I have a 3inch exhaust on my gst, and was thinking of going 3 1/2 or 4 on my tsi awd.
anyone have bigger than 3inch

i think bigger then 3" exhaust is an over kill
but thats me personally

Do you have a good excuse to go above 3" or do you "just want it"? If you can prove to yourself that anything bigger than 3" is giving you an advantage than go for it.

I can't find it on thier site but I thouhgt Buschurr did a 3.5".

I've got wayyy more than 3"..
You know.. the bigger the better..

problem is...tough luck finding larger than a 3" muffler.

piping is no problem, but you will run into trouble with shops unable to mendrel bend something larger than 3". Maybe truck shops would become your new best friend.

you might also run into trouble with ground clearance if your car is lowered.

still wanna go bigger than 3"? sure...if you must..but I don't see any performance improvements since your biggest restriction is the turbo's turbine housing....

Adding to the clearance issue.. What about clearing the rear axle?
You can go above or below - would it even fit above? And if you went below, would it clear the ground?

Most people find larger than 3" pipes won't clear the axle/suspension.

I thought Buschur's 3.5" was for an EVO.

I was under the impression that 3" exhausts are usually good for at least 11s, if not better. Beats me why you'd want to bother with anything bigger. Even some 500+ HP cars have 3" exhausts, I think.

better idea for you FWD guys....cherry bombs and side pipes...heheheh.....hows that for flow?


..for FWD, you more or less have to go over the axle which even 3" is pushing it (you only got about 6" of ground clearance under the rear torsion beam..)

Correction the Buschur 3.5" exhaust was for John Shepard and the likes. Had the 'frack you supra sound'.

Yup. 3.5" downpipe shows gains when you are above the 450 WHP mark. That is still hallowed ground that only a dedicated few have crossed.

its probabely a very good choice for losing some descent power.


you make the air flow out of the engine heavily turbulant and chaotic.

sounds cool to tell evey one that you have a 4' exhaust but for a 2L engine that is COUNTERproductive.

Perhaps a 2.0 litre N/A engine.

The best turbo exhaust is no exhaust.

3" dp + electric cutoff for life! followed by the stock crap, etc...

2.5 is pushing it for a normal NA 2L.


no exhaust has NOTHING to do with a big exhaust. It is about fluid dynamics. you create extra back pressure with bigger exhaust.


Smaller exhaust is better in terms of laminar flow.

hence there is a optimal point.

I agree with Jonny and that's the setup I'm going with. Only drawback is it's less fun on the street, especially when the 5-0 catches you with it open While racing

Jonny, are you actually running a cutout? How's the valve holdin up? I got the gtec, I hope it holds up. Do you get boost creep?

I dunno if Amin's theory applies in practice, I guess testing's the only way to find out.

Trevor, have you ever run with the exhaust open after the dp? Or even from the turbo if you so desire but that's optimistic. That should give you a decent indication of what you'll gain from the 4". Then you decide if it's worth it for you. I'm guessing it will be next to no difference assuming you have a straight-thru muffler. Go test it.

I know on my fwd with stock exhaust I gained about 3 thents and 2mph by dumping out the dp versus full exhaust. Still a lot to be gained from the dp which I'll be doing... sometime... I wouldn't be so optimistic for you going from your 3" setup to 4" though.

huh?

Extra "back pressure" with a bigger exhaust? Can you explain how that works?

What you are after with a turbo car is the biggest pressure diferential across the turbine wheel. The best way to get that is to have no exhaust after the turbine wheel. (Or the closest thing to it).

Steve,

open air is open air. But when you make the exhaust bigger the infact disrupt the flow of air.
you need lower bck pressure in ANY engine, that is obvious. But:
when the exhaust has the optimal width the flow of air from the engine is enough to create a steady laminar flow throughout the exhaust and have almost no disruption. it is always moving out.

but when it is too big, the air might circulate and the flow becomes turbulant. curly traces of air around the wall or in the centre. that infact decreaes the flow of air or atleast the "EASE" of flow.

open air in a moving object is a whole other issue. cause the air doesn't get trapped in open air.

Guys have gone 12's and 11's on 2.5" systems, no need for bigger unless you want more sound...

Ok, but keep in mind how much a rotating turbine blade disrupts airfow.

Anything PAST that point is non consequential IMHO.

FWIW: any "fluid dynamics" guy I've talked to HATES the term "back pressure". There's no such thing. It's a restriction.

But a flow restriction does cause a rise in pressure behind it, so it makes sense

Maybe it's not a fluid dynamics term but it works

I don't know if you can even classify turbulence as a restriction. I tend to think of restrictions being physical. But enough about terminology.

I say we let Trevor do his 4" exhaust and he'll do the fluid dynamics experimentation for us

But to be fair I can guarantee that the money can be put to better use elsewhere.

Yes, it does make sense.... and you're right, it's a term that's used often enough.

I can't see a 3" exhaust being a restriction at all for most people, so going to a 4" shouldn't make any improvement.

But, hey... if you wanna build one, why not?

No sh!t, you want 3.5"? 4 "? kickass, do it! I hate hearing techno-babble dribble out of peoples mouths like they know wtf they are saying, said with such conviction you would have to be an idiot not to believe them.

A local tuner just brought in a shipment of 22gauge 3.5", lightweight for sure, and with mandrel bends it will flow all you can throw.

Will I buy it? maybe not, but its cool people DO that sh!t rather than sit on their hands NOT doing fark all and guessing the outcome.

Where Fraser?

The Foo, L&R racing. he has 3.5" SS and 4" SS in the 22 gauge. I guess this is for guys who want to out-supra the Toyota guys.

Thanks Fraser.

3" or larger isn't a question of do I need it, obviously the larger exhaust will have less restriction.

The question is will the difference in restriction make up for the extra weight of the 3.5" (or larger) exhaust. Eventually the extra weight you will be adding to get this less restrictive exhaust will outweigh the gain to be had by less restriction.

I believe 3" about at the limit of restrictin vs weight. if you want to spend the money to have a 3"+ echsust by all means go for it, is it worth the extra weight and price? I wouldn't think so but it's your car and money, not mine.

From www.magnaflow.com:

For turbocharged engines, 2.5-inch is the minimum size pipe that you would want to run, even for the smaller engines. For 2,000cc and bigger engines, 3-inch works well, and for bigger engines the biggest (usually 3.5-inch) you can find is appropriate. It is almost impossible to have too big of an exhaust on a turbo car.

I would go with a 3" Trevor.

you don't worry yourself too much.

Flow calculations and fluid dynamics go in the trashbin once the turbo gets going. Steve is right, it's all about the energy used to spin the turbo. For turbocharged cars, no exhaust is the best exhaust.

For non-turbo cars, there is an "optimal" point where the exhaust pulses move along the pipe most efficiently. If you go bigger than this you end up trading low-end torque for high-end horsepower - a tradeoff some, but not all, people are willing to make.

"Backpressure" is a bullshit automotive term made up by people who didn't know any better at the time. Still, if we must use it, bigger exhausts do not create more "backpressure", they create less.

And I still think he's going to have problems getting a 3.5"+ system to clear everything. There are seriously fast cars running 3" exhausts, so I still don't see the point.

What is a turbo car when the turbo isn't spooling any boost?
By god, it's just like an NT!

So you get a BIG exhaust to support your BIG turbo that spools much later than the stock turbo.

Would the "too big for an NT" theory apply to a turbo car before any boost is spooled? I'm guessing yes. If you apply that theory, then too large an exhaust WILL affect your low end, so long as your turbo doesn't spool straight off the line.

I could be talking out of my tailpipe...
So feel free to discredit this however you may

Even if the turbo where stopped, you've still got essentially a fan blade in the path of exhaust.

You want some restriction (or backpressure, or whatever you want to call it)? You got it!

I agree with Steve.

Nobody cares. Why would they?

Turbo cars are designed to perform under boost. Nobody cares what happens when they're not boosting. Show me one guy who runs around off the boost all the time, much less anyone who does the 1/4 mile without any boost. :rolleyes:

If you wanted a turbo car to make power when not under boost, you would change the pistons to a higher compression to make more low-end torque. Nobody would care about spoolup time on the turbo because we'd all be modifying for unboosted performance. Essentially, everyone would be converting from turbo to non-turbo - a generally pointless exercise if ever I heard of one.

Sean I think you may have missed my point..
It only applies to people with upgraded turbos.

With a bigger turbo you spool later, that's why you put in higher compression pistons - to get some low-end back.

Could a "too big" exhaust hurt low-end performance on an upgraded turbo set-up?
That was my question

No, because of what Steve said.
"Even if the turbo where stopped, you've still got essentially a fan blade in the path of exhaust."

More than enough "backpressure". I think "backpressure" is necessary because of cam timing/overlap issues. In this case, you got it.

To answer your question, the more open the exhaust the better, at low rpms as well as high, because it means the pressure after the turbo is smaller, so it spools faster. Turbos are driven by the pressure differential between the exhaust gases before- and after the turbine, right?

fair enough,

this is some technical discussion now. thanks Sean.

[/qb][/QUOTE]you don't worry yourself too much. [/QB][/QUOTE]

I am not fluent in broken English, what is the intent in this statement.

And please feel free to add more of your delusional self-taught techno babble, its funny as hell

If you can explain where any of this discussion is going wrong, Fraser, you go right ahead.

I don't think so.

Anyone who thinks our engines, stock, have any kind of low-end grunt to them is sorely mistaken. They don't have any kind of low-end torque, at least not when compared to a nice non-turbo V8 engine. Even the stock setup is intended to perform only when boosting.

One might argue that 2G cars are a little different, and they are. The smaller turbo and higher compression design of that engine was specifically intended to restore some low-end torque and make the car more "driveable". And it did, at the expense of high-end power. But even 2Gs don't have nearly as much oomph down low as most performance NTs, as far as I know.

Also as far as I know, people who put in higher-compression pistons do not do so to regain low-end torque. They do it to get more overall power out of the engine, true - but because they want more top-end power, not more low-end power. Low-end power is just a side effect - kind of a perk, if you will.

Now, I suppose I could be wrong. But I have never seen anyone really serious about making big power suggest that you should install higher-compression pistons to combat turbo lag. The preferred solutions to lag is to get a less laggy turbo setup.

Neither have I ever seen anyone making big power complain that the car has no low-end torque. Nobody cares. Drag racers certainly don't give a crap, and autocrossers or road racers just go with smaller, less laggy turbochargers that they can take full advantage of.

Having said all that I suppose you could install higher compression pistons if you wanted more low end. I've never considered it before, but it would work, provided you didn't mind running less boost on an otherwise identical setup.

I just can't figure out why anyone who wants low end power would want a DSM in the first place. It's a terrible platform for that kind of thing, especially when compared to the V6 and V8 cars.

Plus, with the turbo setups you can get these days, there isn't much excuse for the turbo not spooling almost identical to stock. Full boost by 3500 RPM is quite commonplace these days.


But YES, I believe a big exhaust will always affect your low-end power, turbo or non-turbo.

I think Steve and Steve disagree with me here. But I'm not aware of any reason why an NT would require an exhaust restriction because of camshaft/valve overlap issues. As far as I know it's all about the cylinder scavenging that arises from the speed of the exhaust flow through the exhaust piping. Can anyone elaborate on this?

I do disagree, sort of...

I agree that any exhaust after the turbo will add to restriction. (an exhaust after the turbo, HAS to be more restrictive than no exhaust after the turbo...)

Whatever you've got after the turbine wheel is part of a system. Everything in that system affects how the car behaves. There ARE going to be differences between a 3" exhaust, and a 4" exhaust for example.

However, having said that I still believe that pressure differential across the turbine wheel is the major factor here. I don't think anything else in the "system" is going to come close to affecting the car's behaviour more than that.

So, yes, I agree that the exhaust WILL affect the low end of a turbo car. I just don't think it will affect it enough to be noteworthy.

As a side note: the above is all based on the little squirrel cage spinning in my head. It's based on nothing but the (mostly) common sense I would like to think I have..