I realize that the air pump and system (74 L82 4spd) will take away some power, but what other drawbacks are there to it? For instance; will it cause a stumble from time to time at low rpm? The car will run and idle fine once warmed up. Then if you wait 10 or 15 minutes and restart the car, it seems to run rough for a few minutes untill it is warmed up again, then smooths out. Any thoughts? I have a Pertronix ignition, hot coil and use "Rapid Fire" plugs. Thanks, Ray
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Re: A.I.R. system
Emission controlled cars typically have retarded timing relative to pre-emission cars. This increases EGT, which helps oxidize HC and CO in the exhaust, but it reduces fuel economy and can make the car run hotter, which can be a cause of rough running due to excessive vapor generation in the carburetor bowl.
The AIR system does not take a lot of power, but if you don't have to be emission tested it can be removed or "gutted" and left on the car if you want to retain original appearance. Also, the ignition curve can be reworked to a more pre-emission specification, which would normally involve increasing initial timing, driving the vacuum advance from a full manifold vacuum vacuum source and bypassing TCS if installed.
Duke -
Re: A.I.R. system
Mine was stripped of the system, so I cannot tell you about performance from a first person account, but the system should draw minimal power as the pump is driven through a belt and pulley. As to additional performance draws, the pump forces air into the exhaust manifolds to mix with any unspent fuel to reduce pollution, so I can see pressure issues, but am not sure of any other drawbacks.
I have easily passed emissions testing without the system of the TCS, so it may not be needed.Comment
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Re: A.I.R. system
The pump itself absorbs very little power - many will, however, eventually seize as the outer edges of the vanes wear and fill the pump cavity with the fibrous vane material; this is usually preceded by increased noise, so at least you'll get advance warning.
The biggest negative of the A.I.R. system is the retarded spark at idle and the original distributor curve, both of which are readily cured with no visible clues. The other negative is the vacuum leak that occurs when the diaphragm in the diverter valve fails (and they all do - they weren't designed to last 30 years), curable by inserting a BB in the signal hose to the valve.
However, when the diverter valve diaphragm fails, the internal spool valve fails full open, so the pump is dumping air into the exhaust manifolds all the time, which results in "popping" from the exhaust on overrun (when the valve was working, it dumped pump outlet air through the little "muffler" on overrun instead of into the manifolds). This can be cured by "gutting" the pump (removing the vanes so it's simply an idler), and the finish on the tubular air manifolds can be protected by removing the fittings at the manifolds, pulling out the insert tubes, and installing a #10x 1/2" flat head machine screw in each cavity before re-installing the air manifolds.
The diverter valves were discontinued many years ago by GM, are not rebuildable or reproduced, and NOS replacements are both rare and VERY expen$ive.Comment
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Re: A.I.R. system
What about just disconnecting the belt unless you intend to show/judge the car? Will the diverter valves and all of the associated hardware just be standing by.
GaryComment
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Re: A.I.R. system
Gary -
Yes, that will accomplish the same thing in terms of killing the airflow, but you should probably also do the "BB in the vacuum hose" trick to take care of the (potential) vacuum leak.Comment
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