L84 Fuelie Motor On Engine Dyno - Fuelie Fisticuffs

The Carbed L76 Takes On The Injected L84 On An Engine Dyno

Richard Holdener Nov 1, 2009 0 Comment(s)
Vemp_0911_20_z L84_fuelie_motor_on_engine_dyno Fresh_intake_gaskets 1/27

After removing the carbureted intake, we installed the lower manifold using a fresh set of Fel-Pro 1205 intake gaskets.

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.

Vemp_0911_21_z L84_fuelie_motor_on_engine_dyno Upper_injection_manifold 2/27

Next came the upper injection manifold and assembly. The pre-assembled fuelie assembly could be installed as one unit.

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.

Sources

Comp Cams
Memphis, TN 38118
800-999-0853
http://www.compcams.com
Pro Comp Electronics
Ontario, CA 91761
909-605-1123
www.procompelectronics.com
Elgin Automotive
Elgin, IL
800-323-6764
http://www.elginind.com
L&R Automotive
Sante Fe Springs, CA 90670
562-802-0443
www.lnrengine.com
Coast High Performance
Torrance, CA 90505
310-784-1010
www.coasthigh.com
Pony Carburetors
Las Cruces, NM 88005
575-526-4949
http://www.ponycarburetors.com
Chuck Smith Carburetors & Fuel Injection
(760) 749-5755

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