Does anyone know the part number or official name for these "tubes" ?

[DanInMichigan]

This is my head and some of the tubes are cracked.   They go from the exhaust manifold into the valve cover.  There is no air pump on this motor.  I tried looking them up online but I have had no luck.  What do I tell NAPA?

1979 Chevy 250 straight 6:

[zieg85]

Emission Tubes, at least that is what I typed in an eBay search and some came up. 

[DanInMichigan]

Do these tubes help with ring seal or is there some other purpose?  They can't inject air into the exhaust unless there's a boatload of blow-by.  I'm wondering what will happen if I block them off with brass plugs.

Dan

[bd]

The pipes, check valves and "fresh air" plenum chambers on top of the valve covers are part of the Pulse Air Injection Reactor (or PAIR) emission system.  PAIR relies on exhaust pulses to aspirate fresh air into the exhaust system to enhance oxidation of incompletely burned, hot combustion gases.  It's similar in purpose and function to the Air Injection Reactor system on V8s, less the belt driven AIR pump.  It's a passive system that doesn't hurt engine performance as long as it's functioning correctly.  I suspect that service parts (other than the check valves) are long since obsolete and that defeating PAIR would have no drivability consequences other than a minor possibility of occasional exhaust backfire.  You might have to experiment.

[DanInMichigan]

Thanks, that is very good info.  In a kind of related question, would it be normal for my truck to come from the factory without a catalytic converter?  I wasn't sure what year they became mandatory on trucks.

Thanks,


Dan

[bd]

To the best of my knowledge, all 1979 GMC and Chevy light duty trucks, rated 8500 lbs GVW and lower, that were built for US markets, were shipped with catalytic converters.  So, your 79 C10 would have come equipped with a cat.

[Grey73]

I have capped off many of these systems mostly on V-8's and have only had positive results. It may impact getting it inspected but if your not in a major city I doubt it. I've never had a problem.