Reinforced ARP main studs for LANCIA Delta Integrale 2.0 16V

The Delta Integrale 16V engine

This kit fits the Lancia Delta Integrale 2.0 16V, whose engine is a 2.0-litre 16-valve turbocharged four-cylinder, coded 831 D5.000 then 831 E5.000 depending on the series. ARP lists it under the title "Delta 2.0L 16V" for the Delta Integrale.

Originally, Lancia fasteners hold the crankshaft main caps; the M12 x 1.25 studs in the kit take their place in the block.

Reinforced ARP studs for main bearings

The bottom end rests on its main bearings: combustion after combustion, the loads coming from the connecting rods end up on them. Under this stress the main cap tries to move on its parting line, which eventually brinells the mating faces and distorts the bearing bore.

The ARP 8740 steel studs, 12 mm with a 1.25 pitch, replace the original main cap fasteners of the Delta Integrale 16V. The block is cleaned and its threads are chased if needed with the ARP tool, then the studs are screwed in by hand only. Caps, washers and nuts follow, all lubricated with ARP Ultra-Torque, which the instructions prefer to engine oil. Tightening is done in three equal passes, in the manufacturer's sequence, up to 108 Nm (80 ft-lb): 36, 72 then 108 Nm. ARP makes these fasteners in 8740, a chrome-moly steel brought by heat treatment to 190,000 psi tensile strength. As a reference point, an engine's original fasteners generally fall into classes 10.9 and 12.9, whose minimum ranges from 150,800 to 176,900 psi. The 8740 studs in M12 x 1.25 hold up to 1,100 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

No torque is applied to the stud as it goes into the block: it is screwed in by hand. For a permanent installation, the ARP instruction sheet allows a Loctite thread locker.

Follow the cap tightening sequence recommended by the manufacturer when bringing the nuts up to torque; the kit's instruction sheet details each step.

Stronger fasteners change the clamping force: the size and roundness of the main bearing bores are checked after installation, and the bores are line-honed if necessary, using the final fasteners and lubricant.

The torque figures above come from the ARP 175-5401 instruction sheet, revision applicable at publication. The official instruction sheet is authoritative in the event of any difference. Read the ARP 175-5401 instruction sheet

Technical guide

Tightening is done with ARP assembly grease: the torque figures in the table were established with it, not with engine oil.

The ARP brand

Coming from the aerospace industry, Gary Holzapfel founded ARP (Automotive Racing Products) in the early 1970s to put an end to engine failures caused by weak fasteners in motorsport. The company designs and manufactures thousands of part numbers in California, in several material grades depending on the application.

Advantages over the original bolts

Criterion	Original main bolts	Reinforced ARP studs
Tightening	Torque goes through the bolt, which turns in the block thread	Torque is applied to the nut only, the stud stays still
Repeated refits	Each removal and refit tires the threads a little more	Stud left in place, threads spared at each rebuild
Locating the caps	Cap to be offered up and held before screwing	Cap centred by the studs as soon as it is fitted

When studs become necessary

• Delta Integrale 16V built for rally, track or hill climb
• Boost pressure raised well beyond stock
• Engine stripped down to the short block for a careful rebuild
• Main caps that shift under load or damaged block threads
• Rebuild with a new forged crankshaft, rods or pistons

Vehicle compatibility

Why is it the most cost-effective solution?

A Delta Integrale 16V pushed in rally or on the track puts far greater loads on its crankshaft than Lancia planned for. By clamping the main caps better, these studs protect the block and the crankshaft at a cost well below rebuilding a bottom end.