[robchalmers]

Big Big theory


On the forum there seems to be two schools of though of how to improve economy.

Firstly what I’m calling hot camp. The concept as I grasp it is that warmer air is less dense so the is less 02 hitting the lambda sensor in the exhaust – ECU thinks the car is running rich and therefore drops the injected amount. Thus less fuel used. This also goes with the idea of choking the intake to reduce the amount air that can get into the engine for the similar effect. I’m also putting into this group the concept of lower Octane fuel = more economy, that one still puzzles me


Second smaller group is what I call the big bang theory group. I was always told to get the most efficiency you need to get the most from the least. This goes off the CAI theory of more dense air produces a bigger bang per unit fuel, yes the ecu will see more air burnt and resultantly increase the mixture, but the extra work done means you can back off the throttle thus keeping the same mixture ration control by the ECU but just achieve the same work on less fuel. I’m also combining this with the higher octane side too – as to me it relates directly to the calorific/energy out value of fuel. To my mind if your ecu in the car keeps the mixture the same/burnt rate/ timing self optimised as per an modern ecu, for every ml of fuel a (Hi oct) you would generate more energy, per bang than fuel b (lo oct) and as a result you’d require more fuel to provide the same energy needed to cruise at a given speed.

If for example we take a pretty common direct stratified inject petrol engine that doesn’t require the fuel mix to vaporise in between an old school carb and piston would have though the best thing is to have cold dense air to create the most complete bang from a tiny amount of a hi octane fuel?

I’ll grant you that I might be missing something please set me straight