Reinforced ARP cylinder head studs Toyota Lotus 1ZZ-FE 2ZR-FE

The engine concerned

The 1ZZ-FE is Toyota's 1.8-litre petrol four-cylinder (1,794 cc, bore 79 mm, stroke 91.5 mm), naturally aspirated with sixteen valves; it powers the Toyota Corolla, Celica, MR2 and Matrix, among others, as well as the Pontiac Vibe and the Lotus Elise. The 2ZR-FE, of the same capacity (1,798 cc, bore 80.5 mm, stroke 88.3 mm), powers the more recent Corolla, Auris, Yaris and Matrix, and the supercharged Lotus Elise. ARP matches these two engines with a single stud kit, the 203-4703, in ARP2000, with 12-point nuts.

As built, the cylinder head of these engines is secured by head bolts; this ARP kit replaces them with studs and nuts.

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.

A single ARP kit is offered for these two engines: the 203-4703, in ARP2000, with an M10 x 1.5 thread and 12-point nuts. Its instruction sheet has the studs screwed in by hand before the head is fitted. ARP2000 is an ARP proprietary alloy, heat treated to reach 220,000 psi tensile strength, with threads rolled after heat treatment. Standard engine fasteners mostly belong to property classes 10.9 and 12.9 (150,800 to 176,900 psi minimum): ARP2000 therefore offers 24 to 46 % more margin. In M10 x 1.5, the ARP2000 studs hold up to 500 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

Studs 203-4703: 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.

Before fitting, the sheet has the block threads cleaned, with the ARP M10 x 1.5 chaser if needed.

If a stud opens into the water jacket, the part that screws into the block is coated with ARP thread sealer; Loctite remains tolerated for a permanent fit.

Threads, nuts and washers are lubricated with the Ultra-Torque supplied in the kit, never with engine oil, then tightened in three equal passes.

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.

The instruction sheet also calls for ARP lubricant on the washers.

Values taken from ARP instruction sheet 203-4703, 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 203-4703 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

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:

• 1ZZ-FE or 2ZR-FE tuned, with or without added boost: output beyond stock
• 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 1ZZ-FE or 2ZR-FE, it is the original bolts that cap the load on the gasket. ARP2000 studs of 10 mm carry it much higher, for a budget out of all proportion to a cylinder head to be skimmed and a gasket to be replaced.

Consider a reinforced head gasket

Reinforced fasteners and the head gasket work together: the gasket must hold the same pressure as the fasteners. The matching gasket for this engine: