Ultimate fuel system design and discussion (with diagram)

[fredio54]

Hi, I thought I'd draw up a diagram and write an explanation for how a proper track/turbo worthy high hp/high performance fuel system should be built.

heres the picture :



there is text in the picture that explains most stuff that one needs to know when doing an upgrade like this.

obviously the hoses and hard lines to and from various components should be sized according to the flow through them to ensure no restriction to the flow occurs.

its important to realise a few things.

when the engine is stopped or idling, the entire volume of the main "to rail" pump is flowing through the regulator and back to the tank. thus the return line needs to be sized such that the full flow of the pump doesnt generate more pressure by restriction than the regulator is trying to achieve. the main line should be sized to drop no pressure at the full flow of the pump. the less pressure dropped across the main line, the less hard the pump has to work to produce the final pressure at the rail.

if for example your main line fwd was so small as to drop 15psi at the full flow of the main pump, and you wanted a base pressure of 50psi, and a boost pressure of 25psi, the total that the pump sees is 90psi. thats hard work, and a walbro might well pack up and go home if it has to work under those conditions very much. if on the other hand you have no restriction going fwd, your pump will only be pusing 75psi, much much easier for it.

when testing my fuel pump setup i had the return from the reg plumbed out through a hole in the front panel into a bucket, and had the regulator wide open. i turned the system on, and with the hose squirting fuel horizontally increased the rail pressure more and more until i got to 110psi. then i chickened out. my 044 pump did not reduce its output at all from no psi to that level. and that is why i chose it. under the same conditions, the walbros flow has been significantly reduced by the time high pressures like 80 or 90 are reached. the walbros ratings are not at a high load, and as such will make the hp that they claim on a naturally aspirated engine, but will struggle to do the same without leaning out on a high boost application.

i'm sure i've missed some things, but i'll address any errors tomorrow, as i have to sort out dinner now.

fred.

[STW]

Great writeup, but where's the fuel filter? I guess, for those unfortunate few with not enough space for a surge tank, a large pressure accumulator should make an acceptable substitute, what do you think?

Which cars use the Bosch 044 pumps?

[fredio54]

Originally Posted by STW

Great writeup, but where's the fuel filter? I guess, for those unfortunate few with not enough space for a surge tank, a large pressure accumulator should make an acceptable substitute, what do you think?

Which cars use the Bosch 044 pumps?

you can put the fuel filter in a number of places. i put mine a massive marine one before the bosch 910 such that all fuel from the tank gets filtered before it sees any pump. i trusted that the lines and pumps and rail etc was clear of debris. there is a little screen on the 044 inside that would catch larger stuff.

another reason that i did it like that is that that filter of mine is not designed to run under pressure. i couldnt find an oem one with large enough orifices to satisfy my fussy self. you could however parallel 2 or more new stock filters to get the flow needed for big power.

the damper on the rail is a small acumulator of sorts i'm thinking that running dry might be better than a half arsed supply of fuel from a rubberised diaphram. but i could be wrong.

half of the point of it is to run out very suddenly and all at once. there is enough fuel to supply my engine as it stands at 350hp + for a full minute in my surge tank. in that time, the other pump should have scavenged the last of the dregs from the bottom of the main tank and slowly topped it up till there was none left to scavenge.

as for the 044 ;-) WRC cars use it :-) its a motorsports pump. i dont think any road cars came with one, but i could be wrong. the 910 came in some mercs. there is a porcshe pump thats similarly rated to the 910.

fred.

[chief tool]

Good write up...

its almost an exact copy of the system I use in my GC.

I built mine all out of copper, so no ethanol fuels for me!

I think I worked out my surge tank is 250mm length of 80mm copper pipe with two copper endplates (3mm thick) brazed on. Its volume works out to be about 1.2L...I worked out its about 20 sec at full thottle, with no lift pump working.
I use a Bosch (dunno what model) out of a Falcon EFI wagon (about 1600-1800cc/min) the lift pump is a 929 '85 carburetor electric pump...Which I estimate is good for about 900cc/min

The only thing I did differently is the surge tank to main tank return line draws from the top side, not the top...I had some theory about keeping an air space in the surge tank (a small one) but I cant remeber what basis I used for the theory!

One problem I have always had tho...As the surge tannk is in the boot space the car always has a slight smell of fuel vapour in the boot....I pressure tested the system with compressed air for leaks before it was installed....And there have been no evidence of leaks in the last 8 years of use...I put it down to vapours permeating the small amount of rubber hose used to connect the tank to the rigid lines....most of my lines are 8mm copper, all except the last bit to connect to the surge tank, which would be about 150-200mm of rubber

I dont know if anyone else has experiance this phenomenon....but I found a bit annoying, and have been concerned a bit about the safety aspect...
but I am pretty sure that there isnt enough vapour to be ignition worthy, even if parked in the sun on a hot summers day.

A few times I have thought About changing the dimensions of the surge tank so I can fit it under the car...for instance a 150mm dia, 150mm tall tank...
Sure the anti suge properties wouldnt be as good, but I could braze in an internal baffle out of copper plate...
But Its just something I have never got around to.

[fredio54]

yeah, the smell coming through the hose thing had me looking for leaks too :-) but mines not in the car, so i'm not concerned.

your air space theory may have been to do with demand exceeding supply from feed pump and allowing air to expand under vacuum whereas with no air, it has to suck in more fuel instead? i dont agree with that, but i can see the logic.

carb pumps are fine to feed the tank.

its not rocket science. just thought i'd post it around for those that didnt know :-)

fred.

[STW]

One of STW's MeeToo's!

I have the Bosch 044 ordered, and I'm going to use a Walbro 255 for a transfer pump (I had to buy one for certain unfortunate circumstance... my spare pump blew too ) I bought 285mm length of 110mm aluminum tubing for the surge tank (2.345 liters net volume). I'm going to install an extra precaution; a float swich into the bottom of the surge thank to keep the 044 from running dry if the tank is drained for any reason, and stop the pump in case the car is turned over.

I must check the local suppliers to see what kind of fittings I could use, I'm probably going to go with SAE 37 fittings, if I can get those in aluminum; if not, it's AN fittings. I think 3/8" OD tube would do well.


One big problem is where to fit the thing, there's not much places in a wagon where everything is pretty much in sight.

[RobbieRat]

Nice write up Fred, but whats the deal with the fuel damper, is it necessary? most guys i know don't run with one?

Cheers Rob

[fredio54]

rob : its not necessary, but pretty much all cars run them stock, and i went and talked to a fuel injection GURU!! who advised that even though the internal pressure wouldnt be correct for boost it was still a good idea to use it. hence i retained it. its built into the fuel feed on the fe3 stock, so when i moved the feed to the end of the rail i just welded up the old feed and left it in place. easy.

good idea on the float switch dude, but instead of killing the pump, kill the megasquirt and that will stop the engine and kill the pump (pump controlled by megasquirt) as the whole point of running a surge tank is to not run out of gas. killing the pump while boosting up a hill is not a good thing to have happen in the case where the feeder dies.

the walbro will be fine or even excessive (not a bad thing) at zero pressure.

are you by chance building a monster stw??? ;-) or just huge overkill?

fred.

[STW]

A monster... well, who knows

It's a very good idea to kill the whole engine with the float switch, but I think I'll settle just for the ignition.

Also, buh-bye to the Hammer Adjustable pressure regulator! Just bought a nice tunable pressure regulator, even if it is So Last Millennium... I guess PWM and single line fuel system will have to wait until next decade

[fredio54]

sure, but if its still pushing some fuel in, then you will have significant back fires from the exhaust...

dunno what you mean by hammer reg or pwm single line at all?

fred.

[STW]

Hammer adjusted: you crush the stock FPR to increase the spring tension, a VERY crude but cost-efficient way to increase fuel pressure... also rather limited.

Single line fuel system doesn't use return line at all, pressure is instead controlled by manipulating the pump output with duty cycle... haven't seen hobbyists do it yet, though I'm sure MS2E could handle it,

[fredio54]

ah, i've seen it refered to as returnless

i'd ditch it on any application where it was legal to do so. the fuel heating would be less than ideal.

fred.

[moebius]

A nut in the peanut gallery Points out the semi-obvious:

Some of the newer cars are using a single line fuel system, or a returnless high pressure fuel setup for improved emissions. At least that is what the manual in my Corolla says, apparently it has no fuel return line to the fuel tank.

[fredio54]

yeah, less evaporative emissions. when you feed hot fuel into the tank, it gives off vapour...

needs clever ecu control though.

[monoxidechild]

im still on the stock FPR. need to get the fittings to finally install my aeromotive fpr on the damn thing.