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Comp Cams XFI Roller Camshaft Test - Rampaging Rollers
Comp Cams' New And Huge XFI Roller Cams Make 481 Hp In Our 347-Inch Test Mule
Regular readers know we often run several Xtreme Energy hydraulic-roller camshafts from Comp Cams on our 347 dyno mule. Besides running well, those cams are good choices for a test engine because many of you are running them in hot street and hobby cars. At the most recent SEMA show, Comp announced a new line of XFI hydraulic-roller cams for popular V-8s, including two for the small-block Fords. After a quick call to Comp, a pair of the cams were headed our way, along with a bit of background on what these cams are all about.
It turns out that XFI is Comp's designation for its latest cam science. According to Comp Cams engineer Billy Godbolder, the basic idea is to reduce some of the overlap while otherwise bumping up the overall aggression. That means the XFI cams exceed the Extreme Energy line-which are bold units in their own right-and head right out to the physical limit allowed by hydraulic lifters. The result is rather nasty, big-lift, big-duration grinds aimed at seriously modified, larger-displacement small-blocks. These XFIs are high-rpm lobe profiles designed to run at the strip or track, with only minor concern for streetability. They're a real test of thevalvesprings and, in short, overlap flat-tappet cam territory.
Remembering that the XFI cams are designed to work with electronic fuel injection, let's take a look at the two new camshafts' specifications, along with the next largest Comp cam optimized for electronic fuel injection, the 282 Xtreme Energy grind (see chart below).
It's clear the XFI cams are the next step up in duration, but rather than Comp's usual 8-degree jump, the 248 XFI gains 10 degrees of exhaust duration compared with the 236 XFI. Also, the gain in lift is considerably more aggressive, which differentiates the XFI line from the XE line.
Were engineer Billy Godbolder here, he'd no doubt point to how the XFI cams employ 114 degrees of lobe separation angle instead of the XE's 112 degrees. The wider separation angle is required by the long duration, which needs "narrowing" by widening the lobe separation angle, especially if it is to work with fuel injection. This helps keep the cam from being too radical at low engine rpm and, believe us, these XFI cams are already plenty snotty.
Clearly, with six tenths of an inch of valve lift, the XFI cam family gets with the power program. Our guess is they could manage to lurch around on the street given a light car, a clutch, and some help from the rear-axle gearing, but these are obviously not daily driver grinds. With a little tuning, we saw just 8 inches of vacuum at a 1,000 rpm "idle," so there are precious few good manners here.
| ||Duration @ 0.050 in||Valve Lift||Lobe||Rocker|
With the two XFI cams in hand, we knew we could run them against each other, as well as compare them to one of our earlier 282 Xtreme Energy tests, to show where the XFI cams fit in the overall scheme of lifts and lobes. But as these cams promised to make more power than ever from our 347, it was also a chance to see what a few supporting pieces could do should we have enough testing time.
With that in mind, we chose to start the test with the 347 dressed exactly as it was during out last round of intake tests. That meant a Coast High Performance Street Fighter 347 short-block, AFR 185 cylinder heads with heavy valvesprings, and our usual electric water pump, long-tube headers, and FAST fuel injection. Because it squeaked out the highest peak power number in the previous intake test, we opted to fit Edelbrock's Performer RPM II intake manifold, along with a 70mm Accufab throttle body and spacer. This configuration returned exactly 450 hp during the intake test while using the 282 Xtreme Energy cam.