DIRECT INJECTION. The name in and of itself seems daunting to even those of us who played with Electronic Fuel Injection game for years.
One relatively unknown that I have found with the LT1 world (lets face it, theyre all unknown as the whole platform is in nothing but an aftermarket beta form throughout) is the fuel system.
Before I touch on what WE did with our Project Nova, I will speak on some of the basics. Keep in mind, we will not get into fueling strategies in this blog, that will be its own blog. This space will be reserved for components themselves.
Our first blog went over very well. To preface again, I am in no way the worlds absolute expert. However, I have learned much in my last year + of journey in research, development, and beginning to run this new platform, and I feel it a waste not to share.
Before I go any further, I will write this assuming many of the folks reading do not have a full grasp on what direct injection is. Direct injection is a form of injection where fuel is highly pressurized fuel (anywhere from 1500 to 2500 psi and much higher in some applications) and is sprayed directly into the combustion chamber, you read that right, not into the port, but into the chamber. Basically it is a port right across from the spark plug. The reason for this is purely for Emissions to be honest, Direct Injection increases the thermal efficiency of the engine, and more of the gas is burned, and better utilized thereby making more power with less waste (in theory). There is tons of science that goes into all of this, much of it way beyond my knowledge or understanding ability, however, there are some very interesting changes that have to be made to accomodate Direct Injection. First noticable change if you are around one of these engines is the piston design (see picture below). Gen V pistons are specially designed to optimize th fuel burn. These motors do NOT take a standard style piston, infact, much of the magic that happens in these engines happens due to and on the piston itself.
One of the largest downfalls of the Gen V and LT1 engine in general are the lack of aftermarket fuel system parts available. While most camshafts come with an optional increased fuel lobe, many of today's high horsepower boosted engines (Gen V versions anyways) will succomb to the lack of fuel pump and injector capabilities on the market.
At the 2016 PRI show in Indy, I spent nearly the entire time visiting with vendors, developers, and speaking with anyone who would give me a few minutes about possibilities and future plans for big HP fuel capabilities on then Gen V platform. There was an overwhelming response of NO there is nothing coming down the pipeline from all corners.
I will mention there are a few companies claiming they have pumps modified to increase flow by xx percent, or an injector that flows 10-20% higher than the LT4, however, knowing what I know, these things unbiasedly scare me as they are merely modified versions are what currently exist, with about 1/100 or less of the engineering time behind them that the stock components take.
There is almost NO ROOM for failure or inaccuracy on DI engines. The tuning window that gives much forgiveness on an EFI combo is almost gone completely when you talk about firing DI, as the fueling happens between combustion events. I also have learned that the tooling costs for pumps and injectors is so high it is almost cost prohibitive even with an aftermarket begging. There is a large disparity in ideals between major manufacturers, and enthusiasts under the understanding of we need to increase pressure to make more power. The problem becomes if this isn't done in a fashion that is setup properly, you create issues of "sandblasting pistons" among other things, with a stream that is too dense, or creating a fuel pattern that is inneficient. Again, this is talk for someone with two to three more degrees science or physics degree than me, but I wanted to touch on the "where the thought processes are for improvement" currently are.
Back onto the topic of components. We decided it best to learn on GM components as we have found these to be the least scary, most cost concious (there's nothing cheap about it though), and most representative of what our general customer would be using. For DI injectors we used the GM LT4 Injectors, the are the highest hp capable injectors GM has to offer, and reasonably priced in comparison to the aftermarket injectors out there (some of the aftermarket units are 4-5000$ for 8). We also utilized the LT4 high pressure fuel pump (driven off of the cam lobe) with an increased fuel lobe on our cam that was specd by Smallwood Race Development.
One somewhat gray area is, what pump, how, and which regulator system should you deliver fuel to the High Pressure Pump (HPP). If you use a GM swap harness to control DI, or are outfitting a vehicle originally with DI on it already, you will notice GM uses a PWM (Pulse Width Modulated) Module to control a fuel pump. Basically, this pulse width modulates the fuel pump to achieve its target pressure before the high pressure pump. An inline sensor reports to the ECU where pressure is at, which compares to target pressure, and it will alter the fuel pumps signal to raise or lower to adjust.
This quirky system can be completely done away with, and you can actually bypass all of these variables. On our Nova we simply added a Magnafuel MP-9950-B-BLK boost reference return style regulator in line. We placed our inline pressure sensor post FPR and set our pressure as desired by the system. If I remember correctly without opening HP Tuners we set the fuel pressure to a 72 psi level. To me this was a nice piece of mind both for fuel pump longevity running a larger pump, and it will give us more flexibility for adjustment and flow. Additionally, as most fuel system experts know, a fuel pumps capability is typically limited more often than not by its return line than it is the feed line, having no return from the factory and running PWM made us a bit worried about limited feed pump capabilities. At some point I would like to see what if any advantage is gained on a DI system by moving to return style fuel, but I digress. With the DI fuel system, no special types of lines need to be used in any place. In fact, all fuel system is run just as you would on a normal EFI system as all of the "magic" (I'm not sure if that is the proper term) is done after the fuel enters the cam driven fuel pump which is then factory hardlined to all injectors.
Side Note: The Factory Hard lines that connect the High Pressure Fuel Pump to The Rails underneath the intake are ONE TIME USE ONLY. Do not risk high pressure fuel leaks etc. Replace these and have some peace of mind.
For a feed pump or Low Pressure Pump (LPP) we chose to run the Magnafuel MP-4303 Pro Tuner as a go to pump on our DI system as it is an absolute WORK HORSE both in longevity and horsepower potential. This pump may have been overkill, but I operate on a mentality of Go Big Or Go Home. My girlfriend loves to give me hell about going overboard on things, but I feel in this case it was appropriate.
The one portion of the fuel system I have left out thus far is the port injection. We will spend quite some time speaking more on this, as it will be a very real reality for anyone pushing these engines above what the very moderate limits are on DI fueling. But for now just components.
Our intake is a Holley Hi Ram that was modified by our friends at 417 Motorsports. The created a new lower plenum that is much larger and boost friendly, and added EFI ports in the correct location so that we could supplement DI fuel with Port Injection Fueling. For this fuel system which is only utilized in MAP readings above 1 bar I went to some very reliable components. For fuel injectors we leaned on our friends at Fuel Injector Development and a set of their 1600cc units. For fuel pump we are using the Magnafuel Pro Star 750 pump which is a 2500+ hp capable pump as well as another Magnafuel MP-9950 fuel pressure regulator.
Keep in mind for this application, both fuel systems are COMPLETELY separated. This car has 2 separate feed lines, and 2 separate return lines, going to two separated tanks. Our DI system runs on 93 octane, and our Port Injection runs on VP C16 leaded race fuel. This combination is a Drag Week guy's wet dream when it comes to usability and not wasting precious race fuel.
We will touch more on fuel strategies, our supplemental fuel system and more in later blogs. Hopefully this blog has tossed out some pearls, common misconceptions, and helped answer some of the dark unknown questions behind DI and the Gen V engine.
Until Next Time
Go Fast. Be Safe.
Photos Courtesy of General Motors