Reinforced ARP cylinder head studs Honda K20A2 K20A3

The engines concerned

This kit fits the 16-valve inline four-cylinder 2.0-litre i-VTEC Honda K20A2 and K20A3 engines, fitted notably to the Civic Type R (EP3) and the Civic 2.0i Sport.

As standard, the cylinder head is held by Honda head bolts (reference 90005-PNA-003, M11 thread, 155 mm long), tightened to 39 Nm then by two further 90° turns, plus one more 90° for new bolts. This torque then angle method stretches the bolts permanently.

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.

ARP reference 208-4701 is the stud kit intended for these engines: 8740, 12-point nuts, 7/16 in thread. The instruction sheet starts with cleaning the block threads; the studs are then screwed in by hand before the head goes on, and the threads, nuts and washers get the ARP Ultra-Torque lubricant supplied before tightening in three equal passes, in the manufacturer's order. 8740 is a chrome-molybdenum steel, rated by ARP at 200,000 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. In 7/16 in, the 8740 studs hold up to 600 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

No torque is applied to the studs as they go into the block: they are screwed in by hand. The instruction sheet leaves the option of thread locker to mount them permanently, provided tightening is done before the product hardens.

If necessary, the block threads are chased with the ARP thread chaser, as the instruction sheet states.

For studs that open into the water jacket, the sheet recommends ARP thread sealer on the block side.

Follow the tightening sequence recommended by the manufacturer and bring to torque in three stages; the stated values assume ARP lubricant on the threads and under the nuts.

The washers also receive ARP lubricant, as stated in the instruction sheet.

Values taken from ARP instruction sheet 208-4701, in the revision current on the date of publication. In the event of any discrepancy, the official instruction sheet prevails; it also details the full procedure and the tightening sequence. Read the ARP 208-4701 instruction sheet

Technical guide

The stated tightening torques only make sense with ARP assembly grease, applied to the threads and under the nuts.

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
Tightening method	39 Nm then +90° +90°	Three equal torque passes
Block thread	Works at every fitting	Preserved: studs screwed in by hand

When studs become necessary

The original fasteners are sized for the engine as it leaves the factory. They need to be reinforced when:

• Power exceeds stock output, in a strongly tuned naturally aspirated or a boosted build
• The compression ratio rises as the build progresses
• The original gasket is replaced by a reinforced MLS gasket, which requires a high and uniform preload
• The engine has already suffered a lifted head or a gasket leak
• Competition use imposes severe heat cycles and regular head removals

Vehicle compatibility

OEM reference: 90005-PNA-003

Why is it the most cost-effective solution?

The original K20A2 and K20A3 head bolts are sized for stock power: as output rises, they are the first to limit how well the gasket holds. A kit of ARP 8740 studs brings a higher clamp load for a cost far below redoing a cylinder head, gasket and labour included.

Consider a reinforced head gasket

To get the most out of reinforced fasteners, pair them with a head gasket that withstands the same pressure. Here is the gasket we offer for this engine: