Is the carburetor dead and gone?

Not by a long shot, but that doesn’t mean we haven’t come a long way with EFI. Sure, carburetors have been used to provide air and fuel for millions of vehicles for decades, but there is obviously a reason that all the OEMs eventually made the switch to modern fuel injection.

While carburetors perform well when paired with a specific motor, changes made to the motor can sometimes play havoc with the metering. This is especially the case when you toss boost into the equation. Although blow-through carbs have been made to work well, they almost always work well at cruise, part throttle, or WOT—but rarely do they work perfectly for the myriad of combinations of load, rpm, and boost.

This is where electronic fuel injection (EFI) shines.

The key to success is that precise fuel metering from the EFI system is not dependent 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, load, or boost.

fast throttle body efi resting atop a v8 engine
What was the key to successfully boosting our small block? This XFI Sportsman ECU and throttle body from FAST. (Image/Richard Holdener)

The Value of Charge Cooling

To take nothing away from the carb contingent, the one area carburetion offered an advantage over fuel injection was in charge cooling. On a typical carburetor, the fuel delivered by the carb has always been a function of the air being pulled through the venturis in relation to jetting. The introduction of the fuel supplied 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 the fuel injection system introduces the fuel into the air stream from a throttle body located on top of the intake manifold, similar to 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, as extra security against harmful detonation.

A FAST XFI & EZ-EFI Supercharging Combo

Not surprisingly, the folks at FAST obviously recognized the benefits and limitations of a blow-through carburetor, and so, 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 horsepower.

For ease on installation, 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 a total of 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 1-bar 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 one important sensor not part of the throttle body was the ECT, or engine coolant temp.

Meet the “Gladiator 2” Test Engine

For this test, we elected to install the ECT in the intake manifold of our small block Chevy 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.

Naturally we needed a suitable combo to properly test the merits of the blow-through FAST EFI system, and the 372ci small block affectionately dubbed the Gladiator 2 by the good folks at Westech Performance was the perfect choice.

How did the Stroker 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 equipped with a Comp Xtreme Energy cam that offered 0.540/0.562 lift split, a 242/248 degree duration split, and 110 degree LSA.

Finishing up the G2 was a set of free-flowing, CNC-ported AFR 195 Eliminator heads, Edelbrock Performer RPM Air Gap intake, and FAST dual-synch distributor.

Testing the System with a TorqStorm Supercharger

The game plan was an easy one, first we (meaning David 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 1-3/4 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.

engine dyno chart
The only thing better than a supercharged small block is a properly tuned supercharged small block. Thanks to proper tuning and charge cooling offered by the blow-through FAST EFI throttle body, we were able to safely 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) on this non-intercooled combo. 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 372ci 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. (Dyno Chart/Richard Holdener)
fast throttle body efi module
The 4150 throttle body offered conventional Holley-style mounting and linkage along with more than enough flow to support the power needs of our small block, even with the supercharger. (Image/Richard Holdener)
jet ports inside a fast throttle body efi module
This version of the FAST throttle body featured eight injectors with enough flow to support up to 1,200 NA hp. (Image/Richard Holdener)
automotive electrical connector
The throttle body also featured a dedicated map sensor. We upgraded to a 2-bar map sensor for our supercharged test. (Image/Richard Holdener)
side view of connectors on a throttle body efi module
The throttle position sensor (TPS) was attached to the linkage and located on the side of the throttle body. (Image/Richard Holdener)
side view of a throttle body efi module
FAST found a way to integrate all of the important sensors right into the throttle body, including the Inlet Air temp (IAT) sensor. (Image/Richard Holdener)
fast throttle body efi & engine management module
The throttle body was combined with a FAST XFI Sportsman ECU to allow us to dial in the air/fuel mixture on both the NA and supercharged configurations. (Image/Richard Holdener)
distributor installed on a v8 engine
To make things easy, the small block was also sporting a dual-synch distributor. The dual-synch distributor came pre-phased specifically for use on EFI applications. (Image/Richard Holdener)
fast ignition box and coil mounted to a panel
To ensure plenty of spark energy for our boosted small block, we enlisted the aide of a FAST E6 ignition amplifier and E92 ignition coil. (Image/Richard Holdener)
fitting sensor onto an intake manifold
The one sensor not positioned in the throttle body was the Engine Coolant Temperature (ECT). We installed this in the Edelbrock intake manifold. (Image/Richard Holdener)
v8 engine on an engine dyno
Run on the dyno in naturally aspirated trim with the FAST XFI Sportsman ECU, the 372ci SHP small block (with AFR heads, COMP hydraulic roller cam, and Edelbrock RPM Air gap intake) produced 501 hp at 6,200 rpm and 473 lb.-ft. of torque at 4,800 rpm. (Image/Richard Holdener)
centrifugal supercharger on an engine dyno
After running our baseline, we installed the mounting bracket and TorqStorm supercharger using the supplied hardware. (Image/Richard Holdener)
front view of a supercharged engine on a dyno
We then installed the 7.75 inch (8 rib) crank pulley and adjustable belt tensioner to drive the supercharger. (Image/Richard Holdener)
blow through supercharger on a throttle body efi
We configured the discharge tube from the supercharger to the carb bonnet with a blow-off valve (BOV). The BOV was designed to eliminate the pressure build up that occurs during cruise conditions, and the pressure spikes that accompany high-rpm and boost, lift-throttle situations (Image/Richard Holdener)
blow-thru boosted throttle body efi
Boost was fed from the supercharger to the FAST throttle body through this CSU carb bonnet. (Image/Richard Holdener)
venturi mouth on a centrifugal supercharger
To keep the heated air from the headers out of the supercharger, we enlisted the aide of a 90 degree elbow and radiused air entry. (Image/Richard Holdener)
blow-thru boosted engine on a dyno
Tuned to perfection and running 8.3 psi of boost, the supercharged 372 Stroker produced 681 at 6,500 rpm and 601 lb.-ft. of torque at 5,100 rpm. (Image/Richard Holdener)

Keywords
FAST, FAST XFI Sportsman Blow-Through Supercharger EFI System
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Author: Richard Holdener

Richard Holdener is a technical editor with over 25 years of hands-on experience in the automotive industry. He's authored several books on performance engine building and written numerous articles for publications like Hot Rod, Car Craft, Super Chevy, Power & Performance, GM High Tech, and many others.