A little knowlege is a dangerous thing - volume two.

Ok, I see from the shop manual, that there are two emission control systems, imco - used on light duty, 2V, 360's and 390's with automatic transmissions, and thermactor, used on 360's and 390's with manual trannies. It also says that the dizzies and carbs from one do not interchange with the other due to "...special calibrations for each exhaust emission control system."

So, my question is why have I not heard about this on this site before this? Is this so basic that it's just common knowledge (for everyone but me)? Why don't the parts places ask which system you have when you ask about a replacement distributor? I hear nothing about "thermactor heads" or "thermactor exhaust manifolds" - why?

Does anyone out there run thermactor engines? Anyone care to discuss?

 

Seems to me that the 'factory' HAD to specify certain parts in order to qualify an emissions system for sale in the U.S. Otherwise, one couldn't be certain that it would meet the standards of the day... In case you put the wrong dist in, or a carb with a slightly different choke pulldown.. or whatever.
The thermactor system was basically adding an air pump to the exhaust system, along with exhaust manifold(s) that had fittings and injector pipes that stuck into the exhaust gas flow. The IMCO relied upon 'IMProved COmbustion' to cut emissions. They added a bunch of air flow controls to make sure that the incoming air was of a specific temp, thus letting them tighten up the carb specs.. no more 'just adda extra squirt of gas when they step on the gas...' engineering. Fiddled with the dist, using retarded idle timing, limited advance 'only on Thursdays with a full moon and a werewolf in the rear view mirror' with thermal switches.

The exhaust manifolds are definitely different, but most engines will run well and pass emissions tests when kept decently tuned, and having good valves/rings, etc, no matter what carb or distribulator is installed. Those needing a smog pump - thermactor, will need one for the visual part of the emissions test and for the operative part too.

The parts houses can, in some cases, get different distributors for different circumstances. If you lived in California, you often had to specify whether you had Federal or Calif emissions, and if you lived in the other 49, you would have to tell the parts house that you had Calif emissions to get proper repair parts. It just depends.. The old EEC-I aluminum boxes for the electronic ignition had different gizzards depending on the emissions system...

Hope this confuses you as much as it has confused me.
tom

 

> Seems to me that the 'factory' HAD to specify certain parts
>in order to qualify an emissions system for sale in the U.S.
> Otherwise, one couldn't be certain that it would meet the
>standards of the day... In case you put the wrong dist in,
>or a carb with a slightly different choke pulldown.. or
>whatever.
> The thermactor system was basically adding an air pump to
>the exhaust system, along with exhaust manifold(s) that had
>fittings and injector pipes that stuck into the exhaust gas
>flow. The IMCO relied upon 'IMProved COmbustion' to cut
>emissions. They added a bunch of air flow controls to make
>sure that the incoming air was of a specific temp, thus
>letting them tighten up the carb specs.. no more 'just adda
>extra squirt of gas when they step on the gas...'
>engineering. Fiddled with the dist, using retarded idle
>timing, limited advance 'only on Thursdays with a full moon
>and a werewolf in the rear view mirror' with thermal
>switches.
>
> The exhaust manifolds are definitely different, but most
>engines will run well and pass emissions tests when kept
>decently tuned, and having good valves/rings, etc, no matter
>what carb or distribulator is installed. Those needing a
>smog pump - thermactor, will need one for the visual part of
>the emissions test and for the operative part too.
>
> The parts houses can, in some cases, get different
>distributors for different circumstances. If you lived in
>California, you often had to specify whether you had Federal
>or Calif emissions, and if you lived in the other 49, you
>would have to tell the parts house that you had Calif
>emissions to get proper repair parts. It just depends..
>The old EEC-I aluminum boxes for the electronic ignition had
>different gizzards depending on the emissions system...
>
>Hope this confuses you as much as it has confused me.
>tom

Thanks, Tom.

As I mentioned in another thread, my truck was assembled in San Jose, and the DSO was Los Angeles. I live in Iowa, and we have no smog checks, just lots of methane, just ask PigFarmer (lol!).

I was kind of wondering about parts since this was a California truck, and the parts guys in Iowa don't generally ask about emissions stuff.

I'm assuming there are ways to "overcome" these timing and advance issues - care to elaborate for a guy new to this stuff?

Thanks

 

I don't have my books handy but I seem to recall that for '68 the F100 390 auto used IMCO while the stick used Thermactor.

On a FE, the exhaust manifolds are the same, the AIR fittings are in the heads just above the exhaust flanges.

Barry

 

>I don't have my books handy but I seem to recall that for
>'68 the F100 390 auto used IMCO while the stick used
>Thermactor.
>
>On a FE, the exhaust manifolds are the same, the AIR
>fittings are in the heads just above the exhaust flanges.
>
>Barry


You are correct, Barry. Auto's got IMCO, manuals got thermactor.

I'll take your word on the heads