Not your typical cam question

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Feb 10, 2004 | 12:39 PM

Beefcake61

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From: Altoona, PA

Not your typical cam question

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. I will further add that I'm still knew to this game, and don't understand a lot about cams and the like. Thanks for any and all information that you all provide me with!

Thanks
Rob

Feb 10, 2004 | 12:49 PM

BBADWS6

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Well the cam question is pretty easy to answer. When you get a larger camshaft you have more duration which causes valve overlap( the intake and exhaust valves stay open for longer), this is what causes the idle to be choppy. When the valves are open longer you get more fuel into the motor, and more unburned fuel out the exhaust. Since you dont have as clean of a burn you put out more environmently "unfriendly" gasses.

Feb 10, 2004 | 12:57 PM

Beefcake61

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From: Altoona, PA

Thanks for the quick reply BBad, as well as the information. That should help me out with my paper I'm going to write. But would you happen to know if this is a similar reason for why deisel vehicles are less environmentally friendly??

Thanks again
Rob

Feb 10, 2004 | 04:31 PM

BBADWS6

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Man i have no clue aboue deisels! The might be someone on here that knows though

Feb 10, 2004 | 04:45 PM

JakeL

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Quote:

Originally Posted by BBADWS6

Man i have no clue aboue deisels! The might be someone on here that knows though

Diesels are unfriendly for a couple reasons:

1.) Sulfur content in American made diesel (bad for catalysts)
2.) Since diesels don't have a throttle, the engine is controlled directly by the amount of fuel injected. As such, there's usually unburnt *air* leftover (rather than unburnt fuel more common in gas engines), that makes normal catalysts not work as well. I can't recall the reason offhand right now either, but for some reason, they produce more soot too.

I'm no expert, I've just read a few articles on diesels lately, and that's all I can remember.

-Jake

Feb 10, 2004 | 06:09 PM

Jip99z

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Most diesel fuel is getting close to being sulfur free now, epa made all manuf. sut down on sulfur by 97% beginning this year or late last year. A diesel works by compressing air, then diesel is injected into the cylinder and BOOM! you have an explosion. Most diesels DO NOT come with cats because diesels donot let out the harmful chemical, Carbon Monoxide. Diesels are also more efficent then gas power motors (by about 37%) and need less fuel to create more power than gas. And the black soot you see diesel power vehicles emitting is unburnt DIESEL, no 'Air', usualy caused by more fuel than the motor can burn in one revolution. JP

Feb 10, 2004 | 09:04 PM

99 Black Bird T/A

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Also building on what was posted above. The reason the overlap becomes and issue with bigger cams is because reversion occurs. This means the overlap allows some of the exhaust gases to flow back into the intake at low rpm. The exhaust gases dilute the intake charge so it doesn't burn efficiently or completely. This causes the car to burn dirty.