Why the distiction. It seems somewhat arbitrary to me. I know that in theory, R is for "race" and S is for "street", but why? Why are headers not "streetable". Why isn't the intake appropriate for the street? What about cams? Is there any downside to cams? If so, what? And surely there is no reason that the clutch upgrade isn't suitable for street use. Can someone please explain?

 

I believe it all comes down to warranty. "S" products are fully warranteed whereas "R" are not.

Most of the parts are not streetable if they possibly affect emissions. It is illegal to modify a car and affect emissions so everybody labels that "for off-road use only". It's not that the intake, cams or clutch aren't appropriate for the street it's just that Nissan doesn't want to deal with the hassle of making them street legal. Some parts, like clutches for example may cause damage to other warranteed parts (transmission) and Nissan doesn't want to have to be responsible for replace/repair in those cases.

 

a clutch can have an effect on everyday driveability. if you get a clutch that can handle more power, it needs more gripping power which means that the clutch pedal will be harder to push in. also, you would have to rev match exactly or the car will jolt every time you shift.

 

Will these parts make the car emissions illegal, or will they simply "affect emissions". I can see the issue if they make the car illegal for the street based on emission standards,but not otherwise.

 

I know from four other cars that I have modified with higher clamping force clutches that this is not true.

 

Not necessarily. Some may have no effect but because of regulations requiring the manu. to certify that it has no effect they take the easy way out and label it off-road use only.

Some members have reported passing emission test with high flow CATS, etc. That doesn't guarantee it will happen in every state and in every type of test and condition.

Like I said, I believe it is more warranty driven then anything else.