Dodge Fuel Systems Explained Hemi and Hellcat
Let's talk fuel systems! This first part is going to pertain to 5.7, 6.1 and 6.4 cars
The design of the fuel system is the limiting factor. Going to a simply bigger pump, creates problems most don't know about. The factory regulator is just a "calculated" bleed hole, so what happens is a bigger pump throws off that calculation, example, factory pressure is 4 bar (58psi), install a massive pump and in between the pump and bleed off may be 85psi but rail pressure is 70psi. So then (as some may have seen) people say, "I did a bigger pump and yea it flows much more, my car was rich!" Well of course it flows more but running to much pressure all the time was making it rich and makes idle hard to tune with such a high base pressure. The other issue is in the jet pump (passenger side) along with bleed regulator is the main filter, which is small, not capable of efficiently flowing high amounts and not very E85 friendly. It will break down faster. This is why you see guys go full return, to get pressure down, keep fuel cooler and prolong pump life, plus bypass factory filter and add a FORE filter for injector protection. But there is good news, Tapped Performance is a FORE dealer and we have them make a special double hat with a single 267 [450lph] (87psi relief) or a 274 [450lph] pump (higher relief valve 112psi) that is drop in, we supply a wiring kit and it retains returnless operation. If that is not enough then honestly there is not much of a choice for reliability and safe fueling than to go full return and possibly add a pump. The Level 1 drop in kit is affordable at $750 and is fully upgradable, you can add a second pump later, convert to return style, all that, so it's a small investment to get you started on a good fuel system.
Now that we are up to speed on those fuel systems, let's look at Hellcat/Redeye/Demon...Trackhawk...fuel systems!
Let's look into 2015, the year Dodge blessed us with the Hellcat! The homework was done and done with precision by Dodge, they use a 1/2" feed line returnless system that has a fuel pressure sensor in cross-over line between fuel rails, and a Fuel Pump Control Module (FPCM) which the PCM controls based on fuel pressure sensor. With this in mind, unlike the standard Hemi's there is no regulation but merely pump duty cycle (DC). The FPCM pulse width modulates the fuel pump to keep a steady commanded pressure, the Hellcat does have a "jet pump" which oddly also has a check valve along with the stock TI285 pump. As the TI285 pump was about the biggest, baddest, quiet pump the OEM's could use with known reliability, the answer for more fueling was a Boost a Pump (BAP) or adding a second pump, this is where FORE stepped in to give us a double, then triple in-tank hat setups. Tapped Performance stepped in to take this setup to the next level with the complete solution to utilize the factory pump control and simply have it run 2 pumps. While it may sound sketchy the FPCM is on the CAN bus and is not a dominant module, meaning we can add 1 or in theory 10 modules to the bus and each will receive and understand PCM Tx bus commands. Fast forward a few years and the automotive world has a Demon unleashed upon it, which it along with the Redeye Hellcat and Trackhawk basically have this double pump/FPCM in stock form.
Let's also clear up a couple other things, the pumps themselves. Tapped Performance usually only uses TI267, 274, 285 pumps, the 295's are being tested...the 267 and 274 pumps are identical in flow [450lph], dimensions but differ in one important way. The pumps all have a pressure relief to protect pump from lock-up and the 267 is 87psi while the 274 and 285 are 112psi. This is why you will not see that we pair a 267 with the others. Now, why is this that important you ask? Well for example a Hellcat stock will push 90psi under boost, so while sadly some places have offered twin 267's for Hellcat applications, it's not good to have pumps that relief at a lower pressure than what the cars run stock. This can be accounted for and tuned around, but remember running a lower pressure inherently makes the injectors "smaller" and you may run out of injector faster. We generally use the 267's in Nitrous applications where flow is needed, but not necessarily the pressure. In the case of our extreme power hats for the 392 applications, a 274 and a staged 285 is used as both have same pressure relief but on a 392 there is no FPCM. No FPCM means the pump is on full blast and using a 285 as a primary means there is a larger amp draw on the vehicle (idle), the fuel is going to get hotter and pump of course even hotter shortening pump life. The 274 can support a good amount of power on it's own and with a 285 to back it up under boost, it makes for a great combo. To follow up on the TI295 pump as you may wonder...it's a beast! We all know the Hellcat pump (TI285) is known as the 525, as in flows 525lph, well it does that at ZERO PSI (free flow), at 40 psi flow is about 470lph, but the 295 pump actually flows 525lph at 40psi! Another important note on the 295 pump is it has no internal check valve, while Hellcats have a check valve to hold pressure in jet pump, 5.7/6.4 cars do not, meaning you could not pair say a 274 primary with a staged 295 as 295 would bleed off pressure if it's not running. What we are testing is a twin 295 Hellcat system, this works as both pumps are PWM controlled and always on so no pressure bleed off.
RAMS...and some Jeep stuff...now this is really going to annoy the Hemi car guys, Rams 2014+ (could go older have not checked at this time) have a fuel pressure sensor just before rail in feed line and has the EXACT same FPCM as a Hellcat! But the likeness stops there! Here is what is odd about the Ram fuel system, while PCM looks at pressure and commands a Duty Cycle to pump 10-100% based on load, RPM, torque demands and such, it is a Constant Pressure Fuel system which means any Delta Pressure test performed on the Fuel Pump would show a continuous pressure regardless of the changes in PWM. If a pressure sensor fails or other failures are present; The duty cycle goes to Limp mode (100%) to maintain fuel pressure. What the hell does that mean? English please!? The fuel pump module in the tank, of course has pump, filter and a regulator-this regulator keeps a constant pressure, so even in limp mode (100% DC for FPCM) you won't see any change in pressure (58psi). A Hellcat remember has no regulator, but for a Ram the PCM will slow the pump down watching to make sure pressure holds and if vehicle is say at idle, slows pump down as far as possible (10% min) until pressure drops and picks up enough to maintain pressure, this is also part of the pressure sensor diagnostic. For the most part this is to keep fuel cooler, pump cooler therefore extending pump life, which is an issue for the 5.7/6.4 cars once going big single pump without PWM control.
We hope this helps! As always feel free to contact us with any questions or concerns!