Returnless Fuel Rail

[rjwoods77]

I am going to use that walbro fuel pump kit that they are selling for 100 bucks. If you have a pressure regulator at the pump in the returnless mode which I am interested in using. If you do this there is no need for a external fuel pressure reguator with, correct? Is there any disadvantage to a returnless system? I am using RC 155cc injectors that are rated at 43 psi and the walbro setup is regulated at 47 psi.

[rjwoods77]

I am going to use that walbro fuel pump kit that they are selling for 100 bucks. If you have a pressure regulator at the pump in the returnless mode which I am interested in using. If you do this there is no need for a external fuel pressure reguator with, correct? Is there any disadvantage to a returnless system? I am using RC 155cc injectors that are rated at 43 psi and the walbro setup is regulated at 47 psi.

[DaveC]

I'd really use a return line. Theres good reason whay almost every FI system has one, not that I know every reason... There is much less chance of vapor lock, and its much easier on the pump, the pump runs much quieter and cooler. Plus, fuel pressure is a set quantity for most FI systems, so if it varies, so does your AF ratio. We all know that could be REALLY bad. I'd feel much better with an Aeromotive AFPR setting my fuel pressure, and a Denso pump feeding it. This is just my personal, somewhat biased opinion...

Another thing is, Walbro = crap. I wouldnt run my lawnmower with a Walbro. Their nickname is the Walmart pump. I had a 255 HP in my rally car, and it couldnt push enough fuel thru the stock fuel filter, and I melted my #1 piston. True, the stock fuel filter is restrictive, but I was only making about 225 AWD HP, stock is about 160. That pump was supposed to push lots more fuel than the stock pump at higher pressures. Plus, its really noisy. I now have a pump for a Supra Twin Turbo (315 lph) made by Denso to fuel my new motor, and a whole new fuel system. Denso, IMHO is the $hit.

I know this will add a few hundred onto what you wanted to spend, but this is a critical system, not a good place to save $. I learned this the hard way.

[Travis Garrison]

We're making ~60-80hp, and Rob is going to be making substaintialy less than that http://fsae.com/groupee_common/emoticons/icon_wink.gif flow isn't the issue. Had a chance to talk to a dirt tracker last weekend who was running a returnless fuel system, and I don't think I'd ever wish that on someone...just sounded like maintaining a set pressure was too much of a chore. Maybe the walbro system could do it, but why risk it? Bouts of rich and lean could really screw with throttle response and fuel economy.

[DaveC]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Bouts of rich and lean could really screw with throttle response and fuel economy </div></BLOCKQUOTE>

Or worse... I'm sure the pump will flow enough, but I'd bet it wont keep steady pressure, and I wouldnt be surprised if it fails entirely. Pumps use fuel flow to keep cool, too.

[Charlie]

Majority of new cars run returnless fuel systems nowadays. For the past 3-4 years for sure. Chryslers have been doing it for a decade.

It's not easier on a pump to run returnless. 'Returnless' is sort of a misnomer anyway, you are returning it, just closeby or inside the pump itself. You still return fuel. Pump still continuously pumps. Unless you are doing pulse-width pumps with closed loop fuel pressure sensors (they are out there).

Can't see why fuel pressure would be less consistent. If you have air in the line it will purge itself out, after that it's the same as any other line given an adequate pump. It's just like running a 't' off the line between the pump and reg on a return system.

In heat soak a returnless system gets hotter and stays hotter longer. But after constant operation it is cooler, because you aren't constantly returning hot fuel to the tank. So it's a trade-off.

A return system is probably easier to manage, more parts are around it might be more reliable... but really I'd say the differences are close to a wash.

Walbro sucks DaveC? Why, 'cause you bought one that didn't suit your needs? Did you find pressure drop vs. flow charts and figure out what your filter was going to do, and the pump didn't do what it advertised? Or did you simply make an application error and blame it on the pump.

I've had good luck with Walbro stuff for FSAE... Flow is not a problem on a car like this anyway. I dare ya to find a pump TOO small. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[murpia]

OEM returnless fuel generally uses a rail pressure sensor and a PWM controlled pump to keep rail pressure constant (or controlled to a target). No reason not to use this in FS / FSAE, just that it's more complicated from the electronics / software perspective than the traditional bypass regulator with a return line and vacuum reference.

Vapour lock issues probably depend as much on the details of the installation as on the choice of returnless / returned fuel system. However, having witnessed the chronic hot-start issues of a lot of FS cars, I would encourage rigourous testing of whatever solution you choose...

Ian

[Ben Beacock]

in 2003 we ran the stock Suzuki internal fuel pump with the stock internal FPR, ie "returnless". in 2004 the pump was external and the FPR was down by the pump and tank ("semi-returnless"?). 2005 had a honda FPR in a custom fuel rail with an external walbro pump. Didn't seem to make a difference either way in terms of fuel pressure consistency. I wasn't monitoring fuel temps though.

[John Bucknell]

Like Charlie said, 'returnless' systems have been the norm for about 15 years on Chryslers. Only in the last ten have we bumped fuel pressure up from 43 to 58 psi to totally eliminate any possibility of vapour lock (which was only a problem sitting in traffic in Pheonix in the summer eith 43 psi on some cars). There is a simple diaphragm-type regulator on the outlet of the in-tank pump (literally a spring behind a diaphragm in a can) to control pressure, no fuel pressure sensor and no pwm on the pump. You could make this kind of regulator if you wanted, but much more easily pull a pump module out of a junk yard. It's really dead simple, and fairly reliable (as electric pumps go).

[Dan G]

So John, are you saying the only think keeping someone from going with a "short return" system (ie: a regular or adjustable FPR regulator, right next to the tank) would be high temps and low psi? For the run-of-the-mill FSAE car, ~50 psi and making sure you don't run the fuel supply line inside the exhaust pipe would probably do it?

If so, that would make the fuel system a little easier to plumb!

[welder]

A bit OT.

Just a cautionary tale on the Walbros - it is fairly well known over here that Chinese conterfeits of these pumps are being flogged on various performance car forums and Egay.

There have also been reports of the Bosch motorsport pumps being copied. I would imagine it is only a matter of time before the NipponDenso units appear. http://fsae.com/groupee_common/emoticons/icon_frown.gif

By all reports they flow 1/3 to 1/2 of the genuine pump's rated flow, tend to be noisy in operation and fail in short order.

If the culprit is to be believed, http://fsae.com/groupee_common/emoticons/icon_rolleyes.gifhis supply originates in the US.

[John Bucknell]

Dan,

Yep.

[DaveC]

Charlie,

It just shows how much of a newb you are at tuning cars to defend Walbro. The info I gave about my pump selection makes it OBVIOUS I had a huge pump for my application. Yes, I calculated what it should flow, and it should have supported way more than a measly 225 hp. Sorry if you dont like me calling your pump crappy, but it is. Look, I'm not attacking you, just your fuel pump, so don't get so bent out of shape.

I'm just saying that its going to be more reliable to have a seperate, adjustable fuel pressure regulator than run a returnless Walbro. The Aeromotive AFPRs are a quality product, I'd just rather be adjusting my fp with it. I already said I'ts just my opinion, so take it how you will.

[Charlie]

Flow is based on pressure drop. If you have a drop in the system (you admit you did) then you can't use total flow numbers for your calcs. You have to look at the curves. Which obviously you didn't.

There is a difference between 'tuning' cars and bolting on parts. Call me a ;newb' if you want, I'm not gonna start spouting off about the cool cars I wrenched on. That's not the point, I just try to talk rationally and say facts. Not compare lengths of you-know-whats.

[DaveC]

Why did you say I didnt account for drops in the system? Don't tell me what I did and didnt do. I said I did, if you want to call me a liar then fine. It would be incredibly obvious to anyone fimiliar with this stuff that the fuel system I had should have worked. It ALSO should have worked with just the stock pump, but I wanted more of a safety margin. I probably would have been better off with the stock Denso, which is rated at about 100 lph lower than the Walbro.

Thats why your a newb, you spout off about stuff you obviously (to anyone who has any experience) have NO clue what youre talking about. You also defend Walbro, who has a less-than-stellar reputation for reliability and consistancy of flow. Theyre crap, and only a newb would try to say otherwise. Again spouting off about something you have very limited experience with. Their "Walmart" nickname isnt a sign of respect.

Look, you are not talking rationally, and you're certainly not stating facts, youre attacking me, basically calling me a dumba$$, stating what I did and did not do, and making foolish statements that make YOU look like a dumba$$. Youre trying to tell me I didnt account for the configuration of the fuel lines and fittings, and that I dont know the difference between bolting on parts and tuning engines.

Youre another one of those guys with the big internet personalities, and I know you wouldnt be saying these things to me in this manner in a face-to face discussion. Why dont you watch what you type, and have some respect for other people. Instead of stating I didnt do something, and implying I'm an idiot, why dont you ask with some courtesy if I took this thing into account.

LOL, are you 16 yrs old?

[Charlie]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by DaveC:
LOL, are you 16 yrs old? </div></BLOCKQUOTE>

They say never argue with an idiot, he'll drag you down to his level and beat you with experience. http://fsae.com/groupee_common/emoticons/icon_wink.gif

Not saying you are an idiot, I just see where this is heading and I'm not going there. Not on one of my rare weekend off. http://fsae.com/groupee_common/emoticons/icon_wink.gif

Just wanna say that there is a difference between 'tuning' and engineering. Lots of people build street cars with cool parts, they buy stuff and put it on, sometimes it works, sometimes it doesn't, they get on the message boards and talk about it. It's great fun. But there's not much real analysis going on. So lots of conclusions are drawn based on limited facts.

The problem is when people that have done a lot of projects successfully like this, but never really 'engineered' something, think they know it all. Like you say it should be 'obvious to anyone familiar with this stuff' that you had a good system. Then there is trouble, and it's too bad, because they guys aren't neccessarily dumb. Nothing should be obvious. You need data and a good engineering analysis to prove anything, IMO. It's time consuming and I wouldn't do it on my street car either, but I wouldn't think I knew the gospel, unless I did.

You talk about Walbro like they are one product. No FSAE team would use a 255 Walbro pump. It's way too much flow. Most would use an external, which is a totally different style of pump construction anyway. Your Walbro didn't fail, just didn't meet your capacity. So instead of jumping to conclusions that 'all Walbros are crap, don't use them', consider the application.

Doesn't matter what age I am, or my experience level, just stick to good discussion and not personal jabs, please.

[DaveC]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Doesn't matter what age I am, or my experience level, just stick to good discussion and not personal jabs, please. </div></BLOCKQUOTE>

I will if I'm not demeaned, no matter whether explicit or implicitly. You do a great job of demeaning others without explicit statements. Maybe you should have majored in English... http://fsae.com/groupee_common/emoticons/icon_wink.gif (See, I can do it too. http://fsae.com/groupee_common/emoticons/icon_smile.gif)

Anyway, I was implicitly stating that the Walbro pump I used did NOT flow as advertised. I DID do some calculations and spent some time figuring out if it would work. My conclusion is that it should have worked. I'm not saying its not my fault, I should have flow tested my system to see if it was OK in real life, and I should have done some research on pump brands. If I had, many others would have told me to get a Denso, and steer clear of Walbro. Which is what I'm trying to do here. Steer clear of cheap pumps. I like Denso, Delco, Bosch, Carter, and Aeromotive. I know they most likely will perform up to manufacturers specs, and wont break really quickly.

Your talking like you did the engineering analysis on my car. Unless you did, why do you ASSUME a 255 high pressure Walbro was not big enough if it ran according to mfg. specs?

As great as using engineering is to predict how a system performs (I AM in engineering school), real world experience is REAL. Some things that you feel need "engineering analysis" have been done so many times by so many people before you, they come up with "standards" for the job. That way, we can just look at chart to see what gauge wire needs to be used, we dont have to simulate the circuit on a computer every time we run a wire. I dont know, its tough to talk to people who cant keep an open mind about what anyone has to say because there wasnt a paper written on the subject.

[BryanH]

Rob, back to your original Q. I did research Returnless before building the fuel system and found that the only reason for their existance was to reduce fuel temp, thereby reducing fuel tank vapour emissions to comply with CARB regs.
It also makes fuel system cheaper & quicker to install on the production line.
When the fuel tank is less than 1 US gall. & the pump needs to be in-tank (because there was no space for it outside!) the only 43mm dia high quality pump I found was the fsae walbro.
And if it did fail it could be swapped over in 2 minutes without spilling fuel. I,ll email you photos.
re DaveC I have also had exp. of a very low flow walbro pump,I tested the flow rate B4 driving the car.... but the one used in RO4 was diff design and much higher quality (GCL616-2)

[rjwoods77]

Bryan,

I knew about the evap. emissions thing but i thought it was from the return line doing something. Makes since what you described. Does the fuel stay cooler just because it isnt heating the fuel in the loop like a return system? What is your opinion of the negatives that others have mentioned in this discussion? Run into any of those problems? Find any solutions to these possible problems?

[BryanH]

Rob, IMO if the regulator is at the end of the circuit the pressure drop during the injection event is far less than in a returnless, the fuel is pumped to the rail at a potential 80+psi ( push-on efi hose also dampens the pressure pulsation) The fuel rail on RO4 ran at ambient temp so only heat input to fuel is from pump and radiation into tank. Actual fuel temp was &lt;10c above ambient at end of 22kms.
The layout of a small fsae car means that the tank will have more heat input than the lines and rail so running return style should keep the fuel cooler, which is extremely important. (All the good accel stuff starts to boil out over 40c)
cheers

[John Bucknell]

At the flow rates for FSAE, I would be very surprised if you experience line loss (3/16" line is about the minimum available anyhow). The other method to avoiding pressure drop during the injection event (either return or returnless) is to have a sufficiently large diameter/volume fuel rail. 10mm ID is sufficient for about 90 indicated horsepower per cylinder.

The heat transfer aspect will be different for every installation. Keep in mind that the pump does add heat (albiet small).

[rjwoods77]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bryan Hester:
Rob, IMO if the regulator is at the end of the circuit the pressure drop during the injection event is far less than in a returnless, the fuel is pumped to the rail at a potential 80+psi ( push-on efi hose also dampens the pressure pulsation) The fuel rail on RO4 ran at ambient temp so only heat input to fuel is from pump and radiation into tank. Actual fuel temp was &lt;10c above ambient at end of 22kms.
The layout of a small fsae car means that the tank will have more heat input than the lines and rail so running return style should keep the fuel cooler, which is extremely important. (All the good accel stuff starts to boil out over 40c)
cheers </div></BLOCKQUOTE>


Bryan,

I guess I am misunderstanding you. I thought you said in your first comment that returnless runs cooler that return. Then you say the opposite in your second comment. Which one is it?

I was thinking along the same lines as John B. about pressure loss in the rail by using a large enough ID? In you experience running returnless did you have that issue?

Also I keep hearing you guys ran a cvt years ago. Do you have any pics of it?

[DaveC]

I'd have to add, it seems that consistency of fuel temperature is a factor. It's another variable there is no sensor for (besides the o2 sensor, in a roundabout way). Example: My P/U truck's AFPR (carbureted returnless fuel system) heats up puttering around town, and it makes a difference on the A/F Gauge. In fact, I can tell when its getting ready to vaporlock by the reading on the A/F gauge. So, just like most liquids, gas expands when hot, enough that it will make a significant difference in your A/F ratio, possibly even beyond what your computer is capable of compensating for. I am going to get a return style AFPR for my truck and run a return line to try to keep fuel temps more consistant. (I do realize low pressure fuel systems are more sensitive, but I think its still something to consider w/FI.)

[BryanH]

Dear Rob, sorry for late reply.
If the engine is stuffed in a box with the radiator, 65c air means the fuel rail is an interheater, if the engine is out back in the breeze the fuel rail is an intercooler.
I use 15 to 17mm I.D. fuel rail on everything.

CVT? there's something creepy about it, how can you enjoy a good flat shift? IMHO it's for lawnmowers.
RO4 used a auto clutch in Detroit. No good on dragstrip but good everywhere else.

DaveC you can do fuel temp compensation on Motec or Haltech, from memory change in lambda is about 6% from 25c to 70c fuel temp. I have tested it a fair bit and found a car in race conditions runs consistant temps &lt;30c. It's more important to keep fuel temp low than to compensate for it. On a road car temp compensation is a good thing.
Cheers

[rjwoods77]

Honestly I agree that it is less of an experience with a cvt. And the drone can sometimes be really annoying if it does drone. But I cant deny their usefulness and I have a ton of experience with them.