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Old 12-06-2010, 08:56 PM   #160 (permalink)
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Lets look at it another way, bsfc for most small passenger car diesels are right at 200 or just slightly lower in their sweet spot (generally speaking). For gas engines it's right at 250 (also generally speaking). Take 200 and divide that by .88 and you get 227.2, round that off to 227 and you have more than 50% of the difference due to the energy content of the fuel.

Most of the rest is due to the ability of the diesel to run at mixtures as high as 50 to1 while the gas engine can not do that at this time. Throttle losses also reduce the efficiency in throttled engines by reducing the actual compression ratio in the combustion chamber which is the same as having a lower compression and no restriction.

Not sure if we agree that those two principle factors, fuel energy content and actual in cylinder compression are the majority of the difference in efficiencies between gas and diesel. If you use the best mapped bsfc for each you are placing them in their ideal state of operation.

Looking at the maps themselves reveals what you referred to when you stated that hypermiling will generally result in a greater benefit in a gasoline engine.

I am not disputing you belief that people should be better trained to drive economically. I just think that vehicles could be much better designed (like the INNAS configuration which was a diesel) to allow much of the improvement to be incorporated into the vehicle itself.

From personal experience, when we checked for cam free motion in the L24-28 series Nissan engines we rotated the cam by itself, and checked it at various stages as the valve train assembly was completed. The "spring back" was easy to feel and the actual work to roate the cam and operate the valves was much less than you might imagine, even without pressurized lubrication.

The cheapskates would only machine the bottom of the head, and if they did not machine the top of the head and shim the cam towers to get the timing chain sproket to crankshaft sprocket dimension back in specs, two things could happen.

The camshaft would break in to at the center cam bearing, and the timing chain tensioner would be hyperextended and the chain would rattle or in severe cases the tensioner block could actually come completely out of it's housing with catatrophic results.

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