Paul Piola Takes A Comprehensive Look At The Tuning Options For Vw's 2.5 Liter, Five Cylinder Motor.
In 2006, volkswagen replaced its base 2.0 liter 8v (aka 2.slow) four cylinder engine with a 2.5 liter 20v five cylinder that went into its normally aspirated rabbits and Jettas. In doing so, power rose from 115hp to a more respectable 150hp - a generous 30% gain. Torque rose by 39% to 170 lb-ft, peaking at 3750rpm. Reportedly the engine twists 90% of it from 1750 to 5125rpm - making it considerably more flexible than its predecssor.
Built in mexico for the us market, the 2.5-liter engine is an improvement but should still be putting out significantly more ponies by today's standards. Even if it is missing a cylinder, it's making less power than the e30 bmw 325i from 20 years ago.
If you don't agree, then maybe the 60hp per liter, 8-plus second 0-60mph and 16sec quarter mile numbers help tell the story.
The good news is with a $15k base price, the '06-07 rabbit was a cheap buy compared to its turbocharged gti sibling, leaving enthusiasts with plenty of room for upgrades. However, the aftermarket has been slow to respond to the new 2.5, afraid they might be left with stock on their shelves, as everybody opted for the 2.0t. However, there's been sufficient interest in the new motor that we've finally been able to compile a guide to help improve the five-pot's performance.
Keep in mind, we're assuming a baseline of 140hp to the front wheels. With different cars and dynos, results may vary. And quoted prices don't include labor costs either.
$0-1000Abd racing sells a tig welded, two-piece stainless steel intake system, with an maf relocating big-bore intake tube and 3" lan pipe for $300. Claimed to be the only true cold-air intake (sucking air from outside the engine bay rather than relying on heat shielding), your rabbit should net a peak 9-10 lb-ft gain in the mid-range and see power spike to around 147whp. Apr sells the carbonio intake, for which they claim a peak of 15hp and 10 lb-ft during tests. It features a carbon induction pipe, rechargeable filter and retails for $269. Apr also has its own software, which sells for $499 and includes 91-, 93- and 100-octane programs, as well as valet, fault code erase, throttle body alignment, security lockout and anti-theft modes.
For $675 you can have awe tuning's 2.5" cat-back exhaust, featuring tig welds, 304 stainless steel construction, t-bolt clamps and mirror finish. Not only is it reportedly quieter than anticipated, it releases up to 7whp. Awe is also a giac dealer, and combining the exhaust and software has apparently seen 159whp.
C2 motorsports sells software for $249 that adds 7whp in the mid-range and raises peak power to 144whp. Higher gains are expected with an intake and exhaust. By the time you read this, c2 hopes to have newer software to make the Ecu behave like an '08 model, releasing the extra 20hp the new model gets.
At press time, euro sport accessories hadn't released its exhaust system for the rabbit but hopes to have something by the time you read this.
Evolution tuning specializes in vw's 2.5 liter engine. Its $300 a5301 intake is good for 10 lb-ft at 3700rpm and 8whp at 5000rpm, peaking at 148whp up top. The intake comes with black, blue or red hoses. Combined with evolution's $900 5-into-1 header, power should rise to 152whp, but the true gains are through the rev range. Whereas the stock car peaked at 158 lb-ft from 3600-3900rpm, the intake and header combo can apparently make that figure as early as 2750rpm all the way through 4900rpm, peaking at 169 lb-ft at 3500rpm. The headers include gaskets, hardware and 02 sensor provision.
GHL motorsports takes pride in its exhaust system, claiming to be the only ones using expensive American 304 stainless steel. They offer a 2.25" system for $689 with a resonator and muffler, plus 3" rolled tips.