You were also concerned about knowing what torque spec to use for the studs. New performance fasteners will include torque specs, and you should expect them to differ from stock, since the material used and the dimensions of the studs are going to be different. Make sure to also use the recommended thread lubricant.
This discussion does raise one other issue on resizing. Just to be clear, when connecting rods are fitted with new fasteners, resizing is generally considered mandatory. The clamping of the fasteners has a greater effect on the shape of the rod's journal bore and the alignment between the cap and rod than the main fasteners do on the main saddles. Even when removing and reinstalling the same rod bolts, many machinists will recommend resizing, or at least checking the dimensions, which must be done at several points inside the rod's big end after the cap is torqued in place.
Vexed About VortecI plan on building a small-block using a set of the Vortec iron heads. How many different casting numbers for the Vortec heads are there, and which set flow best? Also, I am confused about something I've heard. Someone told me that the Vortec with the casting number ending with 062 flows better than the heads ending in 906. Is this true? If so, what is the difference?John Andersonvia e-mail
The Vortec iron heads have quickly become the darling of the small-block-Chevy street crowd. These heads were originally used in the L-31 iron Vortec TBI 11/42-ton pickup applications. A similar iron Vortec was also used in heavy-duty 31/44- and 1-ton truck applications. These heavy-duty heads used pressed-in exhaust-seat inserts (as opposed to induction-hardened seats) that intrude slightly into the exhaust port. As a result, the exhaust port flow is not quite as good in these heads as in the lighter-duty applications. According to Ken Casey at Burt Chevrolet (800/345-5744) in Englewood, Colorado, the good casting numbers are the ones you mentioned (10239906 and 12558062). But here is where it gets a little confusing. As far as we can tell, the factory took the existing 906 casting and modified it for the exhaust-seat insert. This means that when you find a used 906 casting, it could be a good one or it could have the exhaust-seat insert. The good news is that this intrusion into the exhaust port could be easily ported out to the exhaust-seat size to improve the exhaust-port flow. We don't know if that ends up being better or worse than a stock Vortec exhaust port. But at least this is some hard data on the different casting numbers.
There are several caveats that are important to know about for using the Vortec heads. Comp has a new machine tool that will reduce the inside diameter of the Vortec iron valveguide as well as the guide height to allow standard-diameter springs that will improve clearance and prevent retainer-to-seal interference. Another interesting tidbit is that you will need to elongate a section of the pushrod holes when adding 1.6:1 roller rockers. If you fail to do this, the pushrods will contact the edge of the slot and rub on the cylinder head sending cast-iron filings into the oil, which is not good. This is because the 1.6:1 ratio moves the pushrod cup in the rocker closer to the rocker stud, creating the interference.
These heads also require the centerbolt-style valve cover. Keep in mind that some of these heads require a narrow-body rocker arm when using roller rockers with some centerbolt valve covers. Also, the stock Vortec heads do not include guideplates, so guided rocker arms are required with these heads. Finally, GM makes an excellent Vortec intake-manifold gasket (PN 12529094) that clips into place without RTV sealer. This does require the GM attachment bolts (PN 12550027), which use a ball design on the end that seats in the heads to prevent over-torquing the intake bolts so as to avoid crushing the intake gasket.