From discussions with calibration instructor Greg Banish from Calibrated Success, the OEMs actually use statistical covariance analysis to determine and quantify "roughness" of an engine. It is a more linear and directly correlated measure of an engine's stability at idle and low speeds. While MAP is not linear and is not as reliable for predicting driving manners for production cars, we did draw some great correlation to MAP and cam overlap that matches our "expert" in-car experience over the years. Since the covariance analysis on our data did not yield reliable results and it would require extensive explanation on statistics, we opted to stick to data more readily obtained by a reader with an inexpensive scanner.
The Cams As Received
We put the call for cams out and received parts from nine suppliers. They all provided nominal specifications for each cam, but Dart was kind enough to let us roll each one on its Cam Doctor to be sure no "ringers" were substituted with a different spec card. All cams measured to within acceptable grinding tolerances and the measurement system so we accepted them all. Three manufacturers provided two cams, so we selected the one that best fit the intent of our criteria. Even within our criteria there is room for subjectivity; you can see that there is a large spectrum of cam specifications, and that "streetable" cams are subjective even amongst the experts. It should also be noted that these cams generally fall in the low to middle-of-the-pack [range] for all of these suppliers-much bigger, higher horsepower camshafts are available, though not tested here.
All the cams were tested on a production 430-horse, 424 lb-ft of torque LS3 engine from GM Performance Parts (PN 19201992), which comes complete with coils, plugs, wires, throttle body, intake manifold, injectors, rails, and much more-ready to bolt right into your hot rod. With just a little coaxing, this already stout crate motor comes alive using only mild upgrades. West Racing Heads and Uncle Robin were gracious enough to run the GMPP LS3 on its Stutska engine dyno using a stand-alone GMPP E-67 controller using only Hooker Competition Ceramic 1.75-inch headers (PN 2469-1HKR) and an electric water pump to baseline at 471.3 lb-ft and 483.1 hp. One base calibration for pump gas was performed that would work well with all the cams [to keep this a constant] and an Abaco DBX mass airflow meter, that senses standard flow as well as reversion to compensate for airflow differences with the cams, were also used for testing. Since most cams required springs to avoid coil bind, we selected a set of Comp 918 springs, likely the most used and readily available spring out there. Several cams came with different springs that may or may not have affected the results of said cams, but for the sake of timing and consistency we stuck with the 918s for all cams.
For consistent engine dyno testing, we carefully monitored water temp and performed at least three power pulls for each cam. After the first pull, the data was checked for consistency and for motor integrity. If all was good, two more pulls were made back to back. With ten cams, including the stock LS3, we had to ensure quality data and balance time on the dyno. Once the production cam was baselined and a new dyno calibration was created for all the performance cams, no further tune tweaks were made as the following procudure was followed:
1. Warm up engine to 175F water temp
2. All cams were set at the idle point of 950 to check actual intake vacuum
3. Make one power pull and check the data
4. Make two more pulls back-to-back