I'm using Delphi 80lb injectors that are about 2.94" long and a holley 9900-172 fuel rail kit and 9901-101-1 manifold. I was test fitting the injectors onto the fuel rails and intake and it seems the injectors are too tall. Did I get the wrong injectors, or do I need to modify the mounting tabs on the manifold to accept them? Here is a link to the injectors.
http://racetronix.biz/itemdesc.asp?ic=FI114991&eq=&Tp=

Update. I got the intake back from the miller today. I milled 1" off the top so it'll fit under the tstock cowl and hopefully let me retain my 4 point STB. He also filled the stock fuel rail mounting holes and re drilled/re tapped them to accommodate for the difference either caused by the injectors being longer or the o-ring being bigger and therefore not seating all the way. I think this will work since the injectors are wedged in there and have nowhere to go. The injectors couldn't really be installed to much deeper or they would be protruding into the intake runners. Here are a couple pics of the finished product.

 

Let's see if anyone else has even tried that custom fuel rail and intake manifold combo.

 

Should the injector nozzle sit down past the top of the runner? I can machine the injector bosses down a little to allow the injectors and fuel rail to work together and still keep the injectors from protruding the top of the runner.

 

Again, without knowing the specific details of the intake manifold runners, and how the injector boss sits in the runner, its impossible to even speculate. In the LT1/LT4 intake manfold, the injector tip is recessed and shrouded from direct impact by the incoming air, and is aimed directly at the valve.

Here's a cross-section of the intake manifold (or at least a little bit of it) and head, showing the intector tip in the upper left corner:

http://www.grandsportregistry.com/lt1vslt4.htm

Sroll down to the first photo of a cross-section, not the full engine.

 

It looks as though I can machine the injector bosses down a little to make this work. Here is another question. Right now the o rings on the injectors don't fit into the bosses, they just kind of sit on top. Should I machine the bosses so that the o rings fit into them like they do in the fuel rails? The bosses are tapered right now. I would open that up and make a straight recess so the injector o rings will fit into the bosses. I sold the stock motor complete so I wasn't able to look at things for the rebuild so I've got a few questions.

 

I would check with someone like Kinsler. They do this stuff every day, and sell the recommended boring bits for various injectors.

http://www.kinsler.com/page--Home-Page--13.html

 

Yes, the O-Ring is supposed to be "inside" the hole, not on top of it. This includes any chamfer, and the hole must be sized to put the correct preload on the O-Ring.

 

So the o ring shouldn't be sitting on the bevel, it should be inside the hole? Any pictures to clarify this. I dropped off the intake today to get this fixed and we were just going to fill the existing fuel rail mounting holes and re-drill for the correct height.

 

No, but this is how O-Rings work. They are not gaskets. They are soft and plyable. The fuel(etc.) pressure on the O-Ring expands the ring which fills and seals the gap. If they sit on top of the hole the pressure will simply displace the O-Ring, and it will leak.

 

Why would they make the injector boss beveled like that instead of just a straight hole if it weren't meant to sit in the bevel? Are there smaller injectors that would fit into this hole. You'd think most injectors would have a pretty standard nozzle and therefore o ring.

 

"Why would they make the injector boss beveled like that instead of just a straight hole if it weren't meant to sit in the bevel?"

It's beveled to lessen the chance of damaging the O-ring during the install. It eliminates having to force the O-ring past a 90° lip. When you remove injectors you realize how tight a fit is needed to maintain a perfect seal in both hot and cold conditions, for years.

 

Sounds like your injector bosses are too small. That's why I mentioned the boring tool. Injectors come in vrious diameters, and have to have the correct boss diameter in the manifold.

http://www.kinsler.com/handbook161.html

 

Updated with pics. Hopefully this will work. Does anyone see any potential problems with the way the o-rings are seated. They really don't have anywhere to go. We clamped the fuel rail down onto the intake with the injectors installed and drilled the mounting holes for the rail to keep them snug. You can see in the pics that the injectors are already pretty close to the top of the intake runner.

 

I think the reason your injectors seem "too long" is because they aren't seating deep enough in the boss. The O-ring should not be visible. It should be between the outside diameter of the injector and the internal diameter of the boss, filling the annulus between the two. That gives the O-ring the correct sealing pressure. The bosses for many popular injectors have inside diameters of 0.530", 0.545"and 0.565". Look at the Kinsler reference for various types, including Rochester and Bosch.

I would ask the manufacturer of your injectors what size boss it needs.