Pumping Air to a Catalyst

[1lejohn]

I want to install cats on my 85 truck. It has headers and dual exhaust. The cats will have to be mounted far back in the system. The stock air pump brackets, fittings etc. are long gone. I would like to go back with them, but they are hard to find. I have an electric pump from a car that I think would work. My thought is the pump would only need to run at start up to help the cats fire off. A couple of check valves welded to the pipes and some hose from the electric pump might work. Has anyone tried this set up? Thoughts concerns?

 

[Ricko1966]

I know nothing about electric air pulse pumps,but do understand how Mazda and Mitsubishi did it without air pumps of any kind. You might want to investigate some,it may be the simplest way. Basics is at Idle a vacuum operated valve opened a valve. This valve allowed air from the air cleaner to the catalytic converter to pass back and forth. A reed valve in the air cleaner kept exhaust pulses from going into the air cleaner on a positive pulse but allowed air to be drawn on a negative pulse. No parasitic draw from a belt driven pump,no electric pump,just exhaust pulses and reed valves.

 

[Matt69olds]

GM warmed the converters in the most reliable way at the time. Meaning they calibrated a cold start with increased idle speed, delayed the converter clutch from locking until the engine reached a certain temp, all to keep engine rpm higher.

They use the same strategy now, except the disable some of the higher gears in the transmission, and moved the converter itself closer to the engine.

I would think as long as the engine is tuned correctly, holding the engine at a higher idle speed right before an emissions check should be good enough.

 

[ali_c20]

I want to install cats on my 85 truck. It has headers and dual exhaust. The cats will have to be mounted far back in the system. The stock air pump brackets, fittings etc. are long gone. I would like to go back with them, but they are hard to find. I have an electric pump from a car that I think would work. My thought is the pump would only need to run at start up to help the cats fire off. A couple of check valves welded to the pipes and some hose from the electric pump might work. Has anyone tried this set up? Thoughts concerns?

You can wrap the exhaust pipes to the cats to warm up quicker and keep the exhaust gas temperatures high. After market race cats are pretty slim and could be mounted closer to the headers in your system.

 

[mibars]

In an S2000 I had some time ago an electric pump run for a minute after a cold start on a timer and it shut off during acceleration. I guess you could make it vacuum controlled.

You can wrap the exhaust pipes to the cats to warm up quicker and keep the exhaust gas temperatures high. After market race cats are pretty slim and could be mounted closer to the headers in your system.

That's a good idea, both moving to a small metal sports cat converter closer to the headers and wrapping the exhaust & headers to keep the heat in. It will help keep the engine bay cool too. I've used a Magnaflow cat in all my cars so far.

layed the converter clutch from locking until the engine reached a certain temp, all to keep engine rpm higher.

I was always wondering why the torquer converter is not allowed to lock on a cold engine, I though it had something to do with viscosity of the ATF affecting how the clutches would be activated when some of the flow was to be redirected to the converter clutch. If I recall correct there is a temperature switch inside 700R4.

 

[CorvairGeek]

I was always wondering why the torquer converter is not allowed to lock on a cold engine, I though it had something to do with viscosity of the ATF affecting how the clutches would be activated when some of the flow was to be redirected to the converter clutch. If I recall correct there is a temperature switch inside 700R4.

Locking a torque converter on a "cold" engine could allegedly cause driveability problems. GM allowed torque converters to lock at about 125F (engine temp) on various platforms, which is still quite cool.