{"id":7548,"date":"2014-08-19T14:45:09","date_gmt":"2014-08-19T21:45:09","guid":{"rendered":"http:\/\/www.racingjunk.com\/news\/?p=7548"},"modified":"2016-11-30T17:10:14","modified_gmt":"2016-12-01T01:10:14","slug":"headers-scavenging-games-part-iii","status":"publish","type":"post","link":"https:\/\/www.racingjunk.com\/news\/headers-scavenging-games-part-iii\/","title":{"rendered":"Headers: Scavenging Games Part III"},"content":{"rendered":"

Drag Race 101:<\/strong> Headers, Part III<\/p>\n

In past segments, we took a long hard look at what happens when the exhaust valve opens in an engine.\u00a0 Getting a handle on exhaust speed is extremely important (exhaust speed is the determined by the diameter and length of the primary pipe).\u00a0 But it\u2019s the not only critical component in a header.<\/p>\n

As far as the collector is concerned, the major objective is to take advantage of the “secondary tuning impulses” from the other pipes in the system.\u00a0 The influence of the collector is generally restricted to the RPM level below <\/i>the torque peak of the engine in question.\u00a0 Collector sizing is more critical in engines that spend the majority of their time in the lower RPM ranges.<\/p>\n

With a series of both exhaust waves and sonic waves entering the collector, it\u2019s easy to see that there is probably a bunch more to collector shape than first meets the eye.\u00a0 For example, a merge collector minimizes the reflected wave, so it has less effect upon the inertia pulses.\u00a0 The actual hourglass shape of this collector design serves to regulate the high and low pressures.\u00a0 It also tends to speed up the velocity of the gas flow.\u00a0 Additionally, the shape \u00a0(particularly in the case of a merge collector) helps equalize the transition of the individual exhaust tube gases.<\/p>\n

The overall length of the merge collector is important.\u00a0 So is the angularity of the tubes that physically “collect” in the collector.\u00a0 You’ll also find a “spear” or “pyramid” inside a merge collector.\u00a0 The purpose of this pyramid is to control the exhaust gases so that they do not re-enter the primary tube and travel backwards into the engine by way of the low-pressure area (exhaust gas dilution).\u00a0 The neck of the hourglass is important too.\u00a0 By reducing the size of the neck, the exhaust gas velocity will increase as it is carried into and out of the secondary tube (collector).\u00a0 This form of collector is so efficient; some manufacturers have found there is an actual increase in the EGT (Exhaust Gas Temperature).\u00a0 The reason is the header assembly is extracting more of the air fuel mixture out of the cylinder and burning it in the collector.\u00a0 Because of this phenomenon, there\u2019s chance the camshaft timing events may have to be revised.\u00a0 And obviously, the same applies to the carburetor jetting.<\/p>\n

There are other types of collectors out there too:\u00a0 Some pair the cylinders based upon firing order.\u00a0 Essentially these collectors simulate a Tri-Y header configuration, and for a few applications, there could be more performance with the setup. And aside from their unique configuration, it’s interesting to note these collectors usually range in length from 23 to 25 inches \u2013 which is well beyond the length of most merge collectors.<\/p>\n

In the end, each and every header collector design in each and every engine for each and every car on each and every track can be different.\u00a0\u00a0 Honestly, there is no magical formula, chart or graph that you can use to determine collector diameter.\u00a0 What it boils down to is good old-fashioned testing (and most likely a wee bit of cutting, welding and testing again).<\/p>\n

In the next segment, we\u2019ll take a look at the simple formulas used to establish a header size baseline and we\u2019ll also take a look at the practical side of header tuning.\u00a0 Watch for it.<\/p>\n