Hello everyone, I have an unsual question for you cam guys. I'm currently working on a paper dealing with vehicle emissions. I was curious to know if anyone knew why it is harder for the larger, more aggressive cams to pass emission tests. I would also like to know who has passed (legally) emission tests with a cam or any other "un" environmentally friendly mods. Thanks for any and all information that you all provide me with!

Thanks
Rob

 

Come on guys, don't you wanna help out a college kid in need?!?!? Does any one have an idea?? Any and all information is welcome

Thanks again
Rob

 

Don't know the answer, but I'd suggest maybe posting this in the lounge...........

 

These big cams usually have more overlap, in which the intake and the exhaust are open at the same time.. In the high rpm's, this helps fill the chamber with fresh intake.. but some of it also escapes out of the exhaust, especially in low rpms.. you'll fail your hyrdocarbon's count. There's a thousand more variables/reasons how this effects the combustion and resulting variosu pollutants.

But basically, the large cams are really only happy in the higher rpm's they were designed for. You can make them more friendly by reducing the overlap and instead getting the valves to simply open even faster and higher.. but that adds alot of stress on your valvetrain.

The lounge or the advance tech guys could probably fill in the real details.....

 

It has a lot to do with the lobe seperation angle, and like ken said the valve overlap. Take a stock 98-00 cam they have a lsa around 118-119 where a good performance cam will have a lsa of about 112. At higher rpm's where the motor is spinning fast the valves are open at the same time a very short amount of time but at say idle they are open together about 10x's longer.

I dont know if this is 100% accurate but it's my theory and attempt at an explination. If it is inaccurate someone please correct me.

 

Thanks guys, its seems to be sinking in a bit. I think i'm begining to understand everything a lot better too!! Thanks again

Rob