injector mounting. what part of injector should take force?

[speedracing944]

I am mounting a Delphi 42 lb/hr injector into a intake runner I am trying to sketch up in Solid Works. The problem I have is figuring out what part of the injector should come in contact with the mounting hole. I will be holding the injector down using a cap and 2 bolts which will be tensioned. This in turn will place the injector in compression holding the O-ringed ends in their respective holes. What part of the injector do I have rest on the intake runner?

[joeelutz]

I believe the injector should not be in compression and should slightly float between manifold and fuel rail. This means you should deign so that your fasteners bottom slightly before the injector body is put in compression. Ideally only the O-ring would be in contact with the manifold. I have read that it is bad for the body of the injector to be in contact with the manifold because more heat is transfered to the injector. I believe this is why some OEM's used little metal clips to hold the injector up in the rail.

[samickguy15]

The other issue with the injector being in compressed or hard contact with the manifold/head is vibration. Although, there's minimal vibration isolation as is...I have seen setups use an injector mount which sandwiched the injector, the sandwich mounted to the intake, and then rubber line to the injector. It was on a VW site...

[fury fan]

I agree on the ‘floating’ method of mounting. In addition, the O-rings seal on their side surfaces, so face-sealing is not critical. Furthermore, you can find some port injectors that couldn’t face-seal anyway, they’ve got metal ridges and such at the bottom/below the O-ring that would interfere. OTH, they aren’t floating around by ½”, either. Tight, but not snug-bolt-tight.

I asked a similar question on here a few years ago, got the ‘side-sealing’ answer, so I started fabricating intake bosses based on that. I’m using a wobbly-‘ole drill press, so my fabrications are far from perfect. I can tell you, though, that injector mounting is somewhat forgiving, as I’ve pressure-tested some of my modified manifolds up to ~40 PSI and saw no leaks around the injector O-rings (even if the boss is a little crooked!).