Is there a significant difference in flow between shorty and long tube header designs?

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My sons car: 86 Iroc,388ci,Brodix,Victor jr,TPI-700r4,3:73.

 

The length of the tube between the exhaust port and the collector has relatively little to do with the "flow" capacity of a header design (by "flow" I take it that you mean the steady volume of gas that can pass through the pipe in a given stretch of time at a given pressure). The problem is that you are not dealing with a steady stream of gases, but rather a sort of staccato pulsation. This is key to understanding the significance of header length, diameter, and collector size/style. In essence, tube diameter affects flow capacity, tube length affects the RPM range at which peak power is produced.

This is an extremely complex topic, but the much simplified rules-of-thumb are:

1. Shorter tube lengths tend to move peak power higher in the RPM range; longer tubes have the opposite effect. In order for this effect to be maximized, header length needs to be matched to cam profile.

2. Tube diameter should be matched to the CID of the engine (i.e. greater cylinder volumes move more gases per stroke), and also to the cam profile, header design, and intended use of the engine.

For instance, a average dragster would use extremely short, wide header design and a very aggressive, high RPM camshaft. A 4x4 pickup designed for relatively slow off-road use would (in general) use a longer, smaller tube design which would maximize torque at lower RPM levels.

There are of course *tons* of gray areas and exceptions to the above (and I didn't even touch on collector size/design), but those are the general ideas.

Hope that helped,
Phil

[This message has been edited by Smokey (edited March 09, 2001).]