Thanks Gaz,
I read through the links, and I from what I can see they all state the same: in simple terms,
"there is no power advantage in running higher octane fuel in a car if you do nothing other than fill the tank"
I agree with this for a grey motor.
I also think that you are right in saying "If an advantage is gained by running the higher RON and adjustment of spark timing, then it well may be that the original settings were less than optimal". If we take Moet's warm grey as an example, he could run 91 (or 93) RON, and increase ignition timing up to the point of pinging, then back it off a few degrees. This is probably the point of optimal power for that fuel.
What I am driving at is to understand whether there is an advantage over doing the above by changing to 98 RON just so you can screw a few more degrees timing in without pinging. The basic theory says that there is an advantage in doing this (more timing = more power). However, the diminishing return rule starts to apply - the extra timing that Moet could run on 93RON may have bought him an extra 10HP, but the timing increases he can make when changing to 98 RON may only gain him another 2HP.
Harv,
The "basic theory" to which you refer is totally erroneous.
With the motor in question there
can be no increase in power if the motor was previously properly tuned for maximum performance and in good condition.
If we can (and should) believe the chemists, there is no more "bang" associated with the higher octane fuel. There will be some increase through using other TYPES of fuel, but not if we restrict ourselves to pump petrol.
If we replace standard with super and advance the timing, all that will happen is that the mixture will start to burn earlier, it will burn slower and cooler, and the fire may go out at the same point as before,
but with the same calorific value.
Where can we gain horsepower with that?
The point of advancing spark timing is to ensure the mix is well and truly alight at TDC.
The mix must burn at a rate adequate to push the piston down progressively, and theoretically should burn out just before exhaust valve opens.
Over-advancing will cause a major burn to occur before TDC, and will rob the process of power by trying to compress an already expanding burn.
If the burn finishes too early, the piston will try to pull down the already compressing gasses before before the exhaust valve has opened, using even more power needlessly.
Any serious attempts to increase horsepower are centred around two things:
Make a bigger bang, and make more bangs per minute.
Using fuel of the same calorific value, bigger bangs are made by any or all of these things:
1/ Increase the VOLUME of correct fuel/air mixture at point of ignition,
2/ Increase the speed at which the mixture is compressed,
3/ Increase the pressure of the mixture prior to ignition.
I won't go into the mechanics of the above as they don't relate to the thread.
I hope that I have made the above simple enough for the layman, without over-simplifying for those already aware, and I welcome comments from those more learned than myself, naturally.
Cheers,
Gaz
