Reinforced ARP cylinder head studs Honda B20A5

The engine concerned

The B20A5 is the naturally aspirated 2.0-litre, 16-valve inline four-cylinder (1,958 cm³) of the Honda Prelude III (BA4), built from 1987 to 1992. ARP offers a single stud kit for it, the 208-4703, in 8740, with 12-point nuts.

As standard, the B20A5 cylinder head is secured by head bolts, which this kit replaces.

Reinforced ARP cylinder head studs

The job of the head fasteners is to keep the cylinder head locked to the block despite the pressure inside the combustion chambers. They keep the gasket compressed; as soon as their clamping force drops, leaks appear between head and block.

For this four-cylinder the ARP catalogue lists the 208-4703 kit, in 8740, with 12-point nuts. 8740 is a chrome-molybdenum steel, rated by ARP at 190,000 psi tensile strength. As a reference point, an engine's standard fasteners mostly belong to property classes 10.9 and 12.9, with a minimum tensile strength between 150,800 and 176,900 psi. As an estimate, this 8740 kit with 12-point nuts suits tuned B20A5 engines beyond the original output.

Technical specifications

Tightening torque

Technical guide

When assembling, the threads and the nut bearing faces receive ARP Ultra-Torque lubricant rather than engine oil. The torque and tightening sequence are to be read in the instruction sheet supplied with the kit.

ARP undercut studs

An undercut stud has a reduced-diameter shank. This profile, ARP explains, spreads stretch more evenly across the studs: the cylinder head is clamped with a steadier force, gasket compression is better compensated and the gasket is less likely to fail.

The ARP brand

Gary Holzapfel, a former aerospace engineer, created ARP (Automotive Racing Products) in the early 1970s to tackle engine failures caused by insufficiently strong fasteners in racing. Today the brand develops and manufactures thousands of parts in California, available in several material grades as needed.

Advantages over the original bolts

Criterion	Original head bolts	Reinforced ARP studs
Engine block threads	Stressed at every tightening	Preserved: the stud stays in place

When studs become necessary

Standard fasteners remain suitable as long as the engine keeps its original combustion pressure. They reach their limits in the following cases:

• Tuned B20A5 for fast road or track use: combustion pressure raised beyond stock
• Compression ratio raised for more power
• Reinforced MLS head gasket, which requires a high and even preload
• Cylinder head that has already lifted or gasket that has already leaked
• Racing or track use, with repeated heat-ups and frequent teardowns

Vehicle compatibility

Why is it the most cost-effective solution?

On a tuned B20A5, the original head fasteners limit the pressure the gasket can hold. 8740 studs with 12-point nuts push that limit back, for an outlay that bears no relation to redoing a cylinder head and gasket.