Which has more Engine Braking? A petrol or a diesel engine? In midst of a discussion on another thread, this came up as rather off-topic.
Which has more Engine braking everything else remaining same. A Diesel Engine or a Petrol Engine.
I used to think Diesel engines have more braking until I came across this Wikipedia entry: Engine braking - Wikipedia, the free encyclopedia Quote:
Petrol (gasoline) engines
The term engine braking usually refers to the braking effect caused by throttle position induced vacuum in petrol (gasoline) engines. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from vacuum.
When the throttle is lifted less air is allowed to pass through the intake manifold, and the engine works against this vacuum. It is the deceleration of the engine against this vacuum which provides the braking effect.
Diesel engines
Diesel engines do not maintain a throttle vacuum as they do not have an intake throttle. The fuel itself is the throttle, and thus diesel engines are not subject to the same engine braking effects as gasoline engines are.
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But the thing is, I feel the statement is fundamentally flawed.
My logic was :
say a 1.4 L diesel produces X bhp at 3000 rpm and a 1.4 L petrol produces as X bhp at 5000 rpm so at the flywheel, which engines is producing more power per rpm? So if you take your leg off the gas pedal, which engine consumes more power from tranny per RPM? So which engine has more braking per RPM?
Even if you want to go stroke by stroke, it is the compression stroke that causes engine braking rather than intake stroke as mentioned there, irrespective of it is Petrol or Diesel.
Also, while an average Petrol's heads compression ratio is at 10:1, a similar Diesel would require 20:1 explaining the peak power output at almost 1/2 RPM values.
So guys please let me know- Am I thinking right? The house is now open for debate! |