Well I have resisted the urge to jump in to this, but it is time so I will jump
in with both feet (albeit 3 days late).
I think there are really three important points to remember here
1 Good complete combustion results in the best power output (for all but quite
radical motors) and lowest emissions. HP and low emmisions are not mutually
exlcusive.
Most vehicles with good relatively modern engine designs (even 60's vintage,
excepting some high performance designs) are capable of passing emisson
requirements well into the 80's so long as they are properly maintained.
Some engines are just not as efficient as others(due primarily to either design
considerations or manufacturing tolerances) This inefficiency sshow up in
unburned HC at the tailpipe.
There are two perfomance modifications that will cause a normally efficient
motor to burn unclean, cam overlap and making the mixture a little richer. A
the cam overlap will spill intake air out through the exhaust valve. With a
good multiport EFI system this problem is overcome by delaying the injection of
fuel until after the ex valve closes. Even with EFI I believe ideal horsepower
mixture is about 14:1 whereas peak economy is about 14.7 -15 :1 (better check
the books though).
2 Many PC devices are really unneccessary, designed primarily to enforce
compliance on cars that are drastically out of tune and or poorly maintained.
Many devices of this nature were fitted on vehicles in the 70's and 80's before
it was an economic requirement to address the matter in terms of point 1. This
is really one of the reasons the Japanese did so well in that period. Unlike
the americans and the british they focused on making the engines stay in tune
longer-- they attacked at the root of the problem. They also made specific
warranty adjustments that were more effective at requireing maintenance.
A great example of this is a 1985 truck I am aware of locally that is running
a dodge 1974 360 engine with all emmisions disconnected (save air pump and cat
required for visual), and non emmision carb . This vehicle passes the sniff
test by a factor of 4. And runs real well. It goes without saying that this
engine is in excellent condition and is well tuned . As any engine new or not
(is going to be dirty when it begins to faild
3 The only test that should be allowed in the ideal world are performance based
tests. I don't mind an inspector verifying that I am using a non vented fuel
tank, But I don't believe any agency should be able to tell me which camshaft I
must use when I do a rebuild so long as the engine passes the sniff. When I
build a motor I will try to build as efficient a powerplant as possible that
naturrally results in better emissions.
There is a cost benefit that must be weighed in all this type of situation.
When we make cars that pollute less than trees (at least at the tailpipe). I
think we are nearing the point where cost may soon exceed benefit. On this note
and I will say I have not found the degree of backup I would like to for this
claim but a friend who worked training dealers on emission systems told me in
1981 that a well tuned new car at idle would mesure less output than a pine
tree ( I assume a large one, apparently it is important to specify the type of
tree as well as some seem to be dritier than others) I also am not aware of
which gases he was refering.
Well now that I have made a complete fool of myself I will put on my flame suit
and retire to my little den and hide
Tom Leake
CTC 50609 L
CTC 50250 L (one of these is a donor, not sure which one yet)
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