I just picked up a set of 906 vortecs. I am planning on sending these to the machine shop within the next few days to have the guides cut down, valve job and the heads tapped for screw ins so i can use guideplates. I want to use guide plates so that i can avoid buying costly self aligning narrow body roller rockers. My question by install the guide plates wouldnt it change the valve train geometry by making the rocker sit up higher on the head? Would i be safe using stock-length pushrods? Any insight/advice would be greatly appreciated

 

You won't know what the right length push rod is, until you assemble the motor that they're going in.

Adding the guide plates doesn't change the required push rod length. Think about what happens if you take a motor and make no other changes besides adding them. The rocker will end up back in the same place it was before, with teh push rod end sitting on the push rod which is sitting on the lifter which is sitting on the cam; the guide plates don't afect any of those things. The other end of the rocker is sitting on top of the valve stem, and the guide plates don't affect that either. In effect, all that you do, is to move the stuf upwards in the rocker, such that more of it would be sticking out above the rocker nut.

There's more to prepping heads for guide plates than just tapping the holes, though. The stud bosses also get cut down some. It takes about 3/8" more or less usually. But it varies alot; the as-cast height of the bosses is all over the place, and machining them for studs sets them all to some particular height, so it's not like you take off some specific amount from every boss on every head. Rather, you aim to get the top of the boss to some particular height above the deck, but I don't know off the top of my head what that distance is.

 

Thanks Rb, sorry i havent responded in a few days, comp problems. I didnt know that when they machined for guideplates that they milled the stud "hump". I am new to the world of modifying cyl heads. I will check with the machine shop when i take them in, i just wanted to have a heads up before i went in there. Thank you. - Bob