It has been many years since I last drove a petrol vehicle, but my gut feeling is that a diesel engine provides much more engine braking than a petrol. I have been told many times I am wrong, but none-the-less, I am still convinced I am correct.
Engine braking - petrol versus diesel
- Thread starter Harry Bloomfield
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I’d say diesel. It would be compression ratio that you slows you down.
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Talking last night about engine braking and specifically about jakes brakes on larger diesel engines being banned in many towns in the USA
www.mathesoninc.com
What Is a Jake Brake and How Does it Work? – Matheson Inc.
www.mathesoninc.com
Talking last night about engine braking and specifically about jakes brakes on larger diesel engines being banned in many towns in the USA
What Is a Jake Brake and How Does it Work? – Matheson Inc.
I couldn't follow that, from the description of how they work - did you understand it?
That description is rubbish, and it's evident that whoever wrote it doesn't even understand how an engine works normally.
A better description here: https://en.wikipedia.org/wiki/Compression_release_engine_brake
A better description here: https://en.wikipedia.org/wiki/Compression_release_engine_brake
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The Jake brake seems to be describing what we call an exhaust brake. But not sure. The exhaust brake does not open the exhaust valves, it just cuts the fuel and puts a flap across the exhaust. You need to release when changing gears, as once out of gear it will stop engine.
However engine braking only works when using a manual car, with an automatic the car will auto select a high gear on over run, so with my wife's Jag the 8 speed box will only slow one down if you have selected to use the paddles to manually change gear.
So with an automatic car in auto mode there is next to no engine braking so does not matter if petrol or diesel, there is very little engine braking with either.
The manual it will clearly depend what gear is selected, and the resulting speed of the engine, but in general the diesel does give more engine braking.
However engine braking only works when using a manual car, with an automatic the car will auto select a high gear on over run, so with my wife's Jag the 8 speed box will only slow one down if you have selected to use the paddles to manually change gear.
So with an automatic car in auto mode there is next to no engine braking so does not matter if petrol or diesel, there is very little engine braking with either.
The manual it will clearly depend what gear is selected, and the resulting speed of the engine, but in general the diesel does give more engine braking.
Thanks, that has always been my impression, and something I have struggled to convince others of. Why there should be such a difference, I am not sure - both compress air in their cylinders, then release the energy rather like a spring. The big difference is the compression ratio, plus a diesel can suck as much air in as it likes - whereas a petrol will be working under a partial vacuum in the cylinders under a closed throttle.
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Now your talking about some thing different, in the old days there was a throttle, and as the name implies to stopped the air going in, but today we have fuel injection, so not so sure any more. But if I look at my Sorento the diesel version only revs to 4000 revs, where the petrol can go to 6000 revs, so it is not that straight forward.