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Can You Run an Aftermarket Downpipe With a Stock Exhaust?

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Unleashing that perfect growl from your car’s exhaust or inching out those extra few horses is often the goal for many car enthusiasts.

Aftermarket downpipes serve as one such popular modification, but a common question that people often ask is: “Can I run an aftermarket downpipe with my stock exhaust system?”

Ultimately, the answer is yes in the majority of cases. However there are a few things to be aware of before you do so which we’ll cover in this guide.

Exhaust Diameter

When you opt for an aftermarket downpipe, chances are you are going for one that is larger in diameter. For example, one that is 3 inches in comparison to the 2.5 inch downpipe on your stock exhaust system.

It’s no secret that larger downpipes can leader to greater power gains by reducing backpressure and helping the exhaust gasses exit quicker.

With this in mind, you need to be aware of the size of the piping that your downpipe joins to on the stock exhaust.

What section this joins onto will depend on your exhaust system, but will usually connect to what is referred to as the “cat-back” section. 

This will usually be comprised of a backbox/muffler and resonator. Check the sizing of this section to ensure it will fit up correctly. 

Many manufacturers of downpipes create them to be able to fit up to the standard exhaust system in most cases, but it’s always good to check.

If it won’t fit, you can always use an exhaust reducer sleeve to help mate them up.

Sound Implications

When it comes to sound, an aftermarket downpipe can have an impact even with a stock exhaust. The larger diameter and freer-flowing design of an aftermarket downpipe often create a deeper, more aggressive exhaust note.

In most cases though, this change isn’t as prominent as upgrading other sections of your exhaust like the muffler/cat-back section. 

If increased sound is your primary goal, then you may want to start by opting for an aftermarket cat-back. This may help give you the sound you desire and if it isn’t loud enough then you can always upgrade the downpipe later on to make it even louder.

Performance Gains

When looking to increase power by upgrading the exhaust, the downpipe usually yields the best returns for the money spent.

Most stock downpipes aren’t fully optimised for maximum power, even on performance cars. Car manufacturers design them with sound levels and budget in mind as well, so you can usually always get some power gains from upgrading the downpipe.

That said, you can also get some power gains from upgrading to a more free flowing cat-back section as well. 

So if maximum power if your goal and you don’t mind your exhaust being a fair bit louder, consider upgrading the rest of your exhaust as well to really get the most performance.

It’s also recommended to get a tune/remap after fitting a downpipe.

The adjustments through a tune aligns the ECU’s parameters to account for the improved exhaust flow, unlocking your car’s full potential.

Happy modding!