Why is the compression ratio so low?
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Why is the compression ratio so low?
<meta http-equiv="CONTENT-TYPE" content="text/html; charset=utf-8"><title></title><meta name="GENERATOR" content="OpenOffice.org 2.0 (Linux)"><meta name="AUTHOR" content="Ryan Patterson"><meta name="CREATED" content="20070625;21134300"><meta name="CHANGEDBY" content="Ryan Patterson"><meta name="CHANGED" content="20070625;21442800"><style type="text/css"></style>I'm looking at the 2008 superduty book my dealer gave me and it lists the trition v8 compression ratio to be 9.8:1 and the triton v10 compression ratio is 9.2:1. The bore and stroke are the same. I thought the v10 was basically the v8 with two extra pistons. Why does ford drop the compression ratio down when adding the extra two cylinders? The best I can come up with is it makes the engine more super/turbocharger friendly. But that can't be the reason. If the v8 can handle 9.8:1 compression shouldn't the v10 be able to handle the same? Wouldn't keeping the compression higher allow the v10 to produce more power and be more efficent? I'm sure ford knows what they are doing so there must be a good reason.
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Originally Posted by Monsta
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There is a serious difference between "static" and "dynamic" compression ratios
Ford's static numbers are simple math based on cylinder volume at BDC vs cylinder volume at TDC
Dynamic compression ratio considers valve timing, overlap, and the extra 2 cylinders load on the various other systems (starting system as an example)
compression ratios relate to more then just cylinder timing/firing sequences and pre ignition... the engineers also consider bore evacuation, pre fill, shape, charge injection velocity and about another half dozen factors to arrive at a formula for decent drive-ability, starting, volumetric efficiency etc...
To compare the modular 5.4 to the 6.8 is interesting but not really relevant --- IMO --- The 6.8 is NOT just a v8 with two extra cylinders...intertnal combustion motor engineering is much more complicated then that
Ford's static numbers are simple math based on cylinder volume at BDC vs cylinder volume at TDC
Dynamic compression ratio considers valve timing, overlap, and the extra 2 cylinders load on the various other systems (starting system as an example)
compression ratios relate to more then just cylinder timing/firing sequences and pre ignition... the engineers also consider bore evacuation, pre fill, shape, charge injection velocity and about another half dozen factors to arrive at a formula for decent drive-ability, starting, volumetric efficiency etc...
To compare the modular 5.4 to the 6.8 is interesting but not really relevant --- IMO --- The 6.8 is NOT just a v8 with two extra cylinders...intertnal combustion motor engineering is much more complicated then that
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