{"id":7266,"date":"2014-08-08T08:00:19","date_gmt":"2014-08-08T15:00:19","guid":{"rendered":"http:\/\/www.racingjunk.com\/news\/?p=7266"},"modified":"2016-11-30T17:12:01","modified_gmt":"2016-12-01T01:12:01","slug":"drag-race-101-the-scavenging-games-headers-part-i","status":"publish","type":"post","link":"https:\/\/www.racingjunk.com\/news\/drag-race-101-the-scavenging-games-headers-part-i\/","title":{"rendered":"The Scavenging Games: Headers Part I"},"content":{"rendered":"

\"Header<\/a><\/p>\n

There are tons of questions when it comes to headers:\u00a0 \u201cWhat\u2019s the real story with headers? Is header \u201ctuning\u201d a waste of time and dollars? Are equal length headers worth the money?\u00a0 Does the collector shape and size really make a difference?\u00a0 Do expensive headers really give you a performance gain for your dollar?\u201d<\/p>\n

Whoa!\u00a0 Let\u2019s start at the beginning:\u00a0 According to the folks from American Racing Headers, a properly designed set of headers create a beneficial pressure balance between the intake and exhaust system. Here, “waves” of exhaust passing through the header pipes are more or less manipulated to extract the burned gasses from the combustion chamber and at the same time, assist in pulling in a fresh intake charge.<\/p>\n

\"You<\/a>
You should find that most non-supercharged high performance headers such as the examples (first photo) from ARH make use of equal length tubes and collectors (or at least close to equal lengths).<\/figcaption><\/figure>\n

Typically, a manufacturer such as ARH will engineer a set of headers using variables such as primary tube diameter and length as well as collector length and diameter to use the engine’s natural pressure waves as an exhaust extraction “tool”.\u00a0 Something that plenty of folks have missed is the point an engine benefits from two different forms of scavenging:\u00a0 Inertial scavenging and wave scavenging.\u00a0 And the design of a header can have an effect on both.<\/p>\n

Inertial Scavenging<\/b><\/p>\n

There are two types of scavenging in an engine \u2013 \u201cInertial Scavenging\u201d and \u201cWave Scavenging.\u201d \u00a0Inertial scavenging of gases begins as soon as the exhaust valve opens.\u00a0 Here, exhaust gases move past the valve and exit through the exhaust port into the header primary tube (and eventually passing into the atmosphere).\u00a0 Generally speaking, the experts feel that the best power is produced with an exhaust gas speed of approximately 300 feet per second (as an example, if an engine has a 36-inch primary tube, it would take 1\/100 of a second for the exhaust “pulse” to pass through the tube).\u00a0 Here\u2019s a key to extraction:\u00a0 When the exhaust valve is closed, these gases still continue to move down the exhaust tube at a rate of 300 feet per second.\u00a0 As it travels down the pipe, the exhaust cools and actually slows in speed.\u00a0 Behind this “pulse” is an area of low pressure that is expanding as the exhaust flows away. \u00a0Once the last of this exhaust gas reaches the end of the primary tube, the area of low pressure has increased in size to include the full length of the tube for that particular cylinder.<\/p>\n

\"When<\/a>
When the tubes have unequal lengths or if the headers operate without a collector (a zoomie such as with the fuel car in the second photo), you can leave plenty of power on the table. Equally important is the fact, you can create considerable \u201choles\u201d in the power curve.<\/figcaption><\/figure>\n

 <\/p>\n

If the engine has no collector (for example, a one-cylinder motor or an engine equipped with zoomies) the exhaust enters the atmosphere once it has left the primary tube.\u00a0 But in most headers, the exhaust enters a collector. If the low-pressure area we talked about above spills into another primary tube for a cylinder where the exhaust valve is just starting to open, the engine will gain an advantage.\u00a0 That low-pressure \u201cfront\u201d will help to pull exhaust gases from that cylinder (which at least to us, makes sense).\u00a0 This means there is less residual exhaust gas remaining in the combustion chamber (which can foul the incoming charge of fresh fuel and air).\u00a0 By manipulating the length and diameter of a specific tube, a header builder can influence the size of that low-pressure front.<\/p>\n

Fits-All Headers & Zoomies<\/b><\/p>\n

What\u2019s the story regarding the relationship between primary tube lengths versus unequal length headers (cheap fits-all headers) and\/or zoomies? When it comes to cheap universal \u201cfits-all\u201d headers with seriously mismatched tube lengths, there can be as much as 50 HP difference between 5500 and 6500 RPM when compared to a set of pipes with more or less equal lengths.\u00a0 50 or so horsepower is a good reason why primary tube length is significant.\u00a0 Zoomies on the other hand will actually run pretty well in a couple of different power bands (typically from 3500 to 4500 and then again from 7000 to 7500 RPM).\u00a0 But, they can give up something like 25 to 35 HP or more from 4500 to 7000 RPM (depending of course, up on the application \u2013 and we\u2019re not talking about seriously supercharge blown alcohol or nitro engines here \u2013 we\u2019re talking about normally aspirated engines).<\/p>\n

\"Tube<\/a>
Tube diameter definitely has a major effect upon inertial scavenging. With all other factors being equal, you will obtain a superior scavenging effect with an increase in exhaust speed.<\/figcaption><\/figure>\n

Remember when we talked about how inertial scavenging helps to pull the exhaust out of the combustion chamber? This also helps to draw in the air-fuel charge, with the end result being higher volumetric efficiency. By varying the length of the primary tube, you physically change the time it takes for the vacuum pulse (low pressure area) to reach the header collector.\u00a0 Essentially that\u2019s what \u201ctuning\u201d header tubes is all about.\u00a0 And this tuning can help to compliment the components you\u2019ve selected for the entire car (camshaft, compression ratio, torque converter, gear ratio, tire diameter and so on).\u00a0 Header tuning can also have an effect upon how the car works at a specific track, but we\u2019ll get to that later.<\/p>\n

Something else that is important is this:\u00a0 When the speed of the engine increases, there the need for a long primary tube is reduced.\u00a0 The reason is, there is, is less time between cylinder firing.\u00a0 The low-pressure front we talked about has less time to travel to the collector.\u00a0 The bottom line here is, primary tube length is something you really don\u2019t want to gloss over.<\/p>\n

\"To<\/a>
To a point, a header builder can control the speed of the exhaust gas by changing the diameter of the primary tube. The smaller the diameter of the tube, the faster the exhaust will flow.<\/figcaption><\/figure>\n

 <\/p>\n

———————————————————————————————————————————————<\/p>\n

So You Want to Be A Drag Racer: Buying, Building, Wrenching and Racing<\/strong><\/em><\/p>\n

The allure of the drag strip is easy to understand \u2013 a place where \u00a0it takes less than 10 seconds to make a stand, prove your skill, speed, and nerve.\u00a0 But the road to the races can be intimidating.\u00a0 The Burnout wants to make that road a lot smoother for aspiring racers, whether it\u2019s through building a new car, modding a used one, or taking that ride all the way up to the burnout box and beyond.\u00a0 This series is a work in progress, an ever expanding comprehensive guide to all the things that take drag racing from concept to reality.<\/em><\/p>\n

Want to chat about this on social media? Use #RJDragRace on Facebook or Twitter<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

There are tons of questions when it comes to headers:\u00a0 \u201cWhat\u2019s the real story with headers? Is header \u201ctuning\u201d a waste of time and dollars? […]<\/a><\/p>\n<\/div>","protected":false},"author":20,"featured_media":7268,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[3448,3465,17,11,3698,9,5010],"tags":[961,1164,1165,321,1166],"class_list":["post-7266","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-drag-race-101","category-drag-racing","category-guest-column","category-how-tos","category-tech","category-tech-tips","category-tires-and-wheels","tag-drag-race-101","tag-headers","tag-high-performance-headers","tag-wayne-scraba","tag-zoomies"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/www.racingjunk.com\/news\/wp-content\/uploads\/2014\/08\/Header-1-Feature.jpg","jetpack_shortlink":"https:\/\/wp.me\/p42YSK-1Tc","jetpack_sharing_enabled":true,"amp_enabled":true,"_links":{"self":[{"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/posts\/7266","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/users\/20"}],"replies":[{"embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/comments?post=7266"}],"version-history":[{"count":5,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/posts\/7266\/revisions"}],"predecessor-version":[{"id":33247,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/posts\/7266\/revisions\/33247"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/media\/7268"}],"wp:attachment":[{"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/media?parent=7266"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/categories?post=7266"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.racingjunk.com\/news\/wp-json\/wp\/v2\/tags?post=7266"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}