Returnless EFI Question

Hi guys, just wondering what the latest consensus is regarding returnless vs non returnless. My searches about this matter have brought up threads anywhere from 5 to 10 years old - consensus there is return style is advantageous (hot soak, better pressure regulation, better transient response, etc.)....does this still hold true or have advancements been made that this argument is no longer valid? Asking because I do prefer the easier install and cleaner look of returnless.
The car in question would be for a 500hp street car.
Thanks for any info!

I did an EFI swap and used a GM LS1 fuel filter/regulator, installed it near the tank so there was no return line going to the engine bay. A lot of the OEM has gone that way so it can't be all bad.

my thoughts exactly, but that is not the feeling I get when reading/watching some videos and other info - but like I said, a lot of that is info that is several years old.....

For 500 hp a dead head system is fine. If you do run into uneven air fuel ratios because of heat soaked fuel, you can tweak the pulse width of individual injectors to compensate.

Unless you're building an all out max power set up, you would likely never notice a power difference in a return style vs dead head

The latest high output factory stuff is all returnless using PWM to control the pumps. The have very high flow pump modules that drop into the tank from an opening on top. The Cadillac CTSV module is one of the highest output pumps. Modified modules with 1, 2, or 3 pumps can easily feed well-upwards of 2000 hp.

A high flow pump running at full output all the time, especially against a dead head regulator generates a lot of heat. They say its the equivalent of having a 240 watt light bulb in you tank. Two pumps more heat and 3 pumps even more heat.

The trick they use to manage this is to keep the pumps from running at full power all the time and heating the fuel. At idle and low volume demand such as cruising, they modulate the power feed to them using PWM (pulse width modulation). The data to control the PWM is gleaned from the ECM/engine computer.

I would try to stay return less for something that gets driven a bunch.

I run a return EFI system on my 68 and I have enough fuel pump for about 550HP and a second pump staged for back up. I have problems with heating the fuel when driving around town or extended highway drives. Because it is returning so much fuel back to the tank from the hot engine compartment it heats up the whole load of fuel. I even added a small cooler with a fan on the return line.

My EFI system can handle PWM control so I am going to think about trying that to reduce the amount of returned fuel under light load conditions.

The fuel heating issue is the only thing I have not been happy with after going EFI. It has never stranded me but the pump sure does scream when its pumping hot fuel.

I just installed FiTech's Fuel Injection with return line and external pump. How will this heat issue present itself, if it does? Stalling? Dying? I did notice a heck of a lot of fuel returns thru that line.

Thanks.

FiTech has the ability to PWM the fuel pump, you can adjust to reduce the amount of fuel returned to the tank.

In my case the pump gets very loud. How I understand it that the fuel is hot and the little bit of vacuum the pump pulls on it causes it to vaporize and cavitate at the entrance to the pump which is why the pump gets loud.

My car is multi port and the rails are bolted to the intake. I think there is more heat soak there than in a throttle body injection. I would use a phenolic spacer if you have room just like a carb. I tried to isolate my rails with nylon washers so there is as little contact as possible but under hood temps are just high regardless. After lots of driving a IR temp gun will read just about any part of the fuel system at 130-140 degrees, including the tank.

We're not talking about dead head regulators. The ones in question are return style regulators mounted near the tank so you have a "returnless" fuel line feeding the engine bay.

Like you already know, your pump is cavatating. That is what is causing your problem.

It is not caused by returning too much fuel and heating up the fuel.

These problems are always on the inlet side of the pump and even with a return that is not going to solve inlet plumbing problems.

I am thinking your pump is not in the fuel tank? Am I correct?

How is your pump mounted and how is plumbed with what size lines.

Its not cavatating until the fuel is hot, the pumps are ultra quite with cool fuel. Just general running around town doesn't cause problems, its extended drives where the fuel gets heated up that is.

This is a new setup and I do think moving the pumps will help, but it won't keep the fuel cooler. The pumps are behind the tank and are about 4" above the outlets in the bottom of the sump.

I am telling you and am sure it is caused by improper inlet plumbing, too small or too much restriction or not gravity fed. Any of that causes the fuel and pump to heat up and makes the cavatating more pronounced when warm. Eventually the pump will die a premature death. It is cavatating from the start even when the fuel is cool, just not as much as when it gets warmer so you don't hear it.

Just trying to help you, not guessing here. IMO you are on the wrong track as to your problems and hate to see bad info get spread around.

I will be the first to tell you I am not an expert. I do not want to spread bad info around.

I am not the only one with this problem though. Lots of drag week guys have this problem. While my pump location could be the problem, and I do plan on moving it. But its my belief most of the problem is flowing 550-600HP worth of fuel but only using a small amount of it so a huge percentage is going back to the tank. Its going back to the tank after it has picked up heat from the 180* engine compartment.

Very few guys know how to properly plumb a fuel system, especially a gasoline fuel system.

I have plumbed many race cars with the smallest being a 1000 hp BB.

Improper plumbing has unnecessary sold 1000s of fuel pumps over the years too.

I am telling you with 100% certainty that the fuel pump has to be gravity fed, flooded with fuel when it is external. Can't suck it up hill, not even a little.

I can say this from experience, if you take the line off feeding the pump it will push fuel out at a rapid rate lol.

I do know a few of the guys I talked to that had screaming fuel pumps had them mounted below the fuel cell. I have not been stranded by this problem but I do know many have. I have seen plenty of guys pack ice bags around fuel cells before lol.

I do realize I need to move my pump but since I am not going to do drag week this year I probably won't do it soon haha. I run a stock tank with a baffled sump so getting the pumps low enough without it looking dumb from behind the car will be a challenge.

you DO need good head pressure to the pump if pulling the fuel - otherwise the fuel just pulls apart (especially if it has any ethanol and is at temp)....if possible, I always advocate pushing the fuel (in tank pump)......

I hear you and agree on the pumps being too low and looking dumb or even be dangerous in a rear end impact.

Put the pump in the tank. Why do you have 2 pumps?

Two pumps for redundancy, and with my EFI I can stage them. I run one pump all the time of course then at greater than 60% throttle and over 3000RPM the computer will kick the second pump on. It will run on one pump but its pretty close to its limits at 550ish HP so the second pump is there for insurance. Plus in the event of a pump failure on the road I can move one wire in the back to turn the secondary pump into the primary pump.

Just something I did to keep a 10 second street car reliable when travelling the back roads of the Midwest on drag week.

Actually, it is you who is talking about return style regulators mounted near the tank. The OP asked about deadhead or returnless systems versus return style systems.

The return regulators near the tank with a deadhead line to the engine compartment are nice, but it is still much better to use PWM to control and match the power to the pump to engine demand in any of these systems.

I have no room for spacer but do have an Eddy Air Gap intake so hopefully that helps some. Mine is throttle body. I haven't driven it much yet. Just haven't had a chance, but I'm dying to drive it more. Haven't heard the pump yet, but then might with more driving. I live in Florida so it's going to be hot, hot, hot in the Summer. From what you're saying, I guess I may be ok though, other than some pump noise when it's really hot? Thank you for information.

The return regulators near the tank with a deadhead line to the engine compartment are nice, but it is still much better to use PWM to control and match the power to the pump to engine demand in any of these systems. [/quote]

Wondering if this variable pump output is a fairly new development, or has automotive been doing this for some time? If so, do all cars use this type of fuel pump system, or limited to high end and/or expensive cars?

Sounds pretty slick, cool idea! I understand wanting to be prepared and then some. Good luck with it!

Fairly recent and limited to high end/high output cars. I would bet the reason for it is that much fuel requires a big pump, and reducing output via pwm is more to do with lowering noise and extending pump life by running the motor slower than it is anything to do with fuel heat.

I know my megasquirt can PWM the pump but I haven't messed with it much yet. It looks like a pretty simple table. I need to add a solid state relay before I can proceed any further.

Wondering if this variable pump output is a fairly new development, or has automotive been doing this for some time? If so, do all cars use this type of fuel pump system, or limited to high end and/or expensive cars? [/quote]

The concept has been around for decades, but actual PWM in production cars seems to be a relatively recent development. There's not much history about it found in a surface search of the web.

Most modern production vehicles use PWM to control the fuel pumps for several reasons including increasing pump life and reducing the heating effect in the fuel tank especially at low volumes. Most factory in-tank EFI pumps are pretty quiet by design and placement. Even smaller displacement low-end cars use this technology, but it is the high flow, high output systems that really benefit from the technology.

Its funny you said this as I remember in 1992 when Mopar went to a returnless EFI system and thats about when I started seeing the fuel filters on the Caravans mounted by the tank with a third line that was a return to the tank. And of course it had no return line of regulator up front. Mopar told us that the PCM was now smart enough and worked fast enough that when you stepped on the gas pedal fast the PCM could increase the pulse width fast enough that it did not need the higher fuel pressure anymore that the vacum controlled press regulator gave it when manifold vacum dropped. At that time they did put the fuel pump on its own relay but it still fed the pump a solid 12 volts through its relay and it's relay shared its ground at the PCM with the shutdown relay so it did not pulse width the pump to change its speed or pressure. I remember in training at that time in 1992 when Mopar first used the returnless system and eliminated the vacum fed press regulator they just told us that the PCM worked fast enough that it did not need the vacum fed pres regulator as the PCM could increase inj pulse width fastenough to handle it. Ron

I have an Aeromotive Phantom 340 system, which is basically their 340lph pump, return system - feeds rails then to regulator and the return, -6 (3/8) feed and return. No fuel heating issues or any issues of any kind. Pump is quiet as well. Easily feeds the 470hp engine.

The PWM is wholly unnecessary, its a "cost saving" idea at the OEMs. Even the corvette style one, you could change your fuel filter and the tolerance could jack with your fueling (bad parts out there).

You don't want to PWM just any fuel pump either.

So, In tank pump and return style is what I would recommend anytime.

Trying to understand this, so a low tech return system worked on your low HP ride with no noticeable issues, then you out think an entire industry in your spare time and gratuitously post your conclusions based on this one experience alone potentially misleading countless readers? Interesting extrapolation based on one result. Keep up the good work.

Wow, thanks for your really really nice reply. Of course, its not like the people who make the fuel pumps also agree with me or anything:
https://www.aeromotiveinc.com/tech-help/faqs/faq-340-stealth-fuel-pumps/
(read line item #6). While they do say you can use a returnless system with a PWM, it's with some caution and doesn't work well with just any pump. Of course I may not have spoken properly and said returnless at the right time.

Funny thing is I work in the auto industry, and I also know what their motivations are. If they can get by with less plumbing, they will. Because the connections cause more assembly problems (cross thread, strip, leaks, more connections to be made during assembly, etc) than plugging in some modules. They are also making the car for one application, not the wildly varying applications that would be used on people's mild to wild modified cars.

The theory of a return system is a lot less complicated, fuel flows from the pump, into the rails, over the injectors, and then the regulator, controlled by a simple spring returns the unused fuel to the tank. Please tell me how this is a bad thing? Provided the pump can keep up with the fuel demands, you don't ever run out of fuel. No worry about hydraulic delay, and the pressure is controlled nearer to the injectors.

The corvette filter just uses a sized orifice to return fuel to the tank instead of a spring...and a small one at that. So if the size is off (low quality part), the pressure can change.

I'd be extremely shocked for anyone to have fuel heating problems with a return system and an in-tank pump. The OEMs also made systems exactly like this for years. Low-tech isn't always bad. I'm not misleading anyone. The higher the HP a modified car is, the more likely you are to see a return system regardless of what it came with. But hey, do what you want, I'd rather see someone run some extra line then spend a lot of money on something they may not be able to troubleshoot easily. The extra line and having a regulator in the engine bay is really the only downside of a return system.

Well said,

Fuel only needs to exceed about 120* to cavitate. That's cooler than a cup of McDonalds coffee. A high flow pump puts out the heat energy of a 240 watt light bulb. Being in the automotive industry, you likely don't run your fuel low in your tank as a general practice for a reason.

A quick search of the internet may be even more shocking on this topic. Even Aeromotive discusses overheating pumps in there literature, and well-designed bypass regulators help dramatically.

There are always exceptions, and in general for low performance systems you are right. But, electric pumps introduce heat into the fuel systems without exception. They are cooled by the fuel by design. This means they transfer the heat the produce into the fuel. Whether or not it becomes an issue depends on many factors, but this can be an issue when high flow pumps aren't voltage limited using PWM during periods of low fuel demand.

Fuel return is the best set up,my opinion, but what do I know, the temps down here in Southeast Texas get above 100 on a regular basis & underhood temps are very high,fuel return works well.