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Hi everyone. It's been a while since I visited the forums. Been very busy. I'm preparing to build a new fuel system for my 87 IROC Z28 project and want to reuse the factory fuel rails. In order for them to work, I'll need to bore them out to maximum inside diameter and I also plan to re-engineer them for AN front and rear inlet/outlet. I wanted to ask who else has done this. I know that I'm not the first. What size did you bore them to? It seems like they would support a 3/8 inside diameter without getting too thin? What type of bit did you use? I was thinking of a long carbide with lots of oil and patience. Any thoughts?
Basically what I did was bore out the front passanger rail(removed the hardline) to a 3/8npt.
The only issue I had was that when you remove the hardline, there is a sleeve that is a bit larger than the drill size for a 3/8npt. I had to overbore the rail, put an aluminum slug in, weld it, machine it and then drill the slug. Otherwise it works really well.
Then used -6 to 3/8npt fittings and braided line to the stock hardlines on the frame rail.
For the return I used the stock regulator and drilled/tapped it for a 3/8npt as well. The only issue with that is that you have to use a drill press to get your drill hole center in the actual block. The stock return line is offset and if you just over drill the current hole (using the current hole as a pilot) you will break through when you tap it.
Thanks hrspwr for your reply. Sounds like it may be more work than I thought. Not a big problem. Just means I may have to tear down the intake at home and rework the rails rather than do the whole job at the shop at the shop. I was hoping to do the rails over a weekend. I don't have the facilities to weld aluminum nor to machine parts. I can only do limited fab work with what I have. That means I'll have to farm out any welding or machine work. Having the car down for a little while isn't a problem since I only drive it a limited amount anyway and only in the summer.
It would probably be good to find a spare set to work over, but the whole idea is to use what I have.
Gun drills are made for deep hole drilling. Be careful of the feeds and speeds, since aluminum is just about as bad as 300 stainless in galling during machining.
However, if you apply a little fluid dynamics you might discover that a very slight increase in pressure will overcome any flow limitation cause by diameter. The equation applies to a practical point, of course, since the resultant flow curve is asymptotic. However, since you likely are not trying to force 600 GPM through the 10mm diameter, there is a fair chance that a slight tweak of the pressure will result in the necessary flow without opening up the passages.
Another method of overcoming flow restriction due to passage size is to change to sequential injection from batch-fire. The resultant smoother flow reduces the peak instantaneous flow rates required, allowing for smaller passages.
I believe I may have been the first one to do the rear feed conversion. I tapped all of them for 3/8" not and used -6 an I believe. I still have the car, and can look at it if you need. You can search powerslave here, I think the pictures of the rail in progress are still out there.
I'll hel however I can, drop me a line if you need.
The real restriction is the feed restrictor . I have cut the feed line off and removed them bye taping it with a 5/16 tap. Use a socket that will go on the od of the insert. Iirc it was 3/4 or slightly larger. You can use a bolt and washer through the socket to extract the pressed in fitting. I have had to heat the rail up with a propane torch as you tighten the bolt to extract the insert. A 1/2 npt can be used to plug the hole after you tap it. The tap will bottom out so you can get the npt plug in a few turns and not block the front crossover hole. You can always drill the plug on it's side if you thread the hole too deep. I don't think it's possible since the tap bottoms out on the step down in the rail.
Iirc the smallest parts of the rail are the crossover 3/8 hard line .
The rails could easily be hogged out to 1/2 if a 1/2npt is about 3/4 .
Last edited by Tuned Performance; 05-05-2015 at 12:26 AM.
I wanted to add it to this thread so more information can be tied together for future searches.
I never followed up on my old thread. I guess I thought there wouldn't be that much interest, only in swaps or non F.I. cars and trucks. I see a lot of folks are or have completed it.
I ended up drilling the steel inserts out and tapping them. Then I used stainless NPT to -an adapters to attach my stainless braided lines to. No leaks up to 70 PSI. Car runs good too!!
Good luck with the conversion. I hope the idea works as well for you as it did for me..
03-31-2015, 09:32 AM
