After the big power gains...
After the big power gains offered in normally aspirated trim, we were anxious to see how the engine responded with the supercharger. In a back-to-back test, the cams upped the peak power by 25 hp (from 532 hp to 557). Though not as much as the hefty gain offered in NA configuration, the cams offered a power gain over a broader rev range with the blower.
With the new Comp XE262AH cams, we noticed the motor had a slightly more aggressive idle. After the first power pull we could see why. In normally aspirated trim, the Comp cams upped the power output from 369 to an amazing 426 hp at 6,300 rpm. Since most of the power gains came past 5,000 rpm, the peak torque was up only slightly to 390 lb-ft. If you check out the supplied power graphs, you'll notice that there was a small cost for the huge power gains posted past 4,900 rpm. That cost was a slight loss of low-speed torque from 3,500-4,900 rpm, though the torque losses were more than offset by the tremendous power gains past 4,900 rpm. It is possible that additional tuning could have improved the low-speed losses, but we had to continue forward with our supercharged testing rather than spending hours fine-tuning the NA combination.
After running the normally aspirated comparison, we installed the Eaton supercharger just as it had been removed from the previous baseline test. Oddly enough, where the Comp cams improved the peak power by 57 hp on the normally aspirated combination, the power gains were less significant on the Eaton supercharged application. Equipped with the Comp cams, the peak power jumped from 532 to 557 hp, a gain of 25. The peak torque was up only 9 lb-ft, from 481 to 490.
The interesting thing to note with the supercharged combination is that though the peak-to-peak gains were not as high as the NA combination; there was much less of a trade off in low-speed power. In fact, the power gains started much earlier in the rev range on the supercharged combination than the NA motor. Where the Comp cams took off at 4,900 rpm on the NA motor, they demonstrated gains all the way down at 3,800 rpm on the blown motor. While the peak-to-peak gains were roughly half as much (25 hp vs. 57 hp), the supercharged motor offered them for another 1,000 rpm. Would the Kenne Bell supercharged combination show the same results?
Testing with the Kenne Bell...
Testing with the Kenne Bell supercharger showed similar results--with the Comp cams upping the power output by a solid 25 hp.
With our Eaton M112 testing completed, we installed the Kenne Bell 2.2-liter twin-screw supercharger, again in the exact same configuration as run with the stock cams. As with all the supercharged combinations, the air/fuel ratio was set at 11.8:1, and the total timing was kept constant at 23 degrees. Unlike chassis dyno testing with the stock computer, the coolant and air temps were kept constant, though neither would affect the air/fuel or timing on the F.A.S.T. system. I guess the flow limitations of the Eaton did not come into play on the cam test as the Kenne Bell (at 10 psi) showed similar power gains.
The peak power jumped from 594 to 615 hp, while torque was up from 493 lb-ft to 512. As with the Eaton, the cams improved the power output starting at just 3,700 rpm.
As a surprise test, we also ran the Kenne Bell blower at 15 psi with both the stock and Comp cams. Equipped with the stock cams, the combination produced 670 hp and 577 lb-ft. Installing the Comp cams upped the power to 704 hp and 597 lb-ft, indicating that the cams offer more of a power difference at elevated boost (power) levels.
Wanting to know if the power...
Wanting to know if the power gains would be any different at elevated boost levels, we ran the Kenne Bell at 15 psi with both the stock and Comp cams. The difference at the elevated power level was 34 hp.
The final test run in Part 3 of our Mods for 4V Mods was a comparison between 1 5/8-inch and 1 3/4-inch long-tube headers. Kooks Custom Headers was nice enough to supply the two sets of trick stainless steel four-valve headers for our test. Both headers featured exceptional build quality and stainless steel construction but differed in the primary tubing diameter and collector size (2.5 vs. 3.0 inches). Given the prodigious power potential of the supercharged 4.6-liter motors, you might immediately assume that the Cobra motor would respond best to the larger header configuration, but testing actually showed otherwise.
Even run at a power level exceeding 600 hp (equipped with the Kenne Bell supercharger pumping 10 psi), the supercharged '03 Cobra 4.6 produced the best overall power curve with the 1 5/8-inch Kooks headers. It should be noted that though the 1 5/8-inch headers were equipped with a 2.5-inch collector, the 2.5-inch collectors were run into the same 3-inch collector extension used on the 1 3/4-inch headers. Thus the power differences can be attributed solely to the headers. Check out the supplied power graphs for complete details, but know that the peak power numbers were almost dead even. The major difference between the two header sizes came in the mid range, where the 1 5/8-inch headers out-powered the larger 1 3/4-inch versions to the tune of 8 to 10 lb-ft from 3,300 rpm to 5,400 rpm. This type of power difference is exactly why we include complete graphs, not just peak power numbers. Look for more four-valve Mods in the next issue.
The final test involved a...
The final test involved a comparison between 1 5/8-inch headers and 1 3/4-inch headers supplied by Kooks.
The stainless steel 1 5/8-inch...
The stainless steel 1 5/8-inch headers featured 2.5-inch collectors.
On the dyno, the modified...
On the dyno, the modified 4.6 responded best to the smaller 1 5/8-inch headers.
The larger 1 3/4-inch headers...
The larger 1 3/4-inch headers featured the more common 3-inch collectors. Both were run with 3-inch collector extensions.
Though logic would seem to...
Though logic would seem to dictate 1 3/4-inch headers for use on a 600hp combination, the 1 5/8-inch headers showed better mid-range power without losing out to the large headers anywhere in the rev range.
Stock '03 Cobra vs. Comp Xtreme...
Stock '03 Cobra vs. Comp Xtreme RPM XE262AH (NA)
The idea behind this test was to determine the effectiveness of the Comp Xtreme RPM 262 cams on a normally aspirated combination. Admittedly the low-compression '03 Cobra motor might not have been the ideal choice for this particular cam combination, but testing the effectiveness of the cams both normally aspirated and supercharged makes for an interesting comparison. Swapping out the stock '03 Cobra cams for the XE262AH-14 cams resulted in a dramatic change in peak power. Equipped with a '01 intake and throttle body in place of the Eaton supercharger, the normally aspirated Cobra motor produced 369 hp and 377 lb-ft with the stock cams. After installing the Comp Xtreme RPM 262 cams, the peak power jump to 426 hp, a gain of 57 hp. As indicated by the power curves, the huge gain in power past 4,800 rpm cost some low-speed torque, most noticeably from 3,500-4,200 rpm. We can't wait to install a set of Comp Xtreme RPM cams on a high-compression normally aspirated combination.
Stock '03 Cobra vs. Comp Xtreme...
Stock '03 Cobra vs. Comp Xtreme RPM XE262AH (10 psi Eaton)
The results of this test are why we went to so much trouble to run the cam comparison both normally aspirated and with the two different superchargers (Eaton and Kenne Bell). Running 9 psi of boost with the Eaton (7.5-in crank and 3.4-inch blower pulleys), the 4.6 produced 532 hp and 480 lb-ft of torque with the stock cams. After installing the Comp XE262AH cams, the peak numbers jumped to 557 hp and 491 lb-ft. The Comp cams improved the power output of the supercharged combination by 20-25 hp through most of the curve, but the gains were not as impressive as experienced on the normally aspirated motor. It should be noted that the supercharged combination did not sacrifice as much low-speed power for the gains experienced. Also note that the improvements offered by the cam swap started down as low as 3,500 rpm, much lower than in normally aspirated form. Thus, though the power gains were not as significant as the NA motor; they could be enjoyed over a broader rpm range.
Stock '03 Cobra vs. Comp XtremE...
Stock '03 Cobra vs. Comp XtremE RPM XE262AH (10 psi Kenne Bell)
The reason for including the Kenne Bell supercharger in this cam test was that we suspected that the Eaton supercharger might skew the results since we were so near the flow limit of the blower. We knew that the Kenne Bell twin-screw blower had much more power to offer, so we ran the stock cams in normally aspirated form and with both blowers (at a variety of different pulley ratios) before installing the new Comp cams. We then performed the same procedure after installing the cams. Running 10 psi, the power gains were much the same as with the Eaton, as the Comp cams added 20-25 hp starting around 3,500 rpm.
Stock '03 Cobra vs. Comp XtremE...
Stock '03 Cobra vs. Comp XtremE RPM XE262AH (15 psi Kenne Bell)
Here's where things started to get interesting. The '03 Cobra 4.6 was equipped with the Kenne Bell pulleyed to produce roughly 15 psi. At this elevated power level, the Comp cams were as much as 35 hp better than the stock cams. It seems that the higher your intended boost (power) level, the more beneficial the cams become.
1 5/8-inch vs. 1 3/4-inch...
1 5/8-inch vs. 1 3/4-inch Kooks Headers
If you check out the Web sites and postings on the Internet, you'll come across a wide variety of opinions on the subject of exhaust systems for the supercharged Cobra motors. Given the impressive power production offered by the supercharged four-valve motors, it is understandable that many enthusiasts would opt for 1 3/4-inch headers, especially on modified versions. Unfortunately, there is much more to the exhaust game than sizing. To illustrate this, we performed a back-to-back test on our modified Cobra motor. Keeping the timing and air/fuel ratio the same, we ran a pair of 1 5/8-inch and 1 3/4-inch stainless steel headers supplied by Kooks. As illustrated by the power graphs, the 1 5/8-inch headers outperformed the larger 1 3/4-inch versions from 3,400 rpm to 5,900 rpm, but lost out nowhere to the larger header. Both headers allowed the motor to produce 620 hp at 6,600 rpm, but the average power production was much better with the smaller 1 5/8-inch headers.