Is it safe to buy a downpipe?

[Escape Hatch]

It says “exhaust system” though. Stock exhaust flows well enough, a catback won’t even get you gains. I wonder if exhaust system = downpipe

For lower levels of performance this is true but once you surpass 400 whp or so you need more flow.

 

[Keehs360]

For lower levels of performance this is true but once you surpass 400 whp or so you need more flow.

Nah. Old wives tale. Once you remove the stock down pipes, you’re gonna be fine for a very long while. Id wager even 500hp would be fine. Honestly, unless you’re going with a big fat ass full frame turbo, the stock exhaust with a catless downpipe will go a very long way

 

[Keehs360]

Back in the day. Faster turbo swapped srt4’s had this problem. A big ass turbo, even with a downpipe with no cat, would blow the welds on a 3” aftermarket exhaust. They’d just start cracking if the turbo was big enough

the solution was either going 4” after the downpipe or going with a custom 2.5” or 3” side exit exhaust

but we aren’t talking about mopar stage 3 srt4’s. These were fully built running low 9’s

stock exhaust with aftermarket downpipe on a GTI will be fine beyond 400whp. This combination would more than likely be right at the limit on a maxed out vortex xl. Any bigger than a vortex xl I’d would be wise to increase diameter after the downpipe

good exhaust welds don’t just pop or crack from back pressure. But sometimes that back pressure, if it’s strong enough to almost cause restrictions at each bend, can crack welds. This phenomenon won’t happen immediately. Just little by little. Till you can actually hear the exhaust leaks. Especially pre muffler

the only one amongst us that’s more qualified to speak on this particular subject is probably gonna be @GTI Jake since he seems to be the only one making cat back exhausts for the masses. Hopefully he can chime in

jakes cat backs are of high quality. And in pics his welds look really well considered, neat and professional. But even his cat back isn’t invincible

the awe and borla and a few others are three inches till the axle back. Then it shrinks to like 2 inches. I can imagine that shrink spot where it goes from 3” to 2” cracking some if the vehicle has a maxed out vortex xl. Where as jakes version stays true 3” front to back, thusly being able to take more abuse vs an awe or borla

 

[jimlloyd40]

Nah. Old wives tale. Once you remove the stock down pipes, you’re gonna be fine for a very long while. Id wager even 500hp would be fine. Honestly, unless you’re going with a big fat ass full frame turbo, the stock exhaust with a catless downpipe will go a very long way

Pretty sure that EQT runs the stock catback on their 10.46 second quarter mile R.

 

[Keehs360]

Pretty sure that EQT runs the stock catback on their 10.46 second quarter mile R.

Not surprised. Getting to 10 seconds can be done a billion ways. If it’s done with a big ass full frame turbo, the stock exhaust could be a problem.

but yeah. I’m sure eqt probably used their vortex or vortex xl. Those put out some decent cfm.

 

[MrFancypants]

On the mk6 you can gut the precat (and leave the main cat alone) for a free exhaust flow upgrade which is probably about 75% of the way to a new downpipe, but with the advantage of not triggering a CEL meaning you can get away with it even in places where emissions are checked.

How’s the mk7 respond to this? I’m sure that at some point there’s a horsepower level where even this would be insufficient, but I’d wager for most people it’s enough.

 

[jimlloyd40]

Not surprised. Getting to 10 seconds can be done a billion ways. If it’s done with a big ass full frame turbo, the stock exhaust could be a problem.

but yeah. I’m sure eqt probably used their vortex or vortex xl. Those put out some decent cfm.

They used their XL.

 

[Keehs360]

On the mk6 you can gut the precat (and leave the main cat alone) for a free exhaust flow upgrade which is probably about 75% of the way to a new downpipe, but with the advantage of not triggering a CEL meaning you can get away with it even in places where emissions are checked.

How’s the mk7 respond to this? I’m sure that at some point there’s a horsepower level where even this would be insufficient, but I’d wager for most people it’s enough.

I think on the mk7 the first cat is the one that’s monitored. Seems like the second one can be gutted if you’d want to.

 

[MrFancypants]

I think on the mk7 the first cat is the one that’s monitored. Seems like the second one can be gutted if you’d want to.

Well that sucks.

 

[Keehs360]

Well that sucks.

U think? I thought the advantage here would be less fuel smell during cold start. I think?

 

[Escape Hatch]

Back in the day. Faster turbo swapped srt4’s had this problem. A big ass turbo, even with a downpipe with no cat, would blow the welds on a 3” aftermarket exhaust. They’d just start cracking if the turbo was big enough

the solution was either going 4” after the downpipe or going with a custom 2.5” or 3” side exit exhaust

but we aren’t talking about mopar stage 3 srt4’s. These were fully built running low 9’s

stock exhaust with aftermarket downpipe on a GTI will be fine beyond 400whp. This combination would more than likely be right at the limit on a maxed out vortex xl. Any bigger than a vortex xl I’d would be wise to increase diameter after the downpipe

good exhaust welds don’t just pop or crack from back pressure. But sometimes that back pressure, if it’s strong enough to almost cause restrictions at each bend, can crack welds. This phenomenon won’t happen immediately. Just little by little. Till you can actually hear the exhaust leaks. Especially pre muffler

the only one amongst us that’s more qualified to speak on this particular subject is probably gonna be @GTI Jake since he seems to be the only one making cat back exhausts for the masses. Hopefully he can chime in

jakes cat backs are of high quality. And in pics his welds look really well considered, neat and professional. But even his cat back isn’t invincible

the awe and borla and a few others are three inches till the axle back. Then it shrinks to like 2 inches. I can imagine that shrink spot where it goes from 3” to 2” cracking some if the vehicle has a maxed out vortex xl. Where as jakes version stays true 3” front to back, thusly being able to take more abuse vs an awe or borla

Interesting, Ed suggested I replace the GTI exhaust with 3 inch when tuning my car and supposedly the Golf R exhaust is much better suited to power than the GTI. I have read (on this forum) the GTI exhaust becomes restrictive once you cross into the 400 whp territory

 

[oddspyke]

Everyone always seems to think that exhausts have a hard cap or limit that you can't go past, which is kind of true at some point, but really it's that resistance increases with flow and at say, IS20 power levels, you might only gain 5hp by opening up the cat back, but when you're on the 400+ HP range, you could see better gains (maybe 15-20hp? Just guessing here) and at 500+HP, it becomes even more worth it. I think just in terms of bang for your buck, it's not worth spending $800+ on until you're pushing serious power.

 

[zucchinies]

I know Bull-X sells a downpipe that is considered CEL free and is euro 6 compliant that you can still order but it’s pricey. Their cat is at stock location and I know someone who is stage 1 CEL free after 2 years

Im not sure how a Golf R and GTI exhaust would differ too much aside from the tips being dual vs quad. They both go down to a 2.5 inch after the downpipe. A lot of 500+ HP Golf R are on stock catback. Once I get a Downpipe in the future ima sell my AWE exhaust and go back to my stock catback.

 

[mr wrong]

I know Bull-X sells a downpipe that is considered CEL free and is euro 6 compliant that you can still order but it’s pricey. Their cat is at stock location and I know someone who is stage 1 CEL free after 2 years

Im not sure how a Golf R and GTI exhaust would differ too much aside from the tips being dual vs quad. They both go down to a 2.5 inch after the downpipe. A lot of 500+ HP Golf R are on stock catback. Once I get a Downpipe in the future ima sell my AWE exhaust and go back to my stock catback.

I have the AWE "guarantee no CEL" downpipe. Going almost 4 years with no issue, but like the Bull-X it was pretty pricy.

 

[Keehs360]

Interesting, Ed suggested I replace the GTI exhaust with 3 inch when tuning my car and supposedly the Golf R exhaust is much better suited to power than the GTI. I have read (on this forum) the GTI exhaust becomes restrictive once you cross into the 400 whp territory

is20 38 and all the hybrids can not max the stock cat back. not enough cfm there. as far as golf r, dunno