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.
Degreeing The CamshaftsCamshaft manufacturers make their cams to a certain reference point so when installed correctly they perform to their design specifications. When installing cams it might seem that just setting your fancy adjustable cam gears to zero means the cams are installed correctly. What if the cam gears are a little bit off in their manufacturing or the dowel pinhole is off a few degrees? How about if the head was shaved and now the cams sit closer to the crank? Any of these variables will affect cam timing and what you thought was zero is now something different. Every proper race engine should have the cams degreed. This doesn't mean retarding and advancing the camshafts until you make more power. It's a process where measurements are taken to ensure the camshaft is installed per the manufacturer's specifications-basically to start from a zero point. Since I'll be testing so many camshafts I need to degree each camshaft to make sure that I'm running them like the manufacturer intended. This process requires a few tools and some patience. You need a degree wheel so you can see how many degrees the crank is turning and a dial indicator to measure the amount of valve lift. I assembled a used "test" engine on a stand for the measuring process. Stiff factory springs can make testing difficult, as the spring force will try to spin the cam around on the opening and closing ramps. To make things easier, I swapped in some light springs.
Every manufacturer will give you some specification on how the cams should be installed. For this example we'll use a cam card provided by Crane Cams. Cam cards give valve lift points in reference to top dead center and bottom dead center. Before we begin we must first find top dead center, where the piston is at its top most position. Using a degree wheel, we mount the device to the crank snout. In our case we're using a digital degree wheel from Altronics. This new device replaces the traditional degree wheel and pointer system.
This method offers some major advantages over the old technique. Screwing in a piston stop into the spark plug hole on cylinder No. 1, we rotate the engine one way until the piston makes contact on its way to top dead center.
A push of a button and then spinning the crank the other way until it hits the piston stop and the Altronics Digicam computes top dead center. This system is much more accurate and quicker than the traditional degree wheel. Next, we mount a dial indicator in a way that we can accurately measure valve lift.
While this sounds easy, it requires some thinking and possibly fabricating some fixtures to hold the dial indicator correctly and securely. As with most engine applications, the 4G63 engine uses hydraulic lifters, meaning oil pressure is constantly adjusting valve lash. Unfortunately, with no oil pressure these lifters start to collapse if you push down on them. In my test, where there was no oil pressure, the cam lobe would ride on the follower and collapse the lifter instead of transferring all of its motion to the valve. Solid lifters to the rescue! Installing these and then adjusting the lifter until there is a little preload ensures that the cam lobe motion will be transmitted to the valve motion.
With our dial indicator installed, we've found top dead center and the cam is ready to be degreed. The Crane Cams card specifies that the intake valve should open 0.050 of an inch at 4.5 degrees before top dead center. We spin the crank over until the Digicam reads 4.5 degrees before top dead center. We look at the dial indicator and see that we're at 0.060 of an inch of lift, which is 0.010 of an inch more than specified on the cam card. The valve is open too far at this point so the solution is to loosen the cam gears and retard the cam until lift comes back down to 0.050 of an inch. Looking at the cam gear, the timing marks indicate the cam is now 2 degrees retarded.
Cam manufacturers can give you valve opening and closing events along with centerline values. Cam centerline is the amount of degrees at the point of peak valve lift. In this case the Crane Cam card specifies that the intake is on a 110-degree (after top dead center) centerline. We move our crank to that point and see that indeed the valve is at its peak lift. Some manufacturers might give valve events while some might only give cam centerlines for installation so it's good to know how to do each one. We repeat the process of the exhaust cam and find that it also is 2 degrees retarded.
Now you're thinking, you degreed the cam in your test engine but what if the engine in my car is slightly different? To make sure I'm installing the cams the same way in my engine as on the test engine I use a little trick to make things easier. It's virtually impossible to put a degree wheel on a 4G63 engine once it's in the engine bay. One way to verify cam timing is to determine cam lift at top dead center, which is relatively easy to determine in the engine bay. On my test engine I rotate the crank until the Digicam indicates top dead center and I record the intake valve lift. Crane provides this specification on their cam card (0.068 of an inch of lift at top dead center) but most camshaft manufacturers don't have this information readily available. Installing the cams in the real engine, we transfer over our solid lifter and the dial indicator to measure valve lift. I screw in the top dead center indicator into the spark plug hole on the first cylinder. Using another dial indicator, I rotate the crank by hand until I find the peak of the piston travel; this is top dead center. According to the dial indicator my valve lift is the same as it was on the test engine.
This may seem like a tedious and complicated process-that's because it is! The time you spend doing this, however, may save you hours of dyno time playing with cam gears and possibly spotting a problem in your setup that would otherwise go unseen.
Measuring Camshaft Lobes And Computing Valve MotionTo correlate the performance of each of these camshafts I recorded the valve motion, which shows the differences in cams and can offer some insight on why certain cams perform the way they do. One way of recording valve motion is to use the equipment I degreed the cams with and just record the valve lift every degree and plot it out on a spreadsheet. While this sounds simple, it's a tedious manual process that's prone to error and not very accurate. The best and quickest way to do this is with cam measuring equipment. Performance Trends offers a cam measuring solution that integrates a cam test stand with software. The cam test stand includes a linear transducer to measure cam lobe lift and a rotary encoder to measure cam rotation. The data is collected in the cam analyzer software and valve lift profiles can be compared and inspected. In the next installment of this article, I'll get more in depth on this procedure and what useful information we can gather from it. :
HKS 272 Intake, 272 Exhaust Camshafts
First off, the HKS 272 idled very well. With the idle set at 900 rpm, my Evo purred and driveability seemed great, especially at a low rpm and part throttle. After a few pulls to dial in the air/fuel ratio and AEM boost control, horsepower peaked out at 453 whp at 22 psi. Next, I retarded the intake cam 2 degrees and ran the test again. This closes the intake valve later and could make some power at a higher rpm. The dyno pull shows a slight loss in low-end power and spool up and a slight shift in the powerband. The peak power is the same but the power curve filled out up top. To see how advancing the cam would affect the power curve, I moved the intake cam 2 degrees advanced from the installed point. The run shows a very slight increase in spool and low-end power but the top end power suffers, losing 6 hp. I moved the intake cam back to the installed specification and turned the boost up to 30 psi. The dyno belts out a 521whp pull.
Crane 272 Intake, 264 Exhaust CamshaftsUpon startup the idle is a little rough. I have to raise the idle to 1,200 rpm to get a smooth idle that won't let the engine stall. Low speed running is a little choppy and requires some careful tuning to make driveability acceptable. On the first 22psi pull I noticed the cam spools later than the HKS cams but starts to run lean as rpm climb. A few tweaks to the fuel curve let me run to the 8,400rpm redline. I had to add quite a bit of fuel at a higher rpm but remove some fuel at low rpm. This tells me right away that top end power should be greater. To my surprise the 22psi pull resulted in 505 whp! The power kept climbing toward redline with no sign of leveling off. I retarded the intake cam 2 degrees and made another pull. Peak power stays the same but low-end power drops off. The power curve takes a hit almost everywhere. Advancing the intake cam 2 degrees from the installed setting shows low and midrange power gain and loses only a few horsepower up top. The power curve is widened with only a slight sacrifice at redline. Putting the cam back to where I started, I ran it up to 30 psi of boost. Peak power climbs to 557 whp. Although a healthy power increase over the HKS 272 cams, the idle, spool up and driveability suffer.
Tomei 280 Intake, 280 ExhaustThe car has a very similar idle to the Crane Cams and the first pull at 22 psi requires no fueling changes. Power checks in at 514 whp at 22 psi, very impressive. Retarding the intake cam 2 degrees does nothing but lose spool up and bottom end power. Advancing the intake 2 degrees from the installed position boosts the bottom end of the power curve with only a slight loss in power up top (5 hp). The power gained throughout the curve easily outweighs the slight loss at redline. At 30 psi, power hits 558 whp, about the same as the Crane Cams. Overall, the power output is very similar to the Crane Cams.
The first batch of cam testing is done and I'm surprised with the differences in the cams. So far we have a well-mannered cam that doesn't produce the best peak power but makes good low-end grunt. The other two cams scream up top but at the cost of idle and spool up. The next installment will explain in detail how camshafts work and the importance of valve timing events. Clear some space in your cranium. It's going to get a little difficult but you'll have the knowledge to choose the right camshaft for your combination.
AMS Mule Engine Specs:BlockEngine: 4G63Bore: 85MMStroke: 88MMPistons: AMS Spec RossCompression Ratio: 8.5:1Rods: OliverCrank: Stock Mitsubishi
Cylinder HeadValves: Supertech 1MM OversizedSprings: Supertech Dual ValvespringsIntake Manifold: AMS VSRThrottle Body: Stock
TurbochargerTurbo: GT35R Steel HeaderHeader: Ams StainlessWastegate: Tial 38MMIntercooler: Ams Evo VIII Street CoreExhaust: 3-Inch Turbo Back
ElectronicsAEM EMS With 3 Bar Map SensorAEM Uego Gauge