Thread: Engine Braking
View Single Post
Old 10-02-2012, 02:43 PM   #10 (permalink)
The PRC.
Join Date: Oct 2009
Location: Elsewhere.
Posts: 5,304
Thanks: 285
Thanked 536 Times in 384 Posts
Originally Posted by Old Mechanic View Post
A dyno test I found showed 20HP of power for 1 unit of fuel at 20 HP for a 4 cylinder engine. When the load was increased to 50 HP the fuel consumed only rose by 50% while the power increased by 150%, at the same RPM.

This is because the in cylinder compression was increased from about 50% of atmospheric pressure to 100% of atmospheric pressure. With twice the actual compression and twice as much fuel, the engine produced 1.5 times as much power.

30 more horsepower on half again as much fuel. 50 HP on 1.5 or 2 HP on 1. The higher horsepower divided by the fuel consumption gives you 32.66 HP per unit, compared to 20 HP per unit at the lower load. Using the higher unit per fuel to add inertai to your vehicle means you can average the same speed while using a lot less fuel. The essence of P&G.

Is this why people say to maximise the the mythical LOD thing on the SG2 which I still don't understand ? In which case I regard this posting as a potential magic key. I hope.

Originally Posted by Miller88 View Post
Newer vehicles don't seem to engine brake as well. Vacuum on deceleration = NoX emissions.
In what way - they stop sooner, no braking or no fuel shut off ? I noticed my TDI would shut off at anything over idle at all, the Aygo Petrol has to be over 1400 when you start engine braking for the ECU to detect it.
[I]So long and thanks for all the fish.[/I]
  Reply With Quote