The Cheapest Exhaust You've Ever Heard Of, Part 2

This article was first published in 2005.

Last week in The Cheapest Exhaust You've Ever Heard Of, Part 1 we assembled the components of our turbo exhaust system. The main bits and pieces – stainless steel flex joint, resonator, cat converter and stainless muffler – cost only $AUD135. Add some nuts for mounting the oxy sensors and a gasket for the flanged joint, and so far we’re still looking at only AUD$146.

Putting the Exhaust Together

The first step in assembling the secondhand pieces into an exhaust was to cut off the bits of unwanted pipe. This can be done with a hacksaw or (easier and faster) with a friction cut-off saw. Once the excess pipe has been removed, the components look much more ready to go into a new exhaust!

In this job, where a turbo was being fitted to a previously naturally aspirated car, the front section of the exhaust needed to be completed before the car could be driven to an exhaust shop. This wasn’t so much because of legal, noise and emissions reasons, but simply because the front section of exhaust could only be put into position with a driveshaft removed from the car!

The secondhand turbo came with an exhaust flange - this was used with the new pipe.

The turbo flange was followed by three mandrel bends – a 180-degree and two 45-degree bends. At about AUD$80 for the three, these bends were quite expensive (much more expensive than they should have been: we stuffed up) but with such a sharp bend right at the exit to the turbo, it was thought important that mandrel bends (rather than cheaper but more restrictive press bends) were used for this section of exhaust.

Following these bends is the flex coupling (it needs to be positioned where the greatest exhaust pipe bending moment would otherwise occur) and then the fabricated flange. Arrowed is the hole for the front oxygen sensor. The oxy sensor was positioned to allow easy access within the engine bay and in a location that allowed the standard wiring harness to reach it. In this view, the assembly has just been tack welded together - with the welder being located away from the car, it was important that the fit of this pipe was tested before final welding was undertaken.

The oxy sensor mounting was made from a nut – in this case, the nut and bolt shop had available only Nyloc nuts. However, that didn’t matter because the thickness of the nut had to be reduced if the oxy sensor probe was to have the right reach into the exhaust pipe. A lathe was used to turn down the nut until it appeared as shown on the right.

If a lathe is not available, the nuts can be cut with a hacksaw and then filed smooth.

The first section of exhaust was then welded together, using a mix of arc....

....and fusion welding. (Note that a MIG was not available at this location.)

A bracket was added to the front section of pipe – this braces the pipe to the gearbox as the original exhaust manifold was braced.

This first section of exhaust was lagged with high temperature fibreglass cladding (AUD$90)...

...which was spray painted black. The lagging was added to reduce the radiant heating of nearby engine bay bits like the electric power steering rack.

Following the flange is the cat converter (which should be placed close to the engine), the second oxy sensor and the resonator. The shape of the floor meant these components could be assembled in nearly a straight line. To allow for the second oxygen sensor and an exhaust hanger, a short section of pipe (arrowed) was used between the cat and resonator.

With the exhaust completed only to the point of the resonator, the car was able to be driven to an exhaust shop to have the final section of pipe and the Corolla rear muffler fitted. Given that less pipe diameter is needed as you go towards the rear of the car, the use of press bends (rather than continuing with mandrel bends) wasn’t a problem.

The new muffler, despite being exactly the same external size as the original, had its hangers located in different positions, so the original hangers needed to be cut off and slightly relocated.

The joints were MIG welded then....

...the exhaust was painted.

The cost for the rear pipework and fitting the rear muffler was AUD$100, giving a total exhaust cost that works out like this:

2 inch stainless steel flex joint, 2 inch cat converter, 2 inch resonator: $75
1.7 inch stainless steel rear muffler: $60
Nuts and bolts, flange gasket: $11
Mandrel bends x 3: $80
Fibreglass lagging tape: $90
Rear pipework and muffler fitting: $100

Total: AUD$416

Subtract the lagging tape and source the mandrel bends at the $12 each I was (later!) quoted and you see a total of AUD$282... Either way, a very cheap exhaust.

Conclusion

The exhaust in this case was designed for a low power car but really, the only aspect of the system restricting potential power below about 150kW (200hp) is the rear muffler. And, if I’d wanted to, I could have sourced a straight-through 2-inch muffler within the same budget. The bottom line is that if you’re prepared to do some scrounging, it’s possible to put together a very good exhaust system for around one-third (or less!) the price you’d normally be charged.