Project Acura RSX Type S

After Part 1, we received a stack (at least two) of readers' letters pointing out how lame it was that Project RSX's Cosworth-built turbocharged engine could do no better than 249hp at the wheels. Fortunately, we had already noted this in the article and said we'd worry about it later, when the rest of the car was done. That time is now.

To review, Project RSX made great torque, with a virtually flat plateau from 3500 to 7000rpm. It took a dive at 7000 (obvious from both the driver's seat and the dyno), making it pointless to pursue the 9000rpm redline enabled by its Ferrea valvetrain hardware. When adjusting the boost controller, we would see roughly 14psi in the midrange, but were unable to get more than 11psi by 8000rpm, which is only 1psi more than we got when running the wastegate on just the spring. This result is typical of flow-limited turbo systems.

On inexpensive street tires and with a dusty drag strip, Project RSX laid down a best zero-to-60mph time of 5.2 seconds and hustled to the end of the quarter-mile in 13.4 seconds.

Megan Racing Test Pipe
The biggest flow restriction on Project RSX was the stock catalytic converter. The ceramic brick was beginning to deteriorate and thick soot covered all internal surfaces upstream. After some research, we decided the best off-the-shelf replacement was a Megan Racing test pipe. It's affordable and seems to be the standard choice in the RSX community for those wanting to make their turbo RSXs fast and stinky.

The pipe is a large, mandrel-bent tube that should flow freely. It comes nicely polished and the welds are good enough. The 'resonator'has an internal perforated core, but no packing we could see. Instead of studs on the exit flange, there are holes. Bolts with washersand locking flanged nuts are included, which actually makes assembly easeier when compared to the stock parts.

The stock RSX cat (left) is divided to act as a 4-2-1 header without the added external surface area that increases the time required to light off the cat. It helps low-end torque when used with the stock manifold, but wasn't doing us any favors for power production.

There were two significant issues with installation. The downstream oxygen sensor bung was clocked too high; it should have been in line with the first bung. We ended up notching our heat shield for clearance.The flange at the forward end of the test pipe is 7/16-in. thick, whereas the stamped steel flange on the stock cat is only 1/16-in. thick. This means the springs holding the flex joint together must be about 3/8-in. shorter when installed. In order to install the test pipe in the car and tighten the bolts, we cut one and a half coils off the spring used on the side with the block-to-downpipe brace (see Part 1, August 2006) and one and a quarter coils off the other, then ground them a little flat atthe ends.

The installed springs are just short of coil bind. The spring preload is much higher than engineered by Acura and there is little room for movement. We seem to have actually gotten away with this because Project RSX's engine doesn't move around as much as stock. We believe the flex joint will not have enough flex to be durable over the long term with stock engine mounts.

The Megan Racing test pipe has a larger diameter, with no impediments to flow.

Also note the amount of spring material we cut was greater than the remaining compression distance, so it seems likely that anyone who has installed this part without shortening the springs has the springs at bind, and thus no flex in the flex joint. A quick web search on the Megan Racing test pipe reveals many forum posts complaining about the difficulty of installation due to this issue.

The whole thing could be fixed by putting the flange in a mill and dropping an end mill on it to countersink the hole to the same thickness as the OE cat flange, with clearance for the spring. That would, however, add another piece of machinery to the manufacturing process.

Tuning
We took Project RSX to Church Automotive Testing in Wilmington, California, to have Shawn Church tune it. The tune we'd been running on was done shortly before our first OE cat melted. There was definitely work to be done.

The OE cat (left) weighs 19 pounds, versus 7.5 pounds for the Megan Racing test pipe. The result is 11.5 pounds of weight reduction, to go with the 74 wheel-hp increase it helped unlock.

The second oxygen sensor bung in the Megan Racing test pipe was out of line, causing the sensor to contact the heat shield. We notched it.