Great discussion guys. Just a few points.
I don't see how you can change cams and get more power without affecting longevity, fuel efficiency, emissions, etcCareful what you lump together. Things like fuel efficiency, emissions, volumetric efficiency, HP, Torque ect can all be measured easily. Especially, since they are single instant metrics. Now, lumping in something like longevity is dangerous. To really get a "longevity" measurement, you would need to test enough engines over x-time to get some sort of significant measurement, but...there are about a thousand things that affect the life of an engine. Driving style is one. Use is another. But...what about an engine that gets a cam and loses a main bearing? The life of *that* engine is shorter, but...it also had a cam. What if the failure was due to something like a bad babbitt on that bearing? Remember all those warning on drug labels? Wonder how death could be a side effect of a simple laxative? Well, someone died during the trial, most likely not because of the laxative, but he still died with the laxative on board, so it is indirectly related. <img src="/forums/images/graemlins/smile.gif" alt="" />
Again, be careful what is included in the trade off discussion. Chase said it pretty well and I think Wayne agrees, there are tradeoffs with when and where power happens. Does this affect the engine? Who knows. I would have to say a proper cam, on a properly tuned engine probably has a marginal effect upon the life of the engine. Run it rich for too long and wash down the cylinder walls and the rings are going to go. Fault of the cam or the operator? Too much lift, not enough valve spring? Again, cam or operator. The operator and operation injects too much variability to make an even close to valid argument either way.
There are tradeoffs, usually in the power/torque curve, but I'll also bet in emissions. This might be important if you're close to the line and living in California. This is a side discussion. Regardless of emissions, if you put a non CARB approved cam in a Ca vehicle it is illegal. The design of the cam, the engine or the car is no longer a discussion point because it does not matter. Now, passing smog with a Delta cam is a good thing, it means that the engine is running "clean". But it is beyond the scope of this discussion. Now, how about the question of "Should Ca (or anywhere) have anything other than a sniffer test?" Does the rest really matter beyond generating revenue for someone, somewhere involved with smog repair?
As far as emissions go, it's increasing the total amount of exhaust gases (because it's allowing more air/fuel into the combustion chambers), but it's not doing anything to increase the concentration of harmful pollutants found in those exhaust gases. Sorry Phil, but this is an oversimplification. A/F ratio, mixing, swirl, burn time, actual compression are all affected by a cam. These, and more, affect emissions. Looking it as just holding the door open a little bit longer is not quite accurate.
Same thing with headers, really...you still have "x" ppm of any given pollutant, but more exhaust in total. Again, too vague. Headers may make an engine more "efficient" in filling the cylinder, but...the overall increase in total exhaust volume is minimal. The engine is still just a big air pump in the end, getting more out is difficult. PPM measurements are still valid.
some redneck tweaker once told me to cut a hole in the exhaust pipe of a car I had that wouldn't pass smog. That wouldn't have done anything to affect the sniffer test because it's measuring parts per million, regardless of how many parts there are in total.The concept is to allow fresh air into the exhaust stream. This reduces the concentration. Tweaker or not, there are people who do this. If fresh air does not get siphoned in, then the exhaust leak also affects the measurement because I belive the machine tests not only via sampling, but via time. Less exhaust flow than actual will give you a lower than actual reading.
Good Luck,
Michael
