| Valve on air cleaner neck question [message #216139] |
Mon, 29 July 2013 16:20  |
Otterwan
Messages: 946
Registered: July 2013
Location: Lynnwood (north of Seattl...
Karma: 0
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Forgive me for what is likely a silly question, but I haven't messed with GM V8's for 30 years and when I did most did not have stock air cleaners. On top of the neck of the air cleaner is a vacuum operated valve. On the lower side is a foil pipe going to the exhaust manifold. The port on the valve is plugged (capped) and there is no trace of vacuum line anywhere.
If memory serves this is designed to draw warm air into the engine when it is warming up. After that is should be open for normal running. Since my coach starts and runs fine, I would assume this is stuck open (cold air) and isn't really necessary and I can leave well enough alone. If this is not the case, please educate me. Thanks.
1977 Birchaven, Lynnwood WA - "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."
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| Re: Valve on air cleaner neck question [message #216140 is a reply to message #216139] |
Mon, 29 July 2013 16:33  |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Sir: the vacuum going to it comes from the rear of the air filter from a bleed valve that is pose to close when the air gets warm. You are fine as u are and I would also remove the vacuum line to the air filter and block at the source. Unless you live in Alaska.
| Otterwan wrote on Mon, 29 July 2013 17:20 |
Forgive me for what is likely a silly question, but I haven't messed with GM V8's for 30 years and when I did most did not have stock air cleaners. On top of the neck of the air cleaner is a vacuum operated valve. On the lower side is a foil pipe going to the exhaust manifold. The port on the valve is plugged (capped) and there is no trace of vacuum line anywhere.
If memory serves this is designed to draw warm air into the engine when it is warming up. After that is should be open for normal running. Since my coach starts and runs fine, I would assume this is stuck open (cold air) and isn't really necessary and I can leave well enough alone. If this is not the case, please educate me. Thanks.
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C. Boyd
76 Crestmont
East Tennessee
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| Re: Valve on air cleaner neck question [message #216141 is a reply to message #216140] |
Mon, 29 July 2013 16:55 |
Otterwan
Messages: 946
Registered: July 2013
Location: Lynnwood (north of Seattl...
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Thank you for confirming my suspicions!
1977 Birchaven, Lynnwood WA - "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."
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| Re: Valve on air cleaner neck question [message #216173 is a reply to message #216139] |
Mon, 29 July 2013 20:16 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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| Otterwan wrote on Mon, 29 July 2013 14:20 |
If memory serves this is designed to draw warm air into the engine when it is warming up. After that is should be open for normal running. Since my coach starts and runs fine, I would assume this is stuck open (cold air) and isn't really necessary and I can leave well enough alone. If this is not the case, please educate me. Thanks.
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Mine is gone as well, (Jeep horn and outboard air cleaner plus an aluminum intake) however BobR of EBL fuel injection fame has his heat tube connected on his injected Corvette.
We tend to want to get rid of the heat. So we block off the crossover, or put aluminum manifolds with no crossover.
Some in old vehicle land believe if it has to do with smog requirements it is bad, doesn't work and robs us of power. On the other hand my '37 Ford flathead V8 had a crossover to heat the intake manifold, long before anyone was thinking of smog.
It is true that cold air is more dense and can carry more oxygen for more power. However, if you don't vaporize the gasoline, you are not going anywhere. BobR suggested some of the EFI guys think about adding heat in cool weather. Even Carbs can ice up in cold weather.
So, if you live or run your GMC where it is cold, there is another way of thinking about that little valve and aluminum tubing. I was looking at my old air cleaner the other day...
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: Valve on air cleaner neck question [message #216175 is a reply to message #216173] |
Mon, 29 July 2013 20:23 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Yes us minnesotans realized they were a good thing to have in the winter....
for a summer only car like a GMC, nop, it's gone.
Mine is completely gone I didn't want it blocking any airflow. That does make it a lil louder BTW
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: Valve on air cleaner neck question [message #216183 is a reply to message #216139] |
Mon, 29 July 2013 20:53 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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The AutoThermAC is part of the EFE (early fuel evaporation) System. Basicly 2 functions, emmisions and drivability. By prewarming the intake air during warmup, it gave better atomization and less wet fuel pooling in the manifold. Result was being able to run a little leaner for emissions. Also it's hard to tune the carb with a variety of temp conditions so the ThermAC thermal vacuum device sensed air cleaner air temp and blended hot and cold to try to maintain about 117 degrees target and use that as a benchmark to tune the Qjet to. It was a drivability while still being as clean as possibie balancing act. At heavy or WOT vac drops and the blend door goes to full cold snokel air by the return spring so there is no power loss down side other than the restrictive silencer design itself. I have this correct and fully functional in all my 60s-70s GM vehicles. Keeps emissions down which translates to cleaner oil if only slightly.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Valve on air cleaner neck question [message #216187 is a reply to message #216183] |
Mon, 29 July 2013 21:04 |
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JShot
Messages: 485
Registered: October 2006
Location: NW Ohio
Karma: 0
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David,
Why don' I have you listed in the GMC Registry???
Please go to the Registry web site listed below and fill out the on-line form there, and send it to me.
Thanks,
John (shot)
John Shotwell
Ridgeville Corners, OH
78 Royale Center Kitchen
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