Synthetic Oil
I know that most owners manuals are calling for longer intervals now, but that does not make it better. The new trend is making less maintenance for a vehicle, because trust me, most people do not like spending money on routine maintenance. Mercedes, who uses only synthetic from the factory for a couple of years now, got themselves into trouble with this. They pushed this lack of maintenance so that their oil change lights were reported by some owners for 20,000 to 30,000 mile intervals. This was a good thing for all their new car owners until their engines starting gumming up and locking up. Now Mercedes had a lawsuit filed against them. The moral of this story is that car companies are pushing their service intervals as long as they can, so that the part fails at an acceptable time. And if major failure happens at an acceptable time, (i.e. 250,000 miles) the consumer won't be so pissed off at it. On a performance basis, changing that fluid frequently, will make the engine last a lot longer, retaining factory performance, or close to it, especially when using a synthetic oil. Synthetic oil is such a better lubricant for the vehicle that I can guarantee that it is going the be the lowest standard for all qualities of oil in the near future. The oil standard this summer should be going up again, which may possibly be a partial synthetic, because it is supposed to cost "substantially more" than the current oil. Ford switched to partial synthetic as the standard for transmissions a long time ago. Anyone here of Mercon V? Mopar switched last year for transmissions. Now Ford and Mazda switched to partial synthetic for the motor oil as well. They wouldn't spend the extra money on all that motor oil (partial synthetic is about double the cost as conventional oil) if it wasn't for a very good reason. And partial synthetic is only barely worth the investment when compared to full synthetic, considering the convential motor oil in it still breaks down after 2,500 miles. On another note, that extra half a court left in the engine is not from a lack of draining time, that is from oil left in the bottom of the pan, because no oil pan has a perfect design to drain all the engine oil. There are always oil lines as well, and deposits left in the motor. We have a Bilstein engine flush machine that we use to clean out engines that have deposits, and after running this machine, the motor will take about half a quart more oil on the fill up. Also, if you ever checked a service manual (not owners manual), sometimes it will list total fill and refill with different numbers. Also, 5,000-7,500 mile intervals are for "normal driving conditions," which upon reading the descriptions, most enthusiasts are in the "severe driving contions". Which usually calls for 3,000 mile intervals.
Maybe when I have more time I will also post something in here that will retain your horsepower far more than using synthetic oil. If you have over 49,000 miles, you've already lost more horsepower since your car left the factory than any cold air intake could make up for.