Michael Galimi
May 5, 2010
Photos By: Steve Baur

"Head studs offer better clamping than head bolts due to a more consistent clamping force. Head studs only have one force when you are tightening them, whereas a bolt has twist and stretch while it is being torqued. I recommend studs when you build an engine with nitrous, a supercharger, or a turbocharger. It is also good for when you are removing the heads frequently," noted Sink. Fel-Pro's Rotunno also suggests a switch to studs because the more times you remove a bolt, the greater the chances of wearing out the threads in the block.

Some believe that adding more torque to the bolts will yield better clamping force, but it is just the opposite. "If you over-torque the fastener, you can take it past its yield point. The yield point is the stress level to which a given material exhibits a permanent deformation. Once that occurs, you've compromised the material," stated Sink.

Adding larger head studs is one way to achieve more clamping force. The stock 5.0L utilizes 7/16-inch head bolts or studs, but it can be modified to accept larger 1/2-inch studs or bolts. However, if you need to modify a stock block for 1/2-inch hardware you're better off going with an aftermarket block (which will have provisions for 1/2-inch hardware). The larger hardware allows for a greater torque range when bolting down the heads-75 ft-lb for the 7/16 versus 105 ft-lb for the 1/2-inch studs. The 4.6L engines usually run just the 7/16 inch.

One of the most important things to know when dealing with bolts or studs is that some sort of lubricant must be used on the threads and under the head of the bolt during the torquing process in order to get accurate torque readings. Assembly lube or special lubricant from ARP is the best stuff to use, but we've seen motor oil used in a pinch. The torque ratings vary depending on the lubrication used, so we suggest checking with the manufacturer prior to any installation.

Specs You Should Know

  • 5.0L stock head-gasket thickness: 0.041 inch (compressed)
  • 4.6L stock head-gasket thickness: 0.036 inch (compressed)
  • 4.6L stock head-gasket thickness: 0.041 inch ('03-'04 Cobra engine, compressed)

Varying the thickness of the head gasket will change the compression ratio; a thicker gasket will create a larger combustion area, effectively lowering the compression. A thinner one will have the opposite affect. Altering gasket thickness is a good way to make slight adjustments, but it can have adverse effects. Gasket variances will change the height of the cylinder head, forcing a possible change in pushrod length. On a modular engine, it can change the cam timing, so we recommend sticking with traditional-sized gaskets.

Torque Rating

  • Torque rating for 7/16-inch head bolt: 75 lb-ft
  • Torque rating for 1/2-inch head bolt: 105 lb-ft

Torque-to-yield bolt for modular engines:
Two-Valve

  • Step 1: Tighten using 30 ft-lb
  • Step 2: Turn an additional 90 degrees
  • Step 3: Loosen one complete turn
  • Step 4: Tighten using 30 ft-lb
  • Step 5: Turn an additional 90 degrees
  • Step 6: Turn an additional 90 degrees

Three-Valve

  • Step 1: Tighten using 30 ft-lbs
  • Step 2: Turn an additional 90 degrees
  • Step 3: Turn an additional 90 degrees

Four-Valve

  • Step 1: Tighten using 30 ft-lb
  • Step 2: Turn an additional 90 degrees
  • Step 3: Turn an additional 90 degrees