Blower Cam Shootout--HorsepowerStock...
Blower Cam Shootout--HorsepowerStock H.O. vs XE258HR vs XE274HR
Obviously even positive displacement superchargers like aggressive (but not too aggressive) cam timing. The XE258HR increased power from 438 hp at 6000 rpm to 456 hp at 5700 rpm. The difference in the peak power rpm was valve float. It is likely that the peak power might have exceeded 460 hp with the XE258HR cam had the stock hydraulic roller lifters not given up early. Adding new lifters allowed the XE274HR cam to rev freely to 6000 rpm (but not beyond). The supercharged motor pumped out 485 hp at 6000 rpm with the XE274HR cam. The boost pressure dropped from 8.5 psi with the stock cam to 7.5 psi with either of the two Comp Cams. Oddly enough, there was no drop in boost pressure between the two Comp Cams.
It is worth mentioning that the test motor was equipped with all the accessories and a complete exhaust. The supercharger was equipped with a 31/8-inch drive pulley which produced 8.5 psi from 3500 rpm all the way to 6000 rpm. With the stock cam in place, the supercharged 302 produced 437 lbs.-ft. of torque at 3900 rpm and 438 hp at 6000 rpm. The rather high power peak can be attributed to the lack of upper intake runners in the Kenne Bell casting. The short runners produced peak power all the way out at 6000 rpm, much higher than the 4800-5000 rpm shown for a stock 5.0. The positive displacement supercharged motor had no trouble demonstrating its torque producing capabilities, thumping out over 400 lbs.-ft from 3500 rpm all the way to 5600 rpm. The horsepower curve was impressive as well, topping the 400 horsepower mark from 5000 rpm to 6000 rpm. The output was pretty impressive considering the mild stock cam timing.
Now it was time to see if the positive displacement supercharger worked well with the same cam timing as a centrifugal. I selected a pair of cams that have worked well in the past, namely a pair from the Comp Cams Xtreme Energy line. Both of these grinds have proven effective on normally aspirated and centrifugal supercharged motors in the past, so I was curious to see how they would perform on this Kenne Bell-equipped 302. First up was the milder XE258HR, a dual-pattern cam offering a .533/.544 lift split along with a 208/216 split in duration. Note that the dual-pattern cam favored the exhaust, something I have found to work well especially on supercharged applications. This cam was tested previously for MM&FF and found to increase the power of a normally aspirated 302 by as much as 30 horsepower. How would it fare on the supercharged motor?
Blower Cam Shootout--Torque...
Blower Cam Shootout--Torque Stock H.O. vs XE258HR vs XE274HR
Perhaps the most telling evidence of the desire for more aggressive cam timing is in the torque production. More often than not, we see a trade off between low-speed power and high-end power. A larger cam generally trades horsepower for torque, but no so in this case. Both of the Xtreme Energy cams increased power across the board compared to the stock cam. The 302 was just begging for more lift and duration. Equipped with the XE274HR cam, torque production of the supercharged test motor never dropped below 424 lbs.-ft. That's one impressive 302.
Installing the new cam on the dyno took a couple of hours. After we had the supercharged motor buttoned back up, we warmed everything up and were ready to rock. After putting the hammer to it, the first thing we noticed was that the boost pressure was down by 1 psi (to 7.5 psi). The next thing we noticed was that even though the boost pressure had dropped with the new cam, the power was up, everywhere. The XE258HR cam improved power across the board. The motor really responded to the new cam timing, as the peak torque was now up to 449 lbs.-ft. at a slightly higher 4100 rpm and peak power was up to 456 hp at 5700 rpm. We noticed during the pull that the motor experienced valve float around 5700 rpm--not a desirable situation. The valve float was the reason for the lower 5700-rpm power peak. Had the motor been able to rev freely, we see no reason why it would not have exceeded 460 hp at 6000 rpm. Even with the slight valve float problem, the Xtreme Energy cam provided a significant power gain. The cam was worth as much as 24 additional horsepower.
Next up was one of my favorite 5-liter cam grinds, the venerable XE274HR. With 224 degrees of intake duration and 232 degrees of exhaust duration, the XE274HR is what might be considered a sizable cam for a street 302. The truth is that this profile works great on street motors, both supercharged and normally aspirated. After another mad thrash, the new XE274HR, was installed in place of the XE258HR. We took the opportunity to install a set of new Comp Cams roller lifters in place of the tired factory units. We wanted to give the new cam every opportunity to shine.
Boy, did it shine. How does 485 hp at 6000 rpm and 456 lbs.-ft. at 4100 rpm sound? That translates to a gain of 47 horsepower from a simple cam swap. Once again, the boost pressure was down to 7.5 psi, but the power was up everywhere. The XE274HR cam increased the power output across the board, from 3500 rpm to 6000 rpm. Though not definitive by any means, this test indicates that your Kenne Bell-supercharged 5.0 will respond favorably to the same cams that work so well with centrifugal superchargers.
The lifters were still smoking...
The lifters were still smoking hot when we pulled them from their bores. We would later replace them with a new set from Comp Cams.
Comp Cams supplied a new timing...
Comp Cams supplied a new timing chain and gears for our test motor. With the lifters removed, we unbolted the cam gear.
Removing the timing chain...
Removing the timing chain set up allowed access to the cam retaining plate.
After unbolting the two retaining...
After unbolting the two retaining bolts, we could now install our cam removal tool.
A long bolt was used to remove...
A long bolt was used to remove the stock cam and then install the XE258HR cam. Note the use of full accessories on our supercharged test motor.
After installing the XE258HR...
After installing the XE258HR cam, the power jumped to 456 hp, but valve float was now present. The torque took a big jump as well to 449 lbs.-ft at a slightly higher 4100 rpm.
The very same cam-removal...
The very same cam-removal procedure was followed yet again while we installed the XE274HR cam. The only change being that we installed a new set of lifters in place of the apparently weak stock units. As before, the power jumped again with the larger XE274HR cam, this time all the way to 485 hp (at 6000 rpm). The torque output was also up, this time to 456 lbs.-ft. at the same (as the 258 cam) 4100 rpm. That the larger XE274HR cam offered a power increase across the board is proof positive that this motor was just begging for wilder cam timing.