I think the whole point of this discussion is that in the seventies the
technology hadn't developed to the point where cars could be designed to
meet emissions and produce maximum power. Instead of saying that
emissions controls sap power, let's say that it's more difficult to
design an engine with maximum power and proper emissions. The only
reason race cars aren't designed with emissions controls is that they
don't have to be. I'm sure a Cosworth IndyCar engine could be designed
to put out the thousand or so horsepower it gets, even with emissions
controls. Of course, there's also the extra weight that emissions
components add.
That good emissions and high power aren't mutually exclusive is quite
true. However, modern cars manage this with complicated electronic
equipment undreamed of by Harry Webster and his team.
According to the Haynes Zenith Stromberg Repair Manual, gas burns most
completely at about a 15:1 A/F ratio. At about 12:1 it produces the most
power. At about 18:1 the engine runs the most efficiently. It would
seem that somewhere between 14:1 and 18:1 would be the best emissions.
One wonders how such a device as an EGR valve actually reduces emissions
when it lowers efficiency somewhat. Apparently, it decreases some
emissions at the cost of other, perhaps less toxic, emissions.
I can't imagine what owners of later TR6's think, but the emissions
controls on the '72 seem to be very practical in nature. There's a
crankcase breather hose, which even the PI models had. That the spark is
supposed to be 4 ATDC may not be desirable for power, nor is the 7.75:1
CR, compared to the 9.5:1 of the PI's. However, the vacuum retard on the
distributor can't possibly have any negative effects. It simply retards
the spark when the throttle is closed during deceleration. I'd say the
ZS 175 CD-SE is about the best designed carburetor for meeting emissions
without sacrificing power, at least when it's new. As with everything,
after several years of wear, all bets are off. I'd say we're better off
cursing Lucas than Zenith, anyway. Zenith did a great job of producing a
carburetor, while Lucas fell down on the task of making a clean-burning
injection system. Don't forget after all, the '71-'73 TR6's are more
powerful than the '69-'70's, if only by a few points.
Jim Ruwaldt
'72 TR6 CC79338U(being restored)
Bloomington, IN
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