Failed Emissions Test
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
1. I'd have shop if you don't have a welder cut about 12-16" of the head pipe and have the shop weld a flange on each side where it was cut out of and place a gasket between the flanges bolt it back in place..
2. Now call it fixed or just cut the head pipe and re-weld it back together.
Then call it fixed
That's the ez way
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
When a drag motor is tuned it's done with headers open un-corked runs leaner. A race motor on the streets will load up the spark plugs with closed headers as it's jetted richer.
A shorter then 18" header pipe can damage the valves.
This why some times when runner headers you have to go to larger main jets. RUNS TO LEAN!
orich
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Postmaster
Joined: Nov 2012
Posts: 2,806
Likes: 8
From: Langley, BC
Whenever you throw on a better exhaust system you pretty well always have to compensate at the carburetor for it by jetting rich. I remember explaining it in detail on here before when the information was fresh in my mind but I can't for the life of me find the post. During the exhaust pulses, exhaust can be leaked out and fresh air can be sucked in. An exhaust leak allows exhaust gases to escape early as well as draw in outside air and therefore allows for inconsistent, premature exhaust cooling and velocity decrease. I wish I could find that post I made...
On a modern car, the O2 sensor detects the lean condition at the exhaust and compensates by sending more fuel to the cylinder. It is therefore very difficult for an EFI car to have any burnt valves from an exhaust leak, but fuel economy will suffer.
On a modern car, the O2 sensor detects the lean condition at the exhaust and compensates by sending more fuel to the cylinder. It is therefore very difficult for an EFI car to have any burnt valves from an exhaust leak, but fuel economy will suffer.
Cargo Master
Joined: Mar 2014
Posts: 2,031
Likes: 72
We don't do sniff tests, but at least three inspectors my little town rejected mine because of no heat riser tube terminating into the air breather. An exhaust guy came up with a work-around the met the test for me. Now, when I install the EFI manifolds, going to have to figure out another way to skin that cat.
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Postmaster
Joined: Nov 2012
Posts: 2,806
Likes: 8
From: Langley, BC
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Fleet Mechanic
Joined: May 2001
Posts: 1,396
Likes: 4
From: Cupertino
The issue here is not open headers and mixture. I think we all get it that raw exhausts reduce back pressure, increase scavenging, require richer jets to keep up the fuel/air ratio.
The issue is a leak at the collector as 351 has posed.
Negative pressure at a collector leak sucking air back in? Hardly.
Good discussion.
The issue is a leak at the collector as 351 has posed.
Negative pressure at a collector leak sucking air back in? Hardly.
Good discussion.
Lead Driver
Joined: Jul 2011
Posts: 8,679
Likes: 191
From: On the Edge of the Desert
The issue here is not open headers and mixture. I think we all get it that raw exhausts reduce back pressure, increase scavenging, require richer jets to keep up the fuel/air ratio. The issue is a leak at the collector as 351 has posed. Negative pressure at a collector leak sucking air back in? Hardly. Good discussion.
But the idea of it pulling air in is a long shot.
This uses the same theory that the newer diesel trucks are using. They have slits in the exhaust pipe to draw fresh air to help post combustion and cool exhaust gases.
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