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  1. #1
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    VTT STG 2's and stock exhaust?

    A while back I sold my vanguard exhaust and went back to stock. I looooove the stock exhaust bc the booming wound of the vanguard became a nuisance.

    Now I have VTT stg2 turbos on order and I plan on running 93+meth. Will I still be able to run the stock exhaust? I'm sure it will rob some hp/tq but will the increased back pressure be a issue?

    Is there anything I can modify on the stock exhaust to keep the subtle sound but free up the flow a bit? FYI, I have a 335 coupe.
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    Click here to enlarge Originally Posted by bobS Click here to enlarge
    A while back I sold my vanguard exhaust and went back to stock. I looooove the stock exhaust bc the booming wound of the vanguard became a nuisance.

    Now I have VTT stg2 turbos on order and I plan on running 93+meth. Will I still be able to run the stock exhaust? I'm sure it will rob some hp/tq but will the increased back pressure be a issue?

    Is there anything I can modify on the stock exhaust to keep the subtle sound but free up the flow a bit? FYI, I have a 335 coupe.
    You could either swap in N55 midpipes and weld in some vibrant resonators, or remove the secondary cats on your factory midpipes and weld vibrant resonators in their place.

    Pros - less back pressure, fairly cheap for vibrants plus labor ~$300-350 installed.

    Cons - No cats = fuel smell, black soot on tips/bumper, might be a little louder
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    The backbox doesn't make any difference in terms of power. Only the sound is different. Even the midpipe cats don't do much for backpressure, that's mostly related to the DPs. I replaced the secondary cats with 100cell racecats and it didn't make a tangible difference in power (but it did in terms of sound).

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    you could def run the stock exhaust with catless downpipes...

    my 135 was FBO and i always found myself going back to stock exhaust for the reason you mentioned and never noticed any speed loss with stock mid and muffler....

    trapped 120mph with stock exhaust , you should be fine
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    I'm in the same boat as far as exhausts go but I do want the PE exhaust for that extra grunt. Upped turbos first tho!

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    Ok I have cat less DP's now, but I always thought the stock 335 exhaust was a little bit restrictive. I heard the 135 is less restrictive so that's not a great comparison. I don't want to install my vtt's and have issues with running the stock exhaust if it's to restrictive.

    So far it sounds like i should be ok?
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    The Macht Schnell down pipes have a 1/8" NPT port for temperature measurements that is pretty much useless because it is post turbo. It would be interesting to take some pressure measurements from there with the stock exhaust. Such a bung could be welded into any down pipe I'm sure.

    I've heard the 135 exhaust is restrictive, and the 335 no so much. If you look at Cobb's list of maps, it lists an exhaust as a requirement for all maps.
    Eppur si muove.

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    BobS, I was also in a big debate about this, I will be doing 2.5" (stock size) straight piping with resonators where OE secondary cats usually are back to the stock mufflers. I like the way the stock exhaust sounds and hoping to only change the pitch a little but moreover just make it a bit louder. If there is additional power to be made on top of eliminating secondary cats I can't imagine it being more than 5 HP, which is negligent IMO.

    Edit: I do already have catless downpipes as well
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    135s is more restrictive i thought... T runs stock exhaust Click here to enlarge
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    Click here to enlarge Originally Posted by ajm8127 Click here to enlarge
    I've heard the 135 exhaust is restrictive, and the 335 no so much. If you look at Cobb's list of maps, it lists an exhaust as a requirement for all maps.
    What I said here is ambiguous. Cobb lists exhaust as a requirement for all maps (stage 1 and 2) on a 135, and for the other N54 platforms it lists exhaust as a requirement for only stage 2 maps. What this means to me is the 135 exhaust is more restrictive.
    Eppur si muove.

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    Cobb lists it as suggested for the 135i, not required.

    http://www.cobbtuning.com/Accessport...maps/bmw/IJE0S
    "135i: Sug*
    Other: Any"

    "* We have found that the 135i stock catback exhaust system is restrictive compared to other BMW models. To achieve estimated HP and TQ gains as listed in the map notes, an upgraded catback exhaust with less restriction is necessary. Retaining the stock catback exhaust will result in lower than estimated HP and TQ gains, but will not adversely affect the safety and driveability of the tune."

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    Click here to enlarge Originally Posted by Freon Click here to enlarge
    Cobb lists it as suggested for the 135i, not required.

    http://www.cobbtuning.com/Accessport...maps/bmw/IJE0S
    "135i: Sug*
    Other: Any"

    "* We have found that the 135i stock catback exhaust system is restrictive compared to other BMW models. To achieve estimated HP and TQ gains as listed in the map notes, an upgraded catback exhaust with less restriction is necessary. Retaining the stock catback exhaust will result in lower than estimated HP and TQ gains, but will not adversely affect the safety and driveability of the tune."
    OK guess I read it wrong. Still though it says the 135 is more restrictive.
    Eppur si muove.

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    Pretty sure the 335 coupes have the least restrictive exhaust on an N54 equipped car. You might lose a few ponies, but the OEM exhaust isn't supposed to create restrictions until 500 WHP. You'll be right in that area on a Race Gas/E85/Meth map with the VTT S2s, but on pump you'll prob be 475-480 and it shouldn't be an issue
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    Click here to enlarge Originally Posted by bobS Click here to enlarge
    Ok I have cat less DP's now, but I always thought the stock 335 exhaust was a little bit restrictive. I heard the 135 is less restrictive so that's not a great comparison. I don't want to install my vtt's and have issues with running the stock exhaust if it's to restrictive.

    So far it sounds like i should be ok?
    its the other way around, 135's exhuast free's up power, 335 is fine. id stick with stock rear too. I think i said it before, but the next best thing to stock rear is the miltek, but even that has a bit of boom in the lower rpm, but not like vanguard

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    Click here to enlarge Originally Posted by benzy89 Click here to enlarge
    Pretty sure the 335 coupes have the least restrictive exhaust on an N54 equipped car. You might lose a few ponies, but the OEM exhaust isn't supposed to create restrictions until 500 WHP. You'll be right in that area on a Race Gas/E85/Meth map with the VTT S2s, but on pump you'll prob be 475-480 and it shouldn't be an issue
    im planning on running meth and these will be the batch 2's with larger compressor wheel and other changes, I hope to easily be in the 500+ hp range.

    Lm- yea I thought about miltek, but im sticking with the oem for now if its not going to be a issue
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    1 out of 1 members liked this post. Reputation: Yes | No
    I doubt the stock catback would cause any issues with achieving the HP you desire. Like others have mentioned, DPs are the choke-point.

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    @bobS, I'd say its not required, no. The OEM rear section even with cats will be just fine from the "health" point of view once you go with larger stock frame turbos. You'll be leaving about 10-12whp on the table on a good day at peak power but that comes at a benefit of the quite OEM exhaust which many enjoy after they've been with an aftermarket catless setup daily driving for a while. In your case it sounds like you'd like to keep your OEM exhaust as the trade off isn't much.

    On a 1 series though I'd say it should be replaced. Again, not mandatory, but recommended. At the minimum the midpipes need to be swapped out for better flowing ones.
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    Click here to enlarge Originally Posted by dzenno@PTF Click here to enlarge
    @bobS, I'd say its not required, no. The OEM rear section even with cats will be just fine from the "health" point of view once you go with larger stock frame turbos. You'll be leaving about 10-12whp on the table on a good day at peak power but that comes at a benefit of the quite OEM exhaust which many enjoy after they've been with an aftermarket catless setup daily driving for a while. In your case it sounds like you'd like to keep your OEM exhaust as the trade off isn't much.On a 1 series though I'd say it should be replaced. Again, not mandatory, but recommended. At the minimum the midpipes need to be swapped out for better flowing ones.
    This will be my next mod. I just can't decide whether to run the N55 mid pipe or have a Y pipe right after the DPs, boost operated cut out and then resonators. The N55 option will be the easiest but the second option really is tempting...
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    As long as you can find a cut out that doesn't leak, always opt for going ALL OUT
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    Click here to enlarge Originally Posted by dzenno@PTF Click here to enlarge
    @bobS, I'd say its not required, no. The OEM rear section even with cats will be just fine from the "health" point of view once you go with larger stock frame turbos. You'll be leaving about 10-12whp on the table on a good day at peak power but that comes at a benefit of the quite OEM exhaust which many enjoy after they've been with an aftermarket catless setup daily driving for a while. In your case it sounds like you'd like to keep your OEM exhaust as the trade off isn't much.

    On a 1 series though I'd say it should be replaced. Again, not mandatory, but recommended. At the minimum the midpipes need to be swapped out for better flowing ones.
    Good to know! Thanks
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    I picked up a Perf Exhaust yesterday.. Im hoping its the perfect setup..

    if anyone wants an exhaust with carbon cyba tips in the NY area I will have one available for next to nothing.. just wanted to add a cat back in as mine is catless and baby is due in two weeks, wanna try to eliminate him/her smelling like a race car when I drive my car lol
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    ran stock exhaust with rear cat delete on my rbs no problems.

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    Stock exhaust is what, 2.25 inches or 2.36 inches? I have seen conflicting reports. I wonder how much of a gain you would pick up on stock turbos by going to 2.5 inch piping. I know it would be even greater on upgraded turbos.
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    Click here to enlarge Originally Posted by Stucks Click here to enlarge
    Stock exhaust is what, 2.25 inches or 2.36 inches? I have seen conflicting reports. I wonder how much of a gain you would pick up on stock turbos by going to 2.5 inch piping. I know it would be even greater on upgraded turbos.
    I was under the assumption stock piping was 2.5", or maybe that's the performance exhaust with the performance package? I guess that's what I have then...just not sure


    Edit: I know I have the performance exhaust, just not sure what the difference is, if there is, in the piping. lol
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    Click here to enlarge Originally Posted by Stucks Click here to enlarge
    Stock exhaust is what, 2.25 inches or 2.36 inches? I have seen conflicting reports. I wonder how much of a gain you would pick up on stock turbos by going to 2.5 inch piping. I know it would be even greater on upgraded turbos.
    Stock pipes are 60mm OD, or 2.36 inches. I just measured them. I wouldn't wast time or money going to dual 2.5 OD pipes.
    Eppur si muove.

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