Power Pages: 1999 Mitsubishi Eclipse GS-T

In the second round of our '99 Eclipse we get a little more in depth as far as the electronic fuel tuning and boost-controlling aspects of the 4G63 engine are concerned. In the first round we were able to net 188.1 hp utilizing an Ingen air intake, Thermal Research & Development exhaust system and a Buschur Racing downpipe.

One of the biggest downsides to the '95 and up Eclipse is the Mitsubishi 16G turbo. The factory 16G turbo offers great low- to mid-range power but falls off in the high rpm range. The factory bypass valve acts as a horsepower governor; by doubling as a pop-off valve and bypass valve and it doesn't allow boost pressure to exceed 15 psi. Thanks to the Turbo XS blow-off valve, bleeding boost pressure is a cinch.

Performance Components
With the three basic upgrades completed, the next three modifications go a little past the street-legal aspect and move on to the "screw being legal let's make some horsepower!" mentality. We decided to remove the restrictive OEM catalytic converter, up the boost pressure, and add some fuel tuning to the mix.

The straight pipe is a custom unit made by Dynamic Autoparts just for testing purposes. The factory cat becomes very restrictive when upping the power on the 4G63 engine. By simply removing the cat and replacing it with a straight pipe, the true power can be unleashed from the vehicle. As a reminder, this is something you want to do only in race trim. The pipe can be made at any fabrication shop. The straight pipe was made with 2.5-inch piping, with two two-bolt flanges to make installation and removal much easier.

From our first round we learned that the OEM turbo is pretty much maxed out when it comes to providing power in the top end. Its small compressor is proof that the engine's true potential cannot be realized unless we scrap the baby snail for a much larger one. In any case, we are going to find out how much power we can extract from the turbo. Boosting up the pressure is a Turbo XS manual boost controller. The unit is equipped with two adjustment screws to ensure accuracy, one for course adjustment and a second for fine adjustments.

Our third installment is one of the key players when it comes to fuel tuning. The APEXi S-AFC is not new to the Power Pages; it is one of the most widely used piggyback computers on the market today. Fuel tuning can be made in low- and high-throttle applications, ranging in almost any rpm desired. With our engine running and the blow-off valve open, the AFC also allows for tuning by throttle position to compensate for the lost air charge through the blow-off valve.

Dyno
From our last session we lost a little power. Whether it needs a tune up or it's just miles on the turbo, the loss is very minimal. Regardless, our first installment will up the power level. Our baseline came in at 181.7 hp and 199.6 lb-ft of torque.

Our first installment was a modification made at Dynamic Autosports. The straight pipe was designed to replace the factory catalytic converter with no cutting and welding for installation. With the cat replaced with the straight pipe, we picked up a whopping 27.9 hp. Due to the lower level of restriction we also noticed almost 2 psi of boost pressure over stock. The car was able to generate more power in the mid-rpm range than at high rpm. This is mainly due to the quick response of the turbocharger generating power quickly but falling off on the top end. In any case, the car was able to pick up anywhere from 20 to 30 hp in the midrange, along with torque picking up to 205.8 lb-ft.

Our second trick was to get the turbo to pump out more pressure. Using a Turbo XS boost controller and dialing it in with a few test runs on the Our second trick was to get the turbo to pump out more pressure. Using a Turbo XS boost controller and dialing it in with a few test runs on the dyno led to a max pressure of 19 psi. Although max pressure was set at 19 psi, the turbo would fall off pace at 4500 rpm, where boost would drop off to about 13 psi. The power made in the midrange was what was amazing, picking up between 20 to 50 hp. The top end also gained 8.2 ponies over our previous run. Since max torque is made in the mid-rpm range, this upgrade did wonders for our torque curve, picking up as much as 50 lb-ft of torque.

With boost pressure 4 psi over stock, we decided to do a little fuel tuning. Since boost pressure fell off on the top due to the turbo, we decided to enhance the top end area to pick up a little more power. With the boost pressure losing 2 psi from the factory level, we decided to lean out the top end, and the end result was a peak power figure of 221.3 hp.

Although equipped with an inferior turbocharger, it is obvious that the 4G63 engine posses the potential to produce plenty of power. It seems that if the O.E. turbo were swapped out with one capable of keeping up with the engine, the Eclipse would generate more power.