When was the last time you saw a Rochester fuel-injection system on an engine dyno?
Just a few short years after Chevy introduced the original 265 small-block, the company followed up by offering a true legend in the form of the fuel-injected 283. Often touted as the first mass-produced motor to offer 1 horsepower per cubic inch, the fuelie 283 started a small-block Chevy performance trend that would continue for decades. The 283hp 283 of 1957 was eventually replaced with Chevy's new wonder motor, the 327. Compared with the 283, the 327 offered an increase in both bore (from 3.875 to 4.00 inches) and stroke (from 3.00 to 3.25 inches). Continuing the performance trend started a few years earlier, Chevy topped the hot 327 with the latest version of its mechanical FI setup. The pinnacle of this combination was the famous L84 fuelie motor that offered no fewer than 375 hp in 1964 and 1965.
Whereas the fuelie 283 offered 1 hp/ci, the L84 sported an amazing 1.146 hp per cube. In fact, until the release of the quad-cam LT5 in the ZR1, the L84 was the highest-rated production small-block ever offered by Chevrolet. Of course, there's a major difference between the gross power numbers of the muscle-car era and the modern net-rated versions. Gross ratings were obtained on an engine dyno under ideal conditions and without accessories. The current net ratings comply with SAE standards and are taken at operating temperature, using the factory tune, and with full accessories, induction, and exhaust (including catalytic converters). Thus the 375hp L84 is likely closer to 325 hp by today's more exacting standards.
Though the L76/L84 engines were originally equipped with two-bolt blocks, our test 327 sta
Looking at the specs of the L84, you can see that the 327's power came courtesy of an elevated compression ratio, a set of high-performance heads, and aggressive cam timing. Back in the days of high-test fuel, factory motors could get away with a combination of iron heads and the 11.0:1 compression offered in the L84. Similarly, the L84's hairy solid-lifter cam yielded a crotchety low-speed idle that wouldn't be tolerated in the modern era. Whereas lesser motors offered 1.94/1.50 valves, the "double hump" fuelie heads (461 castings) sported a larger 2.02/1.60 combination. Of course, the main reason anyone purchased the L84 was the Rochester FI system. Interestingly, other than the fuelie induction system, the L84 was the same motor as the carbureted, 365hp L76.
Sales figures indicate that the L76 was much more popular than the L84. There are two distinct reasons for this, the first being price. While the L76 cost just $129 more than the base engine, the fuelie motor tacked on a whopping $538, or $246 more than the 425hp 396! Another factor was that fuel injection was completely foreign to most enthusiasts at the time. In fact, a great many fuelie owners removed the injection setup altogether and replaced it with a single- or dual-quad combo for street/strip racing.
Sorting through their many available cores, the L&R crew were able to locate a suitable 3.
The popularity of the carbureted engine and the general inaccuracy of the output ratings of the time gave rise to an interesting question: What was the real difference in power between these legendary small-blocks? Did the L84 really produce 10 more peak horses than its carbureted sibling? If so, what was the difference in power elsewhere along the curve? And what about fuel metering? Did the injected combination improve the air/fuel curve compared with carburetion?
To accurately answer these questions, we needed to first build a suitable test motor. We decided to assemble not just a small-block, but something that would replicate the original 327 combinations of 1965. This meant an 11.0:1 327 equipped with period-correct cylinder heads, a reproduction of the original solid-lifter cam, and the factory high-rise intake. Obviously we also had to have an original Rochester FI system on hand to compare to the carbureted combo.
Probe Racing supplied the necessary forged pistons, while the 6-inch forged connecting rod
To achieve the desired 11.0:1 compression, the forged pistons (right) required a slight do
Elgin Industries supplied the reproduction Duntov 30-30 cam. In addition to cams and other
The necessary gasket set, oil pump, and neutral damper all came from Pro Comp.
Pro Comp also supplied a new set of stainless steel valves, while Comp Cams came through w
Fuelie heads typically feature 64cc combustion chambers, though ours were slightly smaller
The heads received a number of valvetrain components from Comp, including factory long-slo
To save time and money, we decided to build an engine that duplicated the power potential of the original 327s without being an exact replica. For example, while the early 327s were equipped with two-bolt blocks, we sourced a four-bolt block from L&R machine. And while the original engines came with small-journal steel cranks, we outfitted our late-model block with a large-journal cast piece. Fortunately, none of these changes would have any impact on output.
There was one area, however, in which we were forced to deviate in a way that might stir controversy. Since the 327s came equipped with 11.0:1 compression, we needed to duplicate this reading on our test motor. The number was arrived at using the 64cc combustion chambers on the fuelie heads (more on these later) and a set of forged aluminum pistons from Probe Racing. Rather than going with a set of reproduction TRW forgings, we opted to have Probe duplicate the (roughly 7.5cc) domes using one of its own forgings. The only downside to this route was that the compression height differed from stock and therefore required the use of a 6.0-inch connecting rod. Like the cast crank, this minor discrepancy shouldn't affect the outcome of our back-to-back tests. Whether we'll be chastised on the Internet for running a long rod in the legendary small-block remains to be seen.
L&R freshened up the stock heads with a light surface and a factory-style valve job. The r
With our short-block taken care of, we moved on to the heads, cam, and induction. For the cam, we used an Elgin Industries reproduction of the solid-lifter "Duntov 30-30" grind (0.484-inch lift, 254-degree duration, 114-degree lobe separation) that came in both the L76 and the L84. Looking at the specs, this would seem to be a pretty aggressive cam, but the combination of relatively short lift and long duration produced a mild ramp rate that was actually easy on parts.
When it came to the heads, we were able to obtain a suitable set of 461 castings from Rick Stoner at Westech Performance. All we did was install a new set of Pro Comp valves, perform the requisite valve job, and add a set of heavy-duty valvesprings (130 pounds of seat pressure and around 325 pounds open) suitable for our flat-tappet cam.
We also took the liberty of flowing the heads before installation. The 160cc intake ports flowed 205 cfm at 0.600 lift, while the exhaust ports flowed 141 cfm at the same lift. More important for our needs was the flow at 0.500 lift-just over the 0.484 offered by the factory cam. There, the intake checked in at 206 cfm, while the exhaust flowed 140 cfm. While these numbers aren't anything special by today's standards, they set the standard for small-block performance in their time.
Topping off the fuelie heads was an original high-rise intake wearing a 461 casting number
Before getting to the induction systems, we should mention that our test motor required a number of other smaller components in order to be completed. In addition to supplying the 6.0-inch connecting rods for the build up, Pro Comp came through with things like a high-volume oil pump and pick up, a neutral-balance damper, and stainless steel intake and exhaust valves.
In terms of ignition, the early 327s were offered with transistorized systems. Rather than attempting to go the numbers-matching route, we once again opted for something a little more modern, this time to eliminate any chance of misfires during testing. The Rochester-injected setup was run with the specific distributor it required, but the carbureted motor was equipped with a modern MSD electronic unit. Basically, we wanted to run both combinations in a state of optimized tune in order to see what each of the induction systems had to offer.
Unfortunately, the original intake had previously been modified to eliminate its center di
Rather than run a factory Holley 3310, we opted for a modern version in the form of a 750
If you must have a numbers-matching carburetor on your L76, check with the guys at Pony Ca
Rather than run the engines with the factory cast-iron exhaust manifolds, we chose a set o
On the dyno, the carbureted L76 produced peak numbers of 355 hp and 366 lb-ft of torque.
Next up was the factory fuel injection. This system came courtesy of fuelie legend Chuck S
After removing the carbureted intake, we installed the lower manifold using a fresh set of
Induction chores were handled by a GM high-rise intake manifold, also borrowed from Stoner. The casting number (461) indicated that the intake was originally installed on a 1964 or 1965 L76 327. For carburetion, we chose not to go with the original 3310 Holley but instead went with a simple Holley 750 Street HP unit. The new carb offered no airflow advantage over the factory piece, and the diminutive 327 wouldn't have needed the extra air even if it had. (If you've just got to have a numbers-matching original carb for your L76, one can be obtained from a specialty shop such as Pony Carburetors.)
The fuelie unit came courtesy of legendary fuelie tuner Chuck Smith, of Chuck Smith Carburetors & Fuel Injection in Fruitvale, California. Smith's help was critical to our test, since rebuilt Rochester fuel-injection units can run as much as $9,000. That such hardware adds value to an original fuelie Corvette is without question, but what would it do on our test motor? It was time to find out
On the Dyno
Before running the engine combos on the chassis dyno, we needed to perform a proper break-in procedure. Due to the lack of zinc in most of today's motor oils, break-in is especially critical in any motor running a flat-tappet cam. We began by being sure to use plenty of assembly lube when installing the cam. Next, we combined Lucas 20W-50 oil with the company's high-zinc break-in additive to provide the necessary protection. The final step was to pre-lube the engine using a drill to spin the high-volume oil pump. Once we had oil visible on all of the rockers, we were ready for start-up.
Next came the upper injection manifold and assembly. The pre-assembled fuelie assembly cou
After the 20-25 minute break-in procedure, we readjusted the valves and made some power pulls. On the carbureted setup, our best numbers came with 38 degrees of total timing and a jet package of 78/84 in the Holley Street HP. Run in this configuration, the carbed 327 produced peak numbers of 355 hp at 5,700 rpm and 366 lb-ft of torque at 4,100 rpm. (Note that for convenience and to keep costs down, we ran all of our tests with a set of long-tube 1.75-inch dyno headers.) The dual-plane intake helped produce a healthy torque curve, with more than 330 lb-ft available from 3,000 to 5,600 rpm.
After tuning every last ounce of power out of the carbureted combo, we installed the Rochester fuel injection. The restored system went on without a hitch, including the unique distributor equipped with the necessary tach and fuel-pump drive. Some tuning was necessary (no doubt due to our lack of accessories and use of long-tube headers), but after installing the largest factory injector nozzles and making some minor adjustments to the float, we were rewarded with a near-ideal air/fuel curve of 13.0:1 and plenty of extra power. In fact, the fuelie 327 produced almost exactly 10 more horsepower than our carbureted combination, and offered more power from 4,300 rpm through 6,500 rpm. Below 4,300 rpm, the carbed motor made slightly more torque, but overall the fuelie was unquestionably the hot setup for this 327.
Before pulling the 327 off the dyno, we couldn't help but try to improve the output of the L76 carbureted combination with a simple cam swap. Mostly, we wanted to demonstrate just how far cam technology has come in the last 40-odd years. Would it be possible to improve power while maintaining-or even improving-idle quality and driveability? To find out, we installed an XS274S cam from the Comp Cams catalog. This solid flat-tappet unit offered a 0.501/0.510 lift split and a 236/242 duration split (measured at 0.050). This represented a slight increase in lift but sizable drops in intake and exhaust duration (18 and 12 degrees, respectively) as compared with the original Duntov grind. Nevertheless, the more-aggressive ramp rates of the Comp unit increased the power output of our carbureted combination from 355 hp and 366 lb-ft to 370 hp and 380 lb-ft. The "milder" cam also improved power throughout the rpm range, offering improvements of as much as 20 hp and 20 lb-ft of torque over the factory Duntov stick.
Whereas the carbureted motor was run with an MSD billet distributor, the Rochester fuel-in
To achieve the desired air/fuel ratio on our injected 327, it was necessary to increase th
On the dyno, the fuelie Vette motor showed its worth by out-powering the carbureted combin
Before pulling the 327 off the dyno, we decided to run a cam-comparison test. We replaced
Graph 1: L76 vs. L84 The dual-plane 461 intake and Holley carb offered slightly better to
Graph 2: Duntov 30-30 Repro Cam vs. Comp XS274H Replacing the Duntov 30-30 reproduction c