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Pg 24-103 in WSM for euro layout

Pg 24-208 in WSM for US 85-86 layout

If you look at the euro layout i do not see how you could only use 1 RRFPR and expect both sides to be near equal or 'adjusted' . (to Brendan)

You are right about the US layout mark.

mark kibort

Here is how you should see it. Both regulators are in parallel. both regulate the pressure together with what ever spring tension they have on the diaphram
by increasing the spring pressure, you leave more of the pressure from the fuel pump to the fuel rails. If one fuel regulator is closed off, the other holds the burden of regulating the system pressure by letting the excess fuel back to the fuel tank. the function of the vacuum line is to pull back the diaphram to let more pressure out of the system during part throttle or idle conditions.

you cant have differential pressures in both rails, just because you have only one path back to the gas tank. this is why, we were succesful in only using one rising rate fuel regulator on the US Ljet system (same as euro 84-85)
proof is on the S4 system, one fuel regulator on the passenger side of the rear of the fuel rail system . also think of the fuel system as one big loop, with the entrance up front at the damper and the exit of the damper to the two fuel rails in parallel meeting in the back of the engine. One or two regs in the back, it doesnt matter.

we were able to dial in the fuel presure to create a 12.5:1 fuel air ratio.
we also were able to take a look at the plugs after race day, and they all look identical. Im sure if there was any issues, we would have seen it in some area.

I think the reason that they used two regulators, was that it was easier to pull back pressure at idle with two regulators with vacuum, rather than one. with the S4 and only one regulator, using the map and LH computer, they could pull back fuel in addition to the one fuel regulator. (thats my guess)

MK




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heinrich

Mark very nice explanation thanks. However, I still don't see why the 2 dampers on the S4. Because the rear damper works *only* for the driver's rail, and the other damper up front works for the two rails both.... Could one drop the rear damper and just go straight to the regulator?

BC

I am putting the regulator at the passenger side. The driver's side will get a dampener. But I have to take out some ofthe piping at the back. While I am doing this I will replace the short rubber lines that are fossilized there at the injectors. NO big deal, easy job.

heinrich

Do like I did on the S4 ... go from the reg to the return feed at the firewall and say goodbye to the cooler. As well as the dinosaur hoses. None of those.

BC

Thats exactly what I did H. The only rubber left is my new stuff and the short supply hose next to the engine on the passenger side.

heinrich

I knew we were twins separated at birth, I just knew it

mark kibort

actually, it was tough for me to see at first, as the entire system is a big loop, with two dampers, one at the entrance to the fuel lines and one near the return area. dont think of it being on one side or the other, as the entire loop's pressure pulses are reduced by the dampers. thats all they do, smooth out the pressure pulses.

trust me, i was a little suspicious, but with some of my fluids experience and consulting with others with even more experience, i decided to try it. (Plus it was on scots car!! ha ha. just kidding)
anyway, it worked and worked like we thought

MK

mark kibort

That was the idea that got me thinking. why use a damper with as you have to find a fitting to connect to the return line, where usually that is the fitting that the fuel enters from. anyway, if you close it off, it then is just a direct "short" connection accross the fuel passage. what you want to do is remove the damper off the one side, and put the entire burden and return line back to the tank on the one regulator, or a new rrfr. for those of you that just want to boost fuel pressure, this can be done without even a regulator. just clamp off that return line of the driver side regulator, then you basically just have a short circuit directly on the fuel line. this way, the return line now only 1, instead of two, and sure, the diaphram will move due same line pressure, but there is only one to return fuel back to the tank, thus raisng the fuel pressure slightly. (remember the one damper now will have all the burden for fuel return)

it seems to work well. the idea of using a damper is fine too, as that does the same thing, but you need to get a damper and you have to find fittings to put it in the same configuation. I also think that if you route the fuel from the t , there is no resistance , so fuel will just return freely back to the tank, and lower pressure over all, in fact, it may remove all your fuel pressure. (i really dont know how exactly you plan to use the damper)
anyway, since the design is fairly simple, just clamp off , even in stages at the dyno, til you find the right pressure.

Mk

SMTCapeCod

Glad I'm not the only '83 (and similar) Euro seeing power with a rich mixture. Hm. Wonder if something is off. Or whether its the shape of the curve (similar power but coming on more abruptly because its dampened by a rich condition until higher rpms).