03-10-2013, 10:26 AM
Whoa whoa, the whole "keep the engine off boost" is total trash - in a petrol, yes, you've got an AFR to keep to - to stop the pistons melting..
Diesel the more air you can cram in the engine (to a point... Pumping losses...) the higher your thermal efficiency - Turbocharged Diesels use a slightly lower compression ratio, so any increase in thermal efficiency will help... That's precisely why Diesels are significantly more efficient, they've got greater thermal efficiency than a Petrol engine... 21:1 compression vs 9:1 Compression (if you're lucky)...
For example, with a OE T2 I was achieving around 45mpg on the motorway, when I fitted my VNT, that'd be producing between 8 and 10psi constantly on the motorway, my economy rocketed to ~60mpg...
Think about it in terms of power being a function of torque or RPMs... Think of your foot as a "Torque Request" pedal - that's how the governor in the pump works, the harder you press, the more torque you get - but at the same time, if you don't press hard and let the engine rev higher, you get automatically more power, since you've got the same amount of torque, it's often MORE efficient to allow the engine to rev slightly higher rather than injecting loads of fuel to create torque to tug you along...
Diesel the more air you can cram in the engine (to a point... Pumping losses...) the higher your thermal efficiency - Turbocharged Diesels use a slightly lower compression ratio, so any increase in thermal efficiency will help... That's precisely why Diesels are significantly more efficient, they've got greater thermal efficiency than a Petrol engine... 21:1 compression vs 9:1 Compression (if you're lucky)...
For example, with a OE T2 I was achieving around 45mpg on the motorway, when I fitted my VNT, that'd be producing between 8 and 10psi constantly on the motorway, my economy rocketed to ~60mpg...
Think about it in terms of power being a function of torque or RPMs... Think of your foot as a "Torque Request" pedal - that's how the governor in the pump works, the harder you press, the more torque you get - but at the same time, if you don't press hard and let the engine rev higher, you get automatically more power, since you've got the same amount of torque, it's often MORE efficient to allow the engine to rev slightly higher rather than injecting loads of fuel to create torque to tug you along...
