Oddly enough, the catalog listed the effective operating range from 1,200 rpm to 5,400 rpm. From testing, we know these figures to be a solid 1,000 rpm off the mark. While the cams may well improve the power output at 1,200 rpm (we have never tested this low on the engine dyno), we know that even stock cams produce peak power above 6,000 rpm. Given the extra duration offered by the Comp profiles, we suspected, and were rewarded with, a shift in effective operating range of nearly 500 rpm.
While the cam profiles promised improved power and torque, it is paramount to have them properly degreed in, as we ("we" meaning Accufab's John Mihovetz) went to the trouble of not only degreeing the new Comp cams, but also adjusting them the full range of the factory sprockets (there is slop in the key ways), then removing the keyed sprockets on the intake cams and replacing them with the early keyless sprockets to allow further adjustment of the intake cam timing. According to Mihovetz, who has extensive experience with these engines, the 4.6 Cobra engines (both early and late) respond well to adjustments to the intake cam. They are less responsive to changes in the exhaust cam timing, though it must still be close to settings recommended by the cam manufacturers.
After reaffirming our baseline power numbers with the stock cams, we tore into the 4.6 to allow Mihovetz to work his magic. The first order of business was to install the new cams. After installing them, the factory sprockets (see photo) were adjusted all the way to one side (all slop removed from combination in one direction). Mihovetz then checked to see where the cams were installed, and we came up with numbers of 119.5 degrees on the intake and 114.5 degrees on the exhaust on the driver side. Adjusted in the same manner, the passenger-side cams checked in at 117 degrees on the intake and 112 degrees on the exhaust.
It is important to note that Comp recom-mended setting the cams (both intake and exhaust) at 112 degrees. After loosening up the cam retaining bolts, all of the slop was taken out in the opposite direction. This was done to illustrate the change in cam timing available just from the imprecise fitment between the key on the factory sprockets and receiver groove on the cams. Adjusted in the opposite direction, the driver-side cams checked in at 116 degrees on the intake and 112 degrees on the exhaust, while the passenger side dropped to 114.5 degrees on the intake and 109 degrees on the exhaust.
While these are a lot of numbers to be thrown around, know that this exercise illustrated that even using the factory keyed sprockets allowed for a change in cam timing of nearly 3 degrees on each bank. Combine this with the changes in the opposite bank and the slop in the crank key, and you have the makings for one improperly degreed set of camshafts
This issue is not restricted to the installation of aftermarket cams, as we have measured differences in cam timing of 9 degrees on a brand-new factory Four-Valve 4.6. Apparently, even the factory has a hard time equalizing the bank-to-bank cam timing. Ever wonder why some stock Cobras make more power than others? The range of adjustment provided by the slop in the keyways allowed Mihovetz to adjust the exhaust cams on both banks to 112 degrees as per the cam card. Pulling a little trick from his years of modular experience, he recommended advancing the intake cams beyond that level, but only after checking piston-to-valve clearance (0.052) at each successive timing position (112, 111, and finally 110 degrees).
Generally speaking, advancing the intake cams improves low-speed power production and (according to Mihovetz) does not negatively affect the top-end power (at least not in the useable rev range or our mild combination). Given his background, we took his word on positioning the cams. Once installed, the final cam timing was 110 degrees for the intake and 112 degrees for the exhaust.
Off came the valve covers...
Off came the valve covers to allow access to the cam towers, rockers, and lash adjusters.
We then removed the damper...
We then removed the damper and front cover to provide access to the timing chains and tensioners.
The first step was to remove...
The first step was to remove the rockers to eliminate the spring load on the cam towers. Do not attempt to unbolt the towers without removing the rockers, or damage to the towers will result. Someone obviously did not heed this warning as we found one of the towers already damaged on our specimen.
The factory lash adjusters...
The factory lash adjusters were removed and carefully bled down using a vice. Bleeding down the lifters makes installation much easier after swapping the cams.
Off came the cam towers to...
Off came the cam towers to make way for the new Comp cams.
Mihovetz installed a degree...
Mihovetz installed a degree wheel and dial indicator to establish TDC before degreeing the cams. Even using the keyed sprockets, there were 3 degrees of slop (per cam) in the factory setup.