Coc or nox of nissan skyline

[drifter17a]

live in the UK, and London has introduced a Low Emission Zone (LEZ) that requires individuals to pay £13 if their car doesn’t meet the required emissions standards.

 

The standard specifies that NOx emissions must be less than 0.08 g/km (i.e., the vehicle must meet Euro 4 standards or better, which generally results in NOx levels of around 0.08 grams per kilometer).

 

I reached out to Nissan UK, and they advised me to contact Nissan Japan directly. Does anyone have contact details for Nissan Japan or any certifications of conformity that show the emission details or NOx levels for the RB25DET engine?

 

Any guidance would be greatly appreciated.

[GTSBoy]

3 hours ago, drifter17a said:

Does anyone have contact details for Nissan Japan or any certifications of conformity that show the emission details or NOx levels for the RB25DET engine?

No, but they will be WAAAAAAY too high. You will never get your ticket.

[soviet_merlin]

I presume it would take more than just slapping a big modern catalyst on the exhaust?

It's interesting though, looking at the old sales brochures and listings it does not mention anything about emissions. No one cared.

[MBS206]

If you're driving something like an R32 through to R34, no chance of meeting Euro4.

Euro4 came out in 2006, and car manufacturers back then were complaining how hard it would be to meet those regulations. Not a chance a vehicle 10 years earlier is going to be compliant.

[Kinkstaah]

Well, I have my IM240 results with a cammed LS1...

My Nox was 0.11 and my CO g/km was 0.2.

Euro4 is 0.08 and 0.1 respectively. I'm gonna say for a stock RB this is actually plausible, BUT in Australia they were complied pre-Euro2, so the limits were:



Which as you can see, is way higher. I'd say a stock RB with a new OEM Cat could? actually pass Euro4 for NOX but you'd probably have to do a hell of a lot of testing to prove it, and getting a car emissions tested and carrying a certificate of emissions when/if you get pulled over may be cost prohibitive if it's even allowable to get your car tested and re-classified.

You'd have to find out what the UK Govt is using as reference material. It may be non-negotiable.

[MBS206]

2 hours ago, Kinkstaah said:

Well, I have my IM240 results with a cammed LS1...

My Nox was 0.11 and my CO g/km was 0.2.

Euro4 is 0.08 and 0.1 respectively. I'm gonna say for a stock RB this is actually plausible, BUT in Australia they were complied pre-Euro2, so the limits were:



Which as you can see, is way higher. I'd say a stock RB with a new OEM Cat could? actually pass Euro4 for NOX but you'd probably have to do a hell of a lot of testing to prove it, and getting a car emissions tested and carrying a certificate of emissions when/if you get pulled over may be cost prohibitive if it's even allowable to get your car tested and re-classified.

You'd have to find out what the UK Govt is using as reference material. It may be non-negotiable.

Having a read online, need to get the emission standard from their logbook, or the manufacturer as to what Euro it meets.

If it doesn't meet it, you can modify the car to meet it, and then go through a big government process.

 

As vehicle is pre Euro4, it won't be meeting it.

 

I'd honestly doubt anything but the NEO motors have a chance of getting near the EURO4.

NEO is specifically for getting better emissions.

[Murray_Calavera]

Would it be possible to meet these emission standards on e85?

[GTSBoy]

41 minutes ago, MBS206 said:

I'd honestly doubt anything but the NEO motors have a chance of getting near the EURO4.

Nah, for the Neo. The Neo met the then-current Japanese LEV numbers, which were only a small step change better than what the vanilla RBs were doing. And.... I strongly suspect that the only Neo RBs that actually met the LEV rules were the NA ones. It seems hella unlikely that any late 90s turbo engine could meet the CO limits. NOx and fuel consumption maybe - the turbos were lower CR so stood a chance of being OKish on NOx, and if the testing regime didn't require running at enough load to make a lot of boost, then the specific fuel consumption could have been OK. But really, as soon as any significant boost was on board the mixtures get quite rich, CO inevitably has to go up, and fuel consumption goes to hell.

The amount of ECU required to meet Euro4 was substantially higher than what was in those things too. Lots of modelling. It's probably mainly the reason why there were no real turbo offerings from Nissan, even in the Skylines, in the 2000s, because they just couldn't make them meet the standards. So we got that pox-ridden French V6 instead.

35 minutes ago, Murray_Calavera said:

Would it be possible to meet these emission standards on e85?

Maybe, but there's no that many pineapples in the UK, so I don't think they get to even know what burnt E85 smells like. And I'd be pretty sure that you'd have to jump through even more hops to get a certification of some sort that was limited to a specific fuel.

[Kinkstaah]

I was just working on the assumption that a cammed V8 is significantly less polluty than a Japanese I6 turbo was at the way they tested it in an IM240. Perhaps I'm wrong! Perhaps cutting one of the readings I got in half is a tall order.

I don't know too many people who actually got their cars emission tested with a RB to really compare the data.

[Murray_Calavera]

33 minutes ago, Kinkstaah said:

I don't know too many people who actually got their cars emission tested with a RB to really compare the data.

I'm one of them.

I wasn't trying to game the system when I had this test done, the tune was as I drive it every day. 

[Murray_Calavera]

Forgot to add, this was on pump 98, stock turbo @ 10psi, stock injectors, Haltech pro plugin ECU. 

[soviet_merlin]

43 minutes ago, Murray_Calavera said:

I'm one of them.

I wasn't trying to game the system when I had this test done, the tune was as I drive it every day.

Had a good chuckle because it is listing THC g/km. Though it is not tetrahydrocannabinol but total hydrocarbons.

Interesting how the numbers seem so much worse compared to Greg's big V8.

[Murray_Calavera]

11 minutes ago, soviet_merlin said:

Interesting how the numbers seem so much worse compared to Greg's big V8.

I'm not surprised, I favour a bit of a richer tune which for sure isn't helping the emission numbers.  

[GTSBoy]

Let's face it. 90s turbo 6 with 80s tech in it is not going to be the thing that runs as clean as a whistle.

[Kinkstaah]

46 minutes ago, Murray_Calavera said:

I'm not surprised, I favour a bit of a richer tune which for sure isn't helping the emission numbers.  

The way they do the test you would be very lucky to ever hit any cell that isn't aiming at 14.7



This was my result... Really not sure what's going on there!

[GTSBoy]

20 hours ago, Kinkstaah said:

The way they do the test you would be very lucky to ever hit any cell that isn't aiming at 14.7

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.

[joshuaho96]

23 hours ago, Murray_Calavera said:

Would it be possible to meet these emission standards on e85?

I'm pretty sure if it's considered a gasoline powered vehicle you have to do certification against a fixed, very expensive certification fuel. 

20 hours ago, GTSBoy said:

Let's face it. 90s turbo 6 with 80s tech in it is not going to be the thing that runs as clean as a whistle.

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.

On 3/12/2025 at 9:19 AM, drifter17a said:

live in the UK, and London has introduced a Low Emission Zone (LEZ) that requires individuals to pay £13 if their car doesn’t meet the required emissions standards.

 

The standard specifies that NOx emissions must be less than 0.08 g/km (i.e., the vehicle must meet Euro 4 standards or better, which generally results in NOx levels of around 0.08 grams per kilometer).

 

I reached out to Nissan UK, and they advised me to contact Nissan Japan directly. Does anyone have contact details for Nissan Japan or any certifications of conformity that show the emission details or NOx levels for the RB25DET engine?

 

Any guidance would be greatly appreciated.

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. 

[MBS206]

1 hour ago, GTSBoy said:

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.

Many many moons ago, I was chatting with Andy Wyatt, about his auto ignition tuning. One of the HUGE things he said to me, when tuning for power, right where you hit peak ignition timing for your max torque, dramatically increases NOx emissions. He was finding in testing, particularly on engines you could advance timing beyond peak torque, that backing the ignition timing off a couple of degrees only made for a small drop in torque (compared to if you keep backing it off further the same amount of degrees) but dramatically reduced NOx emissions.

I'd say targetting for 14.7, and he's even mentioned in some scenarios going slightly leaner, and pulling a few degrees of IGN timing will help pass for emissions quite a lot. However, who tunes an RB for emissions

[GTSBoy]

1 hour ago, MBS206 said:

Many many moons ago, I was chatting with Andy Wyatt, about his auto ignition tuning. One of the HUGE things he said to me, when tuning for power, right where you hit peak ignition timing for your max torque, dramatically increases NOx emissions. He was finding in testing, particularly on engines you could advance timing beyond peak torque, that backing the ignition timing off a couple of degrees only made for a small drop in torque (compared to if you keep backing it off further the same amount of degrees) but dramatically reduced NOx emissions.

I'd say targetting for 14.7, and he's even mentioned in some scenarios going slightly leaner, and pulling a few degrees of IGN timing will help pass for emissions quite a lot. However, who tunes an RB for emissions

Yes. All of this.

But even when you get the NOx as low as you can go on an RB, it will no doubt still be way too high. Same with CO and HCs. The tech and the tuning time just isn't there.

[MBS206]

1 hour ago, GTSBoy said:

Yes. All of this.

But even when you get the NOx as low as you can go on an RB, it will no doubt still be way too high. Same with CO and HCs. The tech and the tuning time just isn't there.

100% agree.

Best bet on an RB will be NEO, but even it will be a long way off.

Emissions is one of the big reasons car manufacturers went to DBW and constantly variable cams. When cruising, open the throttle right up, but reduce dynamic compression so low, that it's basically an unrestricted air pump moving very little air.