{"id":5,"date":"2008-07-02T15:12:30","date_gmt":"2008-07-02T20:12:30","guid":{"rendered":"http:\/\/performancetrends.com\/blog\/?p=5"},"modified":"2010-09-22T11:54:06","modified_gmt":"2010-09-22T16:54:06","slug":"oversquare-undersquare-and-borestroke-ratio","status":"publish","type":"post","link":"https:\/\/performancetrends.com\/blog\/?p=5","title":{"rendered":"Oversquare, Undersquare, and Bore\/Stroke Ratio"},"content":{"rendered":"<p>Oversquare vs undersquare referrs to the Bore\/Stroke ratio of an engine.\u00a0 If the <strong>bore is larger than the stroke<\/strong>, the engine is considered to be <strong>oversquare<\/strong>.\u00a0<!--more--> I saw a recent magazine article discussing the advantages of oversquare vs undersquare engine designs.\u00a0 I can&#8217;t exactly recall what they said, but it was pretty off base.Here&#8217;s what you need to know in a nutshell:<\/p>\n<ul>\n<li><strong><em>How much torque an engine can make is based on its cubic inches.<\/em><\/strong> Torque comes from how much air the engine can <strong>ingest every intake stroke<\/strong>.\u00a0 The more the cubic inches, the more air it can take in every stroke.<\/li>\n<li><strong><em>How much HP an engine can make is based on the total valve area.<\/em><\/strong> HP comes from the total air the engine can <strong>ingest per unit time<\/strong>, like every second.\u00a0 The intake valve it typically the largest restriction for air flow in an engine.\u00a0 Therefore, an engine with more intake valve area (total valves in the engine x valve area) can ingest more air than one with less valve area.\u00a0 Or, it can rev higher before it runs out of breath.\u00a0 Higher revs mean more HP.<\/li>\n<\/ul>\n<p>If we look at an oversquare engine, its larger bore allows for larger valves to be used.\u00a0 Therefore it can make more HP than the same cubic inch engine with a smaller bore.\u00a0 That&#8217;s it.\u00a0 It&#8217;s just that simple.The old axiom that long stroke engines make more torque is\u00a0related to this.\u00a0 It&#8217;s not that they make more torque, its just that they <strong>can&#8217;t<\/strong> make HP because the valves are just that much smaller to fit inside the smaller bore.It also explains why 4 valve engines make more HP, lots of valve area for the displacement.\u00a0 It also explains why the engine with more cylinders will make more HP for the same displacement.\u00a0 The total valve area (adding up all valves for all cylinders) is greater.Now there <strong>is<\/strong> a downside to big bores.\u00a0 It takes longer for the flame front to travel across the entire bore, meaning a slower <a title=\"Burn Rate\" href=\"http:\/\/performancetrends.com\/Definitions\/Burn-Rate.htm\" target=\"_self\">burn rate<\/a> and being more prone to detonation.\u00a0 These are typically not a problem until higher RPM.\u00a0 Also, the larger valves are harder to control at higher RPM.Now I&#8217;m sure you are thinking that superchargers, cam timing, runner lengths, etc all have an effect.\u00a0 They clearly do.\u00a0 But I was trying to keep it simple.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Oversquare vs undersquare referrs to the Bore\/Stroke ratio of an engine.\u00a0 If the bore is larger than the stroke, the engine is considered to be oversquare.\u00a0<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[16,19,17,18],"_links":{"self":[{"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5"}],"collection":[{"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5"}],"version-history":[{"count":2,"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5\/revisions"}],"predecessor-version":[{"id":227,"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5\/revisions\/227"}],"wp:attachment":[{"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}