In a world of small-blocks where bigger is better, the 327 still gets a lot of respect. Compared to the original 265, the 327 was obviously larger and more powerful, but where the 327 fell short was after the introduction of the larger 350. The 350 had more torque and a production lifespan that endured for decades until the end of the Gen 1 SBC.
Despite being down on inches to the 350, the 327 Chevy still lays claim to the most powerful production conventional small-block ever produced, the L84. Rated at 375 hp, the fuel-injected 327 was a high-winding screamer, as satisfying to drive as any big-block. At the other end of the spectrum, the 327 was also offered at much more pedestrian power levels, as low as 210 hp (gross). Regardless of the original output, the 327 (like any small-block), is a solid foundation for a performance build up. Like many of you, we still love the 327 and wanted to do a quick buildup with one.
Loyal readers will remember that some time back, we included the 327 in our salute to the legendary small-blocks. Taking a look back through the pages of history, we built and tested a number of the most popular and powerful small-blocks from yesteryear, including the DZ302, the LT-1 350 and the L76 327. Those of you who didn't catch the results can look online at superchevy.com—it makes for good reading.
The borrowed fuelie heads and expensive factory dual-plane, high-rise intake were all returned, but the upshot of all that testing was that we were left with a healthy 327 short- block just begging for upgrades. For those just tuning in, the short block used to simulate the 365hp L76, included a four-bolt block, a 3.25-inch (cast) crank and forged domed pistons that produced the requisite 11.0:1 compression ratio with 64cc chamber heads.
The idea behind this story is to provide a route for increased performance for 327 owners. The best way to demonstrate the merits of our modifications was to compare them to a known baseline. Given the vast number of different 327 configurations available over the years, it was difficult to pinpoint the ideal candidate. For this test, we simply relied on the L76 numbers generated previously for our legendary small-block series.
The 365hp 327 configuration served as a high water mark for factory motors, so our baseline motor was best case scenario. With the exception of the injected L84, every other factory 327 would start out producing less power than the L76, making the gains offered by our proposed modifications that much more impressive. Equipped with the legendary fuelie heads, hot Duntov cam and aluminum high-rise intake, you might think this combination would be tough to beat.
Well, time and technology have marched on since the introduction of the L76 and though it was certainly hot for its day, modern cams, intakes and (especially) cylinder heads offer huge power gains over their factory counterparts. Despite the 365hp rating offered by Chevy, run on the dyno, our L76 327 reproduction produced peak numbers of 353 hp and 368 lb-ft of torque.
As mentioned, our 327 featured domed pistons designed to produce a static compression ratio of 11.0:1. For our build we took full advantage of the elevated compression, but know that the heads, cam and intake package described here work equally well on any low-compression 327-equipped with flat-top pistons. The pistons will require valve reliefs to work with the Comp solid lifter cam.
With a healthy short-block at our disposal, we set off to improve the power output by making changes to those components most responsible for power production, namely the heads, can and intake. As good as the factory components were back in the day, the new stuff is so much better. Off came the L76 heads, cam and intake, replaced by components from AFR, Comp Cams and Procomp Electronics. The key to the success of any build up is to make sure the components were all designed to produce power in the same rpm range. Only working together will they optimize power production. Miss with just one component and the combination will suffer.
We started off with the cylinder heads. Compared to modern heads, the original fuelie heads were both down on flow and up on weight. Chevy never successfully offered aluminum heads on any of the small-block motors back in the day, but they are certainly the hot ticket for performance now. Our heads came from AFR, and where the stock heads had trouble exceeding 210 cfm on the flow bench, the AFR heads flowed 100 cfm more. In fact, the exhaust ports of the heads flow more than the intake on the factory fuelie heads.
What the massive head flow did for our combination was allow us to produce exceptional power without resorting to wild (unstreetable) cam timing. The heads featured full CNC porting, a 2.08/1.60-inch valve package and 66cc combustion chambers to slightly lower the static compression ratio.
In addition to a significant drop in weight and tremendous flow, the aluminum heads also reduced the chance of harmful detonation. Capable of supporting over 600 hp in normally aspirated trim, our relatively mild 327 was not taking full advantage of what they had to offer. These heads were chosen as much for what the 327 might become in the future (think stroker) as its current configuration.
Next on the list was cam timing, and here we actually took a step backward, at least in total duration. In truth, our cam selection from Comp Cams was significantly more powerful than the Duntov 30-30 cam, despite a drop in duration at 0.050. Though hydraulic roller cams are all the rage, in keeping with the old-school nature of the 327, we stuck with a solid flat-tappet grind. Compared to the 254 degrees of duration offered by the Duntov cam, the still healthy 236/242-degrees offered by the Xtreme Energy grind seems tame, but there is much more to cam than simple numbers. The Comp cam also offered a 0.501/0.510 lift split, a 110-degree LSA and a recommended lash adjustment of 0.016.
1. Our 327 build up started with a four-bolt 350 block. The block was bored 0.030-over before installation of the reciprocating assembly.
2. Though the 302, 327 and 350 all share the same 4.0-inch bore, they all run different cranks. The 3.25-inch 327 crank splits the middle between the 3.0-inch 302 and 3.48-inch 350.
3. Our build up featured a set of 6.0-inch Crower rods, though the factory rods will suffice at this power level.
4. Wanting to duplicate the 11.0:1 compression used in the L76 327, the short-block featured domed pistons from Probe Racing.
5. Valvetrain components were from Comp Cams. Even though we have less duration with this stick and the famed 30-30 Duntov cam, we’ll still make more power.
6. Moroso supplied a trick pan, pump and windage tray for our 327.
7. One of the keys to performance on any motor is head flow. The AFR heads featured fully CNC-ported 227-cc intake ports that flowed over 300 cfm.
8. The extensive CNC port work is evident in this shot of the bowl and valve guide. These AFR heads improved head flow by 50-percent over the factory fuelie heads.
9. The exhaust flow was equally impressive. The 85cc exhaust ports actually flowed more than the intake ports of the fuelie heads (226 cfm).
10. Comp Cams also supplied a set of 1.5 ratio High Tech roller rockers for our build. We also tried a set of aluminum Gold rockers (same ratio) that allowed the motor to rev a little higher without valve float.
11. To illustrate the differences in induction system, we tested a pair of intakes on the 327, including this dual-plane, RPM Air Gap from Edelbrock.
12. Designed to optimize power production higher in the rev range, we also included this single-plane intake from Procomp Electronics.
13. Fuel was supplied by a Holley 950 HP carburetor. Likely a tad oversized for this application, the 950 Holley performed flawlessly on the 327.
14. MSD supplied the ignition system for our build up, including this billet distributor, wires and a 6A ignition amplifier.
15. Exhaust was sent through a set of 1-3/4-inch Hooker Super Comp headers to 18-inch collector extensions.
16. Run on the dyno with the single-plane intake from Procomp Electrionics, the modified 327 produced 462 hp at 6,800 rpm and 412 lb-ft of torque at 5,200 rpm. This represented a jump of nearly 110 hp over the L76 configuration.
This Comp cam was easily 35-40 hp better than the Duntov grind with no other changes, but as we will see, it also worked very well with the new heads and intake. Certainly effective, the factory intake was nonetheless upgraded with a single-plane design from Procomp Electronics. Because of its reputation as a short stroke, rev-happy motor, we tested both a single plane and dual-plane intake on this 327.
With our heads, cam and intake choices sorted out, we finished up the motor with an MSD billet distributor, Holley 950 HP carburetor and a set of Hooker headers. The 327 was first run with the dual-plane Edelbrock Performer RPM Air Gap intake. Since the short- block had already seen plenty of dyno action, there was no need for a break-in procedure and we immediately let the hammer fly. After a timing sweep and minor jetting to the 950 Holley, we were rewarded with peak numbers of 441 hp at 6,600 rpm and 408 lb-ft of torque at 4,900 rpm. Torque production from the 327 exceeded 400 lb-ft from 4,000-5,300 rpm.
After replacing the dual-plane intake with a single-plane, high-rise unit, the peak numbers jumped to 462 hp at 6,800 rpm and 412 lb-ft of torque at 5,200 rpm. As expected, the single-plane intake offered more peak power by shifting the torque curve higher in the rev range. The dual plane offered more power and torque up to 5,000 rpm, but the single plane took top honors from 5,000 rpm to 7,000 rpm.
327 Chevy-L76 vs. Modified
To illustrate the effectiveness of the 327 build up, we used the L76 configuration to serve as a baseline. Note that swapping the heads, cam and intake offered a substantial jump in power, with huge gains coming at the top of the rev range. Where the L76 configuration produced 353 hp and 368 lb-ft, the modified 327 produced 462 hp and 412 lb-ft of torque, pulling hard all the way to 7,000 rpm.
327 Intake Test-Single vs. Dual Plane
The question on every small-block owner's mind is does a single-plane intake make more power than a dual plane? The quick answer is yes, but the graph indicates that there is more to the answer than a simple yes or no. The single-plane intake did make more peak power (462 hp vs. 441), but the dual-plane intake offered more power up to 5,000 rpm. For street use, 327 owners spend much more of their time below 5,000 rpm, meaning they would make better use of the extra power offered by the dual plane. For maximum performance, the single plane is the way to go.