Dynamic Compression Ratio Octane Guide

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Dynamic compression ratio (DCR) is a more important factor in determining how well an engine runs and whether it will run OK on pump gas (93 octane or lower). DCR, quite simply, is the static compression ratio after some of it is bled off by the intake valve closing after the piston passes bottom dead center.

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The purpose of these pages is to helpfully show what DCR (Dynamic Compression Ratios) and SCR (Static Compression Ratios) have worked with what Octane gas. You have to realize that there is more to this than just the DCR.

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Dynamic Compression Ratio Explained. In our attempt to help our customers understand performance and what makes an engine produce power we are going to explain the concept of dynamic compression ratio (DCR). While seemingly esoteric, this is an essential concept in designing an engine for performance use.

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Putting the TA 284-88H with 110* lobe separation and 4* advance through the dynamic compression ratio calculator with a 9.6:1 static compression ratio yields almost 7.5:1 dynamic compression. 7.5 to 8.5 dynamic compression is generally acceptable for midgrade gasoline (our 91 octane). You may be able to get away with regular (our 87 octane …

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Compression makes horsepower on any fuel. Methanol makes more power by providing more heat. Gasoline at 20,943 BTU’s/lb at 14.7:1 air/fuel ratio by mass equals 0.068 lbs of fuel/lb of air or 1415 BTU’s/lb of air. Methanol at 9,770 BTU’s/lb at 6.4 air/fuel ratio by mass equals 1527 BTU’s/lb of air.

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Most gas stations offer three grades of octane, with regular rated typically at 87, mid-grade at 89 and premium at 92 or 93 [source: Federal Trade Commission ]. It’s easy to find what octane rating a gas has: Stations are required to post them on bright yellow stickers on each pump. Click ahead to discover what compression ratio is and how an …

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Re: Dynamic Compression Ratio versus Octane. there is no single answer. the fuel you can get away with is directly and specifically related to the ability of the combustion chamber to not develop hot spots that cause detonation. the ability to do that is a combination of the design of the cumbustion chamber itself as well as about 500 other …

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At this point, because the engine is reaching 100% volumetric efficiency, the dynamic compression ratio IS EQUAL TO the static compression ratio. Again, this is because the amount of air/fuel compressed by the piston in the dynamic situation is now equal to the amount compressed if you simply calculate the compression statically — this is the …

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Anybody now what the recommended maximum allowable DYNAMIC compression ratio is for 87,89,and 91 octane unleaded pump gasoline, for an iron head engine with .040 quench under towing load scenarios? KB’s site suggests no more than an 8:1 dynamic CR under the best (light load?) conditions without getting exotic.

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Therefore with the mild cam it will have a high dynamic compression ratio, probably 9.5:1+ which would be way too high to run safely on 91 octane gas. However, that same 11:1 static compression ratio engine with the radical 259/269 duration camshaft would have a dynamic compression ratio in the neighborhood of 7.5:1, totally acceptable to run …

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Dynamic Compression Ratio (DCR) is an important concept in high performance engines. Determining what the compression ratio is after the intake valve closes provides valuable information about how the engine will perform with a particular cam and octane.

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For example, I have learned that Dynamic Compression Ratio (DCR) is the way to look at the interplay between cylinder heads and camshafts. The consensus (from SpinMonster, of course!) is that with a tight quench (0.030\

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1,586. It is not static compression ratio that guides what octane to use but dynamic compression ratio. My 383 has 10.6:1 static compression but I can run 92 octane just fine because I run aluminum heads and my dynamic compression ratio is 8.46. You can run .5 more dynamic compression if you have aluminum heads.

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Putting the TA 284-88H with 110* lobe separation and 4* advance through the dynamic compression ratio calculator with a 9.6:1 static compression ratio yields almost 7.5:1 dynamic compression. 7.5 to 8.5 dynamic compression is generally acceptable for midgrade gasoline (our 91 octane). You may be able to get away with regular (our 87 octane …

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This equals 62 degrees. With these inputs, the UEM calculator offered 8.198 or 8.2:1 dynamic compression. The generally accepted conservative estimate is 8.0 to perhaps 8.5:1 dynamic compression ratio for 91 octane pump gas. This tends to be true for older, traditional engines with less effective combustion chambers.

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my 414 ci 396 had 11.8 to 1 compression, iron head with a solid cam 262/273 @ .050\

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This is why some engines require 100+ octane with an 11:1 compression ratio while others are perfectly fine on 91 octane with a 13:1 compression ratio. E-85 has an equivalent octane rating of 105, and with an expected operating temperature of around 180°F, the maximum dynamic CR is slightly above 10.5

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COMPRESSION RATIO CHART (Precise est for 10:0 & above comp ratios) Engine Octane Required. Compression / Minimum Octane Required (Some cases need Higher Octane) / # oz per gal. Kemco Required With 93 Base Fuel. 10.0 / 95 / .6.

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Re: Compression Ratio VS Octane Requirement Chart. Another thing to really consider should be actual compression instead of ratio. On my old 70, 795, it has a ratio of 16-17:1, but it only has about 120# compression due to a VERY tall exhaust port. Premium pump gas works way better in it than hi test.

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My 11:1 motor has a dynamic compression ratio of 9.7. According to the chart I just posted, it needs an octane of about 102 with a water temp of 180F. Having ran it for a while, I can say that octane requirement is fairly accurate. I dont think I could get away with E20 as your chart suggests. Quote.

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