To Premium or Not To Premium
Q: I want to buy an FJ Cruiser but it calls for premium fuel. This is an issue for me, as premium fuel is 25 cents more per gallon than regular. Can this vehicle run on regular gas, or can it be tuned to run on regular gas?
A: The 2007 FJ Cruiser is the same basic platform as Toyota's 4Runner SUV, and both use the very same 4.0-liter V-6 engine. So why does the 4Runner owner's manual stipulate a minimum of 87 octane (regular gas) while FJ specifications read 91 or better? Good question. According to David Lee, product education administrator at the University of Toyota, Toyota wanted the new FJ Cruiser to meet the more stringent LEV II (Low-Emission Vehicle) standards, which it was able to achieve, but only while running its V-6 on a 91 octane or higher-rated fuel. Therefore, in order to be officially deemed an LEV II vehicle, 91 octane had to be listed as the required minimum. The good news: you can run the FJ on regular gas without any significant ill effects (spark knock, loss of power), just like the V-6 4Runner (LEV I). The only differences will be a tiny bit increased emissions and an iota less power. On the dynamometer, the higher octane increases engine output by six horsepower and 10 pound-feet of torque at peak rpm, but I don't see that being perceptible in real-world driving.
Big Rims Mean Hot Brakes?
Q: I changed the rims on my F-150 from 17- to 2--inch. Do I need to upgrade the rotors and calipers to match? If so, what size? I was told that due to the changes I made to my rims' size, the brakes are now getting hot and squeaking when I apply the brakes. Is this true?
A: Wheel size shouldn't have a significant effect on the brakes. If you're upsizing the wheels while compensating with tire size to maintain the original tire diameter/circumference, there should be limited effect on drivetrain performance or speedometer calibration, too. But ride and handling is another story. The only other issues would be if the aftermarket wheels are significantly heavier than the originals, if you switched from alloy to steel wheels (alloy disburses heat better), or if there's a problem with airflow through the wheels needed for brake cooling. Not everyone realizes how the aerodynamics of wheels direct airflow to the brakes, especially disc brakes. That's why a few vehicles even have left- and right-side wheels. Installing a left wheel on the right side will reverse the designed inward path of air and potentially cause a brake overheat condition. I've also seen aftermarket shields mounted behind wheels to confine brake dust. It may keep your wheels clean, but it also cuts off the airflow and cooks the brakes. If the wheels were confirmed to be causing the problem, I'd get rid of them before upgrading the brakes. Of course, the squeak in your brakes may be totally unrelated to the wheels. If you're unsure of a diagnosis, get a second opinion.