Is a 3" exhaust actually needed for tuning/turbo upgrade?

[volkswagensRus]

Let me preface this by saying that I'm well aware that the less restriction on the intake/exhaust side of any car, especially a forced induction car, is a good thing... but is it really needed?

My build will be as follows
1- FTG full billet k04-15xl turbo kit
2- tubular manifold
3- 550cc Bosch injectors
4- motoza tuning

This is my daily driver. I really am nervous about going w/ the 3" turbo back kit I've been eyeballing for a few reasons (I work in the city.... Don't want to be hassled by cops... the noise might annoy ME too). So I've done some research, and there is a large amount of people saying that for under 300 crank horsepower the stock exhaust + a good downpipe is fine.


If that's the case, I'm prepared to order my 3" down pipe right now (stock one has busted flex pipe anyhow.... so its win-win for me). Even w/ stock exhaust the 3" downpipe will still increase the sporty sound of the car, but NOT make it obnoxious or unbearable when driving..

[garytightpants]

This is my daily driver. I really am nervous about going w/ the 3" turbo back kit I've been eyeballing for a few reasons (I work in the city.... Don't want to be hassled by cops... the noise might annoy ME too). So I've done some research, and there is a large amount of people saying that for under 300 crank horsepower the stock exhaust + a good downpipe is fine.

your statement confuses me. A 3" exhaust doesnt need to be straight-piped or loud. just get one with muffler/resonators. I dont see you getting hassled by cops unless you drive aggressively or something like that.

[volkswagensRus]

But it does without saying that a stock exhaust + 3" downpipe would be even quieter than a 3" w/ mufflers or baffling. So if I can get away with stock exhaust + 3" downpipe, thats the way that I'm leaning. For my weekend z51, sure... 3" + long tube headers is fine because I drive it 1x per month. For every day driving, quieter is better to a point. I know that a 3" downpipe would definitely increase the "meanness" when under WOT and would make high-rpm shifting sound awesome. But under most circumstances, it will be nice and quiet.

[Davdraco1]

If your in the city and worried about noise, I would just do a test pipe or gutted cat and keep the rest of the exhaust. Now that you want to upgrade the turbo and get more power, I'm not sure where you are going to use it in the city and you will obviously need a larger exhaust. Don't be a dick around the cops and you will be fine.

[volkswagensRus]

If your in the city and worried about noise, I would just do a test pipe or gutted cat and keep the rest of the exhaust. Now that you want to upgrade the turbo and get more power, I'm not sure where you are going to use it in the city and you will obviously need a larger exhaust. Don't be a dick around the cops and you will be fine.

Live in the country, work in the city. Plenty of space to strut the car. So you are saying that I without a doubt, need a larger exhaust in order to run those mods? Just a larger downpipe wont suffice?

[Avant Nate]

I was always under the impression, the larger the exhaust, the harder to be quiet. I didn't go with a 3 inch exhaust for 300hp, because my plans have always been for 500. That being said, I would stick with a smaller exhaust. I was unimpressed when I went from stock exhaust to 3 on a eliminator.

[Seerlah]

2.5" for your setup with hfc or test pipe.

[volkswagensRus]

If I MUST upgrade the exhaust, I'm going w/ a 3" setup I found. But at this point I'm trying hard to keep the stock exhaust.

[crazyquik22023]

2.5" for your setup with hfc or test pipe.

x2 3" sounds like overkill for your goals and setup

[SynapticA4TQM]

Here's the thing... The stock exhaust has crimp bends and however many miles your car has. It's also only 2"... Stepping down from a 3" downpipe to a 2" pipe is a huge reduction.

I recently had the exact same concern. For myself I have a thing about not being louder than I am fast. So one way to handle that is to have a good resonator or two along with the muffler in the back... Which equals $$$. I decided on a 2.5" system that's stainless and resonated. Sound bites I've heard have it sounding real nice, but not too loud. The other thing about it is that it's got mandrel bends and is a larger diameter. So better flow than stock on two fronts. We're my goals for more power I might have planned ahead and gotten a larger diameter exhaust.

Lastly, turbo chargers do MUCH MUCH better when they're able to breath more easily. You would gain some with the 3" downpipe, but it would be wildly restricted by the stock exhaust from the downpipe back.


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[bakedziti]

Personally, I don't feel that our police department would bother you. I do think there's the potential to bother yourself however. In the B8 section, I believe the quickest A4 is running a stock exhaust except the downpipe. As others have said however, a resonated exhaust sounds nothing like a non-resonated, so it depends on what you go with.

[volkswagensRus]

Personally, I don't feel that our police department would bother you. I do think there's the potential to bother yourself however. In the B8 section, I believe the quickest A4 is running a stock exhaust except the downpipe. As others have said however, a resonated exhaust sounds nothing like a non-resonated, so it depends on what you go with.

The buffalo police officers are awesome.... they are really great guys, the ones that I've met. But I was indeed more concerned with myself over the police in terms of sound. Thats interesting that the quickest A4 has a stock exhaust. I've also heard that the stock downpipe, stock cat and stock exhaust manifold are the largest restrictions on these 1.8t's, and I would be replacing all three of those.

[bakedziti]

The buffalo police officers are awesome.... they are really great guys, the ones that I've met. But I was indeed more concerned with myself over the police in terms of sound. Thats interesting that the quickest A4 has a stock exhaust. I've also heard that the stock downpipe, stock cat and stock exhaust manifold are the largest restrictions on these 1.8t's, and I would be replacing all three of those.

There's no doubt that those are the most restrictive portions of the exhaust, but I believe that changing those our for a HFC or test pipe also comes at the cost of my ears. I'm currently on a stock exhaust with some fears of drone if I switch. I work in the southtowns, but live in the city, so my commute is likely a similar distance just without the traffic.

Edit: The police here don't generally bother you, unless you're doing something really dumb, but even then tend to be pretty good guys. The ones I have met have all been pretty cool, so I agree with you there.

[volkswagensRus]

There's no doubt that those are the most restrictive portions of the exhaust, but I believe that changing those our for a HFC or test pipe also comes at the cost of my ears. I'm currently on a stock exhaust with some fears of drone if I switch. I work in the southtowns, but live in the city, so my commute is likely a similar distance just without the traffic.

Lol I live in the southtowns and work in the city. From all of the cars in real life and youtube videos I've heard of catless downpipe + stock exhaust cars, they sound AWESOME under wot but mostly quiet when just putting around. My buddy has a pretty modded 11 second BMW 3 series and w/ ONLY a downpipe + stock exhaust his sounds mean as hell too, but not obnoxious in the slightest bit.

[Seerlah]

Stock exhaust is extremely restrictive. Person who told you just a downpipe, test pipe, or hfc would suffice was wrong. If you want a 3" system, more power to you (see what I did there). But it won't give you more power than a 2 5" system would, with the 2.5" being rather ideal. And for a couple reasons. Main one is it's not an easy task making a small displacement engine sound good on an exhaust that size. The b5 s4 has an upgraded 3" system for comparison. And that car has more displacement and more turbos.

[GOODBYNAAIR]

For what your trying to run 2.5 will be fine and it should sound good. Only need 3" if going gt28 or bigger. The stock exhaust is something like 2.25 but that's not the same as a high flowing 2.25 exhaust.

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[Seerlah]

Pretty sure stock exhaust is sub 2".

[SynapticA4TQM]

I just read last night that the stock exhaust is 2.17"


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[Davdraco1]

Didn't know you lived in the country and had places to do spirited driving. I have the cx racing 3 in exhaust and a gutted cat. It's essentially straight pipe but for the price I couldn't argue. It's quiet at idle and if your jus putzing around town it's not bad. It is very loud at WOT, but I don't mind that. For what you need, a slightly larger resonated exhaust sounds perfect, just like everyone is saying to get. Idk if there's an exhaust shop by you that would build one for cheap. The borla exhaust can be had used cheap, but anything new is going to cost you 600$+

[garytightpants]

in my hands on experience, stock exhuast bigger than 2", but not quite 2 1/8". 2 1/8" stuff will usually work though.

For your goals, like others have said, a decent mandrel-bent 2.5" system with decent flowing mufflers and resonators would be ideal. that being said, you could get away with just a testpipe or a gutted stock cat. i like the gutted cat over the test pipe, as it also acts as a poor mans expansion chamber.
The upgraded exhaust will also help with reducing backpressure, which helps reduce EGT's.
it will aslo help spool time and reduce lag over just a tespipe. will also help with boost taper depending on your desired boost levels. (that has just been my experience.)

As far as noise goes, my girlfriends jetta (1.8t) has a catless 3" dp into 2.5" exhaust with only a single 30" long glasspack resonator, and unless your romping on it it sounds stock driving around and has only the slightest raise in volume when accelerating lightly.
With inner city police, they generally have way more important things to deal with than a loud exhaust. unless you are endangering other people they wont even bat an eye at you.
For a year i daily-ed a 3" turbo back straight-piped b5 in boston (worked and lived in city) and drove rather aggressively like all the other massholes, along with frequent brakestands, launches and sliding u-turns and never once was bothered.
looked and sounded like this

[adam044]

2.5" for your setup with hfc or test pipe.

Yup

[volkswagensRus]

So something I'm a little hung up on. My buddies ~2005 BMW 335i has a stock exhaust diameter of ~2.36". He has a tune and 3" downpipe leading to a stock exhaust system, and made 380whp and ~420 ft/lbs of torque on it.

With that being said, everything I've gathered about my 2001 AWM stock exhaust size is it's right around 55mm, which is right around 2.16". The most restrictive part of the exhaust is downpipe, exhaust manifold and the cat.

My conclusion: If a bmw can make 380whp with a massive inline six 3.0 liter with twin turbos on exhaust thats only 1/5 of an inch larger, why should my stock exhaust be a restriction on an engine 1.6x smaller?

[SynapticA4TQM]

(Edited out) ... I don't know how bmw makes their exhaust, but it may be freer flowing than Audi's stock exhaust... Especially when his car is at a minimum 4 years newer and is the higher line of the 3 series models... Granted it's not an m3... But it is higher up in the model line. It's meant to have more power than the lower models. Compared to Audi, a 325i may be like an a4, the 335i like an s4, and the m3 like an rs4 (very loose comparison there)



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[SynapticA4TQM]

Oh, my point for the model comparison is that bmw may have designed the exhaust system better since it's a higher trim than the lower models... Like Audi did with the s4 compared to the a4. Twin turbos aren't the only performance difference between the a4 and the s4 obviously... That said, your comparison is off point by being NA vs FI, and is pushed further out by comparing different model levels.


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[tar]

Stop trying to compare ur exhaust to a bmw its stupid.

And to the guy above me what 335 is na? And how does a na make that much power in ur mind. Use some logic

[SynapticA4TQM]

My bad... Not very familiar with bmws... Thought it was similar to the 330... Shrug...


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[Sumo337]

Frankenturbo F21
APR Carbonio
Forge DV - yellow spring
550cc injectors
Private stage 1 tune
Runnin 21psi
42DD 3" turbo-back no cat

[vrmm]

I've always thought stock was 1 7/8" id... But I may be thinking of a different car.

imo 2.5" will be loud even with a resonator and good muffler. There's not really any way around that unless it's a stock like muffler with a zillion baffles. I hate loud exhaust, but it's required on my car :/ when I say loud I mean anything louder than stock. If I were in your shoes with a k04 I would go catless and get a legit downpipe. Not like a stock boral with the crazy restrictive bend in it. And leave the rest stock.... But that's just me.

[volkswagensRus]

Oh, my point for the model comparison is that bmw may have designed the exhaust system better since it's a higher trim than the lower models... Like Audi did with the s4 compared to the a4. Twin turbos aren't the only performance difference between the a4 and the s4 obviously... That said, your comparison is off point by being NA vs FI, and is pushed further out by comparing different model levels.


Oozed from a pustule of thought somewhere within the recesses of my mind...

The 335i is a 3.0 liter inline 6 twin turbo. It's 1.6x larger than my 1.8t and only has .2" larger exhaust, stock. Granted, you might be correct in that it could possibly be a more efficient, free flowing exhaust. That I do not know.

Stop trying to compare ur exhaust to a bmw its stupid.

And to the guy above me what 335 is na? And how does a na make that much power in ur mind. Use some logic

I'm comparing my 2.16" exhaust to my buddies 2.36" exhaust that runs 380whp through it. I think thats a pretty damn fair question.

I've always thought stock was 1 7/8" id... But I may be thinking of a different car.

imo 2.5" will be loud even with a resonator and good muffler. There's not really any way around that unless it's a stock like muffler with a zillion baffles. I hate loud exhaust, but it's required on my car :/ when I say loud I mean anything louder than stock. If I were in your shoes with a k04 I would go catless and get a legit downpipe. Not like a stock boral with the crazy restrictive bend in it. And leave the rest stock.... But that's just me.

the stock downpipe and cat are DEFINITELY smaller than 2.16".... supposedly the cat/downpipe are ~1.78". Which is exactly why I'd go w/ aftermarket catless DP + tubular manifold. One would think 2.17" would be plenty large beyond the DP. I think I'm gonna run a 3" 034 Motorsports DP

[SynapticA4TQM]

But going from 1.78" to 2.17" diameter promotes better flow characteristics for a turbocharger... Going larger to smaller does the opposite. There was a post on FI exhaust theory that explained that the best possible flowing exhaust would gradually step up to larger and larger diameter piping. Reducing the diameter will create back pressure...


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[volkswagensRus]

Every dyno I've seen of an aftermarket catless downpipe has shown gains on stock exhaust though..

[SynapticA4TQM]

Ya know what? I give... There's information available on exhaust flow dynamics and turbo exhaust design. I'm not being rude when I say this, but go ahead and do the high flow manifold, test pipe, and downpipe that you're thinking about. I honestly hope it does what your hoping it does, and isn't too loud. However, almost every post (except yours) has led to the same conclusion... a 3" would be overkill, but a 2.5" turbo back would be an ideal compromise for both sound levels and performance enhancement.

You will see some gain by installing those parts, but replacing the rest of the stock exhaust parts after that would allow you to gain more, I guarantee it! But it sounds to me like you don't really want to hear that...


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[volkswagensRus]

Ya know what? I give... There's information available on exhaust flow dynamics and turbo exhaust design. I'm not being rude when I say this, but go ahead and do the high flow manifold, test pipe, and downpipe that you're thinking about. I honestly hope it does what your hoping it does, and isn't too loud. However, almost every post (except yours) has led to the same conclusion... a 3" would be overkill, but a 2.5" turbo back would be an ideal compromise for both sound levels and performance enhancement.

You will see some gain by installing those parts, but replacing the rest of the stock exhaust parts after that would allow you to gain more, I guarantee it! But it sounds to me like you don't really want to hear that...


Oozed from a pustule of thought somewhere within the recesses of my mind...

No I'm definitely trying to avoid an aftermarket exhaust if I can. If it will hurt performance too much when upgrading, then so be it I guess I'll have to bite the bullet. But I'm really trying hard to circumvent that.

[SynapticA4TQM]

It'll hurt your potential performance gain, not your existing performance... You've never said which 3" system you were considering, but if be willing to bet that compared to it, you could gain more bang for your buck, while saving money vs getting the 3" system.

Is your real concern cost? Installation? Noise level? Why the resistance to replacing the stock system?


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[Davdraco1]

Aftermarket won't hurt performance. Find a cheap exhaust and add good mufflers and resonators to it. Have a shop weld them in.

[volkswagensRus]

It'll hurt your potential performance gain, not your existing performance... You've never said which 3" system you were considering, but if be willing to bet that compared to it, you could gain more bang for your buck, while saving money vs getting the 3" system.

Is your real concern cost? Installation? Noise level? Why the resistance to replacing the stock system?


Oozed from a pustule of thought somewhere within the recesses of my mind...

There's a few reasons I've strayed from it. First, the noise. I want a car with some throat... thats fine. I do NOT want a car that screams when I just putt-putt about. Next thing, cost. I've sunk money into this car that I wasn't expecting, which has set me back in terms of mods. If I could knock ~550 dollars off of total costs (the 3" cxracing exhaust + install), then I'd be that much further ahead.

Aftermarket won't hurt performance. Find a cheap exhaust and add good mufflers and resonators to it. Have a shop weld them in.

Money + headaches are my primary concern.

[SynapticA4TQM]

Fair enough... I think I mentioned that I was in this exact same choice. It was between the cx racing 3" system and the SSAC 2.5" exhaust system. I ended up choosing the SSAC for all the exact reasons you state... Budget and noise level. A lot of the reviews I've read said that the cx racing was a decent enough system, but everyone recommended cutting the muffler that comes on it off and replacing with a borla or a Magnaflow... Or muffler of your choice.

It is also my opinion that a car shouldn't be louder than it is fast... Yeah the screaming exhaust when you've only added 10% power ... Screams poser/loser to me.

Cost wise the two are very close the same price I believe, except the cx racing exhaust (following others recommendations) would have the additional cost of a muffler. Install wise, I'm look forward to a pretty straight forward install with the way the SSAC system came... Here's a pic of it sitting in my living room...



It came with a couple fat 1" wide clamps and in 3 pieces.


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[demonmk2]

Youre over thinking this....

[tar]

Youre over thinking this....

Wants to avoid headaches, goes with ftg turbo and ssac stuff

Op 2.5 won't be bad at all go with a quieter brand avoid ssac/cx tons of soundclips, look at f21 setups for similar turbo noise. I have a cx, and borla right now, and before had ssac, and magnaflow. Borla is best sounding. Ssac fitment was meh, and cx is still in box it has ugly tips, and a stupid 2.5 taper flange on dp even tho listed at full 3.

[SynapticA4TQM]

Wants to avoid headaches, goes with ftg turbo and ssac stuff

Fwiw, I've yet to actually see someone who personally had issues with his turbos post anything first hand. However, I've have seen a number of posts of people who have purchased turbos from FTG state that they have better than 20k and 40k miles on their turbos without any issues.

Lee has always been pretty cool with me, my turbo has around 18k on it and I'm happy with it. As far as the exhaust goes, I've not installed mine yet due to sickness and weather.

What I have seen a bunch of is a bunch of people who "know" someone who had lots of issues. Anyone else can choose to proceed how they like, but I'm gonna trust personal experience.


Oozed from a pustule of thought somewhere within the recesses of my mind...