Reinforced ARP cylinder head studs Honda D16Z2 D16Z5

The engine concerned

ARP intends this kit for the Honda D16Z 1.6-litre four-cylinder (1,590 cm³, 75 mm bore, 90 mm stroke), in D16Z2 and D16Z5 form, excluding the D16Z6 and D16Z7. It powers the Honda Civic IV and V, Concerto, CRX II and Domani, among others.

As standard, the D16Z cylinder head is held by 11 mm head bolts (M11); ARP kit 208-4301 replaces them with 10 mm studs.

Reinforced ARP cylinder head studs

Cylinder head fasteners work constantly: they hold the head tight against the block, crush the gasket to the right value and hold back the push of the gases at every combustion. If they lose even a little tension, the gasket starts to leak.

ARP kit 208-4301 pairs M10 x 1.5 studs in 8740 with 12-point nuts. According to the instruction sheet, the studs are screwed into the block by hand before the head goes on, threads, nuts and washers take the ARP Ultra-Torque supplied, then the nuts are tightened in three equal passes up to 60 ft-lb. 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 M10 x 1.5, the 8740 studs hold up to 500 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

The studs are fitted into the block by hand, without a torque wrench. For a permanent installation, the instruction sheet accepts thread locker, with tightening to be completed before it sets.

The instruction sheet calls for the block threads to be cleaned thoroughly before the studs go in.

For a stud that reaches the water jacket, the instruction sheet specifies the ARP thread sealer on its block-side end.

Final tightening is done in three successive stages, following the manufacturer's tightening sequence; these torque figures only hold with ARP assembly lubricant on the threads and under the nuts.

According to the instruction sheet, ARP lubricant is also applied to the washers, as on the threads.

Source of these values: ARP instruction sheet 208-4301, revision current at the time of publication. The official instruction sheet applies if any discrepancy appears; it covers the entire procedure and the tightening sequence. Read the ARP 208-4301 instruction sheet

Technical guide

To obtain the intended preload, ARP assembly grease must be present on the threads and under the nuts: the torque figures in the table are established with it.

The ARP brand

ARP (Automotive Racing Products) was born in the early 1970s from the initiative of Gary Holzapfel, an engineer from the aerospace industry, determined to eliminate engine failures caused by weak fasteners in motorsport. The company designs and manufactures thousands of parts in California, in several material grades suited to each use.

Advantages over the original bolts

Criterion	Original head bolts	Reinforced ARP studs
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:

• D16Z2 or D16Z5 tuned: output above the stock level
• 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

Why is it the most cost-effective solution?

On a tuned D16Z, the higher combustion pressure works the head gasket harder. ARP studs in 8740 clamp the head with a higher load than stock, for a cost out of all proportion to reworking a cylinder head, gasket and labour included.