Reinforced ARP bolts and nuts for OEM rods PORSCHE M44

The Porsche M44 engine concerned

The M44 is the four-cylinder of the Porsche 944, 924 S and 968; the NGK catalogue lists it under codes M 44.01 to M 44.60 as a 2.5-litre (2,479 cc), a 2.7-litre (2,681 cc) and a 3.0-litre (2,990 cc), on coupes and convertibles built from 1981 to 1995.

This ARP kit takes the place of the original rod bolt on that four-cylinder; ARP presents it as a set of bolts press-fitted into the connecting rods and supplied with their nuts, for the Porsche 944.

Reinforced ARP bolts and nuts for connecting rods

At every revolution, the rod bolt takes the pull of the rod and piston assembly, which tries to force the cap away through inertia. As original equipment, it is sized for stock power.

Made of ARP2000, this kit is installed in two steps: the bolts are press-fitted into the rods first, then the nuts are tightened, preferably by measuring the stretch; without a gauge, the ARP instruction sheet gives 74.6 Nm. Material: ARP2000, an alloy steel developed by ARP, heat treated to 220,000 psi tensile strength, with threads rolled after heat treatment. Against classes 10.9 and 12.9 of original fasteners, between 150,800 and 176,900 psi minimum, the margin is 24 to 46%. The engine speed allowed by the ARP2000 bolts goes up to 11,750 rpm (calculated estimate).

Technical specifications

Before the press fit, the ARP instruction sheet asks you to make sure the hole in each rod has an adequate chamfer to house the radius under the bolt head.

Tightening torque and stretch

For this part, ARP favours tightening to a measured stretch, the key to an exact preload; torque is given only when no gauge is available. The figures in the table assume ARP lubricant.

The values above come from the ARP 204-6002 instruction sheet applicable at the date of publication; it is authoritative in the event of any difference. Read the ARP 204-6002 instruction sheet

Assembly is done without thread locker, as the ARP instruction sheet calls for none: ARP Ultra-Torque grease is applied to the threads of each bolt and to the bearing face of its nut.

Once the fasteners are fitted, the ARP instructions call for the big ends to be checked and resized by a machine shop.

Measuring bolt stretch

Stretch measurement supplements torque tightening and gives the most accurate preload. It is done with the bolt in place: the gauge, fitted with a dial indicator, bears on both ends of the bolt and shows the stretch achieved, to be brought to the value in the table above. This avoids the variations caused by friction, which matters on a highly stressed engine.

Technical guide

Torque and stretch figures are only valid with ARP assembly grease, applied to the bolt threads and to the bearing face of the nuts.

The ARP brand

ARP (Automotive Racing Products) came into being in the early 1970s, when Gary Holzapfel, who came from the aerospace industry, decided to tackle the engine failures caused in motorsport by inadequate fasteners. Today the brand produces thousands of part numbers in California for the cylinder head, the main bearings and the connecting rods, in materials suited to each application, with manufacturing known for its consistency.

Vehicle compatibility

Why is it the most cost-effective solution?

On a tuned Porsche 944, every rod bolt takes inertia loads on each engine revolution. Should a single one let go, the rod, the piston and the block are lost: an ARP2000 kit costs well under a full rebuild of the bottom end.

Matching connecting rod bearings

New bolts, new bearings: find below the connecting rod bearings suited to this engine.