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By joshuaho96 · Posted
I'm pretty sure if it's considered a gasoline powered vehicle you have to do certification against a fixed, very expensive certification fuel. If you add two precats and then replace the main cat with two cats back to back you can get an RB26 to do 0.24 g/mi HC, 1.6 g/mi CO, and 0.3 g/mi NOx on the FTP-75 drive cycle. Found this out courtesy of California's laws at great expense. Divide by 1.61 to get g/km. So even with extra cats + precats you're blowing past the NOx limit by probably 2.3x. Probably the only way to get an RB25 or RB26 to meet euro 4 purely from an emissions per km standpoint and not durability/OBD2 requirements is retrofit at least intake side VVT, clearance the pistons to allow the full 50 degrees of advance so part throttle EGR can be maximized, and change the wastegate control from conventional 7 psi spring for example to one that is always fully open if the wastegate line is at 1 atm or higher and only close it in response to vacuum. See BMW's N54 engine as a reference for how this works. You would need to find space for a vacuum tank to function as an accumulator in this system. That way you can avoid any heat loss to the turbine as much as possible during cold start to heat the catalyst faster. Then find some way to eliminate as much as possible cold start enrichment to light off the catalyst rapidly. Maybe secondary air injection if there's no way to avoid cold start enrichment. Close coupled catalysts in the downpipe are probably necessary. I would also probably swap to EV14s, pick something with the correct spray targeting + dual cone pattern for the intake manifold you're using. EV1 style injectors to pass anything resembling modern emissions requires a very annoying air assisted injector system to break up the droplets at part throttle/idle which still doesn't work that great compared to just having smaller droplets from the injector to begin with. Realistically, you're probably going to be financially ahead if you just pay the fines instead. Or don't drive it into the city center. There's a reason why Nissan never bothered to even attempt certifying an RB for CA/US emissions. The VG30 needed external EGR on top of NVCS to pass in the 90s. Doing all of this work is also distinctly expensive and you're going to struggle to find anyone who is remotely interested in helping. -
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IIRC, it only cost me a couple of hundred dollars to get an Liverpool Exhaust to fabricate a custom stainless resonator for me to fit in the available realestate that I had under the car I actually watched as they did it, took about 1 hour to cut up the material, tig weld the body of it, and then add it to the exhaust 4"in and out, with a packed 5" body, that was about 12" long In the end, it is some blindly simple sheet metal work for an exhaust shop, and some welding
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Highest combustion temperature is achieved at 14.7:1. (or, I should say, lambda=1, because 14.7 is not constant for all fuels). NOx increases exponentially with combustion temperature. So it is in the engine designer/s best interest to find a way to operate at lower than stoich max temperatures if they want to minimise NOx. If you want to minimise CO, you really need to run at least 14.7:1. Any extra fuel can realistically only ever report to NOx. O4 HCs if you are sufficiently sub-stoich, or if the engine's fuel-air mixing is up the shit. All of this presumes that the catalyst is not doing anything, of course. In reality, the cat is there, it is doing things, and how capable it is of eliminating either NOx or CO will depend on its age, quality, design, operating temperature, and how much the engine/ECU is designed to help it along, with fuelling strategies, air pumps, etc. And of course, RBs, even those with very capable aftermarket ECUs, usually don't have anything to help. They are just tuned to make power. -
It's... way cheaper than what SP have on their website? I can only imagine if I say "can you make this muffler, but entirely different dimensions outside of the spec you offer as customization on your page" it would get even more pricey. I was looking at their race mufflers or their 'ultra quiet resonators' which are just smaller mufflers. They start at $166 USD which is $264. SP mufflers resonators start from $299 and are too long/not wide enough/can't be made short enough.
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