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Cure to 2500 rpm lean spike

Discussion in 'Engine/Tuning' started by TP03, Sep 23, 2020.

  1. TP03

    TP03 Active Member Established Member

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    My rails (fore) have a -8 on the front as well but I don't think there was enough room with the diameter of the damper being too great. I ended up going with the 3/8" npt version and buying a stainless adapter to go to 1/8" npt. Then I just threaded it into one of the 1/8" ports made for gauges.
     
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  2. 01yellercobra

    01yellercobra AKA slo984now Established Member

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    It's a full return style. The return line is connected to the regulator.

    Usually the damper is used for returnless because the pumps are pulse modulated. That's why I was curious about what the pressure was doing. I think you'd have to look at an actual pressure gauge versus the FRPS. But I'm glad it fixed your issue.
     
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  3. 03cobra#2

    03cobra#2 Hobbyist Of Many Hobbies Established Member

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    I run a dead head setup. I have the regulator mounted in the drivers side wheel well. The return line goes runs from the regulator back to the tank. I like this setup because it keeps the engine compartment a little cleaner and have not noticed any fuel pressure issues driving or in my logs.
     
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  4. SVT GI

    SVT GI Well-Known Member Established Member

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    I run a dead head return style as well. I’d bet if you used a small balance line in the front of the rails it would have solved that spike.
     
  5. TP03

    TP03 Active Member Established Member

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    Maybe but the two lines are connected at the regulator (balanced) therefore pressure (in theory) would be the same at anywhere in the two lines.
     
  6. SVT GI

    SVT GI Well-Known Member Established Member

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    if that was the case you wouldn’t have the issue you had. That would also mean you would need to run another dampener on the other rail. Unless you’re running dual widebands you were only seeing the spike on one bank. The regulator is the dampener not a balancer.
     
  7. TP03

    TP03 Active Member Established Member

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    You do realize that the two lines are connected together at the regulator, getting the same regulated pressure on each line. That’s why the damper effects pressure on both rails.
     
  8. SVT GI

    SVT GI Well-Known Member Established Member

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    Yep pretty sure I understand how a fuel system works. Built my fair share of every style. You realize a dampener is intended to dampen high pressures or pulses? Since when is a lean spike caused by high pulse of fuel?

    Your theory would be correct if the system was static and nothing was happening at the end of the system. And suggests that all cars with the same exact mods make the same exact power on the same dyno. It won’t happen. When have you ever seen an engine with the exact same compression tests for each cylinder? You won’t. Or injector flow data show exact same percentage? This is about efficiency and volume.

    Your car man, just saying we’ve solved this issue with a balance/crossover line for a long time. Some can get away with it with no issues, some can’t. If it worked for you that’s great. I’m not convinced that when a real demand of fuel is needed this is the solution.
     
    Last edited: Sep 26, 2020
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  9. TP03

    TP03 Active Member Established Member

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    I appreciate your thoughts and understand what you’re saying to a point. I’m not convinced that a balance/crossover line isn’t acting basically the same as a damper by smoothing out the high pulses.

    You suggest volume issue? I’m not buying that either. Remember this is a low rpm lean spike, not wot. My rails and lines are plenty big to support more fuel volume than I’m using, especially at 2500rpm. Deadhead is deadhead whether you’re balanced on one end or both. You say balance line. I say damper. Maybe we’re both accomplishing the same thing, just in a different way?

    Regardless I considered trying a balance line at one point when troubleshooting my issue and couldn’t find any good way to plumb it in and still make it look good. I guess a damper is just another option out there, while still keeping a clean engine bay.
     
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  10. 01yellercobra

    01yellercobra AKA slo984now Established Member

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    I wonder if it's an issue with the set ups that feed each rail separately? A couple of guys have mentioned having to join the other side of the rails with a balance line. IIRC their set ups fed each rail from a Y block. I'm running a dead head, but the feed line is hooked to one rail, loops to the other rail, and the other rail is blocked off. I don't think I'm having any feed issues. I do have one wideband that shows richer than the other, but that's only at idle.
     
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  11. RainyP71

    RainyP71 Member Established Member

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    This is definitely an interesting topic, and as I am not a mechanical engineer yet, I can't offer any exacting input, but thinking aloud about this is terrific. It is rare in this community a new technical topic comes up to be fleshed out.

    That being said, I am also still leery of the damper. Assuming the damper is the cure to the root problem, I want to know the root cause of the problem. What regulator are you running?

    Is it possible the crosssectional area of your regulator is simply not large enough to adequately regulate the pressure, and subsequently the pressure fluctuations of your setup, but still large enough to easily meet fuel flow demand? That is why the damper in my mind is fixing the problem, but probably not completely remedying the root cause, it's fixed it enough to correct the tune and your AFRs however.

    I would LOVE to know if removing the damper and the problem comes back, and then installing a very large regulator like the Aeromotive 13134 while maintaining all current routing, fixed the issue.

    Sent from my SM-G975U using Tapatalk
     
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  12. TP03

    TP03 Active Member Established Member

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    I’m running a Fore innovations F4i regulator. Interesting take on this for sure. I never really thought of the regulator being under sized? I too believe that there’s probably more to this to get to root cause. For now I’m happy with the damper and the drivability.

    I actually think I might try a balance line next year if I can figure out a way to route it without going under or over the snout. Might try twin 180 degree fittings out the front of the rails routed around the back of the blower? If I try this, I will remove the damper and see if I can tell the difference between the two setups and which seems better. Maybe both will be the way to go? I’m going to e85 next summer as well so maybe running both will be beneficial.

    For now since the season here is winding down, i plan on enjoying the boost season for a couple more weeks and then putting her into storage.
     
  13. RainyP71

    RainyP71 Member Established Member

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    All that sounds great to try. Also this idea came to me today, what if your pumps or tank setup is somehow introducing air into the system? If youre pumping aerated fuel to the rails, the way your setup is there is no where for air to escape like in a return system, the air usually would follow the system back through the return line into the tank making less of an effect. What if that damper is doing nothing but acting as a "catchcan" high point where air is finding it's way to and settling there, allowing air to settle out of the fuel so you get only fuel through the injectors. I might install clear lines to the rails and do a visual inspection. That could explain your mixtures leaning out as well.

    So it could possibly NOT be a pressure issue, but is presenting as one. The air has just now settled into the new high point of the returnless section at the rails (the damper) and that damper + the compressable air there is now somewhat trapped, and the pumps and regulator as well as the damper are working to compensate from that compression/release cycle of the trapped air, but it's still running better, just shifted the problem. You did say your regulator was mounted low in the fenderwell, you could be unknowingly making your rails the high point for air in the system!

    Sent from my SM-G975U using Tapatalk
     
    Last edited: Sep 28, 2020
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