EGR Valve
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From: charlestown in
EGR Valve
I put an L-82 intake on my 73 SB 350. This intake has a threaded screw hole and two small unthreaded holes in front of it. I assume an egr valve fits in all three holes, but I'm not sure. My question is, can I plug the threaded hole and leave the other two holes open, or do they have to be plugged as well to avoid a vacuum leak? The engine is not up and running yet, but close. I have no egr valve to put there.
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
give us some references and hole diameters,such as ... drivers side front, by water pump, 3/4" hole, 1/4" hole...... the egr is on the passenger side approx 3/4 of the way towards the back of the engine. do those holes go into the chamber area or are they just tapped and end. if they go into the chamber area they have to be plugged.
Burning Brakes
Joined: Aug 2004
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From: Tyler Texas
I concur with Bob; need more information. Is it an OEM factory 1973 intake? The 73 manifold had a clamp that held the EGR on to the manifold--passenger side. Post photo if possible; or give more information.
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From: charlestown in
Egr
It is a GM factory intake. The threaded hole is the farthest back, about 9/16ths or 5/8ths. The two smaller holes set directly in front of the threaded hole and are about 2 1/2 inches apart. These are located on passenger side towards the rear, right at the corner of the carb base. I have never tried to post a photo, but i will try. 
Burning Brakes
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From: Tyler Texas
Mike: If it is a 73 factory manifold, the rear threaded hole is for the one (1) bolt that secures the clamp to the intake manifold. The clamp holds the EGR valve in place.(73 was 1st year for EGR on corvette). Been awhile since I removed and cleaned my EGR valve, but as I recall the EGR valve "sits" in place on the two non threaded holes. Those holes act as a guide to position the EGR valve on the intake manifold. Look at bottom of EGR valve if you have one and you should see how it fits into the two holes.
Intake manifold casting numbers for 73 should be either 3997770 or 3997771. Both are cast iron in 73.
Intake manifold casting numbers for 73 should be either 3997770 or 3997771. Both are cast iron in 73.
Race Director
Joined: Sep 2004
Posts: 11,874
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
"will this affect performance " yes, in a positive fashion. its an anti pollution device... be sure you don't need it to pass emissions test if they are required where you live.
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Race Director
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by joe73vette
You can make a plate to cover the holes and use an EGR gasket to seal it. EGR does reduce detonation, though. Joe
just curious how does it do that??? by reducing heat???
Burning Brakes
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From: Tyler Texas
Bob: Short answer to your question is "yes". Bob is correct.
The EGR valve is used to slightly reduce the peak temperature during the combustion process. (This reduces oxides of nitrogen (NOx) emitted from the engine exhsust). EGR first used in 1973 models.
At idle the EGR valve is CLOSED. When throttle is opened to accelerate, the valve begins to open at 3 inches of mercury pressure drop in the throttle body.
At full throttle the EGR valve is CLOSED
During the 30 to 70 miles per hour range when cruising is when the EGR valve is primarily in use, but even then only a small portion of the exhaust gases is utilized .
The EGR valve is used to slightly reduce the peak temperature during the combustion process. (This reduces oxides of nitrogen (NOx) emitted from the engine exhsust). EGR first used in 1973 models.
At idle the EGR valve is CLOSED. When throttle is opened to accelerate, the valve begins to open at 3 inches of mercury pressure drop in the throttle body.
At full throttle the EGR valve is CLOSED
During the 30 to 70 miles per hour range when cruising is when the EGR valve is primarily in use, but even then only a small portion of the exhaust gases is utilized .
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
thks for the explanation, mine was incorrectly hooked up to a full time ported nipple when i first got the vette and man did it run badly!!!!!!!!
