Split Dump Pipe

I took possession of the 180sx with only a cat back exhaust system, which is 80mm and from Bee Racing I am quite sure. The catalytic converter was a small and nasty item fitted during compliance. The pipe work between the turbo and the cat was still the very small factory dump and front pipe. Researching available aftermarket items I discovered that it was possible to purchase one piece of piping that replaced both the factory pipes. I also decided I wanted to fit a twin pipe system, where the wastegate receives its own dedicated pipe to separate its gases from the main turbine gases. The advantage of a long pipe going from the turbo the entire way to the cat was that this wastegate pipe could integrate smoothly into the other pipe for best flow characteristics.

dumpbefore dumpafter

The CES Racing Dump

My attention was brought to an item from Queensland company CES that fitted the above description perfectly. This pipe was meant to be an improved copy of a HKS pipe, and copious power claims were quoted by many fans. To the best of my knowledge the exact same piece of equipment is the one distributed by NSW companies such as Unique Auto Sports, and so I purchased one from UAS to suit an S13 180sx, as well as the two required gaskets for $650. I believe a price rise may have recently been introduced, and it may also be cheaper to buy direct from CES in Queensland. The decision was made to fit the pipe myself with the help of friends.


Factory vs Aftermarket

As can be seen from the photos the factory piping pales in comparison with the CES pipe, in terms of diameter, smoothness and wastegate arrangement. The factory cast dump forces the the wastegate gasses directly into the stream of the main turbine gasses, creating turbulence as well as being restrictive. After this the front pipe is reasonably smooth but very small in diameter. That is in terms of a good condition pipe, but once removed from the car it was apparent that the piping was severely crushed in one area. It is an amazement to me that the car ran so well and put down such a healthy dyno figure.


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Fitting the Pipe

True to the claim the pipe was a direct replacement, bolting up nicely to the back of the turbo and the cat. With the pipe off I had access to the back of the turbo and was able to inspect its condition. Luckily I found this to be excellent, with no chips in the turbine blades, free rotation and zero shaft play. Only two problems arose fitting the dump. Amazingly enough all the the fastening nuts and bolts came undone without a hitch. Thank you to DRIFTDAVE and Micra_psi for their great help installing the pipe.

The first was that a shorter bolt was required for one of the exhaust housing’s five nuts and bolts. Due to the width of the new pipe the head of the bolt would foul on the pipe and not be able to turn. The solution as mentioned was a shorter bolt so when first trying to catch the thread the head was inline with the flattened section of pipe closer to the flange.

The second problem required a little more work to solve. The nut welded onto the new pipe for the oxygen sensor was in the correct diameter for a large size generic sensor, instead of the smaller sensor that the S13 SR20DET comes equipped with. Over the next few days an adaptor bolt was made, starting with a trip to the local exhaust shop to find a large bolt to plug the hole. A suitable item was obtained and then taken to my university workshop to be modified. First it was machined on a lathe to shorten it so when the oxygen sensor was in place a decent amount of it would be exposed to the exhaust gases. Thanks to Stephan Lie for this.

Next a trip to the Engineering Workshop to have the same thread as the oxygen sensor cut into the center of the bolt. The thread was quite unusual in being M12 x 1.25mm. The bolt was left overnight with the oxygen sensor and when I picked it up the correct thread was in place so the sensor could screw into the centre of the adapting bolt. Much thanks to the staff of the Engineering workshop. A reset of the ECU whilst fitting the sensor was undertaken to ensure that no fault codes remained that could have been created from the car been driven oxygen sensorless. Apparently an oxygen sensor from CA18DEt will fit the hole and connect to the appropriate plug to solve this problem. The s15 sensor is also the large size but I am unsure on the plug connection.

factoryturbo adaptorbolt

Driving Impressions

The greatest thing about this modification was that it made the car much more tractable on road. Boost arrives earlier and harder with a greater spike (now 0.8 bar compared to 0.7 bar) before settling down a little higher than before at 0.65 / 0.7 bar. After the boosting period the car feels a little faster but this is definitely not where the greatest gain is had. A good way to describe the performance gain overall is as ‘stronger’, with the car feeling torquier throughout the rev range and very drivable. A recommended modification that perhaps would have made a greater difference with a larger turbo or more boost, but worthwhile nonetheless. Seat of the pants impressions told me the new rear wheel kilowatt figure would be in the low 140 kw range…

Dyno Run

A short while after having the pipe I was able to have the car dynoed again for a comparison between before and after. Between this and the fitment however, I had found the performance of the car inconsistent. For a few days before the test the car had felt particularly flat, and the boost gauge reflecting this by showing about the same boost that the car had been making before the addition of the dump pipe. More lag was also apparent, and when finally spooling the shove in the back seemed to be reduced. Despite this the day of the dyno run the car had felt very crisp boosting, spiking to higher than ever before (over 0.8 bar). So then the dyno run took place. Watching the graph plot itself in real time, I began to be excited as the power curve swelled quickly over the previous curve early in the rev range, reflecting my driving impressions. However at mid rpm the car seemed to give up a little and flatten back to near the original power curve, also matching my seat of the pants impressions.

The graph below shows the best power run from the latest run, with one of the others from the dyno day (not the 132.7kw run, this was not chosen to print by accident). The second line shows boost, and it can be easily seen the quicker spooling the dump pipe gave. If this were the 132.7kw run and the new 134.9kw run, the curves would be a lot closer up top.


Problem Solving

The guys at Unigroup told me that the car was running too lean, and still experiencing slight detonation high in the rev range. I have several possible theories as to what this could be:

1. The fuel pump is lazy, even though it is an aftermarket pump. I will hook up a fuel pressure gauge to the car to see if fuel supply decreases as load increases.

2. The fuel filter needs replacing, which I will probably do either way as they are cheap and easily installed.

3. The standard intercooler is restricting flow at high rpm, and capping power gain.

4. The adaptor used for the transition from air flow meter to POD filter is causing incorrect readings. When it was installed, even though the adaptor was for a SR20DE(T), the hole for the POD attachment really didn’t line up with the opening of the afm. I have read articles in the past detailing how the flow characteristics of a POD filter and its associated piping can upset the reading of the afm with turbulence. If the other tests show up clear then I will switch back to the factory airbox to see if this makes a difference to the air fuel ratio.

I will update with news on the main page as it occurs.


Recently I have noticed an exhaust leak to which I first believed to be a worn turbo to manifold gasket, but on closer inspection I noticed that the dump pipe had developed a large crack in the area joining the main pipe to the flange. Hopefully this can fixed ASAP.


Dump Pipe Repairs

I finally got around to pulling off the dump pipe myself. When in a lazy mood one day I obtained a quote from an exhaust shop to fix the crack, and the guy wanted a few hours and $150! The key to getting the dump pipe off yourself is doing it when the car is completely cold. Trying to work around the back of the turbo and the cat when both hot is very difficult due to the immense heat. Being able to get underneath the car is essential too, use wheel ramps at a minimum, to ensure no chance of the car rocking and falling. It took me only 15 minutes to get the pipe off the car with basic hand tools, by myself. There’s really not much too it, so keep this in mind if ever being quoted to have a dump pipe fixed.

Once off the extent of the crack could be seen, spanning over half the perimeter of the pipe.


I limped the car (no exhaust off turbo!) over to the local industrial area to find a mechanic to weld the crack for me. I found one that would weld the crack and give the inside a slight grind for smoothness for $20 that day. Shows the advantage of knowing what are doing and being able to perform a lot of the hard work yourself to save labour costs. The dump was ready within the hour, and upon inspection showed that the mechanic had not been scared to add a lot of welding. There were a lot of lumpy regions inside the neck of the pipe which concerned me, but I put the pipe back on the car. It was much quieter naturally, but seemed a little flat around the midrange. A few days later I pulled off the pipe again for inspection.

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It’s hard to see the full extent of the internal surface as now the car had deposited a layer of carbon, but it can still be seen that a large ridge extends around the inside of the primary pipe. Using a grinding attachment in my cordless drill I began trying to remove material to give the surface a smooth face. Eventually the drill kept on losing battery charge and my cheap grinding bit wore away. I was forced to reinstall the pipe with minimal improvements after a quick sand with wet and dry to polish the surface.

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In the future I wish to remove the pipe again and use a proper die grinder to fully port and polish the internal surface, I believe this will give a great gain in the midrange as the turbo begins spooling as even after this minor work it felt slightly more responsive.