Words and Photos by Richard Holdener
Let’s face it, small-block Chevys are awesome in every way, no matter what displacement you choose. Sure, a 283 is better than a 265, as is a 350 better than the 327, but, no matter which displacement you choose, they all have one thing in common. Scratch that, the one thing all owners of the different displacements have in common, is a desire to make more power.
The 265 and 327 owners look longingly at the extra torque offered by the 283 and 350, and they in turn, all look up to the mighty 400 small block, but we have gone off on enough of a tangent here. The topic for today is the quest for more power, regardless of the cubic inches. It is with this in mind that we set off to compare a couple of cam profiles offered by COMP Cams on a mildly modified small block. Normally we’d choose a run-of-the-mill 350 Chevy; after all, it was the workhorse of the small block lineup. Rather than follow the crowd, we decide to take the road less traveled and perform our mods on a 305 Chevy (a.k.a the 5.0L).
More than just a smaller motor compared to the 5.7L 350, the 5.0L 305 was a different animal. Where the 327 and 350 shared the same 4.0-inch bore size and differed in stroke length, the 305 shared the 3.48-inch stroke of the 350, while the difference in displacement was made up in the bore size. Rather than the desirable 4.0-inch stroke offered by the 327 and 350, the 305 featured a 3.736-inch bore. More than a simple drop in displacement, which obviously decreases power, the smaller bore size also limits head flow and available (performance) cylinder heads. Where the larger-bore small blocks can enjoy the plethora of available Chevy heads, the 305 is limited to just a couple.
Luckily, that list of available heads included the desirable TFS Super 23 heads. The simple fact the heads were aluminum was a significant step up the performance ladder compared to the iron heads used on our TPI 305. The Super 23 heads offered a dramatic increase in flow over the stock iron heads (from any 305), thanks to 175cc intake ports, a 1.94/1.50 valve package, and 56cc combustion chambers.
Since the camshaft is the heart of any performance motor, we decided to compare a pair of different cams on the TFS-headed 305. In the more streetable category was a 268XFI cam that offered a .570/.565 lift split, a 218/224-degree duration split, and a 113-degree lsa. In the slightly wilder corner was a COMP XR276HR-10 cam, that came to battle with slightly less lift (.502/.510), slightly more duration (224/230-degree split), and a tighter, 110-degree lsa.
We were most curious to see if the extra lift offered by the XFI cam could compensate for the added duration offered by the XR grind, all without sacrificing idle quality and drivability. To add a little extra spice to the test, we also tested both cams in carbureted and injected trim. After all, the XFI cam was designed with fuel injection in mind, so we wanted to make sure it had a proper home. As we would find out, the difference in the cams was consistent whether equipped with carburetion or fuel injection.
For the first cam test, we equipped the modified 305 with an Edelbrock Performer RPM Air Gap intake and Holley 650 Ultra XP carburetor. Ever the popular combination for any small block, the dual-plane RPM Air Gap never fails to offer a balanced combination of horsepower and torque. Equipped with the smaller XFI cam, the carbureted 305 produced 361 hp at 6,000 rpm and 350 lb-ft of torque at 4,400 rpm.
After installation of the hotter XR276 cam, the peak numbers changed slightly to 361 hp at 6,000 rpm and 353 lb-ft of torque at 4,500 rpm. A peak at the respective power curves (see graph 1) reveals that the 276 cam offered slightly less power down low, but slightly more in the middle and upper rpm ranges. The differences were only slight, not really enough to warrant choosing one over the other, unless you were more interested in things like idle quality and drivability.
Satisfied we had coaxed every last ounce of power out of the carbureted combos, we swapped out the carbureted induction for fuel injection. The EFI set up included FAST XFI controlling the injectors on a Holley Stealth Ram intake. The question now is would the injected small block respond differently to the pair of cam combos than its carbureted counterpart?
Once again, we ran the pair of cams, and the injected small block responded with similar differences in power. Equipped with the XFI cam, the injected 305 produced 367 hp at 6,000 rpm and 349 lb-ft of torque at 4,800 rpm. After installation of the other X cam (with more duration and a tighter lsa), the injected small block belted out 370 hp at 6,000 rpm and 349 lb-ft of torque at 4,800 rpm.
As with the carburetor, the smaller XFI cam offered more power up to 4,000 rpm, then the two produced near identical curves up to 5,700 rpm. From there, the extra duration of the XR cam offered minor gains. Given the minor differences, in the battle of these Xs, the winner will be any small block with either cam.
Sources: COMP Cams, compcams.com; Edelbrock, edelbrock.com; FAST, fuelairspark.com; Holley, holley.com; Lunati, Lunatipower.com; MSD, Msdignition.com