I have removed the steel line set from my fuel rail to use braided lines and -AN fittings. Where the feed line hits the fuel rail, it is has about an inch that extends into the rail. I cut the line flush, and noticed the internal size of the restrictor (the part of the line inside the passenger fuel rail) is pretty small, about 1/8" or so. It is restricted like this, at point for both fuel rails.

My question is should I open them up some? This restriction is there for a reason, but I don't know why, and for performance it looks like it would limit fuel at some point.

Have any of you that have modded your engines dealt with this before?

Sorry I don't have any pictures. I can get some if it is confusing.

Thanks,
Scott.

 

Surely someone here knows something about this, or added aftermarket lines.

Or is modding the fuel rail a no-no?

 

I'm not sure what you are referring to. Do you have a pic? I've gone to -6AN lines but I just bought adapters...

 

Here is what I want to do. Thread the feed and return, and put NPT to -AN fittings in.



Here is the passenger side fuel rail after cutting the steel feed line off. The steel line is apparently pressed into the rail.



Looking into the bottom of the hole, you can see it is severely necked down. It is necked down on the side that feeds across to the drivers side rail just the same.



I'm trying to figure out the reasoning behind this. It can't be to make pressure, since it opens back up behind the steel insert, plus there is a regulator.

Any ideas why it is really this way? That little hole will not flow very much fuel I would guess.

 

honestly, I don't think there is any real purpose for that. I would drill it out if you need to...

 

Pretty sure it is to make pressure. Like when you have a garden hose and place you thumb over the end to make it spray better, that's building pressure, just like that small hole does as it feeds into the rest of the rail, because the fuel has to shoot over to the driver side rail.
That's just what I think though.. I may be wrong

 

I'm in the process of doing the fuel rail rear exit and saw this thread about drilling out the restrictor. So, I drilled the rail out from the front and also where the crossover tube comes in from the side. It turns out that the fuel rail is not a solid piece of aluminum and there must be a hollow area b/c I was left with 2 small holes on the inside of the fuel rail. It might not have been a problem since the fuel probably can't leak out, but I wasn't going to wait until I had everything bolted back up to find out that I was wrong. So, using a spare rail, I decided to not drill out the restrictor.

 

so just to clarify. the pressure line goes into the regulator and the return line would go out through where the ninth injector was?

 

No, you have it backwards. Pressure to rail, return from regulator.

 

No, that is the fuel regulator's job. GM did some ridiculous things back in the 80's w/the F-Body's, with that fuel rail restriction being one of them. I remember cutting off the same line to a TPI fuel rail but off of a Corvette, and that restrictor wasn't there....

 

I dont see how it was ridiculous when it supported the stock engine and then some.

 

It would only make pressure behind the restriction, which is in the fuel line. you want the pressure in the fuel rail behind the injectors. <Pressure regulator's job. I've seen the same thing behind an fuel rail I pulled from an 85 Vette. There was no restriction there...........

It looks to me as if they were put in there to handicap those cars or something.


You can only flow as much fuel as the smallest restricted part in the system will flow...............

 

Your obviously not looking at the overall picture. It is in fact ridiculous because there was simply no need for them to do that in the first place, but they went out of there way anyway to do so. Of course it supported the stock setup, as I'd imagine that they wouldn't of sold any cars back then if it didn't lol....

Key on prime's the engine and pressure is immediately built in the fuel rail w/out even starting the engine, simply depressing the schraeder valve will immediately embellish this. The fuel pressure regulator, whether it be a dead-head, or an adjustable, controls the amount of pressure being supplied to the injectors. The injectors fire either sequentially, or in batch mode, they are not always open, so pressure is going to build behind them via the fuel pump regardless if that restriction is there or not....

Agreed....

 

I do see the big picture thats why I dont agree with you. You have no idea why GM did what they did with the fuel rail. It may have been cheaper to produce for all we know.

 

it was most likely there as a surge suppressor, the small orifice helped smooth out fuel flow. regardless of why it's there and the purpose it served, it is a flow restriction, and it has been removed before. The guy(marty) that ran the junkyard twin turbo trans am into the 9's from the turboforums removed the restrictions. I would only open it up as much as the ID of the fuel line, anything bigger is not necessary.

 

There is one more restriction to deal with, in the feed for the driver side fuel rail. It is in the same steel insert in the passenger side fuel rail, (previously discussed) where the driver side feed tube meets the passenger side fuel rail. If you look in you can see the small opening. There is another small hole 180 deg. in the back, like they were drilled and a groove was then milled in the insert. I know that the two holes will flow "X" amount of fuel, but I opened the hole feeding the driver side tube. Both will flow more fuel than I will ever need for this engine.

 

So far I'm ~500hp which is the same fuel amount for ~600hp n/a without anything drilled out. I know Marty's #'s were higher, but I'm curious if his setup was actually being restricted or if he drilled the fuel rail out because he thought it would be a restriction.