Reinforced ARP cylinder head studs Toyota 20R 22R

The engine concerned

The Toyota 20R (2.2 litres) and 22R (2.4 litres) are eight-valve inline four-cylinder engines, fitted notably to the Celica, Corona and Cressida. ARP matches both engines to its 203-4201 stud kit, in 8740, supplied with 12-point nuts.

As built, the 20R and 22R cylinder head is secured by head bolts; ARP kit 203-4201 replaces them with studs and nuts.

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 203-4201 brings together 8740 studs with an M12 x 1.25 thread and ten 12-point nuts. According to the instruction sheet, the gasket and head go on first, the studs are then screwed into the block by hand, and threads and nut undersides take ARP Ultra-Torque before torque tightening. ARP makes these fasteners in 8740, a chrome-molybdenum steel whose tensile strength reaches 190,000 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. On this four-cylinder engine, the limit of the 8740 studs in M12 x 1.25 lies at 600 hp (calculated estimate).

Technical specifications

Tightening torque

Each stud is screwed into the block by hand, without torque. This kit's instruction sheet does not mention thread locker; ARP states that some engine builders use a medium-strength (blue) one on the block end, but never on the nuts, never with ARP grease, and only if tightening is finished before it hardens.

The instruction sheet gives two loads: 95 Nm for an original-spec rebuild without machining, 122 Nm for a prepared engine whose block and head have been machined; this page uses the ARP load of 122 Nm.

After the three passes, each nut is loosened and then retightened to the final value, one after the other.

The valve cover may need clearance above the two front studs.

Tightening to torque is done in three steps, in the order set by the engine manufacturer, with ARP lubricant applied to the threads and under the nuts, a condition for the table values to apply.

Values taken from ARP instruction sheet 203-4201, 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 203-4201 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

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
Block threads	Stressed at every tightening	Preserved (studs fitted hand tight)

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:

• Output raised on a 20R or 22R, with a turbo, a supercharger or a heavily tuned build
• 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 pushed 20R or 22R, the original bolts are the first to limit gasket retention. ARP 8740 studs offer a higher clamp load, for a price out of all proportion to a cylinder head to be reworked, gasket and labour included.