- Mon Apr 21, 2008 6:12 pm
#51884
id3379 wrote:hatchin06 wrote:ya people here arent to fond of it? they like yelling and flicking me off when i do it lol. it seems like there is a power increase when they are off. is there?
well some people say it does and it doesn't, naturally i would think there is since there is no pipe's restricting the air flow and it goes straight out, otheres claim since there is no piping that there is no back pressure or something like that, but i feel a little more power when i run them open.
Engines don't run on logic. Engines aren't made by philosophers. They're made by engineers. You can never make logical assumptions about an engine. Every thing has to be tested and worked out mathematically.
Running open header decreases your power. The sound has a psychological effect making you think you've made more power.
It also burns your valves because the primaries are supposed to carry heat away from the head.
Any time anyone uses the word "back pressure", you can be certain that they have no idea what they are talking about. Back pressure is ALWAYS a bad thing.
If all a header did was eliminate back pressure, you would only see a very minimal gain in hp. Yet there is a big difference in power between a cheap header and an expensive header. And even a cheap header gives you more power than running open header. So what is it that one header does better than another? Get the air out easier? No. Back pressure can be measured with a gauge. Any exhaust will give you almost no measurable back pressure.
The first thing to understand is that exhaust does not come out in a constant stream. Each cylinder has it's own combustion event and releases an exhaust pulse. Each cylinder shoots out these exhaust pulses and they travel down the exhaust primaries and come together in the collector, where the primaries are joined. Some headers join all four into one, some join them into two, then join the pairs into one. In your stock exhaust manifold all the pulses simply crash into each other.
Behind each pulse is a vacuum.
The secret to header tuning is to time these pulses so that one pulse arrives in the collector right behind another, so that the vacuum from one pulse pulls on the next. This suction pulls exhaust out of the combustion chamber, and in turn pulls intake air in to replace it; rather than having the intake air push it's way in.
You see, there is a short period of time called "overlap" when both the intake valve and the exhaust valve are partially open. Engine designers did this on purpose to make use of scavenging, which is what I described by having the vacuum behind the exhaust pulse pull air into the combustion chamber.
More air in the combustion chamber allows you to burn more fuel releasing more power.
Back pressure can never be good because back pressure resists exhaust flow. So again, the intake air has to "push" it's way into the combustion chamber.
An engineer might take issue with some of the terms I've used but the concepts are all completely true.
