Proposed Simple Fuel Stinger Designs

[larry cottrill]

These designs should be fairly simple to execute without machining. They are basically "improved" Rosscojectors (though not quite as simple to fabricate). They will not perform anything like Eric's nice designs, but are an improvement over straight pipe stingers in that they try to diffuse the fuel pretty evenly throughout the intake stream, and also provide some "rectifier" action against backflow. Fuel should be delivered through these at a slight positive pressure, somewhat like using the Rosscojector. The gaps should be set up pretty tight (a few thousandths inch), whether for liquid or vapor fueling. These can be made about any size, but the smaller you go the more difficult the welding will be.

The tools you need are a vise, a tubing cutter and a flaring tool, and you need the skill to weld thin plain steel. Materials are steel brake line tubing for the outer shell and a flathead machine screw (and hex nut, for the second design) sized so the head is slightly larger that the tubing OD. You will also need a full-round needle file for the second one.

For the first design, make a good square cutoff and flare the end. Use two good-size hex nuts in your vise to slightly flatten a short section that the shank of the screw can reach through. Drill a small hole clear through the flattened section, then insert the screw in the end, holding it against the flare and finish pinching the tube in hard against the screw. Remove from the vise and fully plug weld the hole in each side as shown. If you want a significant gap, you can use a couple of foil spacers or some such when you do the final pinch, then pull them out before welding.

For the second type, cut a short piece of tubing that will be about as short as you can make it and still be able to flare BOTH ends with your flaring tool. Also flare the end of the long piece that's left. File 3 or 4 ports in the threaded portion of your hex nut with a needle file, as shown - they don't need to be "perfectly" spaced or sized. Cinch the nut and screw up around the short piece, making sure the nut is centered. Tack weld the flare to the front face of the nut. Use pieces of firebrick to align the rear tube with the other face of the nut for tack welding. Finally, finish weld the flare edges all around both edges of the nut. Adjust via a screwdriver to try different gap settings, but again, a pretty tight gap should be used.

L Cottrill

[Jonny69]

That's a great idea Larry, I have one more idea to simplify them further. One could crush the tube as you show in the diagrams but instead of plug welding you could crush the tube slightly too far and run a tap down between. This should result in the screw being very tight but adjustable and no need to weld. Probably.

Edit: If you could find the right size trilobial screw (that's a metal tapping screw for those that don't know) with a tapered head you might not even need the tap.

[hinote]

These designs should be fairly simple to execute without machining. They are basically "improved" Rosscojectors (though not quite as simple to fabricate).

Larry:

Thanks for posting your suggested "real-world" injector designs.

For all of us garage engineers, this is the kind of solution we are going to be best at implementing.

Depending on lots of other parallel developments, I'm considering the purchase of a lathe or lathe/mill combo, to refine the injectors I'm capable of producing. Lots of ideas to explore and test, at this point.

[NickC]

i talked about an injector similar ot this in the APC injector development thread. It would be a 90° injector though. Like this:


and it would use an allen bolt since it is flat blacked instead of angled.

[Eric]

Larry,
I wish I saw this earlier. This is basically the primative version I described that could be made from a tube, two nuts, and a bolt. The second nut comes into play for adjusting the gap distance and locking it tight so that it wont unscrew from vibration.

If you just use one, and the bolt comes unscrewed it can get sucked into the engine, and shot out of the exhaust at around 600 mph, they tend to look like tracer rounds when this happens, and getting hit by one probably wouldnt be much fun at all.

Eric

[Jonny69]

I might disagree actually. While it is a good idea to lock off with a second nut for safety in all reality I think the engine would go out, so the bolt probably wouldn't fly out. I say that because I've tried to fuel one of mine on gas with a large fuel jet, high volume but low pressure, and it simply wouldn't run. When I cranked the pressure up I just got more fire, but no pulse.

[NickC]

eric said it like he's seen it happen before. the whole tracer round description and he fact he's been making thing like these.

[Eric]

Jonny a mechanism for locking it is absolutely necessary.

A lot of engines will run with straight tube injectors, and a lot will run even if only for a second once it becomes a straight tube injector.

Depending on the size of the injector it may rattle around the combustion chamber a bit before getting blown out of the engine, when this happens it is red hot and depending on the height of the engine, if you are running it in a populated area, you could very well hit something / someone with a red hot piece of metal that is going very very fast. I suspect it would be like getting shot by a subsonic round, a subsonic incindiary round that is.

Its not a matter of if this will happen, but a matter of when. High frequency vibrations will unscrew just about anything given enough time, every single non locked injector I ever tried unscrewed itself from 15 seconds to 2 minutes.

Maybe you will luck out and it wont leave the engine that fast, but every single time I have seen them leave the engine they are going fast enough that they just look like a orange beam.

Eric

[larry cottrill]

These designs should be fairly simple to execute without machining. They are basically "improved" Rosscojectors (though not quite as simple to fabricate).

Larry:

Thanks for posting your suggested "real-world" injector designs.

For all of us garage engineers, this is the kind of solution we are going to be best at implementing.

I finally made one of these last night (the non-adjustable one). I decided that the perfect screw to use (for 1/4-inch brake line) was, believe it or not, a No. 6 coarse sheet rock screw! This worked wonderfully for the construction; pinching, drilling and assembly took less than a half hour, and my total actual welding time was about 45 seconds! It looks great, and a test by blowing through it by mouth with the end submerged in a glass of water showed excellent distribution and really good flow. The gap all around is .012 inch (0.30 mm), established by running the screw down tight against an aluminum foil shim (.003 inch foil, folded four layers thick).

I really like using the sheet rock screw, because it is just the right size to use with 1/4-inch brake line, it is highly available and cheap as dirt, and most of all because of the shape of the head: rather than being a classic "flathead screw" shape (as in my drawings), the shape is more of a smoothly flaring curve, quite like the curvature of a traditional automotive intake or exhaust valve! Also, near the head where the thread leaves off, the shank is actually much smaller than the outside diameter of the threaded region. Very nice, really - almost a precision part, actually.

I'll post a new thread showing this when I have the construction photos in hand.

L Cottrill