When thinking about a V-8 performance engine it is easy to visualize our machines as a mechanical symphony working in perfect symmetrical harmony. Such an impression, however, fails to recognize that each of those individual cylinders may not be identical in their resources and their resultant mechanical contribution to the engine as a whole. One of the easiest examples of this reality is to visualize the variance in the induction tract. With the typical single four-barrel induction, the carb physically sits in the middle of the engine, putting it closer to the inner cylinders 3, 5, 4, and 6, than it is to cylinders 1, 7, 2, and 8 (GM and Mopar numbering system). What results is a different flow path, and given the realities of intake manifold design, differing runner length. This might seem like a minor inconsistency to us. To the engine, runner length plays a major role in how the airflow turns into the cylinder. On top of this incongruity, add in the effects of wet flow of the typical intake manifold, and you’ll find that characteristically there are significant variations in air/fuel ratio when considering the inner cylinders with a more direct flow path, and their outboard brethren.
Our individual cylinder lambda monitoring was via electronics from Daytona Sensors. The sy
While we might be comforted by examining the running mixture of our V-8 powerplants by virtue of today’s sophisticated lambda sensor systems, bear in mind that the reading you get from a single oxygen sensor in the collector represents an average of all the cylinders in a given bank. In reality, there is a variance in air/fuel ratios from cylinder to cylinder, and the greater the delta here, the more compromised the engine will be with any given tune. The optimal mixture for maximum power will coincide with the point at which that average is actually working as the best compromise among the cylinders comprising the reading. Obviously, the tighter we can keep the air/fuel ratio variance, the more efficient the engine, and the greater the potential for optimal power production.
The 4-Pattern cam timing strategy is based upon the varied intake flow paths typical of a
Given the realities of the differing induction characteristics of a typical V-8 engine, it is a fallacy to believe that other interrelated operating requirements would remain identical from cylinder to cylinder. This premise naturally brings us to the camming requirements of the engine. The key question to be addressed here is whether a cam timing strategy can be employed that will help compensate for the variance peculiar to the V-8 induction tract. The idea here is nothing new, and at the upper levels of professional racing, such aspects of camshaft design have been experimented with for decades. Subtle variations in specifications designed to compensate for irregularities between cylinders have been employed in venues such as NASCAR, where every horsepower counts. At COMP Cams, the idea was to extend this concept to the street/strip level enthusiast with their new 4-Pattern cams.
Our baseline XR294HR cam is part of COMP’s Xtreme Energy line of hydraulic rollers, long t
Our test engine was based upon the Dart SHP short-block, which has provisions for all of t
The Dart block also features lifter bores and valley bosses designed to accept the standar
Strategically, what the 4-Pattern cam does is vary the cam timing for the inside cylinders versus the outer cylinders. The objective of this strategy is to better use the flow dynamics and induction length of the cylinders with the aim of higher output. The outside cylinders are given a slight increase in duration and intake lift, while at the same time the lobe separation angle for the outside cylinders is increased. The result is the intake valve closes later for the outside cylinders, while the exhaust opens earlier. With this strategy, the intake opening and exhaust closing for each cylinder remains constant keeping the overlap the same. The objective is to capture more air/fuel mixture in the deprived outer cylinders, boosting their contribution to overall engine output.
While on the surface the timing strategy is the most significant quality of these new camshafts, the lobe profiles themselves are improved. Notably, the lift for a given duration level has been increased, making the 4-Pattern cams more aggressive than the former state-of-the-art Xtreme Energy lobes. While the faster lift action is readily apparent from the basic lobe specification numbers, the profiles take advantage of the latest technology in lobe design to push the standards of lobe stability to new levels. Extensive Spintron testing at COMP has qualified these lobe profiles to exceed the rpm capabilities of previous designs. Theoretical power is one thing, but once stability is compromised, power production is over with.
As shown by the air/fuel ratio monitoring system in real time on the dyno, just as predict
Theory To The Test
We were curious about these new cams from COMP. While conceptually we could accept the difference in runner length and position would have an effect on cylinder-to-cylinder requirements, we were not sure what could be done about it. After all, we had to wonder whether a camshaft could compensate for air/fuel ratio, air speed, and wave tuning inconsistencies. Our test engine was a 372-cube Dart SHP short-block topped with a set of AFR 195cc Eliminator heads. These Eliminator heads featured AFR’s well-developed combination of moving parts, including their lightweight valves, titanium retainers, and lightweight springs for exceptional high rpm performance with a hydraulic roller cam. With this test engine we did not expect valvetrain instability to curb either cam short of its maximum potential.
To gauge air/fuel ratios, we bolted on a set of specially prepared dyno headers with lambda sensor bungs in each pipe. The O2 sensors worked with the electronics from Daytona Sensors to give a reading of the mixture from each hole. Our small-block Chevy was fitted with a Holley Strip Dominator single-plane intake manifold and Holley’s hot 750 Ultra HP aluminum-bodied carb. First up was the COMP XR294HR cam as our baseline. This cam is a member of COMP’s Xtreme Energy line of hydraulic roller cams, the standard of the industry for performance hydraulic rollers. As expected, the engine performed flawlessly, pulling solidly to 7,000 rpm to set our baseline numbers of 473 lb-ft of torque at 5,300-5,400 rpm and 527 hp at 6,500-6,600 rpm. The Xtreme Energy cam set a mark that would be hard to beat.
Aiding in swapping cams with the minimum of hassles was the two-piece COMP Cams aluminum t
Thanks to the COMP two-piece aluminum timing cover, we had the new 4-Pattern cam stabbed in our small-block Chevy in a matter of minutes. This stick featured more lift with virtually identical duration by virtue of its more modern lobes, plus the unique valve timing strategy of the 4-Pattern. Pulling it to the redline showed an overall increase in power throughout our test range from 3,100 to 7,000 rpm, with a substantial gain in torque production through the low and midrange. Scrutinizing the individual cylinder lambda readings from our Daytona Sensors system, we found the cam did improve the air/fuel distribution, tightening the ratio variance by 0.11 ratio points between the inside and outside cylinders. With more power and more even flow into each hole, our COMP 4-Pattern cam lets each of our eight cylinders work to their potential.
Our cam comparison featured a pair of hydraulic rollers, the new 4-Pattern CS293QIO8 versu
The valvetrain of our test engine was exceptionally functional with COMP’s Ultra Pro Magnu
In order to monitor air/fuel ratio, our test engine was equipped with dyno headers having
To eliminate the potential for any deviation in ignition timing, our tests were run using
With the baseline combination optimized and the dyno data recorded, we moved to COMP’s new
Fuel was supplied by an aluminum-bodied Holley 750-cfm Ultra HP carb. The carburetor was c
BY THE NUMBERS
COMP XR294HR VERSUS CS293QIO8
|Duration intake at .006:||294||293/295|
|Duration exhaust at .006:||300||305/307|
|Duration intake at .050:||242||241/243|
|Duration exhaust at .050:||248||251/253|
|Lobe lift, intake:||0.36||.398/.399|
|Lobe lift, exhaust:||0.375||.389/.389|
|Gross intake lift with 1.6:1 rocker:||0.576||.637/.638|
|Gross exhaust lift with .6:1 rocker:||0.6||.622/.622|
|Lobe separation angle:||110||107.5/108.5|
|Recommended installed intake centerline:||106||102/103|
|Intake opening at .006:||41 BTDC||43/43 BTDC|
|Intake closing at .006:||73 ABDC||70/72 ABDC|
|Exhaust opening at .006:||84 BBDC||84/86 BBDC|
|Exhaust closing at .006:||36 ATDC||41/41 ATDC|
ON THE DYNO
COMP 4-PATTERN CS293 VERSUS XR294 372
SMALL-BLOCK CHEVY TEST ENGINE
|RPM:||TQ XR294:||TQ CS293:||HP XR294:||HP CS293:|