Head studs clamp the cylinder head more evenly and consistently than head bolts and can be reused, so they are the standard upgrade for engines making more power or boost than stock. Head bolts are the factory design, cost less and are easier to service, and many are single-use torque-to-yield bolts. For a stock engine in normal use, quality new bolts are fine; for a built or high-boost engine, studs are the usual choice.
How studs and bolts differ
A head bolt is tightened by turning it into the block, so friction in the threads and under the head, plus twisting of the bolt, all affect how much clamping force you actually get. A head stud is threaded into the block first, then the head is clamped with a nut on top. The stud stretches in a straight line rather than twisting, which gives more consistent clamping force across the head.
Head studs vs head bolts at a glance
| Head studs | Head bolts | |
|---|---|---|
| Clamping consistency | More consistent | Varies more with thread friction |
| Material strength | Usually higher-strength alloy | Factory specification |
| Reusable | Generally yes | Often single-use (torque-to-yield) |
| Cost | Higher | Lower |
| Service | Head may not clear studs in the vehicle on some engines | Easy |
When studs make sense
- Turbocharged or supercharged engines running more boost than stock.
- Diesels with added fueling, where cylinder pressure is high.
- Built engines with closed-deck or reinforced blocks; see closed deck vs open deck.
- Engines with a history of head gasket failure under load, such as some Subaru and Cummins builds; see Subaru head gasket problems and Cummins head gasket.
Installing head studs
- Clean and chase the block threads, and blow out each blind hole; trapped oil or coolant can crack the block when torqued.
- Thread the studs in by hand only, as the stud maker directs.
- Use the stud maker’s thread lubricant on the threads and under the nuts.
- Torque in the sequence and steps the stud maker specifies, which can differ from factory bolt values.
What studs will not fix
Studs add clamping force but cannot cure detonation, overheating, a warped head or a cracked block. Find and fix the cause of a gasket failure, and have the head and deck checked for flatness. For the general symptoms, see signs of a blown head gasket.
Built blocks we list
For Subaru builds, see the IAG 1150 Series EJ25 Short Block ($9,499.99); for Cummins, the D&J Heavy Hauler Common Rail Long Block for the 6.7L ($13,112.99). Check each listing for what hardware is included.
Shipping is a flat $80.00 per order to US addresses, with 15-day free returns. Questions? Ask a parts specialist.