How Best To SuckI've been contemplating building my own air intake. Wouldn't it be just as good to replace the stock box with a cone filter, rather than doing all that shiny piping? Why can't the stock piping work just as well? The air filter makes the most difference because it frees up the air restriction, right?Alex SucairiusChicago, Illinois
The answer to your question is my all-time favorite: it depends.
There are several possible sources of restriction in a stock intake system. Sometimes the air filter itself is restrictive. Though often it's the box the filter is in. According to a dyno test done at BEGI in Texas just three hours before I wrote this, simply opening the airbox lid on a Mazdaspeed3 gains 20hp. Do the same on an R32 Skyline GT-R and you'll see exactly nothing. The airbox on a Skyline is said to be good for over 450hp before it presents a measurable restriction.
The Skyline's problem is in the intake hose itself. The rear turbo is fed by a rubber hose that's corrugated to allow flexing and has a spiral wire stuck in it to prevent it from collapsing. Both these things can cause lots of turbulence that can restrict airflow at high power levels, regardless of which engine the hose is on. At really high power levels, the immense suction can collapse the Skyline's hose, in spite of the spiral wire, choking airflow to the rear turbo.
Occasionally, the air filter box volume is carefully tuned to contribute to resonance tuning in the intake manifold. Try making your own intake for an S2000 or RX-8 and you'll probably just screw up this careful tuning and lose power.
If your car has a mass airflow sensor (MAF), just sticking a cone filter on it can be risky. The ECU is programmed to account for how the MAF reads with air coming through the stock box. If the box has a nice, rounded entrance to the MAF and your filter's entrance is squared off, the turbulence off that sharp corner will screw up the MAF reading. Or if the MAF and filter are too close to turbulent outside airflow, as it once was on our Project 300ZX TT, readings can get screwy at high speed. Every so often, these misreadings will help you, if they lean out an overly-rich mixture, but they'll eventually come back to bite you when you install some other tuning parts designed around a properly functioning MAF and you end up with an overly-lean mixture.
Since you never mentioned what kind of car you had, all I can do is give you gloom and doom stories like this. Odds are reasonably good, in reality, that if you have a normal boring car, you can get a few horses and a much better sound with your filter idea.
Too Many ChoicesExcept for drag racers, most cars, especially Sport Compact Car's test cars, always seem to have the same model tire on the front and rear. Some cars may use different sizes, but invariably it is the same tire at all four corners. Why?
The front and rear of any car have different weight, grip, and tracking characteristics. So, why isn't each end of the car considered independently? Then one would mount the most appropriate tire on that end.Scott GardnerColumbus, Ohio