Here's the official Press Release. The dyno graph is posted here on the website.
FOR IMMEDIATE RELEASE
September 20, 2005
Zzyzx Motorsports Impreza 2.5 RS breaks 300 NA horsepower
TechWorks Engineering (Calgary, Alberta, Canada), Dieman Motorsports (Lees Summit, MO) and Zzyzx Motorsports (Overland Park, KS) conspired to build the most powerful normally aspirated Subaru 2.5L Flat-4 in North America. At more than 300 CHP, the output shatters any previously documented efforts to date.
Utilizing an MD Mustang IMP dynomometer, the engine output hit 235 WHP at 6450 RPM and 209 WTQ at 4600 RPM. "We typically see 233 WHP for a WRX STi, which is rated at 300 CHP, comments Jake Diehl, owner of Dieman Motorsports. "This engine puts down roughly 185 WTQ at 2000 RPM and carries a nearly flat torque curve up to 4600 RPM where it makes 209 WTQ, then tapers off to roughly 185 WTQ at 6500 RPM. Though the peak of 209 WTQ is at 4600 RPM, peak numbers don't readily describe the output of this engine. There is more power under the curve than any stock STi can wish for. Based on the average WRX STi, WRX and 2.5 RS data for our dyno, we're looking at peak outputs of roughly 302 CHP, and 276 CTQ."
The longblock was built entirely by TechWorks Engineering. "The recipe for the engine is less exotic than most would guess.", comments Tom Penner, owner of TechWorks Engineering. This engine uses our off the shelf 11.2:1 CR forged pistons, Stage II SOHC Street cams and headwork to maximize both velocity and flow. We consider this a Stage III engine build as it requires high-octane gas and stand-alone engine management, but simply lowering the compression ratio would still yield impressive output in a more streetable configuration." The TWE headers are a race-only 4-2-1 design, with large primaries. "The design of the headers was twofold: to provide power up top, and to lower dynamic compression in the lower RPMs to avoid torque spikes and detonation.", comments Tom. The trough in the torque curve from roughly 3000 to 4500 RPM is a direct result of the header design.
"I knew we needed to find a different intake manifold as the pre-2005 designs clearly are not meant to make power up top; this is a well documented.", comments Steve Sulatycki, owner of Zzyzx Motorsports. "Looking over the options, it appeared the 2005+ 2.5 RS intake manifold design was clearly superior and I decided to mate a high-flow 65mm throttle body to the '05 intake manifold. I had no idea what kind of numbers we'd be making."
"Once the car made it's first 220+ horsepower pull with very little timing and 11.5:1 AFRs we knew we had a strong motor on our hands. I proceeded to level out the AFRs to a very conservative 12:6:1 AFR and we started making pulls in the 230+ WHP range.", comments Jake. "As this engine was built and is being used for road racing, we stayed with a conservative tune for longevity. This is no dyno queen, and these numbers are real-world, not one-offs."
"The engine makes power everywhere", comments Steve. "This kind of power is useable on the street, at an autocross or road racing. It's perhaps the most versatile power delivery you can ask for and the flat torque curve results in a very predictable and controllable chassis when you have the car at it's limits."
The dyno graph is available at the Zzyzx Motorsports website.
Tech Works Engineering is Subaru performance, upgrades and aftermarket parts