When selecting the perfect cam to match your performance needs, prospective buyers face the daunting task of choosing from 260-, 270- and 300-degree duration camshafts. What does it all mean and is getting the "big" cam the best for your car? I'll shed some light on the subject by doing some real-world tests to show how different camshafts behave. Just like you wouldn't want a gigantic GT45R turbo on your daily driver/autocross car you might want to re-think your camshaft choice before taking the plunge. I'll use a system for testing that will hopefully give you a better understanding to choose the right camshaft for your applications, be it drag racing or autocrossing in the parking lot.
For this onslaught of abuse I put my '04 Mitsubishi Lancer Evolution VIII on the chopping block. The 4G63 platform is rugged and we've spent so much time developing power with it that it makes a perfect test rig. The car is outfitted with a bunch of AMS Performance parts to support over 600 whp. The parts range from an AMS GT35R turbo kit to the VSR intake manifold and AEM engine management system. The car serves multiple duties as a daily driver, track day and drag racing car. For testing, we used a Dynojet model 424x-LC all-wheel-drive dyno. This dyno is reliable and repeatable, which makes it a benchmark in the industry.
We tested each cam using 116-octane race fuel at 22 and 30 psi of boost. Using an AEM EMS with built-in boost control and dataloging, each test was conducted at the exact same boost level. The runs where done in Third gear and start at 2,000 rpm and end at 8,400 rpm. The fuel curve was adjusted for each cam to maintain around 11.5-11.8:1 air/fuel ratio under full boost. Since I'm using an AEM EMS in speed density mode I can tell the power curve by how much I have to adjust the fuel curve. If it runs rich at a high rpm and I need to remove fuel then I know it's making less power there.
How Each Cam Will Be RatedPeak Power: Once ECU adjustments are made to stabilize boost and the air/fuel ratio, two back-to-back consistent runs are recorded. The peak power that each cam makes is recorded. If your primary goal is drag racing, this test is the most important.
Powerband: How many rpm is the usable power curve. If a cam makes peak torque early and keeps making good power to redline it will score higher than a cam making only good power near redline. Most street racers and autocrossers would be interested in this test. A nice wide power curve makes for a fun street car.
Idle/Driveability: A subjective rating of how lumpy or smooth the idle is and the quality of low rpm driveability. Luckily, with the AEM EMS I can make almost any cam idle well but some have to run at 1,200 rpm for stable idle while others run at 800 rpm. With a factory ECU the story is much different. Some more aggressive cams can cause very poor idle or even cause the engine to stall. Also, low speed running can be an issue with some cams and even cause bucking or misfires. I know we're modifying our cars in the interest of making them faster but most of us also use them as a daily driver. That makes this rating high on my list-it's not very fun driving in traffic while your engine keeps stalling out.