Photography by the FSC Staff and Courtesy of the Manufacturers
Prompted by ever-more-stringent emission and fuel economy regulations, car manufacturers are switching to gasoline direct injection power plants in everything from four-cylinder econobox transportation appliances to the “crossover” vehicles that are the minivans of the new millenium, and even in their performance flagships like the Ford Mustang and Chevrolet’s Camaro and Corvette. Predictably, this has been greeted as dire news by some enthusiasts, who see it as an insurmountable obstacle to performance modification. Direct injection will be the death of hot rodding a factory engine, they claim; too expensive to upgrade, too hard to tune, too restrictive compared to what they’re used to working with.
If that sounds like a familiar fear, you’re probably old enough to remember the switch from factory carbureted engines to electronic fuel injection at the tail end of the 1980s, which was also more or less forced upon Detroit by emissions and fuel economy standards that carburetors couldn’t possibly meet. As it turned out, the switch to factory EFI was one of the best things that ever happened to OEM performance, giving us a 30 year run of cars that were more powerful, more reliable, and easier to modify than anything you could previously buy off the showroom floor.
While DI does undoubtedly bring new challenges, it also offers new opportunities as well, and we’ve gathered a few well-known builders and tuners with experience making big horsepower with direct injection engine platforms in order to throw some light into the shadows cast by the fear of this change in technology.
Defining the Problem
First, let’s briefly look at what direct injection is, and how it’s being implemented by the two biggest players in domestic V8 performance, Ford and GM. In a conventional electronic fuel injection system, injectors working at relatively low pressure (typically 60 or so pounds per square inch) introduce fuel into the intake tract just before the intake valve. A gasoline direct injection system moves the injector location to the cylinder head, where it delivers fuel directly to the combustion chamber at very high pressure; 3,000 PSI, or thereabouts.
That high pressure is a necessity for a DI system, because the injectors have to work against the dynamic pressure of a cylinder that’s under compression instead of just spraying a mist into the passing breeze like port injection. The payoff for the additional complexity of requiring a high pressure pump and injectors is manifold; Because the fuel can be delivered in a shorter amount of time and is more precisely atomized, through clever tuning the engine can tolerate higher compression without needing higher octane fuel, and deliver more power than a similar port injection design while still having lower tailpipe emissions and better fuel economy. “I think the biggest misconception people have is that it doesn’t help make more efficient power and that it is only for emissions,” says Jon Lund Jr., proprietor of Lund Racing.
While both Ford and GM have implemented direct injection on their newest performance V-8 engines, they’ve taken different paths. For the 2018-up Coyote, Ford came straight out of the gate with a fuel system that uses both direct and port injection, while GM relies on a DI-only strategy for the naturally-aspirated Gen V LT1 and supercharged LT4, only adding supplemental port injection on the top-of-the-line 755-horsepower LT5.
“The big news on the 2018 Coyote was, of course, that on top of direct injection, you had factory port injection as well,” explains renowned Mustang guru Ken Bjonnes of Palm Beach Dyno. “It starts off when it’s cold, 100 percent on the DI, likely for emissions reasons. It then blends between the DI and port injection depending on load once the engine is warmed up, and it’s going to try to run more off the DI in the mid range and more off the port injection down low. Obviously we change all that once we start to modify things, and it gets pretty extreme once you get into the thousand horsepower range.”
“The OEM tuning strategy has a Port Injection and Direct Injection blend logic,” Lund elaborates. “This is something relatively new for the Ford DI platforms as they did not have both PI and DI in previously year models on the Ecoboost platforms. There is a blend table based on calculated engine load vs RPM that has a blend percentage between PI and DI. At WOT on the 2018 GT, the blend is 90% DI and 10% PI.”
On the GM side, things are a little more challenging, because unless you have the deep pockets to afford a factory LT5 engine, you are faced with the choice of running pure DI or adding a supplemental aftermarket port injection setup. Like any fuel injection system, the capacity of the injectors and fuel pump set the ultimate limit for horsepower; there are some shops that have made 1,000-plus on a DI-only LT, but according to Doug Cook of Motion Raceworks, “I don’t think it’s a very safe way to run when you push it that hard. I see people breaking pistons, breaking heads, all kinds of crazy stuff. And you know that piston technology didn’t go backwards; everything on these engines is way better, but they’re doing things like dropping valve seats out, things that are really indicating detonation. The chamber just gets too hot, and there is no cooling on the back of the intake valve so it gets really hot. Now, I will probably get proven wrong here in a year or two, but I don’t think you are going to see a lot of those combos live very long with direct injection only. They can absolutely deliver enough fuel – I just don’t think it’s a reliable way to make that power.”
Been There, Done That
Cook knows a thing or two about the GM Gen V platform; Motion Raceworks can lay claim to the first Gen V LT in the sevens with their 1972 Nova test mule. “The Nova is a 388 cubic inch stock LT4 block with CID as-cast heads and twin 6766 Precision turbos,” he explains. “It has a stock crank, Carrillo billet I-beam rods and CP pistons. We built that car to find the limits of things, because nobody was really pushing that engine platform too hard. We built that last year, and took a car with a chassis that was already working well and put that engine in it.” While the Nova relies on a supplemental port injection EFI setup, it still retains a factory-style computer and other DI hardware as well.
“The strategy we used on the Nova is that if you know going in that you are putting on port injection, there’s no reason to push the DI super-hard. You’re not really proving anything,” Cook asserts. “We used all LT4 (fuel system) stuff because I don’t really trust the aftermarket parts. The tolerances have to be so precise. And we only ran it to about 80-percent capacity, because like I said, I don’t really see the point of pushing the DI too hard because we have the capacity with the port injection to do whatever we need to do.”
While the 2018-up Coyote offers both DI and PI straight from the factory, Bjonnes cautions that it will need some attention if you’re in search of big horsepower. “Ford made it a lot easier on us than the GM guys because we can lean on the factory port injection,” he says, adding, ”What the entire stock system can provide depends on the lift pump, plus the port injector is really small. So what we have done so far is all port injection upgrades. Our cars all run the stock DI injectors and high pressure pump, and we upgrade to a multi-pump setup in the tank and supply the extra fuel for the upgraded port injectors that way. Now that we have a handle on that, my next step will be to upgrade the high pressure pump from Xtreme-DI on one of these cars so we can run more DI than we have been.”
Adding forced induction to a DI engine will pose different fueling and tuning challenges, depending on whether you’re looking at Ford or GM, and how hard you intend to push things. For Bowtie builds, as Cook mentioned there is already a factory-engineered pure DI solution in the form of injectors and high-pressure pumps designed for the LT4. Rated to deliver warranty-proof levels of reliability at 9.4 pounds of boost and 650 horsepower, an LT4 setup has a bit more in reserve, but for the LT5’s 14 PSI and 755 horses, GM added supplemental port injection, so tread carefully when pushing past factory power and boost levels without it.
While adding a port injection system to a Gen V LT does increase complexity and cost, it has other benefits that are well-suited to a track car that’s daily-driven, too. Cook explains, “One of the really cool things we can do is use a bolt-in fuel cell for the port injection, then fill it with C16 and run pump gas in the regular tank. That’s great for a guy who is going to the track on weekends – when he gets to the track he can turn on the second pump and let ‘er eat.”
For the Coyote, Lund cautions, “So far I’ve seen the stock fuel system down to OEM PI injectors start to struggle around 6-7 pounds of boost at 7,200 RPM. That can dictate different horsepower levels based on power adder and ignition timing, but on pump gas with a supercharger that’s around 600 rear wheel horsepower. A turbo setup would make a bit more depending on efficiency.”
His recipe for a high-horsepower foundation is the product of extensive research and development. Lund states, “The fuel system upgrades mostly depend on fuel type. Non-ethanol obviously doesn’t require as much volume, so we can get away with running 1000cc injectors on the PI side for overhead and a fuel pump voltage booster on the lift pump. I’ve not really pushed that setup hard on non-ethanol fuel, but I’ve seen 800 rwhp with VP MS109 and the lift pump pressure still had some head room.”
Switching to an ethanol blend does a lot of good things for a forced induction engine in terms of charge cooling and added octane, but its lower energy content compared to gas puts a lot more stress on the fuel delivery components. “That same setup on E85 has issues keeping up via the lift pump,” Lund explains. “With a 22V booster on the lift pump we were seeing fuel pressure drop to 30 PSI, and that really starts to negatively affect the pressure going to the high pressure fuel pump. I don’t really like seeing the pressure drop that low feeding the big pump. We saw HP rail pressure drop off when that happened, and we ran into issues [leaning out] around 800 RWHP.”
“We added a Deatschwerks 400 LPH pump with the 22V booster, and the fuel pressure holds better, but it’s not the best solution,” he admits. “Long term, we like to see a return-style fuel system used that has stronger pump volume and uses dual regulators to maintain a constant pressure on the DI pump and a variable pressure on the PI injectors. This is what is being used in the 1000+ RWHP twin turbo 2018 you’ve seen us tuning that was the first to the 8 second ET barrier. We modify the blend in the calibration to depend less on the DI and more on PI.”
Same Same, But Different
The good news, then, is that while there is a learning curve to these new DI engines, they still respond to the same tuning fundamentals we’ve practiced all along. “We’ve made 900-plus [on a 2018 Coyote] with a Whipple, with a ProCharger, and with a Paxton. It’s the most flexible platform you could ask for because it has every trick in the book,” says Bjonnes. “You have a 10-speed transmission, dual fuel system, the same knock sensors and wideband oxygen sensors we’ve had since the beginning of the Coyote… I mean, I can’t think of anything else you could add from the factory that would be more cool stuff.”
“On the cars we are tuning now, they are running between 30 and 60 percent DI most of the time, and they run like stock.” he adds. “It’s unbelievable how well they drive with this kind of power, and you have to remember that we are doing all this with stock transmissions and stock converters. No high stall – they almost don’t really need it, because the 10 speed has such a wide range of ratios. It’s been a big equalizer for the centrifugal cars. They used to have to be perfect to keep up with all the turbo and twin screw cars. But we’ve done the most basic Vortech you can get, on the most stock GT you can do, and on 93 octane it went 138 miles per hour in the quarter mile. That’s with no converter at all. Put one in, and you have a nine second, 93 octane car. That just didn’t happen prior to the 2018. It really keeps the cost down.”
On the GM side, Cook is working hard to prove that his success with the Nova wasn’t a fluke – their current project is a 6th Gen Camaro intended to test and showcase what they can do with a fully streetable boosted LT. “We’re hoping to have the fastest 6th gen in the world when we’re done with this, but we are really just using it as a development platform for our own product line, so we are trying to find all the issues that our customers will run into,” he explains. “We went really fast with that Nova, but everybody threw their hands up and said, “well, it’s a race car!” so we figured we would just do it again with a more streetable car with air conditioning and ABS.”
The Camaro will feature a stock LT block with Precision mirror image twin 64mm Gen 2 turbos, backed by a factory 8-speed automatic. Per Cook, “It’s all just going to be a learning experience for us. We figure we will be a little bit ahead of the curve in terms of what we can do for our customers that way. The whole point of the Nova and the Camaro is that I am not trying to keep this information to myself. I’m happy to share, because I think it’s good for our company overall for people to know.”
Mustang tuner Lund agrees, concluding, “I’m after helping educate our customer base with real world testing results of different DI parts so they can understand better what the benefits are. This is also to help us learn more about it since we’re constantly learning about it.”
RPD was introduced to Xtreme DI’s Uwe Ostmann at the 2018 NMRA/NMCA Super Bowl race where he was hellping tune John Urist’s newly Bosch EFI converted Street Outlaw Mustang. Urist looked to the Bosch Motorsport EFI system as it is a direct relative to the late-model Mustang ECM. By becoming more experienced with it while using it in a motorsports environment, he hopes to learn more about the OEM side of things and direct injection in an effort to better serve his Hellion Turbo customers. With that, he turned to Ostmann and Xtreme DI for help.
XDI’s founder Ostmann staerted working for Bosch in 2001, developing diesel high-pressure nozzles and facing the challenges of tuning a common-rail-based, high-pressure fuel system. He was later put in charge of leading the Audi Le Mans LMP1 project for four years including fuel system and controls development and developing several key technologies at Bosch Motorsport in Germany. In July of 2012, Ostmann was sent to Bosch Motorsport USA where he took over the fuel system development of all OEM race projects based on GDI systems, including the Corvette C7.R and the Ford Daytona Prototype 3.5 EcoBoost among other notable projects. He also developed advanced combustion analysis systems and custom fuel systems and controls for several research projects—all of the above purely with high-pressure fuel systems up to 500bar / 7250psi.
This very impressive resume in direct injection technology and development let Ostmann to quit Bosch Motorsport in 2014 and create his own business as the first and only Bosch Motorsport Dealer and aftermarket supplier in the world with focus on high pressure GDI race projects. Since then XDI has worked on several race programs, on wheels and on water, endurance, drift and drag and again on smaller research programs.
Two years later, XDI released the first custom made high-performance, high-pressure fuel pump (XDI-HPFP35) for the 1st generation F150 3.5 EcoBoost GDI engine. This pump delivers up to +30 percent fuel volume and +33 percent fuel pressure than the OEM fuel pump, which for the first time allowed running straight E85 without any kind of supplemental fueling.
Since then, XDI has created a product line of more than 30 variants of HPFPs for almost all GDI engines in the world market with the latest releases being the XDI-HPFP60 for Ford Raptor (+60 percent volume / +25 percent pressure), the XDI-HPFP45 for 2018 Ford Mustang / F150 (+45 percent volume / +25 percent pressure) and the XDI / Katech XFP3500 belt-driven high pressure fuel pump for Chevy LT1/LT4, which pretty much doubles the flow capability of the DI high-pressure pump system to allow for up to 2000 hp from 3500psi fueling.
“The biggest benefit of this kind of fueling is the much better vaporization of the fuel (down to 5micron droplet size), which leads to a much faster and cleaner burn and the better control and response of the combustion through injection directly into the combustion chamber (no wall wetting delays etc),” Ostmann explained.
“All these upgrades on the high-pressure side mostly require an upgraded low side as well. We have worked with several brands and types of low-side upgrades and quickly came to the conclusion that we need to offer our own range. There are some things on the low side that you can do very well or awfully wrong in a direct-injection environment. We want to offer complete plug and play kits that are individually refined to maximize overall system performance.”