Technical Service Bulletin DME System Modification For Idle Stalling and Surging Resolution

Subject: Center Air Guide

Effected Models: 1965-77 911 models 1975-77 930 models

In 1977 Porsche modified the center air guide on Both the 911 and 930 models. The original center air guides used a solid steel plate between the cylinders. Porsche found that by removing a 25.00 mm strip that the cylinder temperature could be reduced by 5.6°C to 8.3°C, this also helped reduce the stress on the head studs by reducing the amount of cylinder expansion.

All center air guides from 1977 on were supplied with the 25.00 mm strip removed. Engines built prior to 1977 should have the center air guides modified any time they have to be removed.

The effect on the cylinder temperature of the 1965-71 engines remained the same, however because the cylinders in those engines were either Cast Iron or Biral in design the expansion effect is minimal. None the less the guides still need to be modified.

Modifying the Guide

Measure in 25.00 mm from the edge of the guide and scribe a line parallel to front edge. Measure up from the bottom of the center plate 19.00 mm for 1964-77 911 models and 10.00 mm for 1975-77 930 models and scribe a line.

Using a set of tin snips cut out the 25.00 mm strip. After removing deburr, all sharp edges and seal with paint to prevent rust.

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