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