Reinforced ARP cylinder head studs FORD CVH 1.6 Turbo

The engines concerned

Ford's 1.6-litre CVH turbo is a 1,597 cc in-line four-cylinder (80 mm bore, 79.5 mm stroke) with eight valves and an overhead camshaft, boosted by a turbocharger. It powered the Ford Escort RS Turbo from 1984 to 1990 and the Fiesta Turbo from 1990 to 1992.

As standard, the cylinder head of the CVH 1.6 Turbo is secured by cylinder head bolts, which the ARP studs replace.

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.

The 151-4203 is an 8740 kit, 10 mm in diameter. According to its instruction sheet, the studs are screwed into the block by hand before the head is fitted, then the nuts are tightened in three equal passes, once the threads, washers and nuts have been lubricated with ARP Ultra-Torque. 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

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.

According to the sheet, ARP thread sealer goes on the block-side threads when the studs open into the water jacket.

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.

The torque figures above come from ARP instruction sheet 151-4203, 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 151-4203 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

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
Block threads	Stressed at every tightening	Spared by hand-tight fitting

When studs become necessary

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

• CVH 1.6 Turbo built for fast road, rally or track use (raised boost pressure)
• 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?

A standard CVH 1.6 Turbo, 132 hp in the Escort RS Turbo, runs with a reserve sized for series output. As soon as higher boost, a raised compression ratio or a competition build pushes up cylinder pressure, the head and its gasket move to the front line. ARP 8740 studs keep the head pressed down with a steadier clamping load; stripping an engine for a blown gasket costs far more than this kit.

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: