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Originally Posted by Brian Carlton
This is correct with one slight addition:
On a diesel engine, you are compressing air at atmopheric pressure (14.7 psi absolute), so you get the effect of 22:1 compression.
With a gasoline engine at closed throttle, you are compressing air at significantly less than atmospheric pressure (estimated at 4 psi absolute), so the effect of 8:1 compression is effectively reduced by the differential of manifold pressure (4/14.7). The resulting braking force in an equivalent sized gasoline engine is therefore approx. 10% of the braking force in the diesel.
As PEH has mentioned above, the gasoline engine would provide far better braking force if the throttle was open and a full charge of air (14.7 psi absolute) was allowed to fill the cylinders.
This should be quite obvious to all the diesel drivers. We typically don't need to use the brakes much, when the gassers are burning the brake pads at every opportunity.
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I would have to disagree with that...and my brothers Chevy truck with a small block chevy has far more engine braking than my 6.2 equiped truck....
Also my 1.6 L Honda or my 1.9 saturn has far more engine braking than either benz or my truck....by a huge margin...
I have to use my brakes far more on long downgrades with any of the diesels I own than any gasolene powerd I have ever owned. I only needed brakes on the very steepest of hills to keep my speed down on the gassers I have owned.....on any of the diesels I need the brakes on even moderate long downgrades to keep speeds down. I grew up on the foothills of the Appalacians....so I have spend a large portion of my time either going up or going down one hill or other. True they aren't the Rockies.....but they are high enough to make it an issue.