CAR PERFORMANCE

Many Import Performance Tuners start out simply by finding the right information. If that's what you're looking for, you're in the right place.

Most imports are simply classified as being built overseas, however in the industry I work in, imports are defined as not only foreign vehicles, but also the sport compact vehicles of American manufacturers, such as the Dodge SRT4's, Chevy Cobalt and Pontiac Solstice.

Tuning for most people is trying to squeeze every available bit of horsepower from a vehicle, and for some of the less informed, this also means sacrifice engine longevity and reliability (what good is an extra 5whp when it breaks 45k miles sooner).

Import tuning is no different then the hot rod building of the old days. Small lightweight cars with big power plants stuffed into them. Getting the power/weight ratio as high as possible and still maintain reliability.

Import tuning's most basic adjustment hasn't changed. Fuel pressure. Simply increasing or decreasing fuel pressure at the rail has a dramatic effect on air/fuel ratios, as well as Short term and Long term fuel trims.

Modifying your fuel system to support modifications is extremely important. Most items like a S-AFC or a e-manage simply modify sensor values going into the computer to increase or decrease fuel injector duty. While this works in practice, if you're adding 10% across the board to richen a car up, leaving that at 0 and simply increasing fuel pressure is a much safer way to do things, and lets the computer work how it was originally intended.

But back to the fuel pressure. As the most basic and fundamental import tuning point on the car, it is important to get this right before any other adjustments are made. Reearch tells us how Fuel injector flow is based off of a fixed pressure value of a standard viscosity fluid. Most companies rate them differently, but the most used rating for the aftermarket is 43psi, while some vehicle builders test them much higher. The reason this is crucial is because the fuel pressure behind the fuel injector itself will raise it's basic output. A 450cc injector supplied at 37psi at the rail is putting out far less fuel then a 450cc injector supplied at 55psi at the rail.

After doing a few runs with your car, look at your complete air/fuel value for the extent of your test. If you've changed anything to increase the volumetric efficiency of the motor, the motor will be leaner (Air/fuel ratio is higher then before) then when you began. If there is a noticeable need overall in the ratio, then simple fuel pressure adjustments can fix that. At cruising speeds, the air/fuel should always be 14.7:1, an all-motor car under full load should be about 13.5:1, and a forced induction car under full load should aim for 11.2-11.9:1. The higher the number, the leaner (less fuel) the car is. To richen the car to make the the ideal points, increase fuel pressure, and if you need to lean the car out to lower the air/fuel ratio, decrease fuel pressure.

Some cars will not show a change, but need further tuning via the short term and long term fuel trims. Most vehicles these days will let these values go +/- 25%, but ideally the fuel pressure should be adjusted so that they are all +/- 5% so that the maps are open to the car if they're needed.

Run the car a few more times with an obd-2 datalogger on board. Look at the fuel trim values, and see where they are resting. If the vehicle is adding a lot of fuel trim (increasing the numbers) then adding a few more psi of fuel pressure (generally 1-2psi and recheck) can greatly reduce that number. Likewise, if you see it pulling fuel trim, decreasing the fuel pressure will off-set this. This is very important to allow the vehicle it's full range in making adjustments for varying conditions, such as weather, temperature and altitude.