Twin exhausts and NCT?

Atlantic Dawn

If a car has twin exhausts from new which exhaust do they test emissions for or do they test both?

The lips

On my old S2000 they just tested one and allowed the other to flow freely.

j2dab

Atlantic Dawn wrote: »

If a car has twin exhausts from new which exhaust do they test emissions for or do they test both?

Usually if they're right handed they test the right one and left handed testers test the left one

bazz26

Depends really some twin exhausts tips are just for show and one of them is actually blanked out or they both go into the same back box. However if they are real then I would imagine it would make no difference which one they would test.

MetzgerMeister

bazz26 wrote: »

Depends really some twin exhausts tips are just for show and one of them is actually blanked out or they both go into the same back box. However if they are real then I would imagine it would make no difference which one they would test.

If you think about it though, when a car has 2 exhausts, 2 silencers etc. when they test one of them alone, is the emissions figure not effectively halved?

Actually, thinking about it now, they probably just double whatever figure they get

bazz26

MetzgerMeister wrote: »

If you think about it though, when a car has 2 exhausts, 2 silencers etc. when they test one of them alone, is the emissions figure not effectively halved?

Actually, thinking about it now, they probably just double whatever figure they get

And then add 400 for good luck. :pac:

Technoprisoner

most twin exhausted cars are v6 or v8 engines...one side would do cylinder 123 and the other 456. They both have lambda regulating probes and separate catalytic converters. so technically both sides would need to be tested. i have never seen one of these cars being tested so im not sure of the procedure but i would imagine they would have to test both sides as they could give different emissions

pippip

MetzgerMeister wrote: »

If you think about it though, when a car has 2 exhausts, 2 silencers etc. when they test one of them alone, is the emissions figure not effectively halved?

Actually, thinking about it now, they probably just double whatever figure they get

Open to correction but aren't emissions values "%" or "per unit" so its the same no matter what amount of emissions are used.

MetzgerMeister

pippip wrote: »

Open to correction but aren't emissions values "%" or "per unit" so its the same no matter what amount of emissions are used.

I haven't a clue

Technoprisoner

pippip wrote: »

Open to correction but aren't emissions values "%" or "per unit" so its the same no matter what amount of emissions are used.

emissions could be different on each exhaust

TestTransmission

I've had 2 different cars with twin exhausts through the NCT.They only test from the one side

Matt Simis

pippip wrote: »

Open to correction but aren't emissions values "%" or "per unit" so its the same no matter what amount of emissions are used.

HC and "soot" are parts per million type figures while CO is a % of total flow. They only ever test one side, no idea if their software is configurable to allow multiple exhausts to be tested (and alter any part of the emission calc).

Not all V6/8/12 cars split the exhaust evenly left and right per bank, but most do, so it would be hard to make a workable "double/quadruple the figure" rule.

zapata

They test the one opposite the fuel filler as that's where the exhaust is located on most regular single exhaust vehicles - for fairness loike....

joujoujou

Stop guessing, start reading. :P



Source: NCT manual available for free on NCT's website.

Matt Simis

Cars dont typically have a higher and lower exhaust but do have a left or right.. :P

joujoujou

LOL

dar83

5 cylinder and twin exhaust... I have the NCT booked in just over a week. I'll try and watch and let you know. :P

Supergurrier

Mine is on the 8th at ten to nine in ze morning

cruizer101

Matt Simis wrote: »

Cars dont typically have a higher and lower exhaust but do have a left or right.. :P

Course they do, your just driving the wrong cars

Cee-Jay-Cee

Technoprisoner wrote: »

most twin exhausted cars are v6 or v8 engines...one side would do cylinder 123 and the other 456. They both have lambda regulating probes and separate catalytic converters. so technically both sides would need to be tested. i have never seen one of these cars being tested so im not sure of the procedure but i would imagine they would have to test both sides as they could give different emissions

Not entirely true. I've had three cars with factory twin exit exhausts and they've all been 4 cylinder engines (accord/S2000/Legacy) I've NCTd all of them and they only ever stick the probe in one side (usually drivers side as its nearest the testing equipment/monitors)

dar83

cruizer101 wrote: »

Course they do, your just driving the wrong cars

Christ, if a Vauxhall is right, I'd prefer to be wrong...

Technoprisoner

CJC999 wrote: »

Not entirely true. I've had three cars with factory twin exit exhausts and they've all been 4 cylinder engines (accord/S2000/Legacy) I've NCTd all of them and they only ever stick the probe in one side (usually drivers side as its nearest the testing equipment/monitors)

but in that case the emissions should be the same from both sides as they use one cat and the lambda probe is on one stream of exhaust fumes