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#1
03-12-2022, 06:17 PM
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What is this?
Small vacuum manifold-looking thing on the right side head of my '77 400. Never had any vacuum lines attached to it. It's between the #6 and #8 spark plugs
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#2
03-12-2022, 07:17 PM
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It’s to control the vacuum advance depending on temp.
Pic is wrong year, but same idea.  Sent from my iPhone using Tapatalk
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1979 Firebird Trans Am 301/4spd (Now 428) 1977 Firebird Formula 400/Auto 2007 Grand Prix GXP 5.3L |
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#3
03-12-2022, 08:15 PM
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Thank you!
Based on what I'm finding, it switches the distributor vacuum advance from ported vacuum to manifold vacuum when coolant temperature reaches 227f... why would I want to run the vacuum advance from ported vacuum anyways? This valve sounds like purely an emissions thing to reduce NOx at idle... |
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#4
03-12-2022, 08:28 PM
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There is a slightly different schematic for an auto car but all kinds of vacuum thermo switches in these things!
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
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#5
03-12-2022, 08:29 PM
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huh, upon reflection, that might actually be a good thing. The original one switched from ported to manifold vacuum at 227f. However apparently there's different ones that switch at different temperatures, including 120f. That would be useful for getting the engine warmed up to 120f at idle more quickly (ported vacuum gives no vacuum advance at idle, which causes the engine to run hotter), thereby reducing wear from running a cold engine. Above 120f, the switch wouldn't be doing anything bad. Hmm... wonder if I can find one of those
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#6
03-13-2022, 09:12 AM
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what's the chance of that switch actually functioning today ?
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#7
03-13-2022, 09:14 AM
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Pretty good, actually. Those old thermo switches rarely fail, they mostly break when things hit them
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