I'm rebuilding a 351EFI for my 89 F250. I will be using a pair of 70 two barrel heads with some minor porting on the engine. Because of the lack of smog holes in the back of the heads I don't know what to do with my air pump. Seeing as how the holes just dump air into the exhauts ports on the later heads I could plumb some lines into the headers. Or do you think that this is a waste of time and I can do away with the air pump all together? Does the air pump effect the operation of the O2 sensor at all? Also will the slightly improved air flow of the bigger heads screw up the speed density system? The cam I am using isn't that radical so vacume shouldn't be a problem. Any information would be apriciated.

 

[updated:LAST EDITED ON 09-Dec-02 AT 01:32 AM (EST)]These are good questions. Continuing to use the AIR pump is a good idea. It helps keep the Oxygen sensors clean. It also helps the Oxygen sensors get warm enough to operate. And it helps keep the catalytic converter from clogging. In addition, it helps get the Reduction catalytic converter warmed up so that it can operate.

I believe that you can have your 70 heads 'gun drilled' for a Thermactor passage. Then have the thermactor bumps drilled to intersect that newly drilled passage.

The thermactor systems is used during the warm-up cycle. When the engine reaches operating temperature the diverter valve switches the air supplied by the AIR pump away from the theractor ports and to the Oxidation side of the catalytic converter. Then the computer goes into 'closed loop' mode where the Oxygen sensor feeds a signal back to the computer about the mixture.

So, to make a long answer short, yes, the thermactor system would goof the Oxygen sensor if the diverter valve did not divert the air around the thermactor system after the engine warmed up.

Edit; regarding the ported heads affecting the computer controlled system. No, if you keep the stock cam or use a computer compatible cam, the speed density system will work fine.

 

Thanks for the help,
I've seen kits that headman offers for it's headers on chevy engines that allows you to use the air pump. I believe that chevy has the passages in the manifolds rather than the heads. I think that I might try using some 3/8 brake line and make some external thermactor passages on my headers rather than drill the heads. The end result should be the same.

 

Since it was locked up anyway and I also had the earlier heads, I canned the entire thermactor system on my '87 when I replaced the engine. I researched this before doing so as well. The computer really doesn't care as long as you leave the TAB and TAD solenoids plugged into the wiring harness. Leave them out and it will set a trouble code. I never had any problems whatsoever. BUT - I wasn't running cats either. I'm not sure how this will affect that situation for sure, but I'm sure that Paul is probably right. It won't do them any good.

Batman