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The Cheapest Exhaust You've Ever Heard Of, Part 1

You simply don't have to pay huge dollars for a performance exhaust

by Julian Edgar

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At a glance...

  • Sourcing cheap exhaust bits
  • What to look for
  • Diameters and designs
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This article was first published in 2005.

Do you think: ‘WTF?’ when you look at the price of aftermarket exhaust components like mufflers, cat converters and exhaust tips? After all, there’re mostly just bent bits of metal... Well, if you’re running a modified car developing under about 150kW (200hp), take a good look at this story. In it you’ll see how we sourced a stainless steel braided flex joint, resonator, cat converter and stainless muffler for a total cost of AUD$135.

The bits are just crap are they, then? Nope – in fact, they’re of a quality superior to many aftermarket goods. So they must flow really badly? Again – no. All right then, it was a ‘mate rates’ job – someone just about gave you the bits? Wrong: they were all bought at normal commercial rates.

In this case we were assembling the exhaust components for a low powered modified car, but with the exception of the rear muffler, they’d also be good for power outputs up to the 150kW mentioned above. (And we saw plenty of mufflers at the same price that would be happy at this higher power figure.)

So what’s the secret? Simple: take advantage of the fact that people love ripping off near-new exhausts and replacing them. If you’re running a modified car that has less power than those other cars had as standard, you’ll be laughing all the way to the bank.

The Rationale

While many think that a modified car with less than 1000kW is for losers, that just ain’t so. In fact, as I said at Driving Emotion, a lightweight, good handling car with a sweet spread of torque is fantastic on a winding road – even if the kilowatt number is relatively small. And in modification, aiming for an all-round fun package without concentrating on just power also gives you a huge advantage – you can make use of the bits and pieces that everyone else thinks are valueless.

Like those from exhausts.

It simply doesn’t make sense to assume that a 3-inch muffler is the minimum needed for performance. Or that all 2-inch resonators are suitable only for the tip. What you need to do is to look at the flow requirements versus cost and performance. So for example, here in Australia, a Falcon XR6 Turbo cat converter is suitable for power outputs up to about 250kW – and so with two of them, for power outputs up to 500kW! On a saner level, cat converters off the local Holden V8s will be happy flowing well over 200kW, and even base models of the local late model six cylinder cars have exhaust systems designed for over 150kW.

In short, unless you’re looking right at the top end of the power spectrum, using single or dual versions of these systems will provide plenty of flow, plenty of sound suppression - and all at a low cost.

And there’s another advantage: many of these components are now being produced in stainless steel, so they will probably never need replacing!

Click for larger image

For us at AutoSpeed, using factory exhaust bits and pieces from more powerful cars isn’t a new idea. We’ve previously covered putting a Commodore muffler on a turbo Nissan EXA (see Edward the Elephant's New Exhaust - Part 1 and Edward the Elephant's New Exhaust - Part 2, and installing a Commodore cat converter and Skyline rear muffler on a Nissan Pintara (see Lung Transplant). Both systems flowed very well, cost very little and were relatively quiet.

Doing It

In this particular application, an exhaust was wanted that would be 2-inch off the turbo, running through at least a 2-inch cat converter (typically, the cat is the most restrictive part of a free-flowing system, so going larger than nominal pipe diameter is better), a 2-inch resonator and then a rear muffler which would be either 2 inch or a little smaller. (Why would smaller be OK? Almost all factory cars reduce their exhaust diameters as you travel towards the back of the car. Whether that’s because the cooling exhaust gases take up less volume – or some other theory – the bottom line is that the factory engineers don’t have a problem with this approach, and it doesn’t harm power. Some aftermarket turbo kit suppliers also do this.)

The first step was to very carefully measure the available room under the car. This step cannot be over-stated – you simply must know how much room you have to play with. For example, in the car we were dealing with, the underfloor volume for the cat converter was strictly limited in width, being less than 160mm – which is damn’ narrow! On the other hand, the resonator could be as wide as 160mm and as along as 500mm – quite unusual.

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A flex joint was needed because the engine is mounted transversely – as torque loads are applied, the engine twists on its mounts, which causes the exhaust pipe to be bent. Without a flex joint, the pipe will end up breaking, usually at the exhaust flange. Many factory cars use a type of ball-joint with a special gasket, but it’s easier in the aftermarket to use a stainless steel flex joint – and plenty of cars use these ex-factory as well.

The next step was to visit a wrecking yard – one of those that allows you to wander at will. Armed with calipers, a tape measure and a piece of paper with the max possible dimensions for the muffler, cat and resonator on it, I spent a solid two hours walking, measuring and comparing. So what did I find?

  • Flex joint

Plenty of front-wheel drive cars have stainless steel flex (those that don’t use the ball-joint described above) but very few are larger in internal diameter than 2-inch. That size was fine in my application, but in a common wrecking yard you won’t find too many that are bigger. Note that the flex joints are almost all welded into place – so to get the flex you’ll need to buy that complete section of exhaust.

Common in the wrecking yard where I was looking were Magna flex joints – the front section of the V6 exhaust has multiple, short braided joints. However, I ended up selecting a longer flex joint which was also on a simpler-shaped piece of exhaust (and so was likely to be cheaper!). It was from a Daewoo Lanos.

  • Cat converter

When looking for a cat, initially I was disappointed – in a field of perhaps 500 cars, there didn’t seem to be more than two or three cats still on the cars. Then I twigged: the cats contain precious metals and so are removed for recycling. When I finally found the recycling bin, I had a choice of many cats. As mentioned, the required cat needed to be relatively long and thin - but with such a wide selection of cats to pick from, it wasn’t hard to find the ideal candidate. Of course, I cannot tell how many kilometres it has done, but an internal and external visual inspection showed no apparent problems.

  • Resonator

It’s easy to think that a resonator isn’t needed – and in some exhaust systems, that’s the case. However, if you dislike droning resonances (which can be particular problem in auto trans cars, especially those with continuously variable transmissions), a resonator is good insurance. A straight-through resonator without punched louvres projecting into the pipe will have near zero flow restriction, weigh little and if buying from a wrecking yard, cost nearly nothing. So I wanted a resonator!

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The chosen one was long and thin, and like plenty of other factory resonators, the internal tube was not perforated along the full internal length. In other words, this resonator acts as an expansion chamber, with the smaller number of holes slowing the rate at which the gas can expand into the cavity. I selected a long, thin design. It was a floating orphan in the yard, so I am not sure what model car it came from.

Hmmm, No Rear Muffler

Finding an appropriate rear muffler proved to be a real challenge. The trick is to fit as large a canister as possible – sure, a muffler much smaller than standard will also fit in the space, but the chances of excess noise are much higher than if you use the largest one that you can squeeze under the car. (This is an oft-overlooked fact.) In this case, the original muffler was fairly small, and so nearly all 2-inch mufflers were too large to fit. In fact, despite looking under every car in the wrecking yard, I couldn’t find one.

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So at this stage I carted to the front counter of the wrecker the bits of pipe containing the flex joint, cat converter and resonator. All three components came with attached sections of exhaust tube, some with flanges and some with rubber mounts. The total cost? AUD$75.

More Looking for Mufflers

I then went to the other excellent source of cheap secondhand exhaust bits - a muffler shop. Note that some muffler shops dislike selling secondhand mufflers – despite making money on what they’ve been given free of charge, they often seem reluctant to admit to having any good mufflers that they’ve taken off cars! However, the muffler shop that I went to had perhaps 40 secondhand mufflers – at AUD$60 each.

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I selected a near-new stainless steel muffler off a late model Corolla – this was ideal as it was exactly the same external size as the muffler it was replacing, except instead of using the 1.3 inch tube of the original, it uses 1.7 inch tube. (So while it’s not 2-inch, it’s still 70 per cent bigger in cross-sectional area than the original tiny muffler pipe size.)  And at 100kW, the power output of the Corolla is about double what the modified car will be developing - so the flow capacity should be fine. (At the muffler shop I also saw at the same price big mufflers off an HSV V8 Maloo ute – these mufflers would be fine up to 150kW.)

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So far, the total price for all the exhaust system components was AUD$135. Add AUD$5 for a new gasket to suit a flanged connection, and AUD$6 for two nuts suitable for mounting the oxygen sensors, and the total reached AUD$146.

Flanges

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Despite some of the bits of exhaust bought from the wreckers having flanges, there wasn’t a matching pair. (Memo to self: next time, make sure you measure the flanges you’re getting at the wreckers!). Rather than buy a second flange, I had one cut out by a welder wielding an oxy acetylene cutting torch.

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However, this may be false economy in both time and money: by the time I had ground and filed the flange edges to precisely the right shape, it would have been easier to buy a new flange (and much cheaper to have got one at the wrecking yard!).

Next week: we put the exhaust together

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