Words And Photos: Richard Holdener

Ask any group Chevy enthusiasts about the best small block ever made and chances are someone will say the 327. Sure, some may argue that the 283-horsepower, injected 283 was the first Chevy to reach 1 hp per cubic inch, while others will counter with the Trans Am-winning DZ302 and still other might chime in with LT1 350 as the last great high-compression small block. What we quickly learn from this discussion is that there were a number of great small blocks produced during the muscle car era, but only one can lay claim to having the highest factory power rating. The fuel-injected L84 327 was factory rated at 375 horsepower, while the carbureted L76 version was rated 10-hp down at 365 hp. Whether these motors ever produced that kind of power in stock trim is irrelevant, as no 283, 302 or even 350 was ever rated higher. Thus, the 327 can lay claim to being the most powerful of all the original muscle-car small blocks. A better question might be how does the king of all muscle-car small blocks compare to modern machinery?

Given the tremendous leap in technology, the first question should be is such a comparison even fair? The short answer is no, since the small block has gone through a number of iterations since the 327. We now have the LT series that offers such technological trickery as dry-sump oiling, variable cam timing and even direct injection. A better comparison for the original 327 might be the 324-inch 5.3L LM7. Not only is this LS-based motor nearly identical in displacement, it has become the defacto swap motor for just about every import and domestic performance application. Hardly top of the performance LS line, the 5.3L was designed for the rigors of truck use. Unlike the high-winding, 365-hp 327, the 5.3L LM7 was tuned for torque. Don’t feel sorry for the little truck motor, as the comparison isn’t as one-sided as it might seem. Remember, time and technology have marched on and the 5.3L has been the recipient of improvements in head flow, intake design and modern fuel injection. Enough about what might be, let’s get to the tail of the tape.

Compared side by side, the L76 327 comes by its displacement using a 4.0-inch bore and 3.25-inch stroke. This compares to the smaller 3.78-inch bore and longer 3.622-inch stroke of the 5.3L. For high-rpm power, the 327 offered a better bore/stroke ratio, but that only speaks of potential, it is, after all, the heads, cam and intake that really determine power. The 327 topped the 5.3L in terms of compression (11.0:1 to 9.5:1) and cam timing (254 degrees vs 191 degrees @ .050), but lost out in the head flow department. Even the relatively small 5.3L truck heads (706 casting) offered significantly more flow than the legendary Fuelie heads of yesteryear. Combine this with the long-runner truck intake and you start to see how the 5.3L is able to match the real-world power output of the legendary L76 small block. To illustrate just how close the modern truck motor is to the classis 327, we decided to run a test on the dyno, both in stock trim and then again after a few simple modifications. For some, the metric 5.3L will never replace the legend, but the comparison helps put the modern muscle into proper perspective.

No one was foolish enough to loan us their numbers-matching L76 for dyno testing so we did the next nest thing, we built our own. Our reproduction 327 consisted of an 11.0:1 short block equipped with domed pistons, 64-cc Fuelie heads and the proper Duntov 30/30 solid, flat-tappet cam. Also present was the factory aluminum, dual-plane, high-rise intake, but we did run the motor with long-tube headers and a Holley 750 HP carburetor. Though the carb was comparable to the Holley used on the original motor, the headers obviously improved the power output over the factory cast-iron exhaust manifolds. To keep things fair, the 5.3L was also equipped with headers, an open throttle body (no air intake) and (like the 327) a Meziere electric water pump (no accessories).

Both were tuned to optimize air/fuel and timing, something neither would have been from the factory. Run in this configuration, the 365-hp L76 327 produced peak numbers of 354 horsepower at 6,300 rpm and 363 lb-ft of torque at 4,200 rpm. Amazingly enough, the seemingly milder 5.3L produced a near identical 353 hp but at a lower 5,300 rpm. The tuned-for-torque truck motor offered some serious grunt, posting 384 lb-ft of torque at 4,300 rpm. A peak at the graph shows the personality of each motor, with the high-performance nod going to the L76, as it offered significantly more power at the top of the rev range. It should be pointed out that this extra horsepower came with low and mid-range torque penalty, as the modern motor easily out performed the legend up to 5,200 rpm.

Nostalgia tells us that the 365-hp 327 was a forced to be reckoned with, but the dyno tells us that even the most common of modern truck motors can match the legendary power output. In stock trim, the 5.3L will never rev like the L76, but what happens when you add a few performance mods to the equation? One of the many things that made the original small block so great was how well it responded to performance upgrades. How well does the modern machinery compare after adding after market heads, a performance cam and intake manifold?

To find out, we stripped both motors down to the short block and added some performance upgrades. To the 327 we added a set of AFR 195 Eliminator heads, a COMP 274S solid flat tappet cam (501/510, 236/242 110 lsa) and a single-plane intake. The mods to the 5.3L were slightly milder, consisting of a set of ported factory 706 heads from Total Engine Airflow and a Crane cam (.590, 224/232, 114 lsa). Though other intakes are available for the 5.3L, it was run with the stock truck intake and Accufab throttle body.

True to their small-block heritage, both motors responded to the upgrades. The new heads, cam and intake took the L76 327 from 354 hp and 363 lb-ft of torque to 462 hp at 6,800 rpm and 412 lb-ft of torque at 5,200 rpm. The mods pushed power production much higher in the rev range, making the already rev-happy 327 even more so. Not to be out done, the 5.3L responded equally well to the upgrades. Starting at 353 hp and 384 lb-ft of torque, the ported heads and Crane cam allowed the 5.3L to produce 471 hp at 6,500 rpm and 425 lb-ft of torque at 5,200 rpm. Though both peaks bettered the modified output of the 327, the test wasn’t designed to provide a replacement for the original small block but rather an alternative. If you are in the market for a high-winding, carbureted 327, chances are you won’t look twice at an injected 5.3L. If however, you are looking for something that combines the power and performance of the original muscle motor with improved drivability and mileage, the 5.3L is by all measure a worthy successor.

Looking just at the power peaks (354 hp vs 353 hp), we would say that the 5.3L and L76 327 were evenly matched, but the dyno curves tell a different story. The 5.3L produced peak power much earlier than the L76 (5,200 rpm vs 6,300 rpm) and as such offered more low-speed torque. By contrast, the L76 offered significantly more high-rpm power than the 5.3L, especially past 5,300 rpm. The increased torque production offered by the 5.3L can be attributed to the mild cam timing and long-runner intake design. The aggressive specs of the Duntov 30-30 cam allowed the power curve of the 327 to continue strong past 6,000 rpm.

In modified trim, the dyno results indicate that both motors responded well to the performance upgrades. Equipped with a set of AFR 195 heads, COMP 274S cam and Speedmaster single-plane intake, the modified L76 327 produced 462 hp and 412 lb-ft of torque. The 5.3L was treated to a set of CNC-ported 706 heads and a COMP 224 cam. The results were 471 hp and 425 lb-ft of torque. It is nice to know that the modern machinery can more than keep pace with the muscle motors of yesteryear.

Sources

Aeromotive
aeromotiveinc.com

COMP Cams
compcams.com

Crane Cams
cranecams.com

Holley/Hooker
holley.com

Speedmaster
speedmaster79.com

Total Engine Airflow
totalengineairflow.com