What exactly is the deal with the Californian Air Resources Board (CARB) as it relates to the secondary charcoal filter air intake requirements on modern cars in the US? Yes, I am fully aware of this "50 states" legal blurb that aftermarket intake parts makers like to quote and I am aware that aftermarket parts manufacturers can obtain an Executive Order from the CARB that makes their parts fully "emissions legal" across all 50 states (TRD even sell a CARB complaint sticker you can stick in the engine bay next to the TRD intake airbox). But such manufacturers can only do this if the part they make has zero effect on the vehicle's emissions compared to the OEM part. And in 99% of cases that I can tell, this means that all air intakes for road-registered vehicles need to have that secondary charcoal filter inside them - restrictive as it is - that absorbs fuel vapour fumes from an engine immediately after shutdown (as they make their way from the inlet manifold back out the throttle body and back out the intake).
But my specific question is this: why do some cars seem to be mysteriously exempt from it when I can personally see no engineering reason as to why? By that I mean I wish to be educated since I am not an engineer nor a pollution guru. Just because I cannot see any technical reason why some cars are exempt from ever needing this secondary filter does not mean there is not a valid reason. But I'd like to know on a scientific basis what that reason is. And yes, I have asked the CARB, but they do not seem to be interested in fielding technical enquiries from the public even though they have a "help line".
So lets take Toyota / Scion for example. Every single current model Toyota and Scion car out there has this secondary charcoal filter with one exception - the Scion FR-S (Toyota 86). This filter stuffs up your throttle response (biggest negative) and will cause a very slight power drop too (admittedly maybe 1 - 2%) but many are permanently heat-riveted into the top half of the airbox so cannot be replaced even though they get very dirty over time. Look at the internet to see how dirty these filters can become after only a couple of years.
Now TRD make an aftermarket intake for almost every model out there, including the relatively new and humble Scion iM (Toyota Corolla Hatch / Auris Hatch). But somehow the FR-S does not need one - either in OEM form or TRD form. Why? There is nothing special about the engine technology and nothing special about the intake system compared to any other Toyota or Scion out there - it's the same deal - if anything, the other models that Toyota make have a more convoluted intake scoop than the FR-S and so less fumes are ever likely to make it out of the intake to begin with!
So what other cars seem to not need these filters and if so, what makes them special? It's almost as if Toyota did some sort of "deal" with someone somewhere so that their budget-priced sports car could do without a piece of emissions equipment that every other car needs. Even all BMWs in the US that I am aware of need these filters! Same with Mercs so far as I can tell.
Sure, a lot of people dremel them out of the intake and that is that but of course doing that no longer makes the car legal in several states.
But my specific question is this: why do some cars seem to be mysteriously exempt from it when I can personally see no engineering reason as to why? By that I mean I wish to be educated since I am not an engineer nor a pollution guru. Just because I cannot see any technical reason why some cars are exempt from ever needing this secondary filter does not mean there is not a valid reason. But I'd like to know on a scientific basis what that reason is. And yes, I have asked the CARB, but they do not seem to be interested in fielding technical enquiries from the public even though they have a "help line".
So lets take Toyota / Scion for example. Every single current model Toyota and Scion car out there has this secondary charcoal filter with one exception - the Scion FR-S (Toyota 86). This filter stuffs up your throttle response (biggest negative) and will cause a very slight power drop too (admittedly maybe 1 - 2%) but many are permanently heat-riveted into the top half of the airbox so cannot be replaced even though they get very dirty over time. Look at the internet to see how dirty these filters can become after only a couple of years.
Now TRD make an aftermarket intake for almost every model out there, including the relatively new and humble Scion iM (Toyota Corolla Hatch / Auris Hatch). But somehow the FR-S does not need one - either in OEM form or TRD form. Why? There is nothing special about the engine technology and nothing special about the intake system compared to any other Toyota or Scion out there - it's the same deal - if anything, the other models that Toyota make have a more convoluted intake scoop than the FR-S and so less fumes are ever likely to make it out of the intake to begin with!
So what other cars seem to not need these filters and if so, what makes them special? It's almost as if Toyota did some sort of "deal" with someone somewhere so that their budget-priced sports car could do without a piece of emissions equipment that every other car needs. Even all BMWs in the US that I am aware of need these filters! Same with Mercs so far as I can tell.
Sure, a lot of people dremel them out of the intake and that is that but of course doing that no longer makes the car legal in several states.
