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Header Scavenging

I will always remember a quote written from an article by Warren Johnson. It stated that you need to run your engine as close to Detonation as possible as the cylinder pressure is at its highest, this is where you will make maximum power. Those were not the exact words as this was a statement I remember from many years ago. But this statement rings true with everything we need to do in a competition engine. Recently I changed fuel in our Stock Eliminator Race Car realizing that it's a low compression engine, and I need to use a fuel that has a very fast burn characteristic. The effect was negligible but we continue to use the fuel as any increase in power is worthwhile to our racing program. As Racers we want it all, we want the biggest effect from each component we put on our race car. The above paragraph was written to remind us that we need to run our race cars on the edge to extract every ounce of power out of them to win races.

A properly sized header and merge collector is a critical component on your race car if you are trying to obtain maximum VE. The header and merge collector combination needs to be designed to pull the maximum allowable amount of air into the engine without over scavenging. This meaning use as small of a header tube and or merge collector throat as possible. Years ago the term over scavenging was less common then it is today. Today we are trying to pull as much air in the competition engine as possible and over time we are learning how to accomplish this feat. Most professional engine builders and header fabricators are trying to use a smaller header and a merge collector when allowed by the engine combination to increase acceleration on the race track. This in turn increases exhaust speed and helps scavenge the engine. The key to designing a header and merge collector combination is trying to pull as much air in and not lose much or any out to the exhaust on overlap, which is where the term over scavenging comes from. This is just another way of increasing VE, by packing the intake charge in the cylinder.

Some engines are virtually impossible to over scavenge, those being applications with a camshaft having low duration numbers and a wide lobe separation, this mechanically gives us minimal overlap. The effects of a good small header and merge collector combination are critical on these engines as it is truly needed to use exhaust speed to pull air into the cylinder. Engines using a tight lobe separation and high duration numbers such as many Super Stock Engines have an excessive amount of overlap, this dictates the use of a little larger header and merge collector throat size or over scavenging will occur if we treat it otherwise.

Our job as professional header fabricators is to design a header and or merge collector combination that will pull as much air as possible into your engine without over scavenging. We as racers try to extract every bit of power out of your combination just as it's our own. We have hundreds and hundreds of previous customers for data and computer software to help design our headers and merge collectors. We enjoy helping you the racer and adding you to our list of satisfied customers.

- Mark Lelchook / Owner

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