When port fuel injection (PI) first debuted in the mid-1980s, no one knew what to make of it. With no carb or distributor to adjust, it was a steep learning curve for hot rodders and the performance industry alike. Initially it was cut and try, learn on the fly until performance parts became available in the mainstream. Well here we are in 2017 and it's like 1985 all over again. More and more new vehicles—including all Generation V GM "LT" small-blocks, the rumored 2018 Ford Coyote, and a posse of four- and six-cylinder DOHC motors have a new Direct Injection (DI) fuel system that sprays fuel at extremely high fuel pressures directly into the engine's cylinders. Thanks to better fuel atomization and reduced spark-lead requirements, production DI motors can run higher compression ratios on pump gas, yielding big power increases without sacrificing fuel economy or clean-air. DI has already demonstrated its potential in high-end racing venues like IndyCar, but at the Sportsman level we'll need to make big changes to the engine management and fuel-supply systems.
Going with Holley ECUs on the COPOs avoids the need to hack either the GM production or the 2012 COPO MEFI-5 computers." —Robin Lawrence, Holley
When you have super-high fuel flow—5080 percent more than the stock injector—our patented K-DI spray technology makes a really big difference." — Frank LoScrudato
There's not much difference between the cam timing events for a direct-injection cam and a port-injection cam." —Billy Godbold, Comp Cams
Chevrolet's COPO drag racing program is helping to kick-start DI's mainstream development curve. The "COPO" is an "off-highway-only" limited-production analogue of the popular camarot model, running a factory-developed performance crate motor that competes in special NHRA Stock classes. One of the engine options available for the COPO is the LT-based DI crate motor (GM PN 19351766), a 6.2L (376ci) normally-aspirated engine that's said to be the first drag racing DI motor.
One car that's already making waves with the new powerplant is Daren Poole-Adams' 2017 COPO Camaro that's tuned and driven by Holley's Director of EFI Business Development Robin Lawrence. Ever since 2013, GM has used Holley fuel management systems in its COPO cars, so the Camaro also serves as a proof of concept and development mule. What Holley and other DI racing pioneers are learning and implementing is broadly applicable to performance street enthusiasts and weekend warriors, not just hard-core class racers. Let's take a closer look at the car and some of the products that make DI work in a performance application.
A] COPOs come from GM with Holley's outstanding Hi-Ram intake manifold. It won't clear production Camaro hoods, requiring a COPO hood or similar high-rise configuration.
B] User-friendly Holley ECUs have been used by GM in its COPOs since 2013. On the DI car, the main controller mounts in the engine compartment, with the add-on DI controller behind the passenger-side foot-well
C] Driven by a rear camshaft eccentric, the LT4-derived high-pressure DI step-up pump mounts on the rear of the engine valley. It operates at 2,600-plus psi.
D] The high-pressure pump is supplied by a Holley VR1 in-tank lift pump working through this VR-series two-port regulator (PN 12-851). Currently, Lawrence runs 110 psi on the low-side.
E] GM's DI ignition coils are the same as those on port-injected LS7 427 engines. So far, they do the job just fine. Even Lawrence's 34-degree total advance is the same as his prior LS7 PI motor.
F] Stock and Super Stock must run the GM-supplied 90mm COPO throttle-body. It's cable-driven for reliable operation. (Street cars have long used a "drive-by-wire" body.)
G] GM has used the Meziere LS electric water pump on LS COPOs since 2012. Adapters permit using it on the LT block's reclocked lower passages.
H] The huge air inlet duct mates to corresponding cold-air ducts on the front of the high-rise 20162017 COPO hood.
I] DI engines use unique spark plugs. The COPO's AC Professional-series Iridium plugs are pirated from the DI LT4 supercharged Corvette.
J] The LT1/LT4 injectors flow 17 g/sec, enough injector for around 710 hp at 7,8008,000 rpm. Lawrence: "If we gain another 2030 hp, it may need more fuel." Nostrum has high-flow injectors.
K] While GM delivers COPOs with full-length headers, Lawrence uses Blackheart headers made by Holley's in-house Hooker headers brand. They're modified to clear this car's manual steering rack.
Earlier factory computers won't work with DI. You'll need either a production computer out of a DI car, or a DI-compatible aftermarket engine-management system like Holley's. Cars that need to remain emissions compliant will be sticking with the factory DI ECU. GM's extremely sophisticated units have tremendous power and overhead, and are tied-in to many other on-vehicle systems including stability control, antitheft provisions, and (if so equipped) the automatic transmission controller. Tuner programs such as HP Tuners or EFI Live can be used to reprogram the factory computer.
For racers a user-friendly aftermarket management system is a good alternative making it easy to dial-in tweaks between rounds and see the results in real time.
Government emission mandates aside, there is a gray area between staying with an OE unit or going with a Holley. What's the crossover point? Answers Lawrence, "If you have just a 200300hp increase over the stock OE application, the stock processor should work OK if reflashed. I've even seen an OE ECU handle up to 1,200 hp, but it really takes an expert, it's not for the average guy.
Like most aftermarket EFI systems, Holley uses Speed Density-based fuel metering, primarily relying on a MAP (Manifold Air Pressure) sensor plus a TPS (Throttle Position Sensor). It can also operate in Alpha-N (TPS-only) mode. You can enable closed-loop operation with the wideband O sensor.
DI Fuel System
As power increases, so does an engine's fuel needs—so one of the first questions faced by racers was: How much growth headroom does the as-delivered LT DI fuel system offer? And when that point is reached, what's the best strategy for supplying additional fuel? Most parts developed for PI engines can't be used with DI because its fuel system is totally different than any previous gasoline-fueled motor, actually closer to a diesel engine.
Achieving DI's high-pressure is a two-step process: Initially, there's a moderate-pressure in-tank electric "lift pump" that transfers fuel from the tank to the engine, where a step-up fuel pump then raises the pressure to thousands (yes thousands) of psi. On the LT engine family, the high-pressure pump is driven off an eccentric on the rear of the camshaft. The special DI nozzles themselves are very costly and—unlike port-type injectors—are specific to the engine design.
The COPO fuel system is based on parts originally developed for the LT1/LT4 high-performance engines, so if you have, say, a milder Gen 5 DI truck motor, that would be the first step up. But racing stresses the system way beyond even a supercharged LT4. The COPO's LT4 injectors have a 17 grams/second capacity at about an 80-percent duty-cycle. "That's not much room for growth, but it's by design," maintains Lawrence. "DI has such a small window of opportunity. The piston has only a certain position on the compression stroke where you can spray—so the strategy is a small pulse-width, but a large volume within that narrow window, which is why the duty-cycle percentage is so high." Around 710 hp is the theoretical limit with the LT4 injectors, but for those who need more, there are several methods for delivering additional fuel.
Pressure and Pumps
One traditional strategy with port fuel injection is to retain an existing capacity fuel injector but turn up the fuel pressure. DI operating pressure at the fuel rails is typically 180 Bar (about 2,610 psi) stock. According to Lawrence, "You can increase that to 207 Bar (3,000 psi)." Beyond that, the injectors probably won't open. Excessively raising the pressure is no panacea, even on a PI motor: It could lead to an over-rich condition on the bottom-end and adversely affect the spray pattern, problems that are only magnified with finicky DI.
During Holley's development process, it also encountered a high-rpm control issue with the on-engine high-pressure pump. This was mitigated by installing a higher-flow/higher-volume Holley VR1 in-tank pump and inline regulator that collectively increase the DI pump's initial inlet pressure to 110 psi. Inlet-side increases don't automatically increase the DI pump's outlet-side pressure, which needs to be set in the control software—but now the DI pump doesn't have to work as hard to reach the programmed outlet pressure.
Comp Cams' alternative for high-rpm stability is a higher-rate DI pump follower spring. To boost low-end pump volume for more downstairs torque, you can order its cams with larger or multiple eccentric lobes; "It's primarily for boosted or nitrous use," explains Comp Cams' Billy Godbold. "If you are seeing a pressure drop, get more 'throw' on the eccentric."
Lingenfelter Performance is offering a new Gen V (LT) high-pressure pump (PN L710156914) that flows 30-percent more than the GM L86/LT1 pumps and 10-percent more than the LT4. This pump is said to support over 1,100 hp on gasoline (it's also E85-compatible).
A common strategy up to this point has been adding an "auxiliary" set of port-fuel injectors in the intake manifold runners that "turn-on" only as demand warrants. As previously noted, just about any size universal port-injector can be had for a reasonable price. Holley's High-Ram LT intake manifold, standard equipment on the COPO, has cast-in PI nozzle bosses in its runners. Holley's Dominator ECU, the DI add-on auxiliary box, and the new in-tank pump can simultaneously support up to eight direct injectors and eight port injectors. The latter must run in batch-fire mode, but in terms of port-injection at high rpm, that's OK.
The latest development (finally!) is high-capacity DI nozzles from Nostrum. The company has worked with OE manufacturers to develop DI nozzles for specific production engines and models, and is now applying that knowledge to the performance aftermarket. Nostrum uses precision EDM tooling to custom-tailor the nozzle orifices, spray pattern, and spray angles to yield what it calls "kinetic particle breakup injection (K-DI), a patented method of vaporizing the fuel by using the energy in high-speed nozzle-jets to fracture the particles in other jets into much smaller particles. The higher the flow, the more important this technique becomes." Nostrum is also applying this technology to custom-tailored port-injectors.
All this precision isn't cheap: Expect to pay as much as $350$450 per injector. Besides the injectors, end-users get an Excel file with specific injector fuel-flow and drive data tailored for use with various publicly available production- and aftermarket-based engine management tuner programs. At this level, Nostrum says you'll almost certainly need the fuel pump upgrades to keep up with the injectors, but by year-end it plans to offer high-flow fuel pump and injector combo kits. Nostrum K-DI high-flow DI as well as port injectors are available direct from Nostrum's web portal as well as through selected dealers like Lingenfelter.
COPO drag-race motors have a GM-supplied hydraulic-roller cam (PN 19351773: 0.621-inch lift with 1.8:1 rockers, 242/285-degrees duration at 0.050, 105-degree lobe separation angle [LSA], 106-degree intake centerline). This is a "Stock Eliminator" grind. It won't survive long on the street.
So what will? Comp Cams' Godbold says that pretty much the same lobe profiles that work on Gen 3/4 LS small-blocks work on Gen 5 DI engines. Actual part numbers differ because all GM DI production LT motors use AFM (active fuel management) plus an eccentric to drive the fuel pump. (For racing, AFM is disabled.) Presently, many of the DI profiles are considered customs because of the various available fuel-pump eccentric options the end-user can specify when ordering. In some cases, due to the unique DI piston configuration, it's necessary to spread the LSA out by two more degrees from previous LS profiles to gain some additional piston-to-valve clearance (for example, from 116 to 118 degrees for a typical 224/236 degrees at 0.050 DI AFM street cam).
Engine Temperature: DI racing engines seem to be less temperature-sensitive. Lawrence: "My port-injected drag engines would run faster at 100 degrees. The DI engines run consistently from 100 to 160 degrees. That could be a big help for bracket-racing consistency."
A/F Ratios: DI racing engines are less sensitive to near-stoichiometric A/F (air/fuel) ratios. Lawrence: "My port-injected stuff runs best at 13.013.2:1 A/F ratios. With DI, we make good torque and better 60-foot times at 12.512.7:1 ratios, the traditional sweet-spot for racing with carburetors. On DI, this slightly richer ratio doesn't seem to affect power; it makes more torque off the hit, plus it's a little safer; there's a wider tolerance on the fuel."
Spark: DI racing engines don't currently seem to need any spark-output enhancements. Lawrence: "We use the same VP C11 racing fuel with the DI COPO 6.2L engine as we did with the port-injected 427 LS7 in Stock Eliminator. The DI COPO ignition coils are the same as the LS7 ignition coils on the port-injected motor."
Timing: DI racing engine ignition tuning guidelines are not much different than a PI engine. Lawrence: "Whatever worked for you before still works with DI. The ignition curve and timing is tied directly to the chamber design, piston design, and fuel used. Yes the DI chamber and piston design is different; fuel is bounced off the piston dish, a specific target area, but I still run a max advance of 33 degrees. I can tailor the timing to the conditions."
Electrical: DI racing engines, with their high-pressure fuel system including the pumps, injectors, and ECU injector drivers places higher demands on the electrical supply system than most racers are used to seeing. Lawrence says the better the charging system, the better the car runs. "I use a 160-amp MSD alternator and still put the car on the battery charger between rounds." You can't have too much alternator: It will only put out its rated current when it needs to.
While it's true that the performance industry is in the midst of a steep learning curve, just three years after the first LT DI engines were introduced in 2014, it looks like the performance parts availability issues are well under way to resolution. We expect big announcements at this fall's trade shows. DI is here to stay, and we need to get with the program (pun intended).