Reinforced ARP crankcase studs and through-bolts for PORSCHE 911 930 3.0 3.3

The air-cooled Porsche engines of 3.0 to 3.3 L

ARP lists this part number for air-cooled Porsche engines of 3.0 to 3.3 L. The ARP page for kit 204-5405 gives neither model nor year, so the compatibility table reproduces the ARP application of kit 204-5405 as published, with no engine code or vehicle inferred.

The factory part number of the original crankcase fasteners replaced by kit 204-5405 is not published in our sources and so does not appear on this page. Kit 204-5405 is flat crankcase hardware, with fasteners at crankshaft main bearings 1 and 7 and through-fasteners.

Reinforced ARP crankcase studs and through-bolts

The bottom end here is a crankcase in two halves, joined around the crankshaft by studs and through-bolts. They are what holds the halves against the loads passed on by the connecting rods; a fastener that yields or relaxes lets the crankshaft work in bores that gradually distort.

This kit brings together ARP crankcase studs and through-fasteners for air-cooled engines of 3.0 to 3.3 L. According to the instruction sheet: two 6.835 in studs for main bearing 1 on the left crankcase half, one 4.553 in stud for bearing 7 on the right half and eleven through-bolts, with double-chamfer washers, acorn nuts and a 12-point nut. The kit is made of Inconel 718, a nickel alloy credited by the ARP catalogue with 210,000 to 230,000 psi of tensile strength; the material is unaffected by corrosion and hydrogen embrittlement. The kit replaces the original crankcase fasteners and is tightened according to the enclosed ARP instruction sheet; no strength value is published for this part number.

Technical specifications

Tightening torque

The studs are screwed in by hand, without torque; the ARP instruction sheet allows a thread locker for a permanent installation. The threads of the studs, through-bolts and nuts are lubricated with Permatex 133A paste, the only product the instruction sheet allows: no other lubricant may be used, or seizing will follow.

Tightening is done in a single pass, to the value in the table, following the sequence recommended by the engine manufacturer: the ARP instruction sheet does not detail it and provides for no intermediate pass.

Values taken from the ARP 204-5405 instruction sheet in force at the date of publication; the official instruction sheet prevails should any difference appear. Read the ARP 204-5405 instruction sheet

Technical guide

The torque figures in the table apply with Permatex 133A paste, the only one the instruction sheet provides for, never with engine oil. The sealing O-rings for the through-fasteners are not supplied with the kit: the instruction sheet says to get them from Porsche or from an engine gasket set.

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 fasteners	Reinforced ARP studs
Material	Depends on the original crankcase fastener of 3.0 to 3.3 L	Inconel 718, tensile strength 210,000 to 230,000 psi (ARP catalogue), kit 204-5405
Thread lubricant	Depends on the original crankcase fastener of 3.0 to 3.3 L	Permatex 133A paste, the only one allowed by the instruction sheet (204-5405)
Final tightening	Depends on the original crankcase fastener of 3.0 to 3.3 L	Single pass to the value in the ARP instruction sheet (204-5405)

When studs become necessary

• Air-cooled Porsche engine of 3.0 to 3.3 L pushed well beyond its standard output
• Crankcase opened to fit a forged crankshaft, rods or pistons on an engine of 3.0 to 3.3 L
• Crankcase seats and threads to be checked, then restored, before fitting stronger fasteners, on an engine of 3.0 to 3.3 L
• Intensive track, rally or hill-climb use, with an engine of 3.0 to 3.3 L often held at high revs
• Complete bottom-end rebuild of 3.0 to 3.3 L with replacement of the crankcase studs and through-fasteners

Vehicle compatibility

Why is it the most cost-effective solution?

On an air-cooled Porsche engine of 3.0 to 3.3 L that is pushed hard, the loads on the crankshaft rise and the crankcase takes them through its fasteners. ARP kit 204-5405, in Inconel, costs little compared with a crankcase to repair and a crankshaft to replace.