I modeled multiple configurations, dual feed single balanced return, DF biased return, single feed end return, single feed balanced dual return, single feed biased dual return....

there are differences, but honestly they are in the mud in a return style system as long as the FLOW (not pressure) of your fuel pump is significantly greater than the injector flow.

400hp on a miata is a lofty target :)

It makes sense that this could be more of an issue with a return system than with returnless. Is it possible that a higher powered returnless NB could benefit from dual feeds? With the regulator in the tank, you'd have to expect pressure to drop with each injector the fuel passes.

IIRC that's where the marketing aimed the dual feed kits when they were first introduced like 10 years ago.

I love the fact that your drafting paper has little stars on it.




That's because there isn't one. Mostly because, as Six and others have pointed out, the stock fuel rail simply isn't an impairment at flow rates which one can reasonably expect to encounter with anything remotely resembling a streetable BP engine. There's a fair bit of empirical evidence to support this.

I compliment your problem-solving nature, but this specific area of the under-hood environment just isn't a problem.

My take on that:

Possibly true with a returnless system stripped of the proper (OEM) dampers.

In return style, there is constant flow though a rail, through the regulator, then back to tank. That will result in pressure drop across the rail, but it is insignificant.

In a returnless, the only flow is that which goes out each injector. Therefore, pulsation is more of an issue than pressure drop.

Therefore, the aftermarket rail creates the problem that they then solved with dual feed.

I bought the Flyin Miata dual feed rail just because I wanted one, looking all pretty with my rebuilt engine.
But for the LIFE of me I can't get it to stop leaking. About to yank it out and put the fugly stock one back in.

Most of aftermarket dual-feed rails I've seen have supported installing the factory pulse damper on them.

achervig: If your rail is leaking then either it's broken or you're doing the NPT/AN thing wrong.

--Ian

I inherited one from someone who couldn't keep it from leaking. If you find the answer let me know.

Last night I took it all apart, put a caliper to the rail at the injector ports and they all measured out the same. Inspected the NPTs and didn't see any damage in the threads, replaced all the O-rings (but not the injector seats), and then put a consistent smear of thread sealant on the NPTs before installing everything back in place. So, pretty much the same thing I've done the previous 4 times, only this time I paid more careful attention to the torque at the 3 rail bolts. No more than 19 ft lbs on these; I think before I was overtightening them. They honestly don't seem tight enough to me, but after letting it sit out the night I warmed the engine up and took it for a short spin this morning, and it seems OK, no leaks. Here's hoping.

Replacing the injector O-rings, lubing them properly, and being really careful not to tear them when installing it is the key, IMHO.

--Ian

I wish AbeFM was still around. He's got a great story about the day his FM rail (the old piggyback version) doused the whole under-hood area with more fuel than was spilled by the Exxon Valdez.

Here is how mine is routed:
https://cimg8.ibsrv.net/gimg/www.mia...b9d3aeabd6.jpg

Yeah, that was the BEGI-designed auxiliary fuel rail that mounted on the outside of the intake manifold. I had one of those too with a lot less problems than Abe's had -- dunno why his was so much worse. :)

--Ian

Was that why FM had recalled a bunch of rails citing thin walls and bursting under high pressure

Whaaaat? When was this? I bought mine maybe a year ago but just put it in a few weeks back.

7/5/2016

https://cimg3.ibsrv.net/gimg/www.mia...a511716ae4.jpg

That's the first I've heard of it, but no. The fuel rail that Joe's talking about was last sold in 2005 or so, and looked like this:

https://photos.smugmug.com/photos/i-...5dfVp7T-X2.jpg

It was used in the early NB FM2 kit, with a Link piggyback computer that controlled the 4 auxiliary injectors on that rail, while leaving the stock computer to control the stock injectors.

The problems that Abe encountered were caused by the tabs that mounted the rail to the intake manifold cracking, thus letting the rail come off the end of the injector. He had repeated problems with it, although the same kit on my car didn't have that problem. There was some speculation about vibration related to engine mounts and removal of the intake manifold brace, but AFAIK it never got sorted out. FM never sold many of these BEGI-designed NB kits, and the piggyback had significant limitations compared to a full ECU, so I'd be surprised if there were many left at this point.

--Ian

Link! Yeah, I totally couldn't remember the name.

My post is not relevant to this thread, as it was a totally different design (Bell), and failed for entirely different reasons. It was just kind of hilarious when it let go, aside from the whole "Oh, shit, the car is really quite severely on fire!" part.

Holy what the fuck am I looking at Batman! This was from FM in 2005? Shit I was running Suzuki ITBs and injectors with a MS1 2.2 and a home made billet fuel rail, not that hokey home depot racing shit! I have my issues with FM, but I have never before questioned their quality.... until now. I could show you a picture of what a 19 year old could build in his dads shop that looks 10x better. Mine was also dual feed :-P