Message text written by "Jim Muller"
>Here is another data point and opinion.
Well, there seems to be plenty to go around...
>On many cars, the pump is siezed so you either remove the belt or spend
>big bucks on a new pump.
Pumps sieze up due to either lack of use or (more likely) someone removing
the belt and the resulting exhaust gas that leaks past the check valve
(which is quickly destroyed since it wasn't designed to deal with exhaust
gas temperatures) and the pump (which is a moving vane style with close
tolerances) corrodes and it is the corrosion that fouls up the works.
>If you're going to remove the belt, you might as well remove the pump
>to save its weight
True, and clutter.
>and plug the injector tubes with the appropriate bolts
>(or weld (or braze or whatever) them closed), easier to do wih everything
>disassembled.
Thus making it that much more difficult for any future owner to reverse the
process.
>As for its contribution to cleaner emissions, its purpose was to
>provide oxygen for the catalyst.
The air pump was introduced on the TR6 in 1974-5. The TR6 never had a
catalyst. The air pump was introduced on American cars well before the
catalyst was so obviously there is benefit to introducing air into the hot
exhaust aside from the benefits to catalytic functions.
>But the catalyst is not likely to be chemically functional after all this
time.
Only if you've run leaded gas in there at some time.
>By today's standards these cars weren't especially clean anyway.
True. But just because it isn't perfect doesn't mean it isn't worth doing.
<snip>
> The air pump did rob a lot of power but mainly due to its
mechanical load, a bigger deal on smaller engines like the Spitfire
than on the TR6.
Looking at the teeny belt that drives it it can't take much power. Less,
certainly, than the alternator. Less than a horsepower, I'd say.
>Exhaust backpressure shouldn't be affected much
>because the amount of air it moves is quite small compared to the
>exhaust itself.
True, but the higher exhaust temperatures means more exhaust gas volume
meaning more resistance to flow. But then, if th effect is trivial at
higher exhaust flow rates (And this is where it counts) then the temp rise
is, too.
<snip>The catalyst itself
was a also big restrictor in the exhaust system.
I was once told that a catalyst presents no more back pressure than an
equivalent length of pipe. Provided the honeycomb hasn't melted and
collapsed.
But then none of us were there when these systems were developped and are
only looking in through the foggy window of time. But, I feel that any
thing we do to flout the emissions laws only makes it that much more
difficult to sustain our hobby in the eyes of the rest of the public (who
wonder why we just don't go buy Miata's and Mini's) so I feel the effort to
keep the air clean is worth while.
And that's my opinion.
Dave
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