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Most kits run the piping underneath the passenger frame rail, around the bumper flanges, into the intercooler, then up through the fenderwell into the engine bay. This represented a couple of feet of latency between our right foot and explosions that would not be appreciated in racing conditions. In addition, our oil cooler and ram air box already occupied the fenderwells. To make our intercooler piping as short as possible, we simply cut the sheetmetal on either side of the radiator, split some fuel hose to protect the sharp edges and ran our piping through there.
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| In an effort to keep our piping as short as possible, we ran it through the sheetmetal surrounding the radiator with these 90° couplers. |
Once we got our route planned out for the piping, it was time to start cutting. Just about any conceivable bend you would need for automotive piping is represented on one 180° U-bend. Need a 90° bend? Just cut it in the middle. 45° bend? Cut it a quarter of the way through. Starting with the turbo outlet, we measured, eyeballed and marked the angle, cut, tacked, and connected our piping together end to end. Once the whole setup was tacked together, and we were happy with the results, I finish welded all of the charge and inlet pipes, painted them with flat black (looks cool and covers up most blemishes), and clamped them in place. To save on fabrication and expense, we re-used the pre-MAF section of our Hotshot cold air intake, and simply rotated it towards the compressor inlet instead of the throttle body. We kept all of our charge piping to a smallish 2″ to reduce response time and to make it easier to plumb, and used 2.5″ piping from the MAF to the compressor inlet.
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| Our completed compressor inlet and cold side piping. |
To protect against compressor surge when the throttle body closes, we ordered Turbosmart's Nissan-specific Kompact compressor Bypass Valve (BPV). This BPV's primary appeal for us was its compact design (it stands at only 2.6″ tall), quick action and Nissan-specific flange that worked with our OEM throttle body inlet. Anodized black and beautifully machined, it certainly added some understated visual appeal under our hood as well.
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| Our Turbosmart Kompact BPV combined function and understated looks. |
Our last physical modification to the car was to fabricate our own downpipe. At first, we were going to simply fabricate a downpipe to mate up with the OEM discharge housing. However, after distant memories of gasket sealing issues (the OEM housing uses an odd donut fitting that's hard to find here) and looking at its poor design from a gas flow standpoint, we decided to fabricate the whole discharge assembly with a divorced wastegate. Why divorce the wastegate? Part of the reason is because turbo cars are simply too quiet on the track. With a divorced wastegate setup, at least the guy next to me with the JWT C6M-cammed SR20 or K20A screaming at over 8000rpm might be able to hear me. Divorced wastegates also improve exhaust flow, and the faster we can get hot exhaust gasses out of the engine, the cooler it will run and the more power it will make. The best reason? It's easier to fabricate.
As a start for our downpipe, we ordered Vibrant's 5 bolt T25 flange with divorced ports in mild steel. The flange is designed for a 2″ discharge pipe, 1.5″ wastegate pipe, and is made of ½” 1018 mild steel. To keep the exhaust flows completely divorced, we added a divider wall cut out of one of the 2″ U-bends and welded it in place. To ensure that it did not block any exhaust flow, we bolted the flange to the turbine housing without any pipes on it and visually confirmed the fit. To fabricate the piping, we again cut the piping at the correct angles to fit, tack welded them together, confirmed fit, then moved on to the next bend. However, because the pipes were in close proximity to each other, we had to finish weld the turbine discharge completely before we could finish weld the wastegate discharge. To accomplish this, we simply ground away the tack welds that held the wastegate discharge to the flange, finish-welded the discharge section, finish welded the wastegate pipe away from the flange, then welded it back on after verifying fitment on the engine. Needless to say, we spent a lot of time crawling out from under the car. The final design has the turbine discharge flaring from 2″ to 2.5″ directly out of the flange, turning down to go under the oil pan, and then flaring out to 3″ for the remainder of the system. The wastegate discharge remains at 1.5″ for its entire length. We used a Vibrant standard flex coupling to ease fatigue caused by engine movement and vibration, and connected it to the same 3″ back section of the exhaust we used with the Hotshot Gen VI header.
Overall, we were very happy with the piece, and especially like that it does not have any of the sharp bends you see on the pre-fabricated pieces out there (we did not have to clear an AC compressor). It also hugs the engine as closely as possible, and should not interfere with any underbody air management we install in the future.
To keep underhood temperatures down, we wrapped the entire downpipe until the section underneath the oil pan (which is exposed to direct airflow) with one of DEi's Exhaust Wrap kits in black. Previous experience with this product has shown that even after a full-tilt session at over 20psi of boost in my street car, you can still directly touch the downpipe without needing a skin graft. One concern with exhaust wrap is that it tends to cause the metal to become brittle over time, so we will make sure to periodically inspect it.
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| Our divorced wastegate downpipe wrapped in DEi's Exhaust Wrap. |
