Fueling the Chevy C7 Z06 LT4 - Pros and cons of increasing fuel to direct injected motors w/ methanol, LPFP, larger injectors, cams, HPFP, port injection etc.

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This is a guide written by Weapon X Motorsports for the Chevrolet C7 Z06 LT4 engine but much of what is written applies to direct injected motors in general. Frankly, it is just an excellent fueling guide and provides a ton of information.

Keep in mind much of what you read below is why engines are going to dual-injection fuel systems including the Corvette:

It is critical for the direct injection LT1 and LT4 engines to maintain proper fuel supply and there is always a lot of misinformation out there about what fuel options there are and what is actually safe. WEAPON-X was one of the pioneers with the direct injection fuel system when we picked up our 2014 C7 Corvette at the end of 2013 and created what would be quite a monstrous 427 cubic inch 13:1 E85 burning beast, ultimately making 612whp on our Mustang dyno and then bringing the pain on top with a 300 shot of direct port nitrous. We have learned quite a lot since then, and I wanted to share some of the things we do every day with the LT motors.

The Overview:
For daily driving, you would normally see the car attempt to target the stoich AFR of 14.7:1 if you have a wideband gauge hooked up; however, with 10% ethanol in a lot of pump gas today, you see the program setup for 14.1:1 to account for that blend in some pump gas. When you mash the pedal to go wide open throttle (WOT), the vehicle goes into what is called "PE Mode" or "Power Enrichment Mode" looking for values approximately 12:1. This defers to another table that has modifiers of your aforementioned stoich AFR values. The Mass Air Flow (MAF) tables and the Dynamic Airflow (VE) tables provide the basis for the manipulated fueling requested, taking into account a lot of other factors like the injector size in lbs/hr, the requested fuel line pressure, the requested fuel rail pressure, and the Start Of Injection (SOI) which tells the injector when to fire.

How it works:
The system essentially uses two pump technologies. The low side AKA lift pumps/in-tank pumps are the pumps in the fuel tank that are controlled by the Fuel Pressure Control Module (FPCM) for power output to the pumps to get the fuel supply from the tank up to the rail. The system requests approximately 50 PSI during normal driving and jumps this up to approximately 72 PSI when going WOT.

From there, the fuel gets to the High Pressure Fuel Pump (HPFP) that is located under the supercharger on the valley of the engine, in-between the cylinder heads. The high pressure pump has a lot of command technology which references it's position as the plunger rides up and down on a specifically ground lobe on the camshaft to pressurize the fuel as it goes through the pump to 20 MPA.

The pressurized fuel enters the CNC bent fuel lines and travels to the rails, and then enters the injectors. These injectors unlike previous years port injection are located similarly to a spark plug, through the cylinder head with the tip projecting into the combustion chamber. Since the engines are direct injected, the fuel is fired into the cylinder at nearly 2,900 PSI on the compression stroke. The injected fuel will vaporize before the piston reaches top dead center (TDC), which allows for much more predictable fueling and more accurate/higher target AFRs. The benefits are less wasted fuel and a better AFR potential as a result; however, some of the drawbacks as you'll see below are fuel supply and delivery vs. cost. Another drawback is the lack of the fuel cleaning the valves, which on a parasitic PCV system like the GM OHV engines use, they use the engine to draw the crank case pressure though it to maintain seal life and longevity, at the expense of future performance if proper care isn't taken.

The Dangers:
We all know with more power, there is a need for more fuel to maintain the proper air fuel ratio (AFR). Also, those wanting to run ethanol will see the need for a much higher fuel demand, approximately 35-40% on boosted engines when in WOT.

So, you're asking the low side to supply this added fuel, the high side needing to supply that much more fuel to the injectors, and the injectors to squeeze out that much more during the same half stroke. Too little fuel volume or fuel pressure can result in catastrophic failure. These are two separate scenarios that can occur together or separately. When the engine needs more fuel, the HPFP has to be able to supply the volume of fuel needed for the engine, but as the fuel demand increases, the injectors become an issue because they can only supply fuel to the cylinder on the compression stroke. Once you exceed about 5m/s of open time on the injector, you're running the risk of fuel "puddling" aka not flashing to vapor as previously mentioned and this part is critical since it's injected right before TDC. This puddling can be seen on the dyno, especially in higher RPMs by a trained eye and a dyno graph that doesn't have a million "smoothing factor" LOL.
The SOI table can be modified some based on the camshaft to start the injection sooner; however, too soon, and you're just spraying fuel out of the exhaust. Widening the SOI also has a direct affect on the rail pressure as well, since the HPFP can only supply so much fuel and maintain the desired 2,900 PSI rail pressure and you want to maintain target by about 5%. If you go too far off of target, the car can go into REP mode trying to protect itself and tragically, we've seen cars that had the code disabled trying to hide this, which is not only unadvised, but just asking for an engine rebuild. The line pressure and feed to the HPFP has a direct correlation to the ability of the HPFP being able to maintain rail pressure as it is a "push" type of logic obviously, not a "pull". So the fuel pressure has to be strong from the tank! If the line pressure isn't force feeding the HPFP, the entire system will falter.

These scenarios are not always realized on the dyno either! It is imperative once you tune your vehicle that you verify the rail pressure on the street, because the car can rip through gears and deplete the rail much more quickly than you can see on the dyno, even a loaded dyno like our Mustang 1100 AWD. So, the more power you're after, the more fuel you need! Next, we'll discuss all of the available methods of getting the much needed fuel.

WEAPON-X Alternative LTX DI Fuel Supply Options:

1. Meth Injection Kit:

https://weaponxmotorsports.com/colle...th-kit-lsa-lt4

WEAPON-X recommended use - as slight cooling and octane boost with proper fuel system supply from the tank.

Pros - Methanol kits are inexpensive starting at $600 and adds octane, cooling, cleans the valves which was an issue with DI motors mentioned earlier

Cons - Uneven distribution, Kit ends up being around $1,200 installed, additional cost to add a meth tank or losing washer tank, refilling and storage of meth, flammable liquid in the trunk or engine bay, potential pump/solenoid failures which can cause engine failure if the car is too dependent on methanol

Notes - Sure a meth kit is cheap, but you'll have 6-8 hours of installation, the hassle of refilling the methanol, and the worst part, keeping an eye on the entire thing and hope the pump doesn't go out when you're heavy into the throttle. When tuning a car that is dependent on methanol for fuel supply, the engine is relying on the added methanol to maintain the proper air fuel ratio, which really is never what alky meth kits were intended for. The second inherent problem with these is fuel delivery. Engines always have what are called "hot cylinders" where the natural airflow path is stronger so you have more uneven cylinder distribution. So, if you're spraying heavy amounts you need to run what is called direct port meth which means there is one nozzle per cylinder to control the flow. This gets really pricey starting around $2,000 plus install because you need check valves and extra solenoids to make sure the pressurized air isn't pushing against the tip of the nozzle, and even in this instance, you always have rich and lean spikes because the methanol nozzles are just not as refined and controllable as a fuel injector tip.

2. Camshaft Kit with 38% Fuel Lobe:

https://weaponxmotorsports.com/colle...te-z06-z07-lt4

WEAPON-X recommended use - obvious performance gains depending on the cam, but for fuel supply on 93/91 octane pump gas builds up to about 750 wheel HP

Pros - Adds desired sound, increased performance, and reliable necessary fuel delivery over 700 HP
Cons - Labor intensive installation taking most cam kits to more than $4,000 installed, added stress on high pressure fuel pump, great for sound and engine optimized performance, but not a great bang for the buck for fuel delivery

Notes - Cam kits are almost always on the list for pushrod V8 guys. The thump of a properly designed cam makes mouths drop and power gains are plentiful. On the gen 5 platform, the "need" for a camshaft is more prevalent because the high pressure fuel pump (HPFP) rides on it's own specific camshaft lobe. So, we quickly figure out you can redesign that lobe on a custom camshaft to overdrive the OEM HPFP for more rail pressure output. The only drawback is this supply is limited and the installation to get a camshaft in properly on an LT engine requires pulling the motor.

3. Low Side Line Pump Kit:

https://weaponxmotorsports.com/colle...te-z06-lt1-lt4

WEAPON-X recommended use - for additional fuel supply to the high pressure fuel pump HPFP for flex fuel/E85

Pros - Inexpensive easy fuel supply increase, added octane from flex, kit keeps HPFP primed for max output
Cons - Only help with lower HP increases but high side will still starve on big builds, no ability to upgrade later, no going back once tank is tapped

Notes - The low side line pump kit is a good option for stock supercharger builds up to a certain point, but big boost over 800 HP will need more fuel than the high side pump, injectors, and rail can deliver... even with an upgraded high side DI system too. These line pump kits aren't upgradeable, so once you've done all of that work to get it in and desire to go larger, your tank is already tapped and you have to undo that and redo a larger pump kit.

4. LPE Big Bore DI High Pressure Fuel Pump:

https://weaponxmotorsports.com/colle...-cts-v-lt1-lt4

WEAPON-X recommended use - this pump supplies 10% more fuel and when used with larger injectors and a line pump kit, can prevent the need to upgrade the camshaft for some 750 HP builds.

Pros - Simple bolt on option once the supercharger is removed, 10% more flow
Cons - Cannot be overdriven with a cam, 10% flow isn't a lot in the DI world, expensive at $1,500 for gains.

Notes - The larger DI pump helps some, but it's not a huge increase as 10% more fuel is not 10% more power. This pump is $1,500 and has it's benefits when used with the larger FIC or Nostrum injectors which add another $3-5,000 to the cost as well as the need for a low side kit still to supply more fuel to maximize the effort. All of this can benefit someone who does not want to do a camshaft, but you're at a minimum cost of about $5,000 plus installation going this route. The DI pump cannot be overdriven by a camshaft lobe greater than 6.5mm either, so anyone doing a cam later would have to go back to the LT4 pump and the LT4 pump with an overdriven +7.8mm camshaft can outflow the +10% pump with a 6.5mm lift by about 15-20% if I recall. This is a great option for someone willing to spend the money on the ancillary times that wants bolt on, reversible parts and doesn't want to open up the motor. It's just limited on max power.

5. Larger DI Injectors:

https://weaponxmotorsports.com/produ...-cts-v-lt1-lt4

WEAPON-X recommended use - The FIC injectors supply 30% and are able to support 1,000, while Nostrum is advertising 50% more fuel and 1,200 crank HP; however, still need the high pressure pump supply. These can be good for sub 1,000 HP builds when combined with other mods like the HPFP or camshaft and low side line pump fuel kits.

Pros - Simple bolt on option once the supercharger is removed, 30% more flow
Cons - Expensive upgrade at $3,000 - $5,000, limited by HPFP and line pump, requires other mods for potential

Notes - The larger injectors help for those looking to do bolt on power, but they require ancillary mods to reach their potential. The injectors are $3-5,000 and need a cam and a low side kit still to supply more fuel to bet worthwhile too, which puts you into a minimum of $9,000 installed. This is a great option for someone willing to spend the money on the ancillary times that wants bolt on, reversible parts and doesn't want to open up the motor; however, while the injectors aren't the ceiling, the max power limitation is restricted by the high pressure fuel pump pressurizing the rail to keep the pressure on the near 3,000 PSI target.

6. Port Injection Fuel System:

https://weaponxmotorsports.com/produ...-cts-v-lt1-lt4

WEAPON-X recommended use - This kit is really for anyone who is looking for proven reliable power with the intentions to get more than 800whp, especially on E85.

Pros - Cost is about the same as doing a low side kit, HPFP, and larger DI injectors or a cam kit installed
Cons - Requires low side, harness, injectors, rails, and modifying your existing supercharger/manifold

Notes - We now have a reasonable solution a true port injection kits specific to Camaros, Corvettes, and CTS Vs! It is a complete kit with plug and play wiring harness, pump, lines, injectors, rails, and we have successfully installed these on the LT4 Whipples, Procharger manifolds, and even the OEM Eaton LT4 supercharger! We offer in-house modifications to those for the port kit too and pricing will be released later this month for all!