Modifing S4 Fuel Rails
 

Now, I'm aware that you can modify the fuel rails to support -AN and run parallel.

I just happened to pick up some NPT taps (1/8", 1/4", 3/8", 1/2", 1/2"). Now I could never make heads or tails of peoples information with regard to the fuel rails of an S4 being just tapped. (I'd read they needed to be welded, and when I'd attempt to confirm it I'd get different people saying that you can just NPT tap it)

My question is, with the sizes I have for the NPT taps will I be able to modify the S4 fuel rail to support the -an lines using an NPT to -AN line adapter?

I'm planning on doing both the Primary and Secondary rails by tapping (as opposed to welding). Will I be able to use the sizes I have (the two 1/2" taps are for different hole sizes: 13/32" (18mm) and 45/64") or will I have to buy a larger/smaller tap?

I'm not sure about the N/A rails, but S4 TII rails are already threaded. Some metric 1.5 pitch, don't recall exactly what.

But have a look at the N/A one's you've got, if the PD and FPR are threaded in and not stamped as part of the rail, just undo them and take a thread gauge to them and purchase the appropriate adapters.

Also, the tap's you've got should fit in the diameter, but there may not be much beef in the rails for a tapered thread if they're stamped pieces..........and if they're not stamped, you won't need to tap because they're already threaded :lol:

The rails should already be threaded...

The secondary rail is not threaded where the Pulsation Damper is. It's a flange.

S4 fuel rails should be all metric threaded.
At least US-spec ones are...
I dunno where you got your secondary fuel rail from, but all US-spec S4 turbo fuel rails have the PD on the primary fuel rail.
The PD end should be 12mm x 1.25.
The other 3 ends should be all 14mm x 1.5.

Aeromotive just came out with an adapter that goes from 5/16" hose end to -6AN male.
This makes it a lot simpler to mate our stock fuel lines to any AN set-up.


-Ted

My rails aren't turbo. I don't have access to my car at the moment, but I will try to snap a picture of the rail. There's definitely a flange.

Just double checked it, there's a flange for the FPR on the secondary. It has two mounting bolts (probably 10mm) that hold it on.

Digging up this old thread: I didn't ever get around to taking a picture of it. Turns out the FPR was what I was talking about and regardless of what the threads were on the three sides that were threaded, to use the most common -AN adapter will need to be drilled out to 3/8"

The FPR on the S4 fuel rails was a flange type, and in my case I had tons of RUST in the fuel rails. Not a good thing, so I drilled out the center with the closest matching drill for the secondary (the primary was surprisingly clean). I have also begun modifying the fuel rails to accept the 3/8" NPT thread by grinding off the cast flange sides and the other "stopper" style casting on the other end of the secondary. I'll still need to drill out and tap the ends to accept the 3/8" pipe thread but all in all this should be a fairly easy modification for a nice result.

Do you need larger fuel line for what you're running or are you just getting into this for kicks? Just curious...

How much boost are you planning to run and what size injectors are you putting into the rails?

Just for kicks, I think a majority of the problem I was having came from the surface finish on the inside of the secondary. It gave a place for the fuel deposits (rust, dirt, crap) to collect before coming loose and getting lodged and disabling the fuel injectors. I drilled out the interior of the fuel rail purely because it was so dirty. The actual increase in diameter was null, I may have increased it by 1/64" if anything at all.

I'm planning on going to -6 AN and running a parallel fuel setup. This will feed 680/720 Injectors. Granted not very large injectors but enough to run 5-7psi (maybe more when I have enough to rebuild/port my engine). I'm also doing this for easier connections and disconnects when I pull the UIM. If I really desired to I could run -8, but there's really no reason to at the moment.

If I had a proper feeler gauge I may port the fuel rails to even larger, but honestly for the power gains I'm looking for it shouldn't be that big of a deal. Only looking to make 200-300HP (a good 33-110% increase in power from what I'm making now).

Use 1/4" npt.

If you dont care about stupid overpriced fancy an lines, you can get an npt to barb adapter and run 3/8" lines which are the same size as -6an and costs way less.

You should be able to make 300whp with those injectors with a proper tune.