Underbody rust prevention
The Indicas have an epoxy coating done already(visible - just get under the car and you will see a scruffy coating that also help in sound deadening) on the underbody so no rusting of the metal there can happen. There is no real need whatsover of an underbody anti rust coating. The only thing that will rust is the silencer's muffler in about 2.5-3 years time and that rusts from the inside because of the water vapour produced as a result of hydrocarbon combustion inside the cylinders.
CH2O + O2 = CO2 + H2O (same basic equation but petrol engines more prone)
So keep all the "rust protection" money with you, it will come in handy for the silencer tube and muffler replacement.
High Octane Fuel
Please go to
Why octane Value of Fuel is so important.
A higher octane value should always result in lesser knocking. Lesser knocking means more 'powered' piston down strokes. That means more bhp for the same number of revolutions and that translates into better mileage, efficiency, pick-up, smoothness and speed etc. Now, car owners do not decide the real octane value of the fuel they buy. That depends much more on the integrity of the companies retailing the fuel. But if there is a company that says their fuel is a certain octane level that my car's manual also says is the most optimum thing for my car - I would buy it and more importantly
try it. Well, my car returns a minimum of 18kmpl in traffic and gave 23.64kmpl on two trips to Vizag and Chirala beach on high octane fuel.
Fuel Additives
There are two ways of keeping your MPFI fuel injectors clean.
A. Keep getting them cleaned at regular service intervals.
B. Use fuel additives that will dissolve the impurities and plaque settled on the injectors. In the long run, cleaner injectors mean better fuel supply and combustion and a cleaner fuel delivery system. The effect is:
Great, if the fuel you buy is relatively clean(the additive does its work)
Nil, if the fuel you buy is absolutely clean(the additive has no work to do)
Useless, if the fuel you buy is really dirty(the additive alone will not be sufficient)
Speed vs. ExtraPremium Claims First
Speed(Bharat Petroleum): high octane fuel
Extra premium(Indian Oil): friction busters, better mileage and smoother drive etc
Even if one takes their claims at face value, one can see that they are promising different things. ExtraPremium simply claims to have a fuel additive like the IFTEXg in it. It is Speed that claims to be 'better burning capacity petrol' because of its higher octane value. So if I use
IFTEXG and Speed then my car should get the best of both worlds - higher octane fuel and an injector cleaning additive.
Hope I answered some of your queries.