Ultimate fuel system design and discussion (with diagram)

[fredio54]

if there is no excessive pressure at idle, why bother?? oem is fine until you outflow it. i only changed because i doubted a 150hp regulator would effectively regulate 700hp of fuel. it may have been ok, but i doubt it and had no time to try and check it etc...

[monoxidechild]

im seeing anywhere from 13.4-14.3 at wide open, and partial throttle i wont even say. i have some tuning to do. thats to say the least. and i know how to mechanically tune very well. but im new to the MS.

[fredio54]

its easy man, just datalog, then look at the numbers, match rpm and map with the cell in the table and adjust up and or down to richen or lean out. you get a feel for how much to go pretty quickly. which engine is this on? and at what boost? or no boost?

in boost should be 10 - 12.5:1 depending on various factors, and 100kpa (pre boost na region) should be 12.5 - 13.5, cruise as lean as you dare. and interpolate smoothly in between. something along those lines will get it going pretty well.

fred.

[fredio54]

bosch vs walbro



be aware that there is a non HP walbro 255 too!

fred.

[fredio54]

heres 044 flow vs pressure to the bitter end, i tested mine to 100psi with virtually no drop in flow. fully impressed!

[fredio54]

There are a couple of things not quite right with this, I'll repeat them here this time, but future fixes and indeed the latest version will always be available here :

DIYEFI.org Forum - View topic - High performance fuel system design

If you run out of gas with an EFI pump as your lift pump and you are driving softly at the time, your lift pump will probably burn up and fail due to lack of cooling and lubrication. A float switch is one option to solve this, another much better is to not use an EFI pump for a lift pump.

I've recently discovered some pumps that are far more suitable for a lift pump than an EFI pump. They aren't killer expensive either and are good quality stuff. The rotor box and carby V8 guys should all know about these anyway, but I didn't at the time and will probably pull my 909/910 for another car and use one of these in it instead. The pumps are Carter low pressure vane pumps :







They push out plenty of fuel to make plenty of power and don't draw as much current and don't make as much noise and don't heat the fuel as much and don't die quickly when starved of fuel etc etc. A far better choice than what I previously made.

The common model is the 4070.

I'll be switching over at some point, I suggest you start off with something more appropriate like this in the first place.

Fred.

[bakmans]

you can also make a tank with a t piece and 2 chambers inside. thisway youl always have fuel no matter how hard you corner. for braking youl have to keep the tank small and a bit stretched. if you are welding your own tank anyway i would prefer this in stead of the hassle with 2 pumps.

tank whili driving straight


tank while cornering hard

[fredio54]

That wouldn't work doing donuts round a roundabout ;-)

More importantly though, you can only choose between :

(cornering) XOR (accelerating and braking)

You only need the pumps pickup to go dry or see air for a very short time to get a lean spot at the engine.

So, if you have it setup from side to side when you gun it hard out of the lights and keep shifting swiftly you could go lean. And if you set it up end ways you could when cornering.

The only really good alternative to two pumps is a foam filled fuel cell.