The gains for platinum/iridium plugs mostly reside in the fact that they last longer and provide consistent spark for a long time.

You can gain a lot of horsepower from the right plugs (maybe 3-4 hp on our small engines), BUT:

- most people don't test them scientifically, as, consider that a dyno test costs a lot (2,500 pesos for a decent one), so it's not worth anyone's time to do ten or twenty tests just to find the right plug.

- then again, some people do take the time, and in the case of some cars, stock plugs or the platinum version of the stock plugs actually give more power.

- and finally, there's no "one size fits all" performance plug. Different cars have different combustion chamber designs, so what's total crap on one car (Splitfires on Sentras) might be pure gold on another.

If you're lucky, there's a dyno test of your particular car online showing which spark plugs give the best performance, but don't count on it. Most tuners who test have highly modified or already powerful cars, tests like on Sentra.net's Kojima's Garage for cheap cars like ours are few and far between.

But you never know. Search for your particular car on the web, read through enthusiast forums, and absorb what you read. You just might find a clue to the perfect plug hidden in one of the thousands of pages on your car on the web.