TheSamba.com :: View topic - Smog pump

Thu Feb 18, 2016 8:46 am

Did not see this line of thinking either here or in the Engines/Performance thread.

:?: 1973-1974 smog pump: Will the introduction of the compressed air into the cylinder heads actually help lower CHT?

:?: Since there was no catalytic converter to use the compressed air, was the intent of this simply to dilute the exhaust?

Thu Feb 18, 2016 9:17 am

If anything, those smog pumps raise CHT.

They work by injecting air into the heads just after the exhaust valves. The idea is to reduce hydrocarbon emissions by throwing some extra air in to the hot exhaust gases so that any unburned fuel in the exhaust burns as completely as possible before exiting the tailpipe. So basically you're having additional combustion in the header which is gonna generate some heat.

Those smog pumps were an emissions-control kludge and nothing more.

Thu Feb 18, 2016 9:26 am

Wasted youth wrote: Did not see this line of thinking either here or in the Engines/Performance thread.

:?: 1973-1974 smog pump: Will the introduction of the compressed air into the cylinder heads actually help lower CHT?

:?: Since there was no catalytic converter to use the compressed air, was the intent of this simply to dilute the exhaust?

No......the function of exhaust air injection ...also "airs"....meanig air injection reactor system. ..was ro inject air into the exhaus5 ports (on most cars that used it) or inject air into the combustion chamber while the exhaust cycle was in process..

The addition of oxygen by the pump caused immediate flash combustion of red hot fuel that was unburned by the combustion cycle because the normal combustion cycle had used up all the oxygen.

Those engines that put the air into the exhaust ports had a distinctly odd exhaust note back in the day because you were hearing external combustion in the exhaust ports of the header.

This system was designed to reduce hydrocarbons. It also had the habit of sometimes making NOX emmisions higher.

Cooling is not one of its functions at all. Typically it raised head temps. On some cars....considerably. its why in many cars it was one of the first things ripped off and thrown in the trash once a car got past the age of needing to be smogged. Ray

Thu Feb 18, 2016 9:33 am

Not sure it would have raise head temperatures all that much as the exhaust gases would do most of their extra burning in the exhaust header pipes and not in the head. It could certainly raise exhaust temperatures though.

Thu Feb 18, 2016 9:48 am

the temps downstream of the air injection went way up if there was any fuel left in the outflow. My jeep had it and during the years I owned it, injection manifolds were only good for about 20,000 miles, and the main exhaust manifold maybe 40,000 miles. They would warp and crack. Any attempts to richen the mixture for a cooler exhaust made it worse downstream of the air injection, and leaning it raised head temps causing warping. It was bad no matter what one did plus the extra belts and bearings made life miserable.

Thu Feb 18, 2016 9:56 am

Here is a picture I took a few years ago when I got my bus, showing one of the four inlet ports on my 1973 bus engine (Type 4, 1.7L) You can see where the PO brazed over the fitting instead of pulling it out and screwing in a plug. One each outboard side of the head. Given that the flow of injection air was indifferent to engine cycle as well as the location of the ports, I would presume the air was introduced post-cylinder, and so post-combustion.

Based on my understanding of what you guys are saying, this design allowed for an increase in the post-combustion oxygen levels to assist unburned fuel in the exhaust stream. Obviously, this would raise exhaust temperature... and perhaps part of the structure as well (that portion of the head and the exhaust structure as well)

As you guys also point out, the increase in parts, hardware and engine load increased engine heat and wear, which contributes to a shorter rebuild interval.

Somehow, I don't see myself restoring this system! :o

Thu Feb 18, 2016 10:08 am

Wasted youth wrote:
Somehow, I don't see myself restoring this system! :o

I certainly wouldn't. If you must re-install the pump for the factory-correct looks, you can at least block the hoses off so no air flows.

My motorcycle had a similar system - it did not use a pump but rather a passive vacuum-operated valve and reed valves at the heads which introduced air to the exhaust ports at the heads just past the exhaust valves. This system generates so much heat that it turns the (double-walled) chrome exhaust pipes blue near the heads. It also contributes to all sorts of undesirable exhaust noise. It was about the first thing I got rid of when I got the bike.

Thu Feb 18, 2016 10:39 am

Right on all counts for everyone. In hot weather states....it most certainly raised head temps on type 4 engines in sustained traffic.

As noted the manifolds get MUCH hotter right next to the heads. I have seen too many wasted manifolds and exhaust studs in the 50k miles range back in the day on California spec engines with this system.

If you are running rich...it will literally roast the muffler and HX's in hot weather states.

It sucked from the start.

Ray

Thu Feb 18, 2016 12:39 pm

raygreenwood wrote:
It sucked from the start.

Ray

Agreed, many air pollution devices actually improved the way an engine ran and some like the PCV system added greatly to engine life. Air injection had very little redeeming value so it has been the one air pollution system I have had no qualms about disabling over the years.

Thu Feb 18, 2016 6:40 pm

I bet the cabin heat would have been great 8)

So the air was injected continuously? And it was inject post-combustion chamber, correct?

Robbie

Thu Feb 18, 2016 11:02 pm

asiab3 wrote: I bet the cabin heat would have been great 8)

So the air was injected continuously? And it was inject post-combustion chamber, correct?

Robbie

On all cars that I studied the system except on decel as that caused backfiring.

Thu Feb 18, 2016 11:32 pm

SGKent wrote: asiab3 wrote: I bet the cabin heat would have been great 8)

So the air was injected continuously? And it was inject post-combustion chamber, correct?

Robbie

On all cars that I studied the system except on decel as that caused backfiring.

Yes....and not,speaking VW specific....there were a few that even got stupid in their control level.....more air...less air...no air at this throttle point ...etc. the few I saw that did things like thise were partly vacuum valve controlled and partly throttle switch controlled ......and as you can imagjne...that ran F'd up pretty quickly.

Engine wear....vacuum leaks....then you are getting popping when you least expect, hot running....and worst of.....no pass on emissions.

Some of the ugliest renditions I ever saw were on already hideous engines in horrible cars....like Chevy Chevettes and similar.....with smogged carbs and tamper proof everything. Even if you could figure out why it was running poorly....adjusting it without making it look like you adjusted was an excercise in stupidity.
Lovely system. Ray

Fri Feb 19, 2016 12:11 am

As long as the air pump driven by the belt is used the air in constantly injected.

The anti backfire valve also needs the air pump to reduce backfiring during
deceleration.

If VW would have applied what Porsche did in the 1973 production year We
would have had the type 4 F.I. engines in California and passed emissions
testing as they did. more$$ for a bus :!:

Porsche incorporated what other manufacturers did in 1973 using the
(overrun) valve. deceleration valve used when the throttle closed (off the pedal) the only change was in the distributor curve allowing the valve to add
air reducing HC EMMISSIONS.

I was a VW tech in 1973 and we Warranted thousands of EGR valves that the diaphragms ruptured do to gasoline damage (vacuum leaks)

So don't buy any 1973 smog heads for a rebuild they are the most Over heated heads on this earth. :oops:

Fri Feb 19, 2016 3:34 am

old DKP driver wrote: ...So don't buy any 1973 smog heads for a rebuild they are the most Over heated heads on this earth. :oops:

I would guess these heads are identified by the air injection ports?

Fri Feb 19, 2016 3:47 am

I have several 73 /1800 heads that appear to have no heat damage --due--I think because -as mentioned- it was the first thing taken off after passing smog. the ones that ran were destroyed years ago.

Fri Feb 19, 2016 6:17 am

old DKP driver wrote: As long as the air pump driven by the belt is used the air in constantly injected.

The anti backfire valve also needs the air pump to reduce backfiring during
deceleration.

If VW would have applied what Porsche did in the 1973 production year We
would have had the type 4 F.I. engines in California and passed emissions
testing as they did. more$$ for a bus :!:

Porsche incorporated what other manufacturers did in 1973 using the
(overrun) valve. deceleration valve used when the throttle closed (off the pedal) the only change was in the distributor curve allowing the valve to add
air reducing HC EMMISSIONS.

I was a VW tech in 1973 and we Warranted thousands of EGR valves that the diaphragms ruptured do to gasoline damage (vacuum leaks)

So don't buy any 1973 smog heads for a rebuild they are the most Over heated heads on this earth. :oops:

Actually. ..VW did apply that system.....in the 1971 model year on the VW 411!s and every 411/412 engine through the end of the line in 1974. It was not a Porsche systen....just like the 914 engine's....both 1.7 and,1.8.....exact same engines.....were not Porsche engine.

But I get your drift......they had the system....why not use it in CA?

Ray

Fri Feb 19, 2016 11:50 am

My bus actually came with the original Smog Pump attached and, as far as I can tell, still working. Not really sure what to do with it persoanlly :?

Fri Feb 19, 2016 1:22 pm

thewalrus wrote:

It's such a novelty that it's all there that it would almost be a shame to rip it off. If you feel like you want to keep it there for looks, I would take that big hose off the pump and insert a marble so it blocks any air flow, then re-attach it. Now it looks like it's supposed to but it doesn't kill your heads.

Or better yet, block the air to the inlet side of the pump.

Fri Feb 19, 2016 1:28 pm

Thewalrus, do you think you could do us a solid favor and photograph the components and connections so we could learn how and where the components are attached?

Thanks!
Robbie

Fri Feb 19, 2016 6:55 pm

thewalrus wrote: My bus actually came with the original Smog Pump attached and, as far as I can tell, still working. Not really sure what to do with it persoanlly :?

I need to visit you.

I had air injection on the Road Warrior for about a month before the pulley delaminated in the Bronx in 1979.

The most sensitive component in that mess is the anti-backfire valve. The most confounding component in that mess is the gulp valve which, if my memory serves me correctly, was signalled with the EGR valve vacuum circuit.

If you made the mixture too rich, the car would surge when you released the throttle. If you made the mixture too lean, it would backfire up a storm at each off-throttle.

Turns out the VW got away with air injection with less pain than most German cars. My BMW 3.0 engines had "thermal reactors" that would shrivel up their internal baffles that then rattled hideously, $1,200.00 bought you silence for another 50,000 miles. The VW"s had huge air-cooled exhaust manifold/heat exchangers . . . :D
Colin