FI Fuel Boost Pump

[RobinHou]

Has anyone tried this: http://www.octaneautosupply.com/Face...-p5214552.html
Or, other type of inexpensive automotive fuel boost pump for an IO engine?

[roee]

Interesting. The pump pictured in the link you sent and the one sold in the FI pump kit by Van's actually look suspiciously similar to each other. I'm guessing it may very well be the same pump, although I don't know that.

However, in any case, note that what's sold by Van's (and comes from Airflow Performance as I recall) is not just the pump itself, but an assembly that also includes a filter, a pressure relief valve, a bypass valve, and a machined manifold and other plumbing that ties it all together into an aux pump system appropriate for use with a fuel injected Lycoming.

And on this topic, the usual words of caution apply: mess with the fuel system at your own peril.

[rv7charlie]

I just ordered one of those pumps to use as a transfer pump. Roee is right about the Van's unit including the regulator, etc, which would be needed. If you want to fabricate it yourself, a usable regulator would be around $30-$ 60 & any cheap inline filter would work if used pre-pump (low pressure side). All fittings, etc + pump & you'd still be out $120-$180 + time to build it. I'd probably do it, but I'm cheap. If pump quality is a serious concern, you can get a Walbro all metal inline pump for a bit over $100. That's what most of the alternative engine guys are using with automotive style fuel injection. If you need a source, drop me a line.

Charlie

[RobinHou]

Thanks Roee and Charlie for your replies. I understand Vans (AFP) FI pump system includes a pressure relief valve. But I wonder why this pressure relief valve is needed if most of the auto inline fuel pumps already have a pressure limiting valve: http://www.picoauto.com/tutorials/fuel-injection.html
Of course, the built-in pressure limiting valve is set much higher (120 psi vs 25 psi for the AFP pump). But if the built-in valve works for the auto system which is around 30 psi, why does one need to add the AFP pressure relief valve which I believe limits output pressure to around 25 psi?
Charlie, can you report back re the quality of the Facet pump?

[DanH]

Because most OEM auto FI systems locate the pressure regulator at the fuel rail. Some late models have a variable pressure pump, but that's another story.

Experimentation with a point is one thing, but fooling with fuel system design to save a few bucks is, well, fuelish

[rv7charlie]

I'll be happy to report on quality, but my planned use is purely as a transfer pump (from an aux tank to main).

I'm certainly no expert, but I suspect that the relief valve you see in the tutorial is intended to be a 'fuse' to protect against a total blockage between the pump & the bypass type regulator (not shown, but described in the tutorial). My understanding is that these pumps are positive displacement, like an oil pump in your engine. If flow stops completely, either something breaks or the pump stalls & burns up.

You need pressure regulated to the design point, because flow through the injectors will change radically if you vary pressure from 20-25 up to around 100psi. Dan's right about early automotive FI; as your tutorial describes, later versions put the bypass regulator in the tank, and even later (current) versions electronically regulate pump speed to control pressure.

To address Dan's comment about experimentation: Some would say that anyone who flies a homebuilt is nuts. After all, if you want to go over 180 kts, you can just buy a Piper Malibu. Avoids that fuelish idea of experimenting with an entire airplane just to save a little money. :-)

Of course, that means that the Airflow Performance & Precision exp. fuel injection systems should be avoided, along with the aux pump that Van sells, since it isn't baptized with alphabet soup, either.

If Dan just means that you should use what others have already used successfully (a reasonable thought), then the Walbro, with any convenient automotive bypass type regulator and a check valve, would fit the bill. The stock engine pump needs the check valve in the supply line so it can draw fuel when the aux pump is not running.

A simpler setup would be FRANKH's pumps: 2 high(er) pressure Facet 'solid state' pumps in series to get around 20-25psi. The only problem is that they seem to be a bit hard to find. If you go all-electric, like he did, you can avoid future ethanol issues with the Lyc mechanical pump. Or, 2 Walbros (main & backup) with bypass regulator, but that means a return line to the supply tank, unless you really do want to get 'out there' with fuel system experimentation.

Charlie

[RobinHou]

Dan and Charlie, thanks for your replies. I am all for experiment and education, but I do know my limitations. Firewall forward and fuel system are not my strong suit, and primary fuel pump is not something I will fool with. Your combined knowledge and experience just save me countless hours of research and hundred of dollars in parts for experiments that most likely would be futile.
Thanks,
Robin