From: mark@wdcwdc.sps.mot.com (Mark Shaw)
Subject: Re: emissions
Organization: Motorola Western MCU Design Center, Chandler Arizona
Date: Tue, 6 Oct 1992 16:20:06 GMT

In article (Wayne Johnson) writes:
|> 
|> I have to confess that I no very little about how emissions stuff works,
|> and there's probably a reason that this can't be done, but I'll ask anyways...
|> 
|> I can see how doing something like installing an EGR system or an air pump
|> would be rather difficult on an older engine, but there must be some modern
|> emissions controls systems that could be retroffitted onto an older car to
|> reduce their emissions.  Would it be practical to add a catalytic converter
|> and one of the new TBI systems Holley sells to an older car?  And, if so,
|> how much of an emissions reduction would you see?  Would it be substantial
|> enough to make it worthwile?  I'd suspect you'd see an increase in fuel
|> mileage and throttle response from the injection system as a bonus as
|> well...
|> 
|> It used to be that everybody yanked out their converters because they
|> caused backpressure which affected your mileage and performance, and so
|> they could run leaded gas, but leaded gas has almost completely vanished,
|> and the newer converters are much more free-flowing, right?
|> 
|> (Yes? No? Maybe?)

This is an interesting set of questions.  The concept of retrofitting
an older car is quite feasible in certain model lines/manufacturers
if they use a particular body/drivetrain style for a long period. 
A good example that I am familiar with is the VW water-cooled line --
virtually every model of Rabbit/Scirocco/Jetta share common engine
and exhaust components from 1975 thru 1983.  Even some later Golf/
Scirocco/Jetta components are similar.   It makes it easier to go to
a junk yard and extract the needed components.  The worst models are
those that have no modern day counter part.`

As far as adapting a Holley TBI to your car, the local word it that 
this design (at least the electronics) is not very reliable.  Too bad,
because (as you point out) this would be a straight forward adaption.

If you are talking about a '73 car, the emissions equipment installed
(if operating properly) was designed in the transitional period. 
Converting to a later '70s equipment would only reduce emissions by
about 1/2.  The real improvement comes with the post-81 hardware which
could give you a reduction of about 10:1.  The later systems are
characterized by a "closed-loop" fuel system with Lambda sensor in
the exhaust and a three-way catalytic converter.   Other changes in
ignition were also provided, but I have found that the simple 
closed-loop Lamdba system on my '84 VW GTi produces the same emission
levels as my '88 Chevy Celebrity with all the whiz-bang electronics.

I have been interested in this topic ever since the emissions control 
effort began in the late '60s.  What really annoys me is the clap-trap
approach that was taken (by most Detroit manuf.) in meeting the standards
during the early '70s.  Much of this was due to the crazy percentage
testing done.  When the industry finally realized that the emissions
thing was here to stay and that they could actually get improved 
performance from the new control systems, things started to move
along on their own.  The tougher 1982 standards and test method really
made the closed-loop systems required.  

Rather than dwell on the removal of older cars, I would prefer that the
government force the issue of retrofit kits (at reasonable cost) so that
the individual can decide whether or not to keep an older car on the road.
Right now there is no incentive to either remove them or make them cleaner.
Life goes on....

FYI here are emission stanmdards as reported by EPA and MVMA ( all numbers
are grams per mile; and the pre-1975 numbers are estimated by EPA using
the current tests, the pre-control numbers are estimated by the MVMA and
are somewhat higher than I would guess).

Year              HC     CO    NOx 
Pre-control    10.6   84.0   4.1
1968-1971       4.1   34.0    No Reg
1972-1974       3.0   28.0   3.1
1975-1976       1.5   15.0   3.1
1977-1979       1.5   15.0   2.0
1980            0.41   7.0   2.0
1981-1992       0.41   3.4   1.0

As you can see there is not a significant difference between 70's
versions of emission control.  The big jumps are pre-control to
70's control and 70's control to post-1981 methods.

Mark
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