Nissan 200SX Club - South Africa

Read and learn.
Thanks autospeed.

Fitting a high-flow exhaust to a moderately powerful car can be an expensive exercise. Large diameter mandrel bends, exotic cat converters, elaborate dump pipes, numerous polished mufflers and many hours of labour can add up to a bill of AUD$1000 - and sometimes considerably more.

But when we decided to fit a high-flow exhaust to our Nissan 180SX we did it for a total cost well under AUD$500. And does the new system perform? You bloody betcha!

In the first of this two-part series, we’ll take you through the process of designing a low-cost high-flow exhaust...

Check the Existing Backpressure
The first step before modification should be to measure the backpressure of the existing exhaust system. That’s a point worth repeating. The first step before modification should be to measure the backpressure of the existing exhaust system.

So why is this so important, you ask?


Well, if you don’t have any idea how restrictive the factory exhaust is, it’s impossible to size the new system so that you don’t unnecessarily spend cash chasing gains that aren’t there. Let’s face it – if the factory exhaust isn’t that restrictive, it’s not worth spending a large wad of cash for what can only be a small gain.

Don’t be scared off by the idea of measuring backpressure. It’s e-a-s-y.

The most convenient way to measure backpressure is to temporarily remove the oxygen sensor near the beginning of the exhaust system. The sensor can be unscrewed from the exhaust and left to dangle in the engine bay. Now you’ll need to find a bolt with the same thread as the oxygen sensor. Drill a small diameter hole through this bolt (from the head through the bottom) and weld a short length of metal pipe to the head. If you don’t have any welding equipment, any exhaust shop should be able to do this for you in a couple of minutes.


This is what your backpressure measurement fitting should look like. The threaded end screws into the provision for the oxygen sensor and the pipe end connects to a hose leading to a positive pressure gauge (any gauge that goes up to 15 psi should be fine).

In the case of our 1.8 litre turbo 180SX, the backpressure measurement fitting was installed immediately downstream of the turbine so that total exhaust system backpressure was being measured. At full power (around 6000 rpm in second gear) our testing showed a peak exhaust backpressure of 9.3 psi.

Standard Backpressure Measurements
Let’s put your exhaust backpressure measurement into context against some other cars.

The highest backpressure measurement we’ve seen came from a bog-stock Holden VL Turbo that we used to own. Peak backpressure (measured immediately behind the turbine) was an astonishing 13.2 psi. We can’t be sure if the exhaust on our particular car had a blocked muffler but, if it is representative of other examples, we can only suggest upgrading your VL Turbo exhaust NOW! See Pure Pipe Perfection - Part 1 for our VL Turbo exhaust upgrade article.

In comparison, a 1994 Subaru Impreza WRX (fitted with a more powerful Japanese-spec engine) saw up to 8.8 psi exhaust backpressure. Fitment of a high-flow exhaust then achieved a power increase of ten percent. Details of our WRX exhaust upgrade can be found at Rex Blows


Meanwhile, the standard exhaust on a 2.4 litre Nissan Pintara causes a relatively low 5.9 psi backpressure – though this was measured before the cat converter, so it’s not representative of total exhaust backpressure. Total exhaust backpressure (after the exhaust manifold) would likely be in the vicinity of 7 – 7.5 psi. Our Pintara exhaust upgrade can be found Lung Transplant

These figures should give you a guide to how good or bad your car’s existing exhaust system is. Be honest. Do you really need to spend lots on an upgrade?

Designing the New Exhaust
Pipe Diameter and Bends
Now that we know the backpressure caused by the existing exhaust system we can make some informed decisions.

Let’s start off by determining the appropriate pipe diameter for the new exhaust system.


Based on some previous AutoSpeed backpressure measurements, we can make some generalisations on what pipe diameter is required to give next-to-zero backpressure at a specific engine output (assuming similar engine efficiency and thus airflow).

Testing on the 2.4 litre Pintara showed that a length of straight 2 inch pipe causes barely any backpressure on an engine making around 100kW. A 2 ¼ inch pipe can be considered plenty big enough for this power output. Testing on the VL Turbo and ’94 WRX showed that a straight length of 3 inch pipe is ample for engines making up to around 200kW. On both of these vehicles, fitment of a full-length 3 inch system (including cat converter, muffler and bends) caused just 2.9 psi backpressure.

Ahhh, but what happens to our pipe diameter hypothesis when pipe bends are thrown into the equation?


Well, not that much changes if you use mandrel bends that maintain the pipe diameter. Some exhaust shops have an on-site mandrel bending machine which means the entire system can be bent from a single length of pipe. This is an ideal situation. But, more than likely, your exhaust shop will use a number of pre-formed 30, 45 and 90 degree mandrel bends which are welded together to form the system. This isn’t quite as good because some of the welding will penetrate the pipe and cause turbulence.


There’s nothing wrong with using cheaper press bent pipe – so long as you have designed the system to take them into account. In situations where a tight radius bend must be made, it’s advisable to use the next larger diameter pipe for that section. For example, you should step up from 2 to 2 ¼ inch pipe where the system takes some sharp turns. This approach will achieve similar gas flow to a mandrel bend that’s the same diameter as the rest of the system. Note that gentle radius press bends offer very nearly the same flow as mandrel bends – it’s only the tight radius bends (which involve heavy pipe crushing) where press bent pipes cause a considerable flow restriction..

So let’s apply some of this info to a couple of real-world examples.

If you are lightly tweaking your Suzuki Swift GTi (which makes 74kW in standard form) you can use the above information to see there’s no need for anything bigger than a 2 inch mandrel system or a 2 inch system with 2 ¼ inch press bends. A 2 ½ inch system is overkill and 3 inch (which we have seen used!) is the stuff of madness.

Now let’s look at our demo Nissan 180SX.


In standard form, the 1.8 litre turbo 180SX generates 130kW. If we were leaving the car near-stock we would probably use a 2 ½ inch mandrel exhaust but, since we plan to take it to around 180kW, we will use a pipe diameter approximately the same as a 3 inch pipe.

Now that we know the diameter of our pipework we can source the appropriate cat converter, resonator and muffler.

Sourcing a Cat Converter
The cat converter is generally the most restrictive component of an exhaust system. It’s for this reason you should make a special effort to buy the freest-flowing cat converter available.


Flowbench information is tremendously important in cat converter selection but, given this type of information is limited, you’ll usually need to rely on other criteria. Buy the cat converter with the largest diameter inlet and outlet pipes, the largest core cross-section and the widest spaced internal honeycomb.

Unfortunately, these large diameter high-flow cat converters are quite expensive - you’ll often pay several hundred dollars for a newie. But there’s no reason why we can’t make use of near-new OE cat converters that are commonly thrown away.

And, yes, there are some very good OE cats to be found.


One of the best cat converters on a bang-for-buck basis is from the Holden 3.8-litre V6/5-litre V8. Independent flowbench testing has shown the Holden AC cat offers gas flow similar to a poor performing 3 inch cat. You can easily pick up one of these cats in good condition from AUD$10 – and they aren’t hard to find...

But, for our 180SX, we wanted a cat that offers really good flow.


The part chosen for the job is a cat converter from a Ford BA Falcon XR6 Turbo. The XR6T cat (which has a single 3 inch inlet pipe and twin 2 ¼ inch outlets) is factory fitted to an engine making 240kW and it is widely acknowledged that you need a very special cat converter to improve flow on the Falcon Turbo. The standard XR6T cat is regularly used in power-up applications close to 300kW and is more than free-flowing enough for our Nissan. We paid AUD$100 for this particular example.

Using the XR6T Cat
The twin outlet of the XR6 Turbo cat converter makes exhaust design more complex than using a single outlet cat.


If there’s enough space beneath the car, you can run twin pipes from the cat all the way to the tips. Keep in mind that a twin 2 inch system has almost the same cross-sectional area as a single 3 inch pipe, and a twin 2 ¼ inch system is considerably bigger.

Unfortunately, the available selection of twin inlet/twin outlet mufflers is relatively limited and you may be forced to merge the twin pipes into a single larger diameter pipe before the muffler. This is what we’ve decided to do.

The cheapest and most readily available 2 into 1 pipe junction can be found in various late-model Holden Commodores. The Commodore pipe junction uses twin 2 inch inlets and a single 2 ¼ inch outlet.


Unfortunately, the inside of the Holden 2 into 1 junction is also pretty daggy. As seen here, the leading edge of the single outlet pipe protrudes into the gas flow and is likely to cause considerable restriction. It might be tempting, but the Holden junction is not the most attractive way to merge a pair of pipes.


A better option is to use a 2 into 1 collector from a set of extractors or an aftermarket Y-pipe (which is designed for the front section of a V8 exhaust). This Redback Y-pipe gave us a nice 2 into 1 junction that’s designed to accept twin 2 ¼ inch pipes and a single 2 ½ inch pipe (which is easily flared to 3 inch).


This photo shows the 2 into 1 Redback junction after the outlet pipe has been flared to 3 inch. As you can see, its internal surfaces are very smooth – a stark contrast to the ugly Holden junction.

Sourcing Mufflers/Resonators
This is where personal preference comes into play.

If you don’t mind a relatively loud exhaust you can get away with just a single rear muffler. This keeps cost, exhaust backpressure and weight to a minimum. But if you want a system that’s quiet you will need to add more mufflers/resonators – and you’ll need to choose them wisely.


If you want to keep noise to a minimum, you should pick a rear muffler that makes full use of the space available beneath the car. A large-body muffler typically contains more sound absorption material than a smaller muffler.

In addition, it’s important to pick a straight-through type muffler because they cause only a 10 percent flow loss compared to an equivalent straight length of pipe (as tested on a flow bench). In comparison, reverse-flow type mufflers can cause up to 40 percent flow loss... See Giant Muffler Comparison - The Mufflers! for further details on muffler types and how they compare in terms of flow.


We chose a second-hand 3 inch straight-through Trust muffler which uses all of the space beneath the 180SX. However, after previously purchasing a second-hand muffler which turned out to be stuffed, we gave this muffler a very close inspection. We thoroughly examined the internal perforations, banged it on the ground to see if anything except carbon came out and checked that the case was in good condition.

Fortunately, this muffler looked in good condition.

OE Mufflers?
In many instances it can be cost-effective to use a second-hand OE muffler.

Most OE mufflers are built with internal baffles to reduce noise. These baffle-type mufflers are quite restrictive compared to a straight-through muffler but if you can find one that has a larger than necessary pipe diameter you can get away with it. For instance, if you’re designing a 2 inch exhaust you can realistically use a 2 ¼ inch baffled muffler from, say, a Holden Commodore or Ford Falcon. These mufflers generally have good sound absorption and – when you pick one that’s suitably upsized – they can perform very well.

For articles that discuss using OE mufflers in a performance application see Lung Transplant The Cheapest Exhaust You've Ever Heard Of, Part 1 and Edward the Elephant's New Exhaust - Part 1

When it comes to centre resonators, you’re pretty safe with whatever you buy – just make sure you’ve got the suitable pipe diameter and it’s a straight-through design.


While new aftermarket resonators are available quite cheaply, a second-hand OE resonator can be picked up for next to nothing. For maximum noise suppression, we suggest using the largest bodied resonator available (for the same reason we go for the biggest possible muffler).


Late-model Subaru WRXs, Mitsubishi Lancers, Honda Accords and Nissan Pintaras all have nice straight-through resonators that range from 1 ¾ to 2 ¼ inch diameter. We used a pair of 2 inch stainless steel resonators from a Toyota Soarer V8.

Another Noise Suppression Trick
Interestingly, it seems that using a relatively small tailpipe or rear-most section of exhaust is an effective method of further reducing noise.

A tapering exhaust diameter is common in many production cars as well as the highly developed APS (Air Power Systems) aftermarket exhausts. For example, the APS ‘210kW’ kit for late-model WRXs uses a 3 inch pipe for the majority of the exhaust but the rear section tapers to just under 2 ½ inch. This particular exhaust is claimed to reduce backpressure from 9.6 to 3.5 psi and we can vouch that it has a very refined and hushed note.

It’s an idea that’s worth investigating if you want the quietest exhaust possible.

Sourcing a Turbo Dump Pipe
If you own a turbo car, it’s likely that the factory dump pipe (the front section that connects to the turbine) should be replaced as part of your system upgrade.

Aftermarket dump pipes can be extremely expensive to buy new. However, most performance exhaust shops (such as Exhaust Technology in Adelaide) usually have some second-hand examples lying around.


A twin-pipe dump (such as seen here) comprises a large diameter pipe adjacent to the turbine wheel and a smaller pipe adjacent the wastegate bypass. The idea of a twin-pipe dump is that turbine and wastegate gases are kept separate and, as a result, there’s reduced turbulence and backpressure.


A twin-pipe dump wasn’t available to suit our CA18DET-powered 180SX so we used a second-hand single entry ‘big mouth’ dump pipe with a 3 inch pipe. As you can see, this dump pipe has a large diameter bend which is shaped to match the shape of the turbine flange. The single pipe dump mightn’t have the theoretical advantage of a twin-pipe dump – but it’s a vast improvement over the cast iron factory part (which measures just 2 ¼ inch diameter).

In the first part of this series (see The Low-Cost High-Flow Exhaust - Part One) we looked at designing a cost-effective high-flow exhaust suitable for moderately powerful cars. Well, now it’s time to put our design into practice – come and see the exhaust fabrication, on-road results and the cost rundown!

Turbo Dump Pipe

The dump pipe we chose for our Nissan 180SX is a second-hand stainless steel job with a single ‘big mouth’ entry leading into a 3 inch pipe. This particular dump pipe was fabricated by the same company doing our exhaust installation – Exhaust Technology in Adelaide .


Prior to installation, the mounting flange of our new dump pipe was ground back to remove some minor surface corrosion (this smoothing helps achieve an effective seal against the turbine flange). Oxygen sensor safe sealant was also used to ensure there are no exhaust leaks.

A two-bolt flange can be found at the base of our second-hand dump pipe. This connects to a newly fabricated 3 inch pipe that extends rearward to the area of the cat converter. The newly fabricated pipe comprises a single 90 degree mandrel bend.

Cat Converter
The cat converter we’re using was pulled from a Ford XR6 Turbo. The XR6T cat is relatively unusual in having a single 3 inch inlet and twin 2 ¼ inch outlet pipes.


For fitment to our 180SX, the factory inlet and outlet pipes were cut from the cat converter. This allows the fitter to fabricate new inlet and outlet pipes which are correctly angled to suit the car.


The XR6T cat is mounted in the virtually same position as the original part and is welded to the 3 inch pipe from the dump pipe.

Dual Pipes and Resonators
Our 180SX exhaust uses twin 2 inch pipes from the cat converter leading into twin resonators before merging into a single larger diameter pipe. Twin 2 inch pipes might seem relatively small, but they do offer similar cross-sectional area to a single 3 inch pipe.


From the back of the cat converter, a pair of 2 inch pipes were bent into the required shape using a press bend machine. Care was taken to ensure the cross-sectional area of the pipes was maintained as much as possible. These twin 2 inch pipes terminate at a pair of centrally mounted resonators.


The resonators we selected are pulled from a Toyota Soarer V8. These are nicely built straight-through stainless resonators with 2 inch inlet and outlet fittings. This photo shows the resonators being cut from the original Soarer pipework.


The 180SX doesn’t offer a lot of under-car space so the twin resonators are mounted closely alongside each other and close to the tailshaft tunnel (to maintain ground clearance). It’s a squeezie fit.

Merge Pipe
Unfortunately, we were unable to extend twin pipes all the way to the end of the system; we couldn’t find a cheap twin inlet muffler that makes use of the available space. Instead, we decided to merge the twin pipes into a single 3 inch pipe (which makes sourcing a suitable muffler much easier).


A search through Exhaust Technology’s used stock pile uncovered this - a Redback high-performance Y-pipe, which we believe is intended for a V8 Holden. The Y-pipe has twin 2 ¼ inch mandrel bent pipes merging into a single 2 ½ inch outlet.


The Redback Y-pipe proved extremely useful in our application. It provided us with a smooth 2 into 1 pipe junction as well as some nice mandrel bends, which we couldn’t resist reworking to suit the 180SX. This photo shows the reworked Redback mandrel bent pipes welded to the back of the resonators and the 2 into 1 junction. Note that the single outlet of the junction was flared from 2 ½ to 3 inch to suit our chosen muffler.

Rear Muffler
The muffler we selected for the 180SX is a second-hand 3 inch Trust unit with straight-through internals. This muffler makes full use of the space available beneath the car and was checked to be in good condition.


As seen here, this particular muffler also came with a mandrel bent entry pipe and mounting flange already attached. These make installation quicker and easier compared to a bare muffler.


The muffler was hoisted into position beneath the car and a 3 inch pipe was fabricated to join it to the outlet of the 2 into 1 junction. A single 3 inch mandrel bend was used for this section.

And that’s it.

Bung on some hangers, whack on a coat of paint and the exhaust is finished.

The Completed Exhaust

This photo shows the main section of our newly constructed 180SX exhaust. With a fresh coat of black paint it doesn’t look much like an aftermarket creation - if anything, it resembles a factory BMW M3 exhaust...

So let’s recap the components that we used.


Starting at the front, you’ll find a second-hand ‘big mouth’ stainless dump pipe, an ex-XR6 Turbo cat converter, a pair of resonators from a V8 Soarer, a merge pipe constructed from a used Redback Y-pipe and a second-hand 3 inch Trust muffler. The only new parts used in the system is a pair of 3 inch mandrel bends, some press bent sections of 2 inch pipe, a couple of flanges and some new hangers.

A Look at the Standard Exhaust
Our testing in the first part of this series revealed the factory 180SX exhaust was causing 9.3 psi backpressure. So, out of curiosity, let’s take a look at what causes this restriction...


Starting at the front, the standard cast iron dump pipe has a lot of internal lumps and bumps (which cause turbulence) and a relatively small 2 ¼ inch outlet.


The first section of exhaust after the dump pipe connects to the cat converter. This pipe is just over 2 inches in diameter and flares into the 2 ¼ inch cat converter. Interestingly, the cat converter is mounted a long way downstream of the turbine – completely different to, say, a Subaru WRX with its cat converter mounted very close to the turbine.


From the cat converter, the next section of pipe is just over 2 inches in diameter and leads into a centre resonator. The entry and exit pipes from the resonator step down to exactly 2 inches.


The final section of pipe takes gasses to the rear muffler and is just over 2 inches in diameter. Again, like the resonator, the muffler entry reduces to just 2 inches. At the rear there are twin muffler outlets measuring approximately 1 ½ inches.

Overall, the 180SX system is very similar to the S15 200SX exhaust – the biggest flow impediments are its small pipe diameter, heavy press bends, a baffle-type rear muffler and a cat converter with a relatively small core cross-section.

In short, there’s plenty of room for improvement – as indicated by our initial backpressure measurement.


Before and After Results
So what improvement came from our custom 180SX exhaust?

Well, in standard form, we measured 9.3 psi exhaust backpressure at full power and the car (with an automatic transmission) managed to accelerate from 0 -100 km/h in around 8.4 seconds. Tailpipe noise was 60db(A) at idle and around 65db(A) when free-revved to 4000 rpm. These tailpipe noise figures were taken with the SPL meter held at 45 degrees from the tailpipe at a distance of 50cm.

Now let’s look at the new exhaust’s credentials.


With the custom exhaust bolted to the back of the turbo we saw a maximum backpressure of just 2.5 psi – a reduction of 73 percent! Not surprisingly, the car now has much improved response and torque in normal driving conditions and is tremendously quicker at wide-open throttle. This is reflected in a monumental 0 – 100 km/h improvement – this time has tumbled from around 8.4 to 7.6 seconds!

Note that this incredible performance gain was achieved through a combination of reduced backpressure and a resulting increase in boost pressure. Turbo boost pressure now builds faster, reaches a higher peak and holds a higher value to the reline. Peak boost has increased from 10 psi to 12.5 psi and at the redline (7000 rpm) there’s 7 psi instead of 6 psi as previously. Certainly, this across-the-board boost increase is a major factor in the recorded performance improvement.

However, tailpipe noise has increased. The system is quieter than the majority of turbo-back performance exhausts but is still obviously an aftermarket development. Fortunately, there are no annoying resonances (which can be a problem in auto trans cars) and the note is nice and deep. In terms of SPL, we recorded 63dB(A) at the tailpipe with the engine idling and 88dB(A) when revved to 4000 rpm. In caparison, a full-length 3 inch exhaust we fitted to a Subaru WRX achieved the same noise level at idle but was considerably louder when revved.

And you may be wondering if the new ‘split pipe’ exhaust is heavier than the standard system.


Interestingly, it isn’t. The factory exhaust (from dump pipe to rear muffler) tips the scales at 24.5kg and the new system manages to undercut it by 1kg. We were expecting the new system to be slightly heavier due to its bigger cat converter and more intricate pipe arrangement. However, this isn’t enough to (literally) outweigh the factory cast iron dump pipe and extensive heat shielding.

Cost
So how much did this low-cost high-flow exhaust set us back?


Well, we shelled out AUD$480 in total – AUD$100 for the cat converter and AUD$380 for the rest of the components and labour. However, we would have saved about AUD$80 if we had sourced the XR6T cat converter from Exhaust Technology – they typically have a couple lying around which can be picked up for much less than we paid.

We should again point out that the second-hand XR6T cat converter is brilliant from a cost and flow point of view – but its twin outlet pipes requires a relatively complex (and costly) pipe system. A full-length twin pipe arrangement is relatively time consuming to build and can be very difficult to fit in cars with limited undercarriage space. Keep this in mind if you decide to follow in our footsteps.

Our 180SX’s exhaust has achieved a 73 percent backpressure reduction with a tremendous on-road performance improvement, a mild noise increase and offers the scope to generate around 180kW while maintaining very low backpressure (and, realistically, it would be fine for applications around 200kW).

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