{"id":142,"date":"2010-04-07T11:23:09","date_gmt":"2010-04-07T16:23:09","guid":{"rendered":"http:\/\/performancetrends.com\/blog\/?p=142"},"modified":"2010-06-22T12:40:18","modified_gmt":"2010-06-22T17:40:18","slug":"compression-ratio-calculator-v2-3","status":"publish","type":"post","link":"https:\/\/performancetrends.com\/blog\/?p=142","title":{"rendered":"Compression Ratio Calculator v2.3"},"content":{"rendered":"<p>When building or modifying an engine for all-out racing, street\/strip performance, trailer towing, or most any application, there are many variables to consider. One critical variable is the Compression Ratio or CR. Compression ratio is the amount of &#8220;squeeze&#8221; the piston puts on the air fuel ratio before it lights\u00a0 the\u00a0fire.\u00a0 And, more importantly, it is the amount of expansion or &#8220;push&#8221; these hot, high pressure, combusted gases put on the piston.\u00a0 The more amount of expansion, the more amount of heat and pressure energy can be extracted from each combustion event.<!--more--><\/p>\n<p>CR is the ratio of the cylinder&#8217;s volume at it&#8217;s greatest volume (piston at Bottom Dead Center), compared to the volume at it&#8217;s minimum volume (piston at Top Dead Center).\u00a0 At BDC, the volume is the cylinder&#8217;s swept volume PLUS the combustion chamber volume.\u00a0 At TDC it is just the combustion chamber volume.\u00a0 Since the swept volume is the engine&#8217;s displacement per cylinder, and is easily calculated from bore and stroke, the more complicated part of the calculation is calculating the combustion chamber volume, which is made up of LOTS of separate small volumes.\u00a0 That&#8217;s why it&#8217;s nice to have the\u00a0\u00a0<a class=\"aligncenter\" title=\"Compression Ratio Calculator\" href=\"http:\/\/performancetrends.com\/Compression_Ratio_Calculator_V2.3.htm\" target=\"_blank\">Compression Ratio Calculator<\/a> to do that hard work, and keep all the math straight.<\/p>\n<p><figure id=\"attachment_189\" aria-describedby=\"caption-attachment-189\" style=\"width: 581px\" class=\"wp-caption alignnone\"><a href=\"http:\/\/performancetrends.com\/graphics\/Compression_Ratio_Calculator_Main_Screen.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-189 \" title=\"Compression_Ratio_Calculator_Main_Screen[1]\" src=\"http:\/\/performancetrends.com\/blog\/wp-content\/uploads\/2010\/03\/Compression_Ratio_Calculator_Main_Screen1.gif\" alt=\"Compression Ratio Calculator Main Screen\" width=\"581\" height=\"350\" srcset=\"https:\/\/performancetrends.com\/blog\/wp-content\/uploads\/2010\/03\/Compression_Ratio_Calculator_Main_Screen1.gif 726w, https:\/\/performancetrends.com\/blog\/wp-content\/uploads\/2010\/03\/Compression_Ratio_Calculator_Main_Screen1-300x180.gif 300w\" sizes=\"(max-width: 581px) 100vw, 581px\" \/><\/a><figcaption id=\"caption-attachment-189\" class=\"wp-caption-text\">Compression Ratio Calculator Main Screen<\/figcaption><\/figure>Unlike many engine modifications, increasing the CR helps fuel economy on the street, lap times at Daytona, ET on the drag strip.\u00a0 It helps overall engine efficiency for any application.\u00a0 So then, why are street cars only\u00a0running with 9:1 compression ratio and race motors only running about 16:1 max?\u00a0 Shouldn&#8217;t they all be running 100:1 CR?<\/p>\n<p>Well, there are some downsides to high CRs:<\/p>\n<ul>\n<li>The amount of improvement you get going from 9:1 to 10:1 (typically about 4%) is much greater than the improvement going from 16:1 to 17:1 (more like 1%).\u00a0 The benefits of very high CRs diminishes rapidly.<\/li>\n<li>It gets difficult to quickly and completely burn a mixture in such a thinly squeezed &#8220;pancake&#8221; of a combustion chamber.<\/li>\n<li>With such an increase\u00a0in pressures, there can be more stress on internal engine components.<\/li>\n<li>It gets difficult to produce such a small combustion space and still package the spark plug, valves, valve reliefs for clearance to allow for any overlap for valve timing (needed for good, high RPM &#8220;breathing&#8221;).<\/li>\n<li>An most importantly, there is is the ever present danger of &#8220;piston destroying&#8221; Detonation (spark knock).<\/li>\n<\/ul>\n<p>Detonation:\u00a0 The higher the CR, the higher the temperature and pressure when the spark ignites the charge.\u00a0 The flame travels across the chamber in all directions from the spark plug to eventually completely burn everything.\u00a0\u00a0This takes some time, 60-80 degrees of crank rotation, and is why you\u00a0fire the spark plug at, say, 35 degrees before TDC and not at TDC.\u00a0 These higher temperatures and pressures can cause the unburned mixture away from the spark plug to auto-ignite, or detonate.\u00a0 This drastically raises temperatures and pressures and can bust out piston ring lands, blow holes in pistons, cause the spark plug to get very hot and glow and cause pre-ignition, and generally &#8220;wreck your weekend&#8221;.\u00a0 To avoid detonation, you\u00a0 use a higher octane fuel and keep the CR to a reasonable level.<\/p>\n<p>So we can see that it is important\u00a0for engine builders to know the engine&#8217;s compression ratio.\u00a0 Some race classes even limit Compression Ratio, so you want the highest CR you can get but not get disqualified in tear down. That is why Performance Trends developed Compression Ratio Calculator.\u00a0 It makes it much easier to keep track of all the little volumes which make up the total Combustion Chamber volume.<\/p>\n<p>The Compression Ratio Calculator includes things you may not have considered, that the head gasket may be a different ID than the bore, the piston top OD is significantly smaller than the bore, providing a space above the first compression ring, etc.\u00a0 The program also includes various engine building\u00a0features like determining the &#8220;deck height stack up&#8221; (piston compression height, rod length, etc) to fit inside the engine.\u00a0 We&#8217;ve also included several utility calculators (some companies call these &#8220;wizards&#8221;) to calculate piston dome or dish volume, find the needed piston dome (or some other parameter) to produce a desired CR, find engine and\u00a0 cylinder swept volume from bore and stroke, and much more.<\/p>\n<p>We are always improving our software and that is why we are now on our third version of this program.\u00a0 For version 2.3 we now have two options, the Basic version and the new Plus version.<\/p>\n<p>In the Basic version you can:<\/p>\n<ul>\n<li>Calculate compression ratio, cylinder volume and engine displacement.<\/li>\n<li>Find a desired compression ratio using chamber CC&#8217;s, deck height clearance and other inputs.<\/li>\n<li>Determine how much of a contribution various dimensions have on the overall compression ratio.<\/li>\n<li>Calculate Bore &#8211; Stroke ratios and Rod &#8211; Stroke ratios, boring and or stroking effects (if you are looking for a desired displacement you can determine the required bore and stroke)<\/li>\n<li>Calculate cranking compression pressure and dynamic compression ratio.\u00a0\u00a0 (Dynamic compression ratio does not use the entire swept volume in the equation, but only the volume in the\u00a0 cylinder at the point where the intake valve has closed.)<\/li>\n<li>Determine piston dome volume or piston dish volume.<\/li>\n<li>Enter head gasket volume as Bore and Thickness or Volume CC&#8217;s directly.<\/li>\n<li>Determine any of the following: rod length, deck height, deck height clearance, piston compression height or stroke based on you specifying the other four.<\/li>\n<li>Allow for English or metric units.<\/li>\n<li>Like most other Performance Trends programs you can save your changes to compare with other versions of your inputs or print out the report to share with your workers, engine builder or your customers.<\/li>\n<\/ul>\n<p>If you choose to upgrade to the Plus version (you can choose to upgrade at a later date) you will get the following inputs on top of all the inputs described above:<\/p>\n<ul>\n<li style=\"text-align: right;\">Calculate Effective Compression Ratio that is used by <a title=\"Supercharging\" href=\"http:\/\/performancetrends.com\/Definitions\/Supercharging.htm\" target=\"_self\">supercharger<\/a> companies to show requirements for boosted engines.<\/li>\n<li>Estimate the rod bolt loads, piston speed and G&#8217;s at a specific RPM.<\/li>\n<li>If you are looking for a better estimate of the Cranking Compression you will have more input details to do so.<\/li>\n<li>Pick the Gasket Bore Diameter from preloaded, known FelPro and other manufacturers of\u00a0gaskets.<\/li>\n<li>If you are going to mill the head this program can calculate the effect of the heads CC chamber.<\/li>\n<li>Calculate the Piston dome CC&#8217;s based on simple geometry (not from CCing the piston).<\/li>\n<\/ul>\n<p>Our Compression Ratio Calculator is many engine builder&#8217;s best friend.<\/p>\n<p><!--mstheme--><\/p>\n","protected":false},"excerpt":{"rendered":"<p>When building or modifying an engine for all-out racing, street\/strip performance, trailer towing, or most any application, there are many variables to consider. One critical variable is the Compression Ratio or CR. Compression ratio is the amount of &#8220;squeeze&#8221; the piston puts on the air fuel ratio before it lights\u00a0 the\u00a0fire.\u00a0 And, more importantly, it &hellip; <\/p>\n<p class=\"link-more\"><a href=\"https:\/\/performancetrends.com\/blog\/?p=142\" class=\"more-link\">Continue reading<span class=\"screen-reader-text\"> &#8220;Compression Ratio Calculator v2.3&#8221;<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8,63,3],"tags":[75,62,72,74,85,73],"_links":{"self":[{"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/142"}],"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\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=142"}],"version-history":[{"count":8,"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/142\/revisions"}],"predecessor-version":[{"id":195,"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/142\/revisions\/195"}],"wp:attachment":[{"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=142"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=142"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/performancetrends.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=142"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}