Engine Drivetrain 1st Gen Cooper S Most liked posts in thread: Return Style Fuel System

The boiling point of gasoline at 1 atmospheric pressure can vary between 100 and 400 Fahrenheit depending upon additive content. Fuel in the R53 rail is under an average pressure of 48 psi (~3.5 atmospheres), which raises the boiling point considerably.

The main advantage of a return system is the ability to operate a redundant pump and delivery system that will maintain fuel supply in the event the primary system fails. Heated fuel is returned to the tank thereby increasing fuel temps, not lowering it.

 

The fuel in the MINIs tank does not get heated by a live fuel system. If anyone has not not tried this conversion how would one base such radical idea's from?
I would be happy to show how it does in fact work at cooling the fuel not heating it. Stop by anytime. Or you can pop into any pit and talk to a crew chief at a race event and strike up the conversation about live fuel rails. Or call Don at DMH Motorsport they have been installing them on race MINIs with success for about 6+ years.
DMH Motorsports



The comment from someone about pressurizing and depressurizing reduces the octane? Please post the formula show how that is possible? I have a list of of performance manufactures, petroleum refineries, racers etc., that I would love to share it with. Just the facts please. Thank you sir.


I would recommend the responses here are coming from some that perhaps have never done a conversion and may not be getting all the correct information about it or other factors pertaining to a live fuel rail. Members interested at this point should go out side this thread and forum.

 

as usual this is a common response from someone who wants someone else to do their R&D for them. I have return systems on both of my cars but for different reasons. The average Mini owner will NEVER need this system, it's just more marketing nonsense to sell more parts and drain pocketbooks..........go talk to the engineers at major car manufacturers they don't agree

 

Can't you reply without kicking someone please?

Again, I'll ask these questions.

Why would we want such a system on a MINI?

What gains are there?

Would a stock MINI benefit in any way? What about a modded one? At what level of modification would something like this be useful if it is useful at all?

What are the downsides of such a system?

If you cannot answer with facts then don't waste the time. Attacks on individuals will not be tolerated.

 

I guess we will never get the info. The battle goes on for info and won't be shared. God forbid anyone contacts another source if their signature contains one of the battling parties for info. Think you'd get a correct anwser? I doubt it. :crazy:

 

I did a little reading

cause I don't have a clue about the advantages either. Only thing I could come up with was an example from adding power to the new GT 500 Mustangs that as you add capacity to the returnless system, when you go from on throttle to off throttle, the pressure in the lines doesn't drop fast enough, and with nowhere for the fuel to go, the fuel pumps get a bit stressed.

Earlier FI Mustangs used a return system as stock, but have gone to returnless. I'm guessing that the returnless is cheaper to do, and probably works fine in almost all cases if it's used as intended, and it's capacity isn't exceeded.

Matt

 

A slightly different approach

I am also considering the critical characteristics of a high performance fuel system & whether I need to go to a return-style system. But I'm starting by thinking about what I want to achieve and working backwards:

From my own measurements, fuel pressure (measured from the fuel rail directly) varies about 20psi between on-and-off load (see log below). Any variation in the rail fuel pressure introduces a load-dependent scaling factor to the fuel tables. As long as the pressure behavior is consistent under all cases, the actual fuel delivered will be consistent.

But given the fact that there is a finite capacity to the high-pressure portion of the system, variation in the low-pressure volume, and a non-zero response-time of the pumps, there's going to be some variability no matter what. The more variability, the less precise is the control over the actual amount of fuel injected.

My analogy is to a steering system with (nonlinear) "slop" in it. The more slop there is, the harder it is to precisely control the direction of the car.

What I would want in an "improved" fuel delivery system would be a reduction in this variability & thus more precise & consistent fuel delivery. This could be achieved by some combination of increasing the pressure in the low-pressure side of the system, increasing the base rail capacity, or even increasing the rail pressure itself.

And my understanding is that these kinds of changes may necessitate a return style fuel system to better control the peak pressures of the system. This makes sense, since in effect you're improving linearity by using a smaller percentage of a bigger system.

However I do not yet have a good grasp on the best configuration to achieve this...yet.

As far as a "normal" Mini needing this...seems somewhat doubtful...

BTW any change like this to the fuel system would necessitate a significant re-tune, including not only re-scaling the whole fuel table but also load-specific adjustments.

Feel free to disagree with my logic...I often do


Some example data:

 

"Works' , could you post a larger picture?

 

Ok, I uploaded a higher resolution version. If you don't see it here, you can get it in my gallery.

BTW, I can easily re-plot this focusing on specific details (e.g. fuel pressure vs. xxx, zooming in on part of the graph, etc.).

 

huh, shows what I know, I thought the OP was referring to a Mini, not a MINI.

I thought all modern fuel injection systems used a return fuel line, I did not know some had gone to a deadheaded system.....

 

Works,
Sorry if I'm not up to speed on your car's upgrades, but from your pics I see a LOT has been done. Now, are you still using the factory fuel system? Is this a track only car?
Can you post another analysis pic with pedal position, RPM, and fuel pressure? Would also be interesting to see what Lambda or AFR is doing in reaction to the above. Without seeing pedal position it's an impossible call, but it seems you run rich. I know little of cars modded like yours, but maybe you have to?
Thanks

 

Sorry for cutting your response down to a easier response read.

This is a really good write up. The only part that I can see might not be altogether so would be the necessity of a re-tune after a conversion?


I use 2 regulators that are set to adjust fuel psi by boost. IMO (I do not use that term often) is a better way to go with increased power levels and larger injectors than relying on the stock regulator and fuel pump.

The bottom line is that a fuel rail conversion is not a modification for everybody. While the benefits are valid the practical application with most is not. Debating its use and advantages is silly because of the small percentage of MINI enthusiast that would actually construct it. I recommend do the research by calling companies that make fuel rails and have solid understanding about this style system. You are not going to get good support or a vast amount informed information here because of the rarity and inexperience of this type upgrade. If anyone would like to build one and is close to my area I will spend a weekend and help you set one up. You can get virtually all needed parts through Summit Racing or Jeggs. PM me anytime.

 

Yes, I still have a stock fuel system (about the only thing left that is).

And yes, this is running very rich here. I believe in this run I was having a problem with a "ghost" correction adding fuel.

I'll put together a chart with those fields...

 

Yes, if you modify the system & succeed in maintaining the exact same rail pressure, you're probably OK without it.

But even if the static pressure is the same & the dynamic behavior changes the fuel tables could be a little bit off...but probably on the rich side rather than the lean side.

 

Why bother asking anymore on this site for anything when I'm told to go look and find the info myself. It only takes one person to share why and how along with an inquisitive group to probe to take it to another level. Telling us all to go figure it out on our own but if I want to do this you'll be glad to spend the time to help hook it does nothing to advance the collective knowledge.

I have more questions.

How can this not heat fuel in the tank? Assuming fuel is at ambient temp it is pumped, adding heat and run through a rail that is heated higher then ambient, some is injected into the engine, the rest is forced through pipes back into the main fuel supply. Having a lot of experiences with pumps and fluids in the aquarium world I know all to well how pumped fluids under pressure retain transferred heat in a closed system.

When going to a system such as this is the fuel pump changed? If not, why, as the goal is to deliver more fuel to the engine how can a system such as this deliver more fuel using the OEM pump?

I'm sure I will have more.

 

In a live system if you have your regulators set for the volume and psi needed you should not have a lean or rich concern. This goes back to both knowing the demands needed at a given rpm range having the devises to monitor the flow and psi and being able to adjust the fuel system for the changes. In all case if properly set up tuning or re-tuning is not needed. work4me I see you have looked into this a bit than you most likely have found the specific flow tables to use for calculation. You may take notice none give values of AFRs or ignition timing.

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Someone refereed to the automakers engineers as a form of(their)expert advise and response. Thank you!

I called my friend an Engineering Power Plant Manager for Nissian in Sacramento and we talked about the The Returnless Fuel Systems. As explained several Auto manufacturers adopted this system because of Federal Emissions Laws. Now the most common fuel delivery system eliminates by a Returnless Fuel Systems fuel returning to the tank were it can cool before being reintroduced in the system. By keeping the fuel hot helps reduces the amount of evaporation emissions. SMOG stuff, thanks US and CA. lol This also lowered the cost of the total vehicle because of less fuel system parts needed for a full fuel return system
So yes the Engineers knew exactly what they were doing! Heating the gas before it goes into the engine. Before the termites come out of the wood yes I very well know the effects and benefits of gas heated for vaporization. But then we are modding the MINIs for performance and not best emissions possible? Right?

 

So we all agree that the fuel being used in the cylinders is hot? So in a return system the excess hot fuel is dumped back into the ambient temp fuel in the tank, but, will not the tank act as a heat sink transferring the heat to the walls and then with the car moving the wind blowing over the walls remove the heat? Would it be possible to use a cooler, like a transmission oil cooler, and run the gas thru that? Nathan in your aquarium is there some kind of heat sink to remove the heat build up? If not, why not?

 

More data

Here's the graphs showing fuel pressure, RPM, load (i.e. boost) and throttle position. The second one is a zoom in on a portion of the graph to show the variations a bit more.

Note: I believe the sampling rate on the fuel pressure here is set to 10/sec (the default). This will hide small spikes, but some would still appear (if they exist).





One correction to my tuning comment: obviously the lambda adaptation of the ECU will auto-correct small offsets. The interesting bit is how that affects the dynamic behavior of the system under various conditions....

 

More visuals of fuel pressure variations; I have also seen a peak of 63psi while revving to 6k rpm.

Pressure at idle:


Key on, cool engine:


A hot engine will increase rail pressure to around 58psi with just the key on.

According to the graph shown by works4me, fuel pressure is able to elevate relative to rpm, and in most cases pressure increase precedes rpm demand.

There must be a problem before a range could be considered "slop". Is anyone having a fuel shortcoming problem that injector size and ECU commands cannot overcome on the MINI? Can anyone provide an example (math formula, proven power loss, or damage) where 48 to 63psi combined with the fuel amount available in the rail and capable fuel injectors, is inadequate for the needs of FI ~1.6liters with an optimistic 100% VE at 4 - 6k and above rpm on a MINI? Larry is applying his considerable knowledge, skills, resources, and talents to investigating fuel delivery on his car, and I respect his input greatly, but what about MINI examples from fuel return proponent(s)?

It is known the on-off gate from the MINI's fuel pressure regulator causes pulsations, however, a healthy fuel pulse regulator on the fuel rail does a good job of responding to those fluctuations, otherwise there would be many examples of fuel starvation from an open injector and weak pressure behind it.

 

This brings up a very good point. If you're trying to tune the car & you assume the ECU is a black box, then you need to correct around it. In this case varying the fuel pressure is a key tool for doing this. Whereas if you have direct control over the ECU (as I do with the Motec), your whole goal is to keep the fuel pressure constant & change the fuel delivery by adjusting the injectors directly.

Both approaches produce similar results as long as you can closely monitor the cumulative system behavior & correct as necessary.

Very interesting discussion...

BTW, that's one of my favorite Engineering forums...(no I wasn't the one who mentioned them before).

Ok, now I need to add a fuel temp sensor too....