Reinforced ARP cylinder head studs Honda H22A4

The engine concerned

ARP designed this kit for the 16-valve inline four-cylinder VTEC Honda H22A4 (2.2 litres), fitted to the fifth-generation Honda Prelude (BB).

As built, the cylinder head is held by ten Honda head bolts (part 90005-PCB-003, M10 x 1.25 thread, 10 mm diameter), tightened in three stages to 39 Nm, then 69 Nm, then 98 Nm.

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 208-4304 is the stud kit intended for this engine: 8740, 12-point nuts, M12 thread. Per the instruction sheet, the studs go into the block by hand before the head is fitted; threads, nuts and washers then take the ARP Ultra-Torque lubricant supplied, and tightening is done in three equal passes, following the manufacturer's sequence. ARP makes these fasteners in 8740, a chrome-molybdenum steel whose tensile strength reaches 200,000 psi. To put this figure in context, original engine fasteners generally belong to classes 10.9 and 12.9, whose minimum ranges from 150,800 to 176,900 psi. In M12, 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.

Where needed, the instruction sheet says to clean up the block threads with the ARP thread chaser.

For any stud that opens into the water jacket, the instruction sheet asks for its block-side thread to be coated with ARP thread sealer.

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 instruction sheet also calls for ARP lubricant on the washers.

The torque figures above come from ARP instruction sheet 208-4304, revision applicable on the day the page went online. The official instruction sheet prevails in case of difference and describes the complete procedure, tightening sequence included. Read the ARP 208-4304 instruction sheet

Technical guide

All torque values on this page are given with ARP assembly grease on the threads and under the nuts; another lubricant would make them wrong.

The ARP brand

Founded in the early 1970s by Gary Holzapfel, who came from the aerospace industry, ARP (Automotive Racing Products) set itself the mission of eliminating engine failures caused by inadequate fasteners in competition. Its thousands of parts are designed and produced in California, in several material grades depending on the application.

Advantages over the original bolts

Criterion	Original head bolts	Reinforced ARP studs
Tightening method	39, 69 then 98 Nm	Three equal torque passes
Block threads	Stressed at every tightening	Preserved: studs fitted by hand

When studs become necessary

On an engine left standard, the original fasteners do their job. Switching to reinforced fasteners becomes worthwhile as soon as:

• H22A4 taken beyond its stock output, as a tuned naturally aspirated engine or with forced induction
• The compression ratio is increased
• A reinforced MLS gasket is fitted, with its need for a high and even preload
• The head has already lifted or the gasket has already failed
• The engine is used in competition, with intense heat cycles and repeated teardowns

Vehicle compatibility

OEM reference: 90005-PCB-003

Why is it the most cost-effective solution?

The original head bolts of the H22A4 are sized for stock output: as power climbs, they are the first to limit gasket retention. A kit of ARP 8740 studs gives a higher clamp load, for an outlay far below that of redoing a cylinder head, gasket and labour included.