Buddy, The reason I went with the cast aluminum girdle was that the pattern already existed (Doug Robinson was kind to loan it to me) and the sheer size of the part to machine from a billet was too much. The girdle has three extra mains and three extra cam supports to help with stability (because of our bigger base circle we are using 460 Ford cam bearings). We also went with Dodge 318 main bearings to uniform everything and moved the thrust bearing to the back. The big draw back I see is that the two metals will expand at different temperatures throwing the bearing tolerances off. For this we came up with a starting procedure to get the tolerances we built to.
There’s no IP involved with the lifter. Its an idea that and Kay Sissell and Mike Kirby came up with a long time ago and something I expanded on with the help of Terry Manton to help valve train stability. Due to the long push rods on the GMC, if your going to run any sort of serious lift the push rods will have odd angles and will be reflected in performance. The small lifter in the head fixes this problem and in our case we are running almost a 1” of lift and needed this to take the angle from the head to the rocker arm (I think I have about three sets left).
The other area you want to look at is the rocker arm attachment. In our spintron runs at high RPM the rocker arms tended to wobble around a bit. To fix the problem we came with a girdle for the rocker arm, which also acts as the bottom of the valve cover. It attaches each rocker with two bolts.
The head you have is very nice head and would be a great XXO motor. In our case we are going with a stock head for both XO and XXO, with the XXO running more CI than the 325 allowed for a 12 port. I don’t want to get into specific valve sizes and flow numbers, but I say it can run with the best of the 12 port heads.
The one thing we did from the start of the build was to see how we could optimize everything. I was very fortunate from the start that a lot of good people was open with help on the GMC, the Ferguson’s, Doug Robinson, Armond and Mike Kirby just to name a few.
Now that you are thinking of turning to the dark side, have fun with it and ask away with any questions you have. There is a lot of GMC knowledge on the boards. Tony
