The Project Pad

Anyone running a returnless fuel system? I am intrigued by this and simplifying the plumbing in my car, as well as keeping the fuel a bit cooler. Seems LS guys dont like it for high HP builds because the furthest cylinders starve for fuel. Im thinking a 5cyl shouldnt be such a problem but wanted to see if anyone else on here is running a setup like this.

Due to the length of these inline engines, I believe you would run into the same issues.

There are two ways to run returnless. The first, and probably mislabeled, is not running a return from the fuel rail, but still having a return from the regulator. The second is no return at all and using the fuel pump to electronically increase and decrease the pressure. The second is what a lot of OEMs do now, and is available from people like Fuelab. If you do either, I would feed both ends of the rail so the lowest flowing point is in the middle, but it should be totally fine if the rail has good volume.

The reason I believe ls guys have problems is because there is only one feed to 8 cylinders. Fuel comes in the back of one of the the fuel rails(firewall side), then travels past 4 cylinders, then over the crossover pipe to the other 4 cylinders. Every injector the fuel passes decdreases the pressure left in the rail. I would think that a single feed to a 5cyl fuel rail would be significantly less distance to have a pressure drop than 8 thirsty injectors over a 5'-6' length of rail

Correct, and if you split the feed to both sides you are only feeding 2.5 injectors each, no real chance of pressure drop there.

You wouldn't be worried about any turbulence from the fuel coming together having an effect on cyl 3 injector?

How much power, flow are you looking for? I guess anything is possible. You should tune by plug color anyways. I have always had to trim a few cyl out. If you have a good size aftermarket rail, you are probably fine with a single feed.

Power should have potential for 600hp+ if detonation can be kept at bay. I am thinking of upgrading to an egt per cyl to better monitor it as well

I am developing a slick solution to egt per cylinder as we speak. It will have all 5 Temps displayed on one lcd and will have 5 analog outputs to send to an ecu. Oh and it will have 5 relay outputs for alarms as well.

Peak and hold??

Yes plz

Ok I should be able to do that. I'm not sure how slick it'll be on the first go 'round, but it'll be functional at least. I'll keep you posted here somewhere when I have significant progress to report. The good news is that it'll be a lot cheaper than what is on the market currently.

Yes, keep us posted.

Vems will be able to interpret that egt data? All 5?

Vems in Europe has this which is what I was looking at
https://shop.vems.hu/catalog/4xegt-ampl ... 3443de04f0

This will be much more feature-rich than the VEMS solution (5 probes, RGB LCD colored to match Audi instrumentation, alarm output(s), and analog outputs to send to ECU (0-5VDC).

Yes, VEMS can take in all the EGT data and use it for controlling the tables/safety features provided that you have enough inputs. If you don't, I hear VEMS is working on an input/output expansion module.

I will create a new thread for this and we can discuss there.

The factory usually does this for emissions reasons. Only one line to worry about for evaporative emissions instead of two. On B6 Audis, for example, the fuel pressure regulator is built into the fuel filter. So the return loop to the tank is short since the fuel pump is like a foot away from the filter.

One big challenge with returnless is that it is difficult to accurately give manifold pressure referenced fuel pressure. Most end up just doing a static pressure. So you first need an ECU that automatically compensates for that (GM ECUs have a 3D table for injector flow vs. differential fuel pressure, based on manifold pressure), and then you also need either a super high base pressure if you're running lots of boost, or huge injectors that will flow well at whatever base pressure minus manifold pressure is.

Sam

ads wrote:The reason I believe ls guys have problems is because there is only one feed to 8 cylinders. Fuel comes in the back of one of the the fuel rails(firewall side), then travels past 4 cylinders, then over the crossover pipe to the other 4 cylinders. Every injector the fuel passes decdreases the pressure left in the rail. I would think that a single feed to a 5cyl fuel rail would be significantly less distance to have a pressure drop than 8 thirsty injectors over a 5'-6' length of rail

That isn't the way the topography of the V8 rails is laid out. The fuel enters at the middle of the left side rail, and the takeoff to the right side rail is also from that point. So it is laid out like an H with the actual feed on one side of the middle leg.

I've seen returnless systems working at 1000hp. The main issue, from my vantage point, is that since fuel pressure is fixed at 58psi, it is easy to make enough boost to make the fuel rail-manifold pressure differential small enough to hurt injector flows. At 15psi boost you are down to 43psi effective fuel pressure. At 25psi... oh no! So switching to a return style system and a fixed fuel pressure differential makes life easier. (1000hp was at only 9lb boost. Lots of cam and near 7l displacement and only a little bit of forced induction on top.)

AFAIK all GMs run a regulator, not a controlled fuel pump. It's either in the fuel pump assembly or it is part of the fuel filter, depending on chassis.