The reduction in power, that results from using 95 octane in an engine designed for 98/99, is down to the ecu detecting "pinking" or "knocking" (where the fuel/air mixture doesn't burn at the point the engine designer intended) and varying the point at which the spark occurs to prevent it, so reducing the power produced.
Seems to me, that having a high performance engine, and deliberately de-tuning it, (with 95 octane), is not a sensible thing to do.
The detergents in modern branded fuels are designed to reduce carbon, and other residue build up in the engine. I believe they do that. While the flaps are not exposed to the incoming fuel, an engine that burns cleanly (a combination of fuel, additives and efficient combustion) will suffer less from the build up of various nasties (including recirculated crud) than an engine that doesn't burn cleanly.
I'll stick with Shell V Power. The additional cost is quite a small percentage of the total cost of ownership after all.
Both 95 and 98/99 octane are good quality fuels, the difference is not in quality, 95 is fine in an engine (virtually all these days) that's designed for it, and using 98/99 octane in such an engine would be a waste of money.
Wizzy additives are separate from octane, and branded 95 (and diesel) with additives is (in my opinion) superior to unbranded without.
EN228, the BS standard for petrol (and it's diesel equivalent) that all fuels must meet, does not specify such additives. So, unbranded fuels, sold at lower cost, will not have those expensive (to develop and make) additives. The choice is yours, of course, but make sure that choice is informed.
Mac.
