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Words And Photos: Richard Holdener
Obviously a fuel-injected motor differs from its carbureted counterpart. Both carburetors and injection strive to deliver fuel as effectively as possible to each cylinder, but the applied methodology is dramatically different. Tested on typical Chevy V8 (like our test motor), fuel is supplied by the carburetor to some type of common plenum on a single-plane intake (two smaller plenums on a dual-plane). Essentially a demand system, fuel delivery is dependant on the induction pulses in a carbureted application. By contrast, a fuel delivery from electronic fuel injection is programmed and therefore independent of the demand. Obviously the supply must be properly matched to the demand, but fuel flow can be controlled irrespective of the demand. In a port-injected motor, fuel is delivered evenly to each cylinder, something not always possible with carburetion. Recognizing the inherent benefits of fuel injection, the OEM’s abandoned carburetion long ago. Given the popularity and performance of fuel injection, what cam should we chose for our injected small block.
Whether you have a factory L98 TPI motor or aftermarket Stealth Ram set up on a hot 355 small block (like ours), COMP Cams has the ideal cam for your injected small-block combination. Though designed for the fuel-injected motors, the XFI cam profiles have also proven plenty powerful on carbureted applications. To illustrate the merits of the Xtreme Fuel Injection (XFI) cam profiles, we first needed a suitable test motor. Starting out life as a ZZ4 crate motor, Project X was augmented with JE forged pistons (and Total Seal rings) then topped with a set of AFR 195 Eliminator heads. Feeding the AFR-headed small block was a trick Holley Stealth Ram EFI intake. The Stealth Ram EFI intake was basically a tunnel ram base converted to fuel injection. In addition to the injector bungs, the lower intake offered near identical runner length, thus ensuring even airflow (and hopefully power) distribution to each cylinder. The lower intake was designed to accept a large box plenum fed by a dual 58mm throttle body.
For this cam test, the Stealth-Rammed 355 test mule was also equipped with Hooker 1 ¾-inch headers feeding a set of 3-inch Magna Flow mufflers, a Meziere electric water pump and a set of COMP Cams 1.52 roller rockers. Also present during testing was a complete MSD ignition and FAST 36-pound injectors controlled by (what else) a FAST XFI management system. The small block was first set up with a mild (but powerful) COMP Xtreme Energy (flat-tappet) cam. The COMP XE250H cam offered a .432/.444 lift split, a 206/212-degree duration split and 110-degree LSA. The flat-tappet cam and lifers were liberally coated with moly assembly lube and we added high-zinc, break-in oil before running the test. Tuned to perfection with the XFI management system, the Stealth-Rammed and Xtreme-Energy cammed small block produced peak numbers of 395 hp and 417 lbs. ft. of torque. No slouch, torque production from the Xtreme Energy cam profile exceeded 400 lb-ft from 3,000-5,150 rpm. The XE250H cam would be an excellent choice for a daily driven small block.
After running the Xtreme Energy XE250H cam, it was time to install the larger 268XFI-HR13 cam. Larger than the XE250H, the XFI profile (pt# 08-466-8) offered a .570/.565 lift split, a 218/224-degree duration split and (wider) 113-degree lobe separation. Combining high lift with the relatively short duration resulted in aggressive ramp rates. These aggressive ramp rates were then combined with a relatively wide lobe separation to custom tailor the profiles for fuel-injected applications. Installation of the XFI hydraulic roller cam required use of the matching hydraulic roller lifters and factory lifter retainers. Remember, the late-model ZZ4 block was designed for hydraulic-roller use. As expected, the XFI cam offered significant power gains on our 355 small block. Equipped with the 268 cam, the injected small block produced 435 hp at 6,000 rpm and 417 lb-ft of torque at 4,900 rpm. The larger cam suffered a loss of torque down low compared to the smaller cam, but offered an additional 58 horsepower at 6,000 rpm. The gains would be even greater had we revved the motor past the respective power peaks. With over 430 hp, Project X was an Xtreme success.
With a fuel-injected small block, it was only natural that Project X received an Xtreme Fuel Injection (XFI) cam. Equipped with Xtreme Energy XE250H cam, the Stealth-Rammed 355 produced impressive low and mid-range power. Who wouldn’t love a small block that offered 395 hp and (more importantly) 417 lb-ft of torque that idled like a stocker? Need more power for those trips to the strip? The XFI profile stepped up the power significantly, from 395 hp and 417 lb-ft of torque to 435 hp and 417 lb-ft of torque.
Sources
COMP Cams
compcams.com
FAST
fuelairspark.com
Holley
holley.com
MSD
msdignition.com
