Reinforced ARP main studs for Nissan VR38DETT

The Nissan engine concerned

This kit is made for the Nissan twin-turbo V6 of 3.8 litres, 24 valves and twin overhead camshafts (VR38DETT), found in the GT-R (R35) in its standard and NISMO versions.

In production form, the main caps are held by bolts that this kit exchanges for studs.

Reinforced ARP studs for main bearings

Each main bearing takes a share of the loads the connecting rods pass on at every combustion. Pulled downwards, the main cap tends to slide on its parting line: over time the mating faces become indented and the bearing bore loses its shape.

This kit replaces the original main cap fasteners of the VR38DETT with ARP2000 studs, M10 x 1.5, and their nuts. After the block threads are cleaned, the studs are fitted by hand only. With the caps in place, threads, nuts and washers receive the ARP Ultra-Torque lubricant delivered with the kit, then the nuts are tightened in three equal passes, in the order set by the manufacturer. Only the nut turns: the torque read gives a better picture of the preload obtained, and the block thread is not twisted. Material: ARP2000, an alloy steel developed by ARP, rated at 220,000 psi tensile strength. Against classes 10.9 and 12.9 of standard fasteners, between 150,800 and 176,900 psi minimum, it offers 24 to 46% more strength. These ARP2000 studs in M10 x 1.5 take up to 3,300 hp on this V6 engine (calculated estimate).

Technical specifications

Tightening torque

The studs are screwed into the block by hand, with no torque. For a permanent assembly, ARP's instructions permit a Loctite thread locker, provided full tightening is done before the product cures.

The nuts are tightened in the sequence the manufacturer specifies for the main caps; the instruction sheet supplied with the kit describes the full procedure.

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.

Values taken from the ARP 202-5802 instruction sheet in force at the date of publication; the official instruction sheet prevails should any difference appear. Read the ARP 202-5802 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

Founded in the early 1970s by Gary Holzapfel, who came from the aerospace industry, ARP (Automotive Racing Products) set out to prevent fastener-related engine failures in motorsport. Its thousands of part numbers are designed and manufactured in California, in materials chosen for each use.

Advantages over the original bolts

Criterion	Original main bolts	Reinforced ARP studs
Tightening method	Bolt screwed into the block up to torque	Nuts tightened in three successive passes
Block thread	Dragged along by the rotating bolt	Stud fitted by hand, no tightening effort
Positioning the caps	Cap to be held while screwing	Cap centred by the studs

When studs become necessary

• VR38DETT with raised boost
• Engine speed or output pushed far beyond the original
• GT-R bottom end opened for a rebuild
• Caps that shift or tired block threads
• Sustained sporting use, track, drag or competition

Vehicle compatibility

Why is it the most cost-effective solution?

A VR38DETT built to go well beyond the original output puts far higher loads on its main caps than in stock form. ARP2000 studs clamp them with a preload well above that of the original bolts, for a small extra cost compared with rebuilding a GT-R bottom end.

Consider the crankshaft main bearings

When the bottom end is open, the bearings are replaced too. Here are the tri-metal crankshaft main bearings designed for these engines: