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1.7L 8v - Type IV
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1.7L 8v - Type IV
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8740 ARP connecting rod bolt and nut kit replacing the original bolts on OEM rods of the 1.7 and 2.0-litre Type IV flat-four engines.
The Type IV is the flat-four of 1.7 litres (1,679 cc, NGK code W, 72 to 80 hp) and 2.0 litres (1,971 cc, codes GA and GB, 95 and 100 hp) fitted to the Porsche 914, the Volkswagen 411 and 412 and the Puma GTI.
This ARP kit replaces the original rod bolt of the Type IV with an 8740 ARP bolt that is pressed into the connecting rod and tightened with a nut.
Few parts of the bottom end work as hard as the rod bolt: at every revolution, it is what stops the cap from pulling away under the inertia loads of the rod and piston assembly. The original bolt is designed for stock power.
This kit brings together 8740 bolts, which the ARP instructions say to press into the rods, and their nuts; tightening is best done to the stretch read on a gauge, with 54.2 Nm as the fallback value without one. 8740 is a chrome-moly steel that ARP heat treats to 180,000 psi tensile strength, with threads rolled after heat treatment. As a reference point, standard engine fasteners mostly belong to classes 10.9 and 12.9, i.e. 150,800 to 176,900 psi minimum strength.
| Part number | Brand | Grade / material | Nut | Thread | Under-head length |
|---|---|---|---|---|---|
| ARP-104-6006 | ARP | 8740 steel | Not published | Not published |
Before pressing, the ARP instructions call for an adequate chamfer around the top of the connecting rod bolt hole, so that the radius under the bolt head is cleared.
| Reference | Tightening torque | Stretch |
|---|---|---|
| ARP-104-6006 | 54.2 Nm | 0.140 - 0.152 mm |
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.
Source of the torque and stretch figures: ARP 104-6006 instruction sheet, in the revision applicable at publication. The manufacturer's instruction sheet prevails in the event of any difference. Read the ARP 104-6006 instruction sheet
No thread locker is called for by the ARP instruction sheet for this kit: the bolts are fitted with ARP Ultra-Torque grease, on their threads and on the bearing face of the nuts.
The ARP instructions for this kit require the big ends to be checked and resized once the fasteners are fitted: this job belongs to an equipped machine shop.
With the stretch gauge, you read directly how much the bolt stretches during tightening: the dial gauge sits on both ends of the fitted bolt, and tightening stops when the stretch reaches the value in the table. Friction no longer comes into play, hence a more consistent preload on a heavily stressed engine.
All the torque and stretch values on this page assume ARP assembly grease on the bolt threads and on the bearing face of the nuts; engine oil does not replace it.
Founded in the early 1970s by Gary Holzapfel, who came from the aerospace sector, ARP (Automotive Racing Products) was born to put an end to fastener-related engine failures in racing. Its thousands of part numbers, designed and manufactured in California for the cylinder head, the main bearings and the connecting rods, come in several materials depending on the application and are recognised for the consistency of their manufacture.
| Brand | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| Porsche | 914 1.7 | W | 80 hp | 1969-1973 |
| Porsche | 914 2.0 | GB | 100 hp | 1972-1975 |
| Porsche | 914 2.0 | GA | 95 hp | 1973-1974 |
| Volkswagen | 411, 412 1.7 | W | 80 hp | 1969-1973 |
| Volkswagen | 412 Variant 1.7 | W | 80 hp | 1972-1973 |
| Puma | GTI 1.7 | W | 72 hp | 1982-1990 |
A Type IV pushed beyond its factory engine speeds, or entered in competition, loads each rod bolt with a tension that rises with revs. The failure of a single bolt often condemns the rod, piston and block: the 8740 ARP kit is a small share of the cost of a rebuilt bottom end.
