How to Buy Performance Downpipes

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How to Buy Performance Downpipes

The downpipe is a vital part of any vehicle's exhaust system, running between the header and the catalytic converter. Many buyers pay very little attention to the downpipe because it does not have a major effect on the performance of a naturally aspirated petrol engine. As long as the downpipe allows for the reasonably free flow of exhaust gasses to the catalytic converter it is doing its job, and for most drivers it can safely be ignored for performance purposes. Most naturally aspirated cars get more benefit from a header than a downpipe.

Where downpipes come into their own is with turbocharged engines, as the downpipe is where wastegate is located, and this is where the turbocharger gets the energy to spin the compressor. A high performance downpipe can greatly increase the efficiency with which the exhaust gas reaches the turbocharger, and thus provide a noticeable increase in performance. Downpipes are a great purchase for anyone concerned with the performance of their turbocharged car. They are also easy to buy.

Understanding Engines and Turbochargers

The first step in understanding how a performance downpipe can benefit a car owner is to understand how a turbocharger, and to a lesser degree an internal combustion engine, works. Both the turbocharger and the engine are essentially pumps. This being the case, the greatest enemy of either device is restriction. Exhaust restriction in a car engine can cost it power by making it work harder to clear the cylinder for the next stroke, using energy that cannot be used to move the car. Intake restriction curbs the charge, the mixture of air and fuel that provides combustion, limiting power that way.

Turbocharger Basics

At base, a turbocharger is a type of supercharger. What it does is compress, or supercharge the air fuel mixture before it enters the cylinder. This increases the horsepower by enabling more complete combustion of the charge. It is called a turbocharger because it is powered by a turbine driven by the engine's exhaust gases. The big benefit of this, and one reason why turbochargers have largely replaced other superchargers, is because this system lets the turbo reclaim energy that would otherwise be wasted. This makes turbochargers a highly efficient way to increase horsepower without increasing engine size.

The Importance of the Downpipe

Where the downpipe enters the equation is that it is where the turbine intake is located, after the header and before the catalytic converter. Downpipes are critical to the operation of turbochargers, as they feed the exhaust gas to the turbine that drives the compressor. As the exhaust flow increases, the turbine spins faster and faster, spooling up until it is running fast enough for the compressor to start producing boost. The big advantage of a performance downpipe is that it provides less restriction than a standard one, thus allowing the turbine to spool up faster and start providing boost earlier. This essentially translates into free horsepower for the engine.

What Makes a Performance Downpipe

Every turbocharged engine has a downpipe, but not all downpipes are created equal; this is especially true of those on mass-produced vehicles. As cars have become smaller over the years, their engine compartments have grown progressively more crowded. A modern car has much less room under the bonnet than one from the 1960s. This means that in order to fit everything in, the downpipe often has to be curved as there is just no way to run a straight pipe from the exhaust manifold to where the turbocharger has to be to do its job.

The Problem With Curves

While there is nothing intrinsically wrong with curves in and of themselves, there are performance concerns about the curves in many stock downpipes on turbocharged cars. The issue comes from the way in which the pipes are manufactured. Many downpipes are shaped using an inexpensive crush bending process. The problem with this process is that it produces an uneven surface inside the downpipe with a number of ripples and ridges. These imperfections create turbulence and reduce exhaust flow, thereby robbing the turbo of power. Performance downpipes are smoother, without these internal ripples, and thus allow for better exhaust flow and more power from the turbocharger.

Things to Look for When Buying a Performance Downpipe

While a performance downpipe sounds like a great idea for all drivers, as in who would not want free horsepower, they may not be appropriate for all cars. There is clearly no point in worrying about one unless the buyer has a turbocharged engine, as stock downpipes are more than adequate for naturally aspirated engines. Prospective purchasers should also note that not every turbocharged vehicle benefits from an aftermarket performance downpipe. Some manufacturers put a lot of care into the design of their turbocharger systems, including the downpipe, and so any gains from the use of an aftermarket model are minimal at best. That being the case, there are three things to look for before buying an aftermarket performance downpipe.

Is it Proven to Improve Performance?

Not all performance aftermarket downpipes actually improve performance. Some vehicles show only minimal results from the use of an aftermarket performance downpipe, while others have been known to see a gain of as much as 40 horsepower. A wise buyer is one who does the research to see which category the vehicle and downpipe combination they are considering falls into. Knowledge is every buyer's greatest tool.

The Number of Bends in the Stock Downpipe

The greater the number of bends in a stock downpipe, the more likely a given vehicle is to benefit from the use of a performance downpipe. This is especially true when the stock downpipe uses crush bends, as several of them can cause a significant reduction in exhaust flow. It is relatively easy to make a straight pipe with a smooth interior, less so to produce a smooth interior if the pipe has a large number of curves or bends.

Boost Level of the Turbocharger

Some vehicle owners like to spend time tuning their engines, and owners of turbocharged engines are no exception. One of the best ways to increase turbocharged performance is by increasing the boost level of the turbocharger, as increased boost normally translates directly into increased power. The concern here is that the greater the level of boost, the more important exhaust flow becomes. A stock downpipe that allows enough exhaust flow for the stock setting may not allow enough for a higher level of boost.

Performance Downpipe Checklist

Before buying or installing a performance downpipe, a prospective buyer should take a look at the following checklist to see if a performance downpipe is right for them.

Factor

Performance Downpipe

Is the engine naturally aspirated?

No

Is the engine turbocharged?

Yes

Are there a lot of bends in the downpipe?

Yes

Has the boost setting been increased?

Yes

Does this downpipe increase performance?

Yes

Prospective purchasers should consider all these factors before looking into buying a performance downpipe. While not all turbocharged engines may benefit from an aftermarket performance downpipe, some may effectively be already fitted with one from the factory, the answer is yes in the above table because only turbocharged engines gain any significant benefit from one.

Buying Performance Downpipes on eBay

One of the best places to buy performance downpipes is eBay. The site has a wide variety of engine parts available, all no further away than the search box on every page. All you need to do is put your needs in the search box and watch the results appear. Once you have your results you can use the filters in the sidebar to limit them to just those which meet your criteria. You can narrow them down by everything from make to price range, or even seller location. Then, you can use eBay's sort function to arrange the results so that they focus on the ones that best fit your needs.

After you have found the right performance downpipes, the next step is to choose a seller. The best place to do that is on their profile page, where you can see everything from their location to their feedback rating. You can also see if they can bundle other performance parts with your downpipe, or even allow you to save on shipping by picking your performance downpipe up in person if you live close enough.

Conclusion

As turbocharged engines become more common, so does the performance impact of the downpipe. For naturally aspirated engines, the restriction created by a downpipe is almost unnoticeable; something that is not the case for turbocharged engines. Because turbochargers depend on exhaust flow to function, overly restrictive downpipes can have a significant effect on both horsepower and performance. One of the best ways to eliminate this is with an aftermarket performance downpipe that provides smoother exhaust flow to the turbine, improving both power and turbocharger response.

Perhaps the biggest issue with stock downpipes is the way they are bent. Many are bent to fit the engine compartment using a crush technique which produces ridges and ripples inside the downpipe. The smooth interior of a performance downpipe helps the exhaust flow more freely and increases the effectiveness of the turbocharger. Anyone who owns a vehicle with a turbocharged engine should at least consider looking into the benefits of a performance downpipe.

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