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BODIES BY JIM GIBSON The last carbureted passenger vehicles were manufactured almost 25 years ago, yet many performance engine builders still rely on . That’s changing, in part due to the availability of many injection options.

uilders of custom street rods and “resto mod” In simple terms, we have either throttle body injection vehicles are generally divided into two camps (TBI), where the are mounted in the throttle body with regard to the engine’s fuel system. They assembly, providing a central point air/fuel delivery atop the either want to retain an old school manifold, or multipoint fuel injection (MPFI), where approach or upgrade to electronic fuel injec- one fuel is dedicated per , with each injector tion (EFI). Since an OE-type fuel injection providing fuel closer to each , at the system may be somewhat limited in terms of performance output end of each intake runner. Band definitely won’t cut it in terms of appearance, builders Aftermarket performance throttle bodies are current- are always looking for aftermarket options. ly available in a variety of configurations, to replace an Today’s offerings allow a choice between a system that fea- existing throttle body on an OE injection system tures a central plenum with a single “dry” throttle body (OE (mounted to a stock or aftermarket manifold plenum) or design approach but with added performance and custom ap- a throttle body that mounts to a 4-barrel-style intake pearance) or one that utilizes a carburetor-style intake mani- manifold. A throttle body that incorporates one or more fold that accepts either a dry throttle body and multipoint in- fuel injectors provides both fuel and air and can be re- jectors installed in the runners, or a “wet” EFI throttle body ferred to as a wet throttle body. A throttle body that with built-in injectors to somewhat mimic a carb setup. serves only to regulate intake air is usually referred to as a dry throttle body. A variety of styles and sizes of dry throttle bodies are de- signed to mount in the same manner as a 4-barrel carbure- tor and incorporate one fuel injector per cylinder, with the injectors mounted in injector bung locations on the intake manifold intake runners. This approach provides an option of a carburetor appearance with the advantage of electroni- cally controlled fuel injection. In addition to single-carb intake manifolds that accept a single throttle body, multiple-injector setups are also avail- able with multiple throttle bodies, providing the appearance of a multiple “downdraft” carburetor theme, with injector rails located at the center of the engine valley, in-between the two rows of velocity-stack-equipped throttle bodies. Photo courtesy Edelbrock courtesy Photo From a performance perspective, the options are varied to This photo shows Edelbrock’s hi-rise Pro Flo EFI system with suit individual taste. larger-than-sto ck throttle body and increased plenum. MPFI systems can be either group (bank) fired (with a continued on page 52

50 April 2014 cates a large-diameter single-throat the required amount of air can pass. throttle body offset toward the front of You can’t compare cfm ratings on an the engine. equal basis between carburetors and Another style features a series of EFI throttle bodies. Just because a throttle bodies with individual velocity throttle body is rated at 1375 cfm does stacks, resembling an exotic downdraft not mean that the engine will be forced multiple-carb setup. The FAST/In- to accept this volume of air; the throttle glese/Weber setup is a good example of body simply makes this amount of air this, with inboard fuel rails and injec- available if the engine needs it. The en- tors that are nearly hidden from view gine will draw only the amount of air it (looks very akin to an exotic “old needs. Fuel delivery is handled as a Photo: Jim Gibson Photo: school” downdraft Weber setup, but separate, controlled issue. FAST offers a composite low-profile intake and dry throttle body for direct with EFI efficiency and tunability). An replacement of OE systems. array of variants exists, allowing your Fuel Rails customer to obtain not only the perfor- Depending on the design of the sys- batch of four being triggered at the mance that he desires, but the appear- tem, external fuel rails may or may same time), or sequential (SFI), where ance that best suits his project as well. not be featured. If the system uses each injector is triggered exactly timed multipoint injection, with one injec- as needed, at a precise angle Throttle Body tor dedicated to each cylinder, each per cylinder, near TDC overlap with One aspect that will undoubtedly con- bank of the engine will feature a fuel the intake valve opening. SFI is a more fuse many folks is the cfm rating of the rail that delivers fuel to an injector complex system, but it’s more precise EFI throttle body. As you begin to re- bank (on a V-type engine, one rail per and—depending on the controller sys- search the various throttle bodies and bank, with the rails secured to the in- tem—injector phasing can be custom EFI systems, you begin to notice that take manifold). A combination throt- programmed for fine-tuning. their cfm ratings are huge, compared to tle body unit that features built-in in- In terms of today’s performance af- those of carburetors. Typically, perfor- jectors may feature a short fuel rail termarket offerings, a wet-style throttle mance aftermarket EFI throttle bodies located on each side of the throttle body type injection setup can offer will be rated at 1000, 1200, 1375 and body (from front bowl to rear bowl). both simplicity and disguise. Two ex- even 2000 cfm. Looking at these num- EFI systems operate under much amples that readily come to mind in- bers with a carburetor mentality, these higher line pressure than a carburet- clude Holley’s new Terminator, which ratings will at first seem way off the ed system—generally in the 40- to looks like a dry performance billet charts. Here’s what you need to under- 60-psi range, as compared to 6 to 8 throttle body and includes an external stand: While a carburetor moves both psi for carburetion. Wherever a flexi- controller, and Professional Products’ fuel and air (and must be sized accord- ble hose or hose clamp is to be in- Powerjection III, which in outward ap- ing to engine size and ), an stalled, make sure it’s rated for use pearance resembles a dual-feed 4-bar- EFI throttle body moves only air, es- with an injection system. Anywhere a rel carburetor. Actually, this is a throttle sentially serving as an air door. Fuel de- long run is needed (tank to to body that hides four injectors (two in livery is controlled by the electronically engine area), a steel fuel line that each bowl), with the ECU built onto operated injectors. EFI throttle bodies the body itself, so there’s no need for an are sized larger (in terms of available external ECU. airflow) to provide greater latitude for At the other end of the spectrum, a range of air delivery requirements. multipoint injection systems are avail- The engine will pull only as much air able that feature a throttle body (strictly through the throttle body as it needs. for air intake/control) mounted atop an If you place a 1000-cfm throttle body intake manifold that features dedicated on a mild small-block engine, the en- injector bungs at the end of the runners gine may need to pull only, say, 600 (one injector per cylinder). Depending cfm. A wild big-block 500-CID with

on the system, the intake manifold (sin- healthy heads and a wild may re- Speed Retrotek courtesy Photo gle-plane or dual-plane) accepts a top- quire, say, 1000 cfm. The same size This is an example of a dry throttle mounted four- throttle body that throttle body can handle this wide body that has been mounted to a resembles a 4-barrel carb (minus the range because, again, the throttle body carb-style intake manifold fitted with bowls); or a ram-type manifold that lo- serves only as a door through which injectors and feed rails.

52 April 2014 your engine’s anticipated horsepower and the engine’s BSFC (Brake Spe- cific Fuel Consumption) number “ef- ficiency,” and the amount of fuel the engine will consume, divided by its power output—how many pounds of fuel will be used per hp produced in an hour (see the box on page 54). Injector size is approached in a somewhat similar manner to that of selecting a carburetor size; bigger is- FAST courtesy Photo Photo courtesy Professional Products Professional courtesy Photo n’t always better. If too large an injec- Wet throttle bodies can be mounted Performance aftermarket throttle tor is selected, you’ll waste fuel and onto conventional 4-barrel intake bodies that offer greater intake air manifolds with no injector ports, volume are available as direct re- hurt throttle response. Low-imped- since the throttle body has built-in placements for OE intake manifolds. ance injectors are available up to 160 injectors and short fuel rails. lbs./hr., so don’t simply jump to a big- meets SAE J526 standards should be ger injector because it sounds like a in different lengths, so between lower used. good idea. Remember, injectors alone O-ring diameter and overall length don’t make power; you must tune the differences, you can really get con- Fuel Injectors system with the most efficient sized fused if you’re piecing an MPFI sys- Fuel injectors are electronically con- injector for the application. Aftermar- tem together without knowing what trolled valves that spray fuel into the ket performance systems will provide you’re doing. That’s why it’s best to combustion mix on demand. the appropriate size injector for your simply purchase a complete system, Low impedance vs. high imped- specific application. Since injector where the injectors are already ance. High-impedance injectors range will vary depending on the an- matched to fit your intake manifold, (about 10 to 16 ohms) and low-im- ticipated horsepower, it’s important to fuel rail and harness setup. pedance injectors (about 1.5 to 4 select the proper system part number Aftermarket performance systems ohms) are available. Which type do to match your needs (or contact the require a fuel injection controller, or you need? Generally, if you’re run- manufacturer for a recommenda- ECU, a and ning an OEM ECU (computer), you tion). an . Depending on the need high-impedance injectors. Commonly used fuel injectors in- system, sensor requirements may in- These feature a somewhat slower re- clude the EV1 and EV6 body styles. clude a knock sensor, intake air tem- sponse time. If you’re running a per- The EV1 is the so-called fat style, of- perature sensor, MAP sensor and formance aftermarket ECU, you ten generically called the Ford style. coolant temperature sensor. If the en- need low-impedance injectors, which The EV6 features a skinnier profile gine was originally equipped with a react quicker. If you run low-imped- and a different connector (such as the fuel injection system, the ignition sys- ance injectors with an OEM comput- EV6 style injectors used in newer tem will already be controlled by an er, you run the risk if damaging the Fords and GM LS engines). The ECM and will likely incorporate cam ECU. thinner-profile EV6 also is available and position sensors. If the en- Most injectors that feature high gine was originally equipped with a flow rates are of the low-impedance , EFI systems are available type. Low-impedance injectors offer that take this into account, providing a faster opening response time and fuel injector control. Instead of piec- generate less heat; they’re generally ing a system together, it’s best to pur- preferred for aftermarket perfor- chase a coordinated system that will mance systems, although this can include the throttle body along with vary depending on the specific after- all necessary control accessories. market system.

Choosing injector size. If you FAST courtesy Photo Fuel Pressure buy a complete system kit, the injec- EFI systems require high fuel pres- Dry throttle bodies designed to mount tors are likely included. If you need atop 4-barrel-style manifolds are avail- sure and low volume. The high pres- to determine your own injector re- able in cast and machined billet alu- sure is maintained in the lines and quirements, this will be based on minum, in an array of anodized colors. fuel rails. When the injector(s) are

April 2014 53 signed for high-pressure applications. Fuel Return Line Any EFI system requires a return line. Use only an approved steel line, not an existing vapor canister line. The return line should enter the at the filler neck (below the flap- per valve, if so equipped) or at the sending unit flange. Use a return line Photo courtesy Holley courtesy Photo 3 size of at least /8 in. I.D. (same I.D. This is Holley’s new Terminator wet- as a –6 AN tube). Co. Motor Ford courtesy Photo style throttle body. Note the short fuel One convenient method of con- An example of a small-block Ford en- rail and base-installed injectors. Wet- necting the return line to the tank is gine with distributor ignition, formerly style performance throttle bodies al- fitted with a 4-barrel carb but low a performance enthusiast to easily with an easy-to-install kit that fea- switched over to a dry throttle body switch to EFI without the need to install tures a 2-in. O.D. tube fitted with a and multipoint injection. 3 a special intake manifold. /8-in. I.D. nipple inlet tube, a pair of buna connection hoses and clamps. system. For example, according to 3 signaled to open, the constant pres- Simply remove a 2 /4-in. length of the FAST, rotor phase is an often over- sure is already there to be dispersed. filler neck hose and splice this looked factor when you’re trying to System vary. In general, the adapter tube in place. The return line obtain proper operation of an after- 3 operating pressure for typical applica- then connects to the /8-in. I.D. nipple market EFI system’s ECM. To pre- tions will likely run in the 30- to 90- tube. If you decide to drill and weld a vent crossfire, it’s important to phase psi range (some systems, again, de- bung or fitting to the tank in order to the rotor (in a distributor-equipped pending on the application, may run accommodate a return line, proper system). This simply means aligning as little as 19- to 24-lb. injectors). A safety precautions must be followed. the rotor with the distributor cap ter- special EFI fuel pressure regulator is If you’re not certain of the proper minal during spark. Though not all also required, as well as a high-pres- method that should be used, the tank will permit independent sure in-line . EFI also re- should be removed and serviced by a rotor phasing, most applications will quires a fuel return line, which may qualified fuel tank specialist. permit the distributor to be rotated to or may not be included in your spe- achieve proper rotor phasing. If the cific kit. Again, it’s best to buy a com- Rotor Phase crank sensor is in the distributor, plete system. For distributor-equipped engines that turning the distributor will require a Note: The fuel filters used must be are outfitted with EFI, rotor phase is change in the crank index off- high-pressure rated (100 psi burst critical in any distributor-type ignition set/crank reference angle (tuned via strength minimum). Don’t use just system, but it’s even more of a con- the program control system, depend- any in-line filter; make sure it’s de- cern with an electronically controlled ing on the system at hand). The most foolproof way to confirm proper rotor phasing is to drill a hole GENERIC RULE OF THUMB FOR BSFC in the top of a spare distributor cap, Naturally aspirated engines: .4 to .5 between the number one terminal Engines with nitrous injection: .5 to .6 and the coil terminal. When the en- (turbo or ): .6 to .7 gine is running and a timing light is connected to the number one spark For engines running methanol, double the BSFC number. plug wire, the timing light can be used to observe the position of the Injector size = engine hp x BSFC ÷ number of cylinders x .8 rotor during ignition. Example: For a 500-hp V8 with high compression, 500 hp x .50 ÷ 8 Fuel injection offers performance x .8 = 39 lbs. engine builders a wide range of op- Theoretically, this application calls for a 39-lb. injector. This is tions, from mild to wild. Unless nos- merely a starting point; depending on the system and as the talgia is your thing, it’s no longer nec- result of tuning, a “larger” injector may be required. essary to rely on big carburetors to make solid horsepower and torque improvements.

54 April 2014