Porting to a 1262 or 1262-RSizePort? Read This!
We may choose to use some intakes that may have been designed with a typical SBF 1250 size port and location and port them for use on larger heads that have larger cross sections and in some cases, a higher port location. When that happens, you need to be aware of something that is likely to happen and how to work with it. Cases in point are a couple of intakes that we will use as examples, A Holley Systemax II and an Edelbrock RPM I. There are other examples; we’ll just use these as they are what I took pictures of while working.
The issue revolves around the injector stop in the lower injector bung barrel. As you enlarge the runner, and especially when the head port may be raised from the stock location, you will be taking material out of the bottom of the injector barrel and may wind up removing the stop all together. If you know this will happen, no issue, but if you did not you may think you ruined the lower. Not so – here is what we do.
First off, here is a pic of the stop that lower intakes have machined in them from the factory
Now, if your new port is larger and higher like the pic below, you will be taking the injector stop out. Please excuse the template; it was done as a quickie just to illustrate a TEA TW 205 port on an Edelbrock RPMI lower.
Another intake where this will happen is a Holley Systemax II lower if you get a good large radius in the roof of the runner. Here is a close up of what a Holley injector barrel looks like with the stop removed. What we need to do is to create a new stop and in the process, we get the benefit of a second seal. What we do is add an o-ring to the injector, be it steel pintel style or plastic disc style. In this photo you can see the plastic body injector with the second seal added beside the injector barrel.
The second o-ring will hold the injector up higher in the injector seal barrel and it will also seat in the bevel machined into the top of the barrel. The injector rail is slotted in the mounting hole brackets to accommodate the slightly higher position and when you tighten the rail, just put about 5 pounds of pressure on the side of the rail to seat the o-ring. The really nice part about the second seal is that if any vacuum gets to it, it will pull the o-ring down tighter into the bevel and create and even better seal.
Here is a pic of the two styles of injector bodies that most of us use – you can see that adding the o-ring is very easy. In the steel body injector, the o-ring is up against a step in the steel body and in the plastic body injector, there is actually a second o-ring grove that seems to be made just for this kind of use.
Here is a Holley lower with all the injectors installed and the new top seals can be seen.
I hope this has helped point out something that you will likely have to deal with at some point if you do some porting and if you did without realizing what you needed to do for a new injector stop, help you realize you didn’t screw the pooch after all.
Tom
tmoss