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Bolt-On Performance



When our '97 Eclipse GSX project arrived earlier this year, we couldn't wait to get to work on it. Although Mitsubishi assembled a fine sports coupe straight from the factory, there's plenty of room for improvement. Like any new car, compromises were made to make it more salable to the general public. But, since we fall into that small percentile that are willing to sacrifice some silence and creature comforts for ultimate performance, we decided to go to work on our pocket rocket.

I was sold on the K&N intake and exhaust and the Eibach springs my One Lap of America car was equipped with, but the car continued to feel unsettled in some cornering situations. We decided to supplement the Eibachs with a set of Koni adjustable struts. However, there was a catch. Koni does not make a rear strut specifically for the GSX Lee Grimes at Koni told us the GST strut fits, but the spring perch is about 10 mm lower than the GSX. As it turns out, it didn't really matter. The additional drop is imperceptible in back (the Eclipse rides a little high in the rear anyhow), and performance is not affected in the least.

Installation of the springs and struts on the Eclipse was straightforward, as these types of installations usually are. Performed at Eibach's headquarters in Irvine, California, we took advantage of some of the high-tech gadgetry that Eibach keeps on hand to test various products. On their spring tester, we discovered that the stock Eclipse springs are rather loose single-rate springs at 277 lbs/in in front and 165 lbs/in in the rear. The Eibachs, on the other hand, are significantly stiffer at 320 lbs/in front and 170-217 lbs/in in the back.

1) Removing the struts and springs from the Eclipse was a straightforward affair. We started with the front struts. The first step is unbolting the wishbone from the strut.

2) Nest, the bottom mount for the wishbone was removed to make room for the strut/spring assembly to be taken out of the car. The tower bolts on top of the struts were removed, and the strut was taken out of the car.


3) As always, if is important to use a spring compressor when removing stock springs from their mounts. Once the spring was held in place the top nut was removed and the spring removed from the strut.

4) The shortened Eibach spring is on the right, the stock on the left. The higher spring rate and shorter length combine for enhanced handling and looks.

5) To find out just how much of an advantage the Eibach springs had over the stock springs, we tested them in Eibach's spring tester. The stock springs were rated at 277 lbs/in in front and 165 lbs/in in the rear, while the Eibachs rated 320 lbs/in in front and 170-210 in the rear.

6) We also took advantage of Eibach's Roehrig shock dyne. By cycling shocks and struts through various speeds, a clear picture of how the strut behaves can be measured. The stock struts-not surprisingly-were significantly softer at all ranges than the Konis.

7) Installation of the struts is a reverse of removal. It is important to make sure the plastic spacer Koni supplies with their struts is installed. If the struts were to bottom out on the bump stop, this tattle piece of plastic will prevent pieces of foam rubber from getting inside the strut body.

8) Koni uses a larger strut shall than the stock unit, so some pieces had to be modified to fit.

9) Rear strut removal is even easier than the front. The two bolts at the top of the strut (located under plastic covers in the cargo area) were removed. Next the lower mounting bolt was removed, and the strut/spring assembly simply slid out of the car.

10) With the spring/strut assembly free of the car, it simply rifled out.

11) The stock spring perch will be used on the Koni, and it easily slides off after a couple of whacks with a rubber hammer.

12) The struts we used were originally intended for the GS-T, since Koni does not make a set specifically for the GSX. Although the perch is 10mm lower in the GS-T, it makes no visual or dynamic difference to the car.

We also tested the Koni struts against the stock struts. Not surprisingly, the stock struts were quite soft, biased more toward a cushy ride than firm control. The Konis, however, were much stiffer than the stock struts even at their softest setting. The Roehrig shock dyno cycles each strut through various speeds and measures the compression force and rebound force. The Konis are adjustable only for rebound, as are most adjustable struts. On their softest setting (although the settings are not notched like some struts, there are effectively three: soft medium and hard) the Konis were significantly stiffer in both rebound and compression. As the Konis were adjusted tighter, the difference became even more dramatic. Although the compression never changed, the Koni strut showed up to three times as much rebound force as the stock strut. This translates to a stiffer ride on the street, but improved handling on the track. In addition, because the struts are adjustable, they offer the driver a quick and easy way to control understeer on the Eclipse by dialing in more stiffness to the rear and leaving the fronts soft. This helps the tail break loose easier, resulting in a more neutral car in the corners. On their soft setting, the ride is not really affected. Large dips at freeway speeds are more firmly controlled, but with none of the floatiness normally associated with those types of humps. Small impacts like freeway expansion joints and Botts dots are also well absorbed. Naturally, on their firmer settings, the ride gets buckboard stiff, but the firmer settings are really meant for the track. 

To take advantage of the new struts, we decided to upgrade the stock rubber with 18-inch Kosei Seneca wheels supplied by ART Inc. of Gardena, California, and 225/40ZR-18 rubber. There are a lot of high-performance tires on the market today, but we wanted to try out the successor to Dunlop's popular SP Sport 8000, called (appropriately enough) the SP Sport 9000. Designed as a performance tire for the world, Dunlop went to great pains to design a tire that would not only perform well in dry conditions (which it does admirably) but also has excellent wet traction and low noise levels. After testing the tire against some of its competition on the track (see sidebar) the choice was clear to us. The wheels we mounted our tires on weigh in at 25 pounds, an important consideration in choosing a wheel. Although not super-light like many racing wheels, they are more rugged and will not bend at the first pothole they encounter. We had our wheels mounted at Wheel Warehouse in Anaheim, California. They also performed an alignment for us, an essential step whenever your car's suspension has been worked on.

With the suspension sorted out, it was time to tackle the power end of the performance equation. We consulted with Road/Race engineering in Huntington Beach, California for further advice on how to get extra power from our Eclipse. Mike Welch, chief Eclipse guru at Road/Race, gave us a couple tips. In addition to the K&N intake and HKS exhaust, he suggested we replace the poorly designed factory blow-off valve. Substituting it with an aftermarket unit (we selected GReddy's adjustable valve) actually adds more boost at the top end by eliminating the stock unit's leakage. Additionally, the blow off valve dumps into a four-inch plastic tube inside the intake pipe in front of the turbo. This dump tube blocks a considerable amount of space inside the intake pipe, seriously impeding airflow. Mike also recommended cutting this piece out to free up the flow. The blow off valve air still needs to dump back into the turbo inlet but the restriction inside the turbo inlet hose is removed. Another important area to modify is the pipe from the intercooler to the throttle body. The stock pipe is plastic, and flattens out under the intake box in the stock car. This convoluted routing obstructs airflow to the throttle body, and kills a good portion of the top end power. Removing it adds power, and is important if an intercooler upgrade is planned for the future.

13) With the Eclipse lowered, it was time to uncork the engine. The experts at Road/Race Engineering started things off by removing the stock exhaust system. The first step was to remove the oxygen sensor. The system was then unbolted from the catalytic converter.

14) Mitsubishi bolts their exhaust systems to the rubber hangers, making removal by one person a little easier. Once all the bolts were removed, the system was lowered out of the car as a whole. For this part, it's a good idea to enlist the help of someone else.

15) Note the difference in size between the stock system (bottom) and the HKS system. Also notice how the bends in the HKS system are much smoother without a decrease in diameter The HKS system also takes a much straighter path from the catalyst to the muffler.

16) The exit from the catalytic converter on the Eclipse is 2.5 inches, but 3.0 inches is optimal for the rest of the system. HKS changes the width of their system after the mid-pipe resonator.

17) To remove the intercooler pipe, the front right fender liner must be removed. Although louvers have been molded into the liner, they barely leave enough room for air to flow through the intercooler.

18) To improve airflow through the intercooler, Road/Race recommends cutting a hole in the plastic behind it. First, an area was traced out around the wire mesh that will cover the hole. Next, a hole was cut in the plastic, about a half-inch inside the line.

19) Finally, holes were drilled in the plastic and the wire mesh was riveted to it.

20) The next step was to free up the restrictive intake system. First, the intake pipe was disconnected from the air sensor, the wiring harness was unplugged, and the air box was disassembled and removed. The intake pipe was then unclamped from the turbo inlet and removed.

21) Finally, the fuse box was unbolted and moved out of the way. The intercooler pipe was then unclamped from the intercooler and removed.

22) The stock blow off valve dumps into a tube inside the intake pipe. This tube-about four inches long-eats up a considerable amount of space inside the pipe. Road/Race recommends cutting this pipe out with in the turbo intake hose. The blow off valve air must still return into the turbo intake hose.

23) Note how much more room there is inside the intake pipe once the dump tube has been cut out. Although the blow off valve is louder without it, Road/Race tells us by itself there is a noticeable power gain from this simple modification.

24) Another problem area for the stock Eclipse is the shape of the intercooler pipe. Because it has to fit under the air box, the shape of the pipe as it exits the intercooler is compromised by both its flat shape and three 90-degree bends. The Road/Race pipe, by contrast, is much smoother, with nearly a straight shot from the intercooler to the throttle body pipe.

25) Another peculiarity about the Eclipse turbo is the stock blow off valve. Made of plastic, it does not seal properly against its seat. In this cutaway, it is easy to see that there is no rubber gasket or anything to maintain a seal. In addition, the spring inside the valve is quite weak, and won't allow boost to be held beyond 13 pounds. Replacing it with a stiffer aftermarket valve (we chose GReddy's adjustable valve) not only lets the engine hold boost. but usually sounds better too.

26) Installation of the intercooler pipe is a reverse of removal. Note how the fender liner will now allow much more air to flow through the intercooler.

27) Another modification recommended by Road/Race is installing a breather filter on the crankcase breather hose that connects to the intake pipe (another connects to the manifold). Oil can be expelled through this pipe, making its way to the intercooler where it reduces efficiency Keep in mind though, this modification is technically not eco-legal, something to remember when you're due for a smog check

28) The last step was to install the K&N Air Charger filter assembly, which simply bolts on to the stock mounting points for the air sensor.

29) To take advantage of our new power and handling, we opted for Dunlop's new SP Sport 9000 tire, 225/40ZR-18 all around, mounted on Kosei Seneca wheels from ANT Inc.

By now, you are probably asking yourself, how do we know how much power has been added? Dynoing the car is effectively impossible because of its all-wheel drive, and removing the engine is impractical. But where there's a will, there's a way. Using our Vericom 2000, we were able to gain road-horsepower results from a second-gear 2500 rpm-to redline pull After adjusting for weight, rolling resistance, temperature, etc., we got an initial horsepower reading of 153.8 hp at 5600 rpm for our unmodified Eclipse. After installation of the performance gear, the same test resulted in 181.5 horses at 5400 rpm. The peak gain was 32 horsepower. By looking at the graphs, it is easy to see how boost builds much more quickly and strongly in the modified car. On the road the difference is dramatic. The car pulls hard almost all the way to redline, with very little drop off in power at high engine speeds. Throttle response is greatly improved, and turbo lag is also significantly reduced. Not to mention the deep, flatulent exhaust note, and heavy breathing of the turbo intake and the sharp hiss of the blow off valve. This is definitely a little more like it! 

Contact Road///Race Engineering
13022 La Dana Ct.
Santa Fe Springs, Ca. 90670
Tel (562) 777-1522     Fax (562) 777-1562
This page created and maintained by last updated 11/02mw