How To: Make a Fuel Rail

[Sang]

First, you’ll need to buy some rail extrusion. I bought some -8 rail through RMR. I’ve had a few transactions with them thus far and all of them have went very well. Scott is a pleasure to deal with.



Next, you’ll have to take some measurements. You have to measure from port to port to drill for the proper injector spacing. I used a digital caliper that I got on sale at a HF retailer locally. Seems to measure pretty accurately to the hundredth millimeter. Now, I bought a special drill bit from RMR. It has been turned down 3 times. It makes a nice taper inside the bore for a good o-ring seal. It also machines a radius on the outer bore so the o-ring doesn’t shear when you install them into the rail. I then put the rail in the drill press and had it drilled just far enough until the bit rounds out the outer bore. RMR recommends to drill at 400rpms and keep the bit lubricated.



I then bought a ¾-16NF tap and tapped each end of the rail. This is the correct tap for you to use -8 fittings.



I then took a grinding stone and created a chamfer. I also took some sandpaper to smooth out the edge. This will allow you to use Earl’s port plugs (O-ring bosses) without cutting the o-ring when tightened down. I’m dead heading my fuel rail, so I will be use a -8 port plug on one end and -8ORB to -6AN reducer on the other.

[Sang]

I took a pick that I use for electrical work and a little bit of sand paper to deburr the injector ports inside the bore.



Here is the inside of the bore after I cleaned it out.



That was the easy part, the reason why more people don’t do custom TFFR’s is the head adapters. Machining adapters costs $$$. This is why I elected not to drill for 14mm bosch style injectors and drill for 11mm NipponDenso style injectors instead. I took a gen2 fuel rail and cut off the ends I then took a file to smooth out the cut. These will be used as the head adapters (Thanks Karl!). Gen2 and Gen3’s are not interchangeable; the bosses are larger on Gen3. (Picture is before grinding it down)

[Sang]

You need o-rings to seal the injector to the adapter. I’m using one that is 9.5mm ID x 15.5mm OD x 2.3mm thick. Just so happens that 3/8” ID x 5/8” OD neoprene grommets fits great, once you take a razor and cut out the middle. Otherwise they are ~6.15mm thick and the injector sits too far away from the head, IMO.

[Sang]

O-ring fitted to the pintle cap



O-ring fitted in the cup



Then use a stock injector insulator to seal the adapter to the head. *I forgot to take a picture of it this time around, but it looks just like what insulators look like on a stock rail* Now that you have the head adapter and rail ready to go, now it’s time to make some L brackets to mount the rail to the head. I bought some 1/8 x 1” aluminum stock from Lowes then bent it to 90* angle

[Sang]

Old fuel rail off, then I mounted the adapter cups into the injector bosses, then set the rail+injectors into place



Drill a 7/16” hole into the shorter leg of the bracket so you can still use the black OEM spacers in the mounting holes. Then use the drill bit that comes with the 10-32NF tap to drill two holes into the longer leg. *My drill can only take a 3/8” shank…so I ended up using an 11/32…still works bit I can’t use the spacer without enlarging the hole slightly with a dremel.*



Mock up the brackets in place and mark where you are going to drill on the rail. Drill and use a 10-32 tap. Now you’re all done, you’ll need some shorter bolts that mount to the head. You’ll also need some 10-32 bolts and lock washers. I’m using loctite on the threads that go into the rail to make sure they don’t vibrate loose. But I’m sure it won’t be needed.

Here is the finished product.




Hook up an air compressor and do a leak test to make sure you're getting a good seal between injector and cup.
Hook up fuel lines and jumper FP and B+ to make sure you aren't leaking fuel anywhere.

Now you're done, pat yourself on the back!

-Sang

[LeePeyton]

very awesome. clean intake too.

[Sang]

Here is V2 of my rail and the changes I made compared to what I made last year.

Thicker bracket out of 1/4" thick 6061 angle.


Inlet/Outlet bored out to 23/32 and hand-tapped for 1/2 NPT. This was probably one of most PITA things I've done. If you don't need the size of a -8 extrusion...I'd just go -6 and tap it for 3/8 NPT instead.


I'm using a single button head M8x1.25x30 with lockwasher to hold the bracket to the rail. After going over the old chrisK et cetera TFFR fire with the bolt backing out, I'm a bit paranoid. But I figure if it's good enough for OEM, it's good enough for me. I also tapped it all the way through so if need be, I can get a longer bolt and put a lock nut on it or use some loctite on the threads since I don't plan to disassemble this rail again...


All that's left is to sand it down and polish it...but the hard part is all done.

[Gairloch]

Nicely done!

[Sang]

Thanks.

For the sake of completion, here is the finished product after a half-ass polish job that is juuust good enough to be install-able. But either way, after nearly a year and only 175 people found it interesting enough to even open the thread, I think it's safe to say the DIY'ers on this side of the internet are gone.

[Gairloch]

Oh, there's still a few guys knocking around. Just gotta bring them out of the woodwork I suspect.

How does the bore of your custom rail compare to stock?

[Sang]

Oh, there's still a few guys knocking around. Just gotta bring them out of the woodwork I suspect.

How does the bore of your custom rail compare to stock?

A stock gen2 SFFR? The bore on the stock 3S rail is about .177" (4.5mm), the bored out gen2 rails from the likes of ATS and KO are around 8-9mm IIRC, Stock 5SFE TFFR is .5", mine is .69".

[1slo4g]

This was very helpfull, thank you!!! I'll post my rail when I'm done!