Header output size
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Posting Guru
Joined: Apr 2006
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Header output size
I just put new headers from summit on my truck today. The factory hole was considerbly bigger that the header. The size of the colector was about the same, but the output "cone" was smaller. The cone was the same at the big end, but it reduced more. The pipe seals at the big end, so the smaller hole has no purpose. Does it? I was thinking of grinding the end. Could the small end reduce back pressure? Comments please. I'm not looking for power, just MPG.
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Joined: Mar 2001
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I'm assuming by "hole" you mean the outlet of the collector. The outlet mating surface is a short tapperd cone and the flanges on both the intermediate pipe and the collector actually come together tho so your cone is all the way inside the intermediate pipe, correct? If this is the case theres 2 schools of thought.
1. The cone actually increases the velocity of the exhaust gas as it exits the collector, moving it faster through the rest of the exhaust system. (think nozzle on a garden hose) In this case, you don't want to grind the cone down.
2. The added velocity of the exhaust gas is not enough to overcome the backpressure of the cone itself, in this case, you should grind the cone.
in this case, if both flange faces do in fact seat against eachother, I would be tempted to grind back some of the cone, leave about a half inch "neck" just to make reinstalling a little easier. I don't believe that leaving the cone alone will be a serious detriment to anything, performance or MPG.
1. The cone actually increases the velocity of the exhaust gas as it exits the collector, moving it faster through the rest of the exhaust system. (think nozzle on a garden hose) In this case, you don't want to grind the cone down.
2. The added velocity of the exhaust gas is not enough to overcome the backpressure of the cone itself, in this case, you should grind the cone.
in this case, if both flange faces do in fact seat against eachother, I would be tempted to grind back some of the cone, leave about a half inch "neck" just to make reinstalling a little easier. I don't believe that leaving the cone alone will be a serious detriment to anything, performance or MPG.
