What to do about gt-40 explorer heads not having thermactor holes

rockyracoon

10 Year Member
Nov 23, 2005
874
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margate NJ
So like the subject line says. I called a machine shop and asked about them drilling the heads for the thermactor system and the said that they would not do that.

Should I try another machine shop or is that common, that they do not drill for the passages ?
Would aftermarket aluminum heads have the passages ?

So what are my options, keeping in mind that I live in philly where they do a full emissions test unless your car is 1991 or older.
I have to retain the cats for inspection
 
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Yes, Al heads can have them. Not all do though. TFS170's do have the ports. Unsure about others.

Drilling the GT40's for he thermactor ports could be done, but it would be rather difficult. The bosses are there, but without a dwg detailing what angle and depth to plunge to, it would be a crapshoot as to how to angle the bits. I can see why a machine shop would say no to this.

The 1993 Cobra GT-40's did have the ports present. You'd have to locate a set of those with the F3ZE-AA part number. The F1ZE-AA head came on early explorers and does not have the provision

Do you actually have a sniffer test to pass or just a visual? Here in MA, there have a visual but cannot pop the hood or do a sniffer test. My air tube only runs down to the cats and not the heads. I've simply blocked the vac line to the diverter and just leave the bypass valve hooked up.
 
My thermactor (air injection) system has been in the trash-bin for about a decade along with the air pump, and we have both visual and sniffer tests in Ohio. Didn't make the tiniest difference to emissions, and they basically only visually checked for the presence of a cat. Modern converters don't even support the air tube, and its only claim is that it increases the life of your converter by helping burn off oil residue and carbon deposits. Which if you install it like @Mustang5L5 suggests - connecting only to the converter - it'd continue to do that just fine.

Frankly I don't have any idea what the AIR tube connection to the head even does - just that it didn't impact my emissions #'s at all.
 
Frankly I don't have any idea what the AIR tube connection to the head even does - just that it didn't impact my emissions #'s at all.

It's for the two pre cats. During cold start, the cats need to be warmed up before they start to really work. The proximity of those two cats near the engine allows them to warm up quickly.

Older engines aren't as efficient as new engines so they tend to be more "dirty". The air pump supplies O2 to help with efficiency and during cold start the air pump feeds the heads and indirectly the two pre cats to help cold start.

Once your engine is warmed up, the diverted sends air to the rear cats which are further from the engine. Most of the time, this is how the system operates.

If you have a 2-car h-pipe there is no need to plumb to the heads. Just plumb it to the main cats permanently by plumb in the WOT bypass dump valve.

During a code check you will get codes for the air injector system not working if you bypass the head because the computer looks for a response from the o2 sensors. Won't affect how the car runs but you'll always have these codes
 
I continued to be curious about the thermactor-to-head function and found a few interesting and plausible sources. It doesn't have much to do with the cats at all - or engine temperature, though the exhaust flowing through the heads would help warm things up (even without the AIR tubes attached). It's basically trying to complete the burn in the exhaust manifold, which would incidentally contribute to the protection of the front cats. Which also wouldn't necessarily be a good thing if you were running tube headers I'd imagine unless you like those blue / burned.


Here's what they said:

The P's aren't drilled from the factory. The EGR passage is probably a remnant of the original design and casting molds, but since the later model Explorers didn't use the thermactor passage, Ford simply cut one of the last production processes which was drilling of the crossover passage as a means of reducing cost. The Explorers took the injected the air directly into the exhaust manifold instead of through this thermactor passage. (jozsefsz comment - I guess this would be an interesting work-around, to weld a couple of bungs onto the exhaust manifold instead of drilling the heads).

Ford term for an early emissions control system, installed on cars from around 1965; by 1967, California specification vehicles were installed with it as standard. The name is a contraction of 'Thermal Reactor', and this type of system is also known as AIR (air injection reaction).

The purpose of the Thermactor system is to reduce the emission of unburned fuel and the products of incomplete combustion. It does this by injecting air into the exhaust manifolds; the heat of the exhaust gases is sufficient to ignite the combustion of anything burnable still remaining in the exhaust. The combustible gases, mixed with oxygen from the injected air, burn in the manifold.

On a later-model vehicle fitted with a catalytic converter, the Thermactor system also helps supply the oxygen needed by the catalysts to do their work.

The air comes from an engine-driven air pump, pushing air through rubber hoses to the distribution system for each manifold. In my 1967 Ford Thunderbird, this involves metal pipes, while in later engines this is integral to the intake manifold, to holes drilled through the cylinder head all the way through to the exhaust manifolds.

The system is complicated by two factors. The first is that if the throttle is closed suddenly, the Thermactor system can make the engine backfire; to prevent this, a device called the backfire diverter valve, operated by high manifold vacuum, diverts the air flow to the atmosphere. The second issue is that high exhaust system backpressure could force exhaust gases back through the Thermactor system. This is protected against by a one-way check valve in the system.

By itself, the Thermactor system certainly does improve emissions, but nowhere near any remotely modern standard; it does however provide a good adjunct to a catalytic converter. Ford used the Thermactor system at least through the 1970s and 1980s in this form.

Disadvantages of the Thermactor include power loss from driving the pump, from increased backpressure in the exhaust system, and greatly increased heat in the exhaust manifolds from the combustion taking place there. Also, it means yet more stuff under the hood and getting in the way of the engine. Although it's technically illegal, it's common for owners of presmog vehicles to remove the Thermactor system and replace the components with those from an unequipped car.
 
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Just stumbled across this and a lot of my questions are answered. In review, my 96 Mystic Cobra had NO cats yet passed emissions in AZ (Tucson and Phoenix metro). Being an OBD2 system they just plugged into the port. They would only check for cats on pre OBD2 cars. However they also sniffled the pipe. Commyfornia is back to 67 and Nevada goes back to 1972. Total BS imo. I'm out of Las Vegas and back to AZ but will strip the emissions out of my 88 LX 5.0.
 
The video i mentioned above should be under "junkyard dog" gt40 cylinder head part II (part 2).

I just learned for im inspections, the thermactor system is only a visual test. On my gt40p heads ill only be tapping it in for a few threads to hold that tube. Basically the tubing will rin into the the wall of my cylinder heads with absolutely of no use.