This article was written in 2004 I believe.
So at this point the Impreza is lowered with .75 lowering Eibachs, turbo’d with a TD04L, Engine management is taken care of with a Greddy E-Manage, 17″ wheels, MP3 player, etc… What else could I want? Well, more power, better handling and better braking. Now that the car has 215,000 miles, the shocks are due for replacement, and the bushings are becoming more worn. In addition, with the additional power on tap the stock brakes are way inadequate.
Here is the plan.
More power: With the E-Manage, I now have pretty good control over the fuel and timing of the car. I also have a way to measure the performance of the car through the airflow voltage at the Airflow Meter. I also have the recent 1/4 mile time at Las Vegas Motor Speedway. 3 low cost steps will be taken to increase the power. (make that 4)
Step 1: Removal of the muffler. I’m hoping it won’t be too loud, but I won’t know until I try. The SRT-4 has no muffler from the factory even. The current muffler on the car is a Dynomax Super Turbo which may be quiet but the reverse flow design makes for some rather poor flow.
Step 2: Upgrading the down pipe. Currently the down pipe is a 2.5″ mandrel bent piece which flows well with the exception of the wastegate. The flapper door opens and the turbulence caused can not be good for flow. That being said I will upgrade the down pipe with a separate port for the wastegate and an extension separating the main turbine exit which will basically simulate an external wastegate thus improving flow and reducing turbulence. This should also improve boost response.
Step 3: More tuning. With each upgrade of the exhaust, tuning will need to be done to keep air/fuel ratios in check. I only have a narrow band o2 and seat of pants feel to tune the air fuel ratios. Timing will also be adjusted. I currently have a very conservative timing map to keep detonation in check. I will be building a low cost knock detector to help with timing adjustments.
Brakes: With the additional power and my increasingly harder driving style, the stock brakes fade entirely too quickly. Some WRX or RS brakes will be going on soon.
Shocks: At $60 each plus shipping, the cost does add up. I will be replacing the rears first and later the fronts. This should help with some of the bouncing.
Bushings: It would be nice to replace all the bushings with polyurethane, but that’s not what this article is about. The steering rack bushings run about $30. From the reviews, they should help improve handling considerably as well as fix a knocking sound coming from the front of the car.
MAF Reading Peak 3.66
Fuel Injector Peak 72
1/4 Mile (100 degrees F) 16.3 @ 81
I’m a little disappointed in the 1/4 mile time, but in the cars defense, it was over 100 degrees outside and I only got a few runs before running out of gas. It should not be too hard to improve these performance numbers, how much though will be an interesting test.
That’s it. Stay tuned for updates as they come.
Part 2: let the MODS begin..coming soon