15 AM   #19
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You realize SuperSprint makes everything from headers on back for the 130i right?

http://www.supersprint.com/en/prod-2...093E280BA.aspx
yes, if you want to spend $7k on an exhaust setup, that's fine
i've never heard a full ss system, but their headers on setups i've heard on E90post don't sound as good as videos of MMW's so far too

basically, i'll be happy with my $2-$3k setup that performs just as well (in theory) as supersprints $7k one lol

even SS headers are like $2.5k or something from memory? yeah 1500 GBP for headers PLUS shipping

i suppose it's a little cheaper for the setup i want (catless blah blah) but still FAR more pricey than anything local.. and i don't believe it sounds good

and their 'racing' muffler is an ugly oval tip, i wanna keep oem offset twin tips for aesthetic reasons./ though the quad tip is suuuper nice looking.

also, you'd still have to get custom cat replacement pipes, they don't offer a straight up catless system.

Last edited by flinchy; 07-29-2012 at 06:21 AM.
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      07-29-2012, 09:02 AM   #20
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I really don't think you would want the race setup either way, the volume on those is generally pretty absurd. Without cats for muffling, you would easily get pulled over for it if your country has any sort of noise ordinance at all. Price is high, but the quality is perfect and they actually do the R&D.

They offer full catless:

Catless headers:

http://www.supersprint.com/en/prod-c...laces_kat.aspx


Catless front mid pipes:

http://www.supersprint.com/en/prod-c...pipes_kit.aspx


Or race cat front mid pipes:

http://www.supersprint.com/en/prod-c..._kat_r__l.aspx
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      07-29-2012, 04:38 PM   #21
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Quote:
Originally Posted by TheSt|G
I really don't think you would want the race setup either way, the volume on those is generally pretty absurd. Without cats for muffling, you would easily get pulled over for it if your country has any sort of noise ordinance at all. Price is high, but the quality is perfect and they actually do the R&D.

They offer full catless:

Catless headers:

http://www.supersprint.com/en/prod-c...laces_kat.aspx


Catless front mid pipes:

http://www.supersprint.com/en/prod-c...pipes_kit.aspx


Or race cat front mid pipes:

http://www.supersprint.com/en/prod-c..._kat_r__l.aspx
I've heard catless with muffler and res before, isn't tooo bad

But really, te only thing you really need to rnd is headers (and a bit in the muffler too lol) - for the price, a custom shop could do me a bloody titanium cat back and i'd still have spare change lol. Any exhaust shop can do you a cat back with the same gains as the ss stuff

Ed: if you read.. Those front pipes aren't catless themselves, they bolt up to the sock cats, so you'd still have to install blank cat spacers.
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      07-29-2012, 08:59 PM   #22
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Not really sure why you think that, the are the same length:







And I'm sorry, Joe Blow muffler shop does not have the R&D and experience of Supersprint, plain and simple.
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