Why people remove smog pump?
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
The A.I.R. system relied on low performance engine timing (4 degrees BTDC initial on an L-71) and resultant incomplete combustion in the cylinder to effect the re-burn of combustion products in the exhaust system, thereby lowering the overall emissions at the expense of performance. By running the timing at a more performance oriented 12-16 degrees like is recommended today, you won't be doing much re-burning in the exhaust and the air pump wouldn't be serving much of a purpose. At the higher initial timing, the engine is going to run more efficiently and definitely feel more powerful.
Le Mans Master
Joined: Oct 2007
Posts: 7,455
Likes: 977
From: RI, Now Franklin/Nashville TN
I don't have an air pump on my '72. A Min of Environment officer pulled me over and did a spot check and he pulled the hoses off the vac cannister. Didn't have that raw gas smell before this but the drive home was awful. Put the hoses back on the next day and no more raw gas stench.
Le Mans Master
Joined: Oct 2007
Posts: 7,455
Likes: 977
From: RI, Now Franklin/Nashville TN
GM's tuning of these engines back in the 70's was based on very primitive knowledge of the whole emissions issue and is a well known issue to start with. Since emissions back then was based almost entirely on passing an idle test, not running, the engines were detuned to meet the IDLE standard, not running at RPM's above that threshold which resulted in setting the engines timing and carb to meet those standards which adversely effected running efficiency.
Burning Brakes
Joined: Feb 2012
Posts: 925
Likes: 7
If you're running no vacuum advance or ported advance, plug the vacuum can hose into a hand vacuum pump, give the pump a few squeezes and you'll hear the tone of the engine change as the rpm comes up and the idle smoothes out.
Le Mans Master
Joined: Oct 2010
Posts: 6,938
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From: melbourne florida
2023 C3 of the Year Finalist - Modified
actually , government bureaucrats decided what the auto industry must due to reduce emissions. i am sure the automakers engineers were thrilled by it. thats sarcasm. the beginning of the government thinking they were experts on something they knew absolutely nothing about. i understand the president now wants the states to put tolls on interstate highways ( and return part to the feds) to pay for road repairs that are supposed to be paid from the tax on fuels that have been directed elsewhere. it may help to study who you vote for
Burning Brakes
Joined: Feb 2012
Posts: 925
Likes: 7
Pro
Joined: Apr 2013
Posts: 535
Likes: 8
From: London Ontario
I don't have an air pump on my '72. A Min of Environment officer pulled me over and did a spot check and he pulled the hoses off the vac cannister. Didn't have that raw gas smell before this but the drive home was awful. Put the hoses back on the next day and no more raw gas stench.
Tim
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Thread Starter
Instructor
Joined: Jan 2014
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Many thanks to everyone's input. The consensus so far seems to be the following:
Takes little hp to drive the pump.
System create clutter in engine bay.
Not very effective at reducing emissions.
Idle performance is poor if OEM ignition timing is adhered to.
Given the above, I will just drive my car a few times and enjoy the A.I.R. free engine for now. Then later in the year I will put back the OEM A.I.R. system before it gets lost amongst all my other car stuff. I will then mitigate the performance penalty by playing with manifold vs port vacuum as well as more advanced ignition timing at idle.
Oh and I'm perfectly OK with -30hp by having the extension tubes into the exhaust manifold.
Regards,
Wayne
Takes little hp to drive the pump.
System create clutter in engine bay.
Not very effective at reducing emissions.
Idle performance is poor if OEM ignition timing is adhered to.
Given the above, I will just drive my car a few times and enjoy the A.I.R. free engine for now. Then later in the year I will put back the OEM A.I.R. system before it gets lost amongst all my other car stuff. I will then mitigate the performance penalty by playing with manifold vs port vacuum as well as more advanced ignition timing at idle.
Oh and I'm perfectly OK with -30hp by having the extension tubes into the exhaust manifold.
Regards,
Wayne
Last edited by cwwhk; May 2, 2014 at 01:33 PM.
Tech Contributor
Joined: Jun 2004
Posts: 20,910
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Makes perfect sense in the chemistry world. With the government mandating the emission numbers, what other choice did the automakers have (other than stop producing the IC engine) than to alter the engine's timing (they didn't "screw it up"!)?
Melting Slicks
Joined: Jul 2009
Posts: 2,091
Likes: 40
I don't have an air pump on my '72. A Min of Environment officer pulled me over and did a spot check and he pulled the hoses off the vac cannister. Didn't have that raw gas smell before this but the drive home was awful. Put the hoses back on the next day and no more raw gas stench.
Dude ... The pollution ***** ....after you .....too funny . ...
Advanced
Joined: Nov 2002
Posts: 58
Likes: 0
From: Mill Hall PA
It's not incomplete combustion (there wasn't a bunch of fuel and oxygen just going along for the ride). Engines back then were always adjusted a bit on the rich side for drivability, so there was always insufficient oxygen in the A/F mix to burn all the fuel (regardless of timing). The AIR system was there to convert exhaust CO into CO2. For the air (oxygen) injection system to work efficiently the exhaust gas had to be damn hot (chemical reactions occur more readily at higher temperatures). By retarding the timing the exhaust exiting the cylinder is hotter than it would be if the timing was advanced properly (for economy and performance). (The retarded timing also lowered combustion temperature/pressure which also lowered NOx emissions.) When the injected air met the hot CO it converted the CO into CO2, harmless compared to CO.
Makes perfect sense in the chemistry world. With the government mandating the emission numbers, what other choice did the automakers have (other than stop producing the IC engine) than to alter the engine's timing (they didn't "screw it up"!)?
Makes perfect sense in the chemistry world. With the government mandating the emission numbers, what other choice did the automakers have (other than stop producing the IC engine) than to alter the engine's timing (they didn't "screw it up"!)?
Le Mans Master
Joined: Oct 2007
Posts: 7,455
Likes: 977
From: RI, Now Franklin/Nashville TN
It's not incomplete combustion (there wasn't a bunch of fuel and oxygen just going along for the ride). Engines back then were always adjusted a bit on the rich side for drivability, so there was always insufficient oxygen in the A/F mix to burn all the fuel (regardless of timing). The AIR system was there to convert exhaust CO into CO2. For the air (oxygen) injection system to work efficiently the exhaust gas had to be damn hot (chemical reactions occur more readily at higher temperatures). By retarding the timing the exhaust exiting the cylinder is hotter than it would be if the timing was advanced properly (for economy and performance). (The retarded timing also lowered combustion temperature/pressure which also lowered NOx emissions.) When the injected air met the hot CO it converted the CO into CO2, harmless compared to CO.
Makes perfect sense in the chemistry world. With the government mandating the emission numbers, what other choice did the automakers have (other than stop producing the IC engine) than to alter the engine's timing (they didn't "screw it up"!)?
Makes perfect sense in the chemistry world. With the government mandating the emission numbers, what other choice did the automakers have (other than stop producing the IC engine) than to alter the engine's timing (they didn't "screw it up"!)?
My only comment would be that the factory engines that I worked on back then (72 Chevrolet 400/73 Nova SS 350) as well as my 78 L-82 all had limiter screws on the carbs which were set to run LEAN not RICH to reduce emissions and to raise the combustion chamber temps.
Melting Slicks
Joined: Jul 2009
Posts: 2,091
Likes: 40
Broke the plastic pump fan blades off inside housing , plugged the rubber lines , 25 years ago. So basically my engine is turning pulleys , bearing and belts. My 74 doesn't even have to be inspected for brakes ,much less emissions garbage. I left the emissions garbage on for stock appearance . But I don't blame anyone for tossing it , just to get more elbow room to work in an already cramped area.
Seems I read somewhere the cheap little PVC valve added in the 60's took care of the majority of emission issues , and the other expensive stuff is to clean up the last 5 or 10 percent .....what I ve always heard anyway.
Seems I read somewhere the cheap little PVC valve added in the 60's took care of the majority of emission issues , and the other expensive stuff is to clean up the last 5 or 10 percent .....what I ve always heard anyway.
Burning Brakes
Joined: Feb 2012
Posts: 925
Likes: 7
It's not incomplete combustion (there wasn't a bunch of fuel and oxygen just going along for the ride). Engines back then were always adjusted a bit on the rich side for drivability, so there was always insufficient oxygen in the A/F mix to burn all the fuel (regardless of timing). The AIR system was there to convert exhaust CO into CO2. For the air (oxygen) injection system to work efficiently the exhaust gas had to be damn hot (chemical reactions occur more readily at higher temperatures). By retarding the timing the exhaust exiting the cylinder is hotter than it would be if the timing was advanced properly (for economy and performance). (The retarded timing also lowered combustion temperature/pressure which also lowered NOx emissions.) When the injected air met the hot CO it converted the CO into CO2, harmless compared to CO.
Makes perfect sense in the chemistry world. With the government mandating the emission numbers, what other choice did the automakers have (other than stop producing the IC engine) than to alter the engine's timing (they didn't "screw it up"!)?
Makes perfect sense in the chemistry world. With the government mandating the emission numbers, what other choice did the automakers have (other than stop producing the IC engine) than to alter the engine's timing (they didn't "screw it up"!)?
Le Mans Master
Joined: Jan 2000
Posts: 8,721
Likes: 108
From: Canada
Out of curiosity what was the outcome of said MOE inspection without the air pump? I have mine in a box due to running headers, but, have all other equipment intact. Interesting thing he said was that if an airpump is req'd the regs do not specify that it has to be working, just in place.
Tim
Tim
MOE = Ministry of Environment, Ontario Canada.
Last edited by gdh; May 3, 2014 at 08:37 AM.
Le Mans Master
Joined: Oct 2007
Posts: 7,455
Likes: 977
From: RI, Now Franklin/Nashville TN
Mine never had an airpump. I do keep a copy of the page from the AIM that proves it stored in the rear compartment. It was having a breather that created the issue instead of venting into the air cleaner. He gave me a warning but logged my vette into their database so if ever pulled over again and I hadn't corrected the problem the car would be towed to one of their sites c/w fine.
MOE = Ministry of Environment, Ontario Canada.
MOE = Ministry of Environment, Ontario Canada.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
It's not incomplete combustion (there wasn't a bunch of fuel and oxygen just going along for the ride). Engines back then were always adjusted a bit on the rich side for drivability, so there was always insufficient oxygen in the A/F mix to burn all the fuel (regardless of timing). The AIR system was there to convert exhaust CO into CO2. For the air (oxygen) injection system to work efficiently the exhaust gas had to be damn hot (chemical reactions occur more readily at higher temperatures). By retarding the timing the exhaust exiting the cylinder is hotter than it would be if the timing was advanced properly (for economy and performance). (The retarded timing also lowered combustion temperature/pressure which also lowered NOx emissions.) When the injected air met the hot CO it converted the CO into CO2, harmless compared to CO.
Makes perfect sense in the chemistry world. With the government mandating the emission numbers, what other choice did the automakers have (other than stop producing the IC engine) than to alter the engine's timing (they didn't "screw it up"!)?
Makes perfect sense in the chemistry world. With the government mandating the emission numbers, what other choice did the automakers have (other than stop producing the IC engine) than to alter the engine's timing (they didn't "screw it up"!)?
And YES the PCV valve is a good thing, the smell in the garage gets worse than a skank very quick without it.....
Fuel smell is interesting, I kept the canister on my '72, but noted that the vacuum controlled valve on top was stuck open...so the vent line from the tank going forward into the canister was always open to the engine from the canister.....I plumbed it into the above throttle blade spot, ported vacuum I think is the phrase.....I have a PCV hooked up to full mani vac.....I have the fuel canister T'd off with a line to one of the valve covers, and NO SMELLS OF ANY KIND.....
I cheat though having DPFI on it, old batch fire setup, nothing super high tech.....
Last edited by mrvette; May 3, 2014 at 09:57 AM.
Le Mans Master
Joined: Jan 2000
Posts: 8,721
Likes: 108
From: Canada
