IN PART 1 of our "Remember The Titans" series last month, we took a look at a few bolt-on performance components for the early ('96-'98) Cobra 4.6. As you know, the early DOHC mod motor differs from the late-model version by way of cylinder heads and intake manifold. The early versions featured dual-port heads and a matching intake, while the late-model Four-Valves were equipped with a single-port head.
The bolt-on performance parts applied to the high-mileage '96 Cobra 4.6 included a set of IMRC eliminator plates, a revised intake manifold, and a shot of nitrous. The test engine was already equipped with a set of headers, an Accufab throttle body, and a FAST engine management system. The motor was run sans accessories and with an electric water pump. Equipped as such, the 4.6 produced 339 hp at 6,100 rpm and 332 lb-ft of torque at 5,000 rpm.
Early 4.6 Cobra engines were not known for torque production, but the curve nevertheless managed to exceed 300 lb-ft from 3,500 rpm to 5,900 rpm. Certainly not huge power by any means, but these Cobra 281s more than held their own back in 1996, and with a little help, can be made to produce impressive power even a decade later.
With our nearly stock 4.6 ready for more improvements, we decided to step up to a set of cams next. Our cam choice was made with streetability in mind rather than maximum peak power. Were we looking to maximize power production in the top third of the rev range (where it is most useful on a dragstrip), our cam choice may well have been different, but we wanted to improve the power without sacrificing driveability and/or low-speed response.
Given the lack of torque production from the oversized intake ports (in both the head and manifold), the last thing we wanted was to further reduce torque production with excessive cam timing. We wanted a set of cam profiles that we would feel comfortable driving every day. That said, we were also hoping for some healthy power gains. Was the combination of additional power and streetability too much to ask for?
We hoped not, with proper cam selection and (every bit as important) proper cam timing. When it comes to 4.6 Four-Valve cams, dialing in the cam timing can make or break the power curve. Excessive advance or retard can literally throw away half of the power gains offered by the more aggressive cam profiles. Naturally, the installation and degreeing of four cams in the DOHC motor are a bit more involved than swapping the bumpstick in your typical pushrod 5.0, but the results are well worth the effort.
First up was the cam selection. In choosing a set of cam profiles (one set of intakes and one exhaust), we purposely went conservative. Rather than skip right to the bottom of the page in the catalog where all the wild grinds reside, we chose a set that not only promised impressive driveability, but also allowed us to install the cams without resorting to a valvespring change. Though such a change should be considered mandatory when changing cams on a motor with 100,000 miles, we decided to illustrate the potential power gains without the benefit of the spring upgrade. We knew the motor was not going to run (effectively) beyond 6,500 rpm (for our testing), so we felt confident performing the cam swap without the springs.
We will revisit the valvespring issue later in the series, and may even readjust the cams from their present position to illustrate the change in the power curve. For this round of testing, we chose a set of XE262AH cams from Comp Cams. The XE262AH (PN 106100) profiles combined 0.425 lift on both the intake and exhaust with a dual-pattern duration split of 226/222 degrees. The wide lobe separation of 114 degrees helped ensure both idle quality and driveability. According to the Comp catalog, the low lift and duration values did not require a valvespring upgrade (PN 26123).
Swapping cams in your early Cobra can yield significant power gains, but make sure to dial
Not a beauty queen by any means, our early Four-Valve 4.6 was a well-used version yanked r
We chose a set of XE262AH Four-Valve cams from the Comp Cams catalog. The XE262AH cams off
The early Four-Valve Cobra motors usually come with keyless drive sprockets. The later eng
Equipped with the stock cams, the engine produced 339 hp and 332 lb-ft of torque.
Despite the use of the keyed sprockets to properly locate the cam timing, there is easily
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 to allow access to the cam towers, rockers, and lash adjusters.
We then removed the damper and front cover to provide access to the timing chains and tens
The first step was to remove the rockers to eliminate the spring load on the cam towers. D
The factory lash adjusters were removed and carefully bled down using a vice. Bleeding dow
Off came the cam towers to make way for the new Comp cams.
Mihovetz installed a degree wheel and dial indicator to establish TDC before degreeing the
If you saw "Ring My Bell" elsewhere in this issue in which we installed these same cams in an '03 Cobra 4.6 (run in normally aspirated trim with an '01 intake), the cams were installed using the factory sprockets and wound up at 117 degrees on the intake and 113/115 on the exhaust. Relative to the cams installed for this test, the '03 Cobra cams were retarded by 7 degrees on the intake and 1-3 degrees on the exhaust. On the later Cobra 4.6, the cams improved the peak power considerably, but actually lost power below 4,500 rpm.
Advancing the cams (per Mihovetz) on this early application resulted in the same impressive peak-to-peak power gains, but the most welcome part of the equation was that the XE262AH cams offered power gains from 3,000 rpm all the way to 6,500 rpm. The largest power gain came at 6,600 rpm where the Comp cams upped the power output by 42 hp. From 5,000 rpm to 6,600 rpm, the cams really came alive, but they offered improved power all the way down to 3,000 rpm. This improved low-speed power ensures driveability and adds some much-needed torque production.
While the cams offered a sizable jump in peak power and even upped the low-speed and midrange torque, we are still a long way from the potential of the 4.6.
As we continue our search for additional power from this '96 Cobra 4.6, we will have another intake manifold to test along with our first shot at forced induction. Kenne Bell has promised us a chance at one of its non-intercooled blower kits for this early Four-Valve mill, and we have a twin-turbo kit waiting in the wings. Of course, we will have to run a centrifugal supercharger, as well.
Before getting to the blower and turbos, we may retard the existing cam profiles in an effort to demonstrate what happens when the cams are installed incorrectly. We wish we had that data for you this month, but degreeing and adjusting the cams on this combination all but ate up the available dyno time. We will probably take the opportunity to change the valvesprings, since the 100,000-mile engine is probably in need of a new set of springs anyway. A huge thanks goes to Mihovetz for performing the cam work on this baby.
The cams were coated with assembly lube to provide lubrication during startup.
The dial indicator was also used to check piston-to-valve clearance since advancing the in
This tool was used to compress the valve spring to facilitate removal and installation of
After setting the new Comp cams at 110 degrees (intake) and 112 degrees (exhaust), the Fou
The power curves illustrate that not only did the mild XE262AH cams provide impressive peak power gains, upping the output from 339 hp to 373 hp, but there were also impressive midrange power gains. The reason we improved the low-speed power so much on this test is that we went to the trouble of degreeing and adjusting the cams during the install. Mihovetz advanced the cams to 110 degrees on this early 4.6. Advancing the cams paid big dividends below the torque peak without sacrificing much, if any, power on top. The Comp cams improved the peak power from 339 hp and 332 lb-ft of torque to 373 hp and 347 lb-ft of torque. Better yet, the cams improved the power from 3,000 rpm to 6,500 rpm.