LS1 Carburetor V.S. Computer Performance Test - Retro Modern Motivation

Run in carbureted trim, the modified 5.3L produced peak numbers of 462 hp at 6,600 rpm and 413 ft-lb of torque at 5,200 rpm.

Run in carbureted trim, the modified 5.3L produced peak numbers of 462 hp at 6,600 rpm and

All the speculation and conjecture are all well and good, but what happens when you run the same motor with both fuel injection and a carburetor in a back-to-back test? Actually this test was not designed to crown a winner, as both systems provide benefits that may be more or less desirable to the individual. You will never convert a die-hard carburetor guy over to fuel injection, nor will a true-blue EFI guy likely replace his system with a carburetor. Rather than provide an answer to the "Which is best" question, we decided to provide the data from both systems and let the readers judge for themselves. Along the way, we decided to set a goal for ourselves and see if we could reach the magical 500hp mark using nothing more than a stock 5.3L short-block. Sure, it would be easier with a 5.7L LS1, LS6 or even a 6.0L LS2, but the 5.3L LS motors are considerably more affordable, and making big power with fewer cubes is all the more rewarding.

Our 5.3L test mule was yanked from a local wrecking yard and then rebuilt back to factory specs by replacing the stock rings and bearings. Truth be told, the motor could have run as is, but we decided to freshen it up since it would be seeing more than its fair share of dyno time. The bores were lightly honed but care was taken to allow use of the standard bore-size pistons (we reused the originals). Run on the dyno in stock trim, the injected truck motor produced just over 350 hp and 380 lb-ft of torque.

After running the carbureted combination, we replaced the Edelbrock intake with FAST LSX EFI induction.

After running the carbureted combination, we replaced the Edelbrock intake with FAST LSX E

First on the dyno was our carbureted combination. As indicated previously, Edelbrock supplied one of its Performer RPM LS1 conversions that included a plug 'n' play ignition system. The Performer RPM intake was ideally suited to an engine designed for street use, as the dual-plane design offered exceptional torque production, especially below 4,000 rpm. The Edelbrock combination was topped off by a Holley 750 HP carb. Rather than run the stock 5.3L with a simple carb swap, we decided to upgrade it with a set of ported heads and high-performance cam.

Since this was intended for street use, we chose our cam profile with both performance and streetability in mind. A little searching brought us to the XFI RPM Hi-Lift section of the Comp Cams catalog, where we found the XR281HR. This cam featured a .571/.573 lift split, a 228/230 duration split, and a 112-degree lobe separation angle. This cam is skewed toward the performance end of our performance street description (especially for the 5.3L), but we have run this profile successfully in the past and for a stick car it really rocks.

To ensure unrestricted airflow, the FAST intake was fed by a 90mm MSD throttle body.

Compared to the 5.7L, the 5.3L LS motor offers a smaller bore size (3.780 vs. 3.898) and as such requires different cylinder heads for optimum performance. The production 5.3L heads feature smaller combustion chambers to help maintain compression ratio, and the installation of most factory LS1-LS3 heads will result in a drop in compression ratio-ditto for many aftermarket heads.

Knowing we required a dedicated set of cylinder heads, we went right to Trick Flow Specialties. Our needs were met by a set of Trick Flow GenX 205 cylinder heads. In addition to the generous (but not oversized) 205 cc intake ports (flowing nearly 300 cfm) and a small-bore-friendly 2.0/1.575 valve combination, the Gen X 205 heads also featured ideally sized 58cc combustion chambers to ensure no loss of compression. We needed a small-chamber cylinder head that offered exceptional flow with minimal cross section and the Gen X 205 heads fit the bill perfectly. That they came fully assembled, bolted right on and worked with all the factory valvetrain hardware was something we have come to expect from Trick Flow.