Cam Wars: Battle of the Xs

Choosing the right cam can make or break your small block build.

Choosing the right cam can make or break your small block build.

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.

We then added the first, and wilder of our two COMP cams. The XR276HR-10 cam offered a .502/.510 lift split, a 224/230-degree duration split, and 110-degree lsa.

We then added the first, and wilder of our two COMP cams. The XR276HR-10 cam offered a .502/.510 lift split, a 224/230-degree duration split, and 110-degree lsa.

We then added the first, and wilder of our two COMP cams. The XR276HR-10 cam offered a .502/.510 lift split, a 224/230-degree duration split, and 110-degree lsa.

To take advantage of the available cam timing, we also upgraded the cylinder heads. The stock iron 305 heads were replaced by a set of aluminum Super 23 heads from TFS.

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.

We then swapped in the 268XFI-HR13 cam from COMP Cams. The XFI grind offered less duration than the XR276 cam, but slightly more lift and a wider lsa.

We then swapped in the 268XFI-HR13 cam from COMP Cams. The XFI grind offered less duration than the XR276 cam, but slightly more lift and a wider lsa.

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?

The Stealth Ram lower was topped with this upper intake and dual 58mm throttle body. Run with fuel injection, the cam swap netted the same results as carburetion, with the smaller XFI cam offering more power at the very bottom of the rev range, but less at the very top. For most of the curve, there was little to choose from between the two cams.

The Stealth Ram lower was topped with this upper intake and dual 58mm throttle body. Run with fuel injection, the cam swap netted the same results as carburetion, with the smaller XFI cam offering more power at the very bottom of the rev range, but less at the very top. For most of the curve, there was little to choose from between the two cams.

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.

Carbureted 305 Chevy Cam Test-XR276HR vs 268XFI HR13  Run with the Performer RPM Air Gap and Holley 650 Ultra XP carb, there was little difference between the two COMP cams. The XFI offered more power down low, from 3,000-3,900 rpm. The XR cam offered 2-3 extra hp up to 5,000 rpm, then bettered the smaller cam once again past 6,000 rpm. In truth, you would be hard pressed to tell the difference in power behind the wheel between the two cams, but the XFI did offer improved idle quality, and likely, drivability compared to the increased duration (and tighter lsa) of the XR grind.  

Carbureted 305 Chevy Cam Test-XR276HR vs 268XFI HR13 
Run with the Performer RPM Air Gap and Holley 650 Ultra XP carb, there was little difference between the two COMP cams. The XFI offered more power down low, from 3,000-3,900 rpm. The XR cam offered 2-3 extra hp up to 5,000 rpm, then bettered the smaller cam once again past 6,000 rpm. In truth, you would be hard pressed to tell the difference in power behind the wheel between the two cams, but the XFI did offer improved idle quality, and likely, drivability compared to the increased duration (and tighter lsa) of the XR grind.

Fuel Injected 305 Chevy Cam Test-XR276HR vs 268XFI HR13 Thinking we should combine the XFI cam with fuel injection, we ran the same cam test after equipping the 305 small block with a Holley Stealth Ram. Though the intake was decidedly different that the dual-plane, carbureted manifold, the results were very similar. The milder XFI cam once again offered improved torque up to 3,900 rpm, then fell behind the XR276 cam above 5,800 rpm. There was a slight bump in power (1-2 lb-ft) from 4,400-4,700 rpm, but that was just splitting hairs.

Fuel Injected 305 Chevy Cam Test-XR276HR vs 268XFI HR13
Thinking we should combine the XFI cam with fuel injection, we ran the same cam test after equipping the 305 small block with a Holley Stealth Ram. Though the intake was decidedly different that the dual-plane, carbureted manifold, the results were very similar. The milder XFI cam once again offered improved torque up to 3,900 rpm, then fell behind the XR276 cam above 5,800 rpm. There was a slight bump in power (1-2 lb-ft) from 4,400-4,700 rpm, but that was just splitting hairs.

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

About the author

Elizabeth Puckett

Elizabeth is a seasoned writer and hardcore gearhead. She was born with motor oil in her blood and a passion for everything that goes fast.
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