Words and Photos: Richard Holdener
Not to knock the venerable carburetor, but we all know that fuel injection is the name of the game. Sure, carburetors have been used to provide air and fuel for millions of automobiles for decades, but there is a reason that all the OEMs have made the switch to modern fuel injection. While carburetors perform well when paired with a specific motor, changes made to the motor can play havoc with the metering. This is especially the case when you add boost to the equation. Although blow-through carbs can be made to work well, they almost always work well at cruise, part throttle OR WOT, but rarely do they work well under all circumstances. Such is the benefit of fuel injection, as precise fuel metering from the EFI system is not dependant on the air supply of the motor. This means not only will the EFI system provide precise metering at idle, but that precision will continue regardless of engine speed or load.
The one area carburetion has offered an advantage over fuel injection is in charge cooling. Air being pulled through the venture of the carburetor is used to draw fuel out. The introduction of fuel into the air stream provides a cooling effect that ultimately improves power. On most port fuel-injection systems, where the fuel is introduced down near the cylinder head, this charge cooling is minimized. Thus a comparison between a carburetor and port EFI on the same manifold will usually result in the carb showing more power from the charge cooling (assuming the proper AF mixture can be produced with the carb). This all changes when a fuel-injection system introduces the fuel into the air stream from a throttle body on top of the intake manifold, in the same manner as a carburetor. The charge cooling offered in this manner is especially important for blow-through, boosted applications. The charge cooling offered by the introduction of fuel on a boosted application acts as a form of intercooling, offering both more power, and, security against harmful detonation.
The guys at FAST obviously recognized the benefits and limitations of a blow-thru carburetor, and decided to offer a powerful alternative. By combining an XFI Sportsman ECU with their already popular EZ-EFI throttle body, they were able to come up with a combination capable of supporting over 1,000 supercharged hp. The 4150 throttle body bolted in place just like any 4-barrel carburetor, including linkage and carb bonnet mounting. Unlike a conventional carburetor, the EFI throttle body featured eight injectors and all the necessary sensors built right in. The throttle body featured sensors for TPS, IAC and IAT, as well as an integrated map sensor. While the throttle body can be run with a map sensor designed for a naturally aspirated combination (with greater resolution), we opted for a 2-bar map sensor that allowed us to apply boost. The lone sensor not part of the throttle was the ECT, or engine coolant temp, which we installed in the intake manifold of our small-block test motor. The throttle body was combined with the powerful FAST XFI Sportsman management system, which allowed full control of the air/fuel and timing, as well as providing data logging capability.
As luck would have it, this test at Westech Performance coincided with a visit by the FAST wizard himself, David A. Page. Rather than have a hack like the author in charge of the air/fuel and timing, we let the maestro whip up a tune for both the NA and boosted combinations. Speaking of combos, our test motor was a 372-inch small block affectionately dubbed the Gladiator 2 by the good folks at Westech Performance.
How did the small block earn the nickname, you ask? The original Gladiator was the go-to small block for literally hundreds of tests and thousands of dyno pulls. It continued to soldier on, and be victorious in every battle, regardless of what we threw at it. This G2 version, offered every bit as much fight, in a much stronger package. Thanks to a Dart SHP stroker short block with a 4.125-inch bore, the Gladiator 2 was sporting forged internals and 372 cubic inches. For this test, the G2 was treated to a Comp Xtreme Energy cam that offered .540/.562 lift split, a 242/248-degree duration split and 110 lsa. Finishing up the G2 was a set of AFR 195 Eliminator heads, and Edelbrock Performer RPM Air Gap intake and FAST dual-synch distributor.
The game plan was an easy one, first we (meaning Mr. Page) would tune the 372 G2 in naturally aspirated trim, then again after the installation of a TorqStorm supercharger. The TorqStorm supercharger was perfect for this type of test, as it allowed easy installation and was sized perfectly for power production near 700 hp. As we expected, Mr. Page had the small block up and running in no time, and whipped up the tune to produce optimum power production. Run on the dyno with 1 ¾-inch dyno headers, the FAST-injected small block produced peak numbers of 501 hp at 6,200 rpm and 473 lb-ft of torque at 4,800 rpm. After scaling the tune for the TorqStorm supercharger, we were rewarded with 681 hp at 6,500 rpm and 601 lb-ft of torque at 5,100 rpm. The blower was pumping out a peak boost reading of 8.3 psi, which we knew was plenty safe thanks to the fuel cooling provided by the 8-injector throttle body. Our thanks to David for taking the time during his visit (for a FAST Seminar) to toss the tune on our small block, and to the guys at FAST for supplying the XFI Sportsman EFI system to Westech for testing.
Graph 1: FAST XFI 372 SBC-Na vs TorqStorm (8.3 psi)
Thanks in no small part to proper tuning of the blow-through FAST EFI throttle body, we were able to realize serious power gains with the supercharger. The charge cooling from the blow-through XFI Sportsman system offered both additional power and safety (from detonation). Unlike a typical blow-through carb application, we were able to dial in idle, part-throttle AND full-throttle air fuel mixtures. Once tuned, the 372-inch small-block stroker produced 501 hp and 473 lb-ft of torque. After installation of the TorqStorm supercharger, the power output jumped to 681 hp and 601 lb-ft of torque at a peak boost pressure of 8.3 psi.