What is the optimal primary length, short, long, of somewhere in the middle. Like many things when building anything for a high performance engine, "it depends".
If you are building headers for a Top Fuel dragster, the primaries are not very long. Of course, the primaries are all there is to a Top Fuel header, there are no collectors. There is also a very small power band in a T/F dragster, it leaves the line at almost the same RPM as when it crosses the finish line.
The primaries on the same engine mounted in a Funny Car are a little longer. Not because they need to be for the power band, but because the wider body requires longer tubing. In a regular street/strip Mustang, the primary length of a Long Tube header is pretty much determined by the room inside the engine compartment (typically between 32" to 34"), and don't forget, these primaries empty into a "collector". We have found that the collector changes the dynamics of the header. Based on what we have learned on the dyno, the length of the primaries are not that important when the primaries go into a collector. A typical 1 3/4" Long Tube header has a 3" collector (8" to 12" in length), but the reality, if the customer is running a 3" exhaust system back to the mufflers, his collector is actually 4-feet long.
A well designed Mid Length header is very close in power to the same header in a Long Tube configuration, when running a full exhaust system. On typical dyno comparisons, the difference between the two (everything else being equal, as in 1 3/4" primairies and a 3" collector) is between 6 to 8 horsepower on an average, all through the horsepower band. The primary length is just not that significant. But when discussing Mid Length headers, the term "well designed" is significant.
If you are building headers for a Top Fuel dragster, the primaries are not very long. Of course, the primaries are all there is to a Top Fuel header, there are no collectors. There is also a very small power band in a T/F dragster, it leaves the line at almost the same RPM as when it crosses the finish line.
The primaries on the same engine mounted in a Funny Car are a little longer. Not because they need to be for the power band, but because the wider body requires longer tubing. In a regular street/strip Mustang, the primary length of a Long Tube header is pretty much determined by the room inside the engine compartment (typically between 32" to 34"), and don't forget, these primaries empty into a "collector". We have found that the collector changes the dynamics of the header. Based on what we have learned on the dyno, the length of the primaries are not that important when the primaries go into a collector. A typical 1 3/4" Long Tube header has a 3" collector (8" to 12" in length), but the reality, if the customer is running a 3" exhaust system back to the mufflers, his collector is actually 4-feet long.
A well designed Mid Length header is very close in power to the same header in a Long Tube configuration, when running a full exhaust system. On typical dyno comparisons, the difference between the two (everything else being equal, as in 1 3/4" primairies and a 3" collector) is between 6 to 8 horsepower on an average, all through the horsepower band. The primary length is just not that significant. But when discussing Mid Length headers, the term "well designed" is significant.
Last edited: