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Hi Jay,
The welded, flat faced triangular flange on the cat inlet uses a flat gasket (p/n 1378872?) between it and a similarly flat faced exhaust manifold pipe flange. Of course this setup, using either 2, 3 or 4 bolts, is common in many cars. Volvo was using the 3 bolt flange well back into the 240 and likely 140 days. Now as I vaguely recall, stresses from the hotter and higher torque engines would lead to premature broken bolts or perhaps encourage cracks in the manifold.
The answer was the donut shaped sealing ring gasket (p/n 9316407?) which uses the flared cat pipe end with the loose (unwelded) triangular flange collar. You'll find that on most, if not all, turbos. I recall my B234F had it. V6s likely used it, too. I recall there was some kind of TSB relating to this (don't have my CD available at the moment, I'll check later). I think it might have related to Volvo standardizing the B234F exhaust system (originally unique to the B234F) with the turbo exhaust system. There were also some mention relating to the support bracket holding the lower end of the exhaust manifold to a bell housing bolt. I don't think those brackets were used much past 1989.
You need the correct exhaust manifold to accept the sealing ring. You may find a few B230Fs that came with it or needed it because of a retrofit exhaust manifold. A flared cat pipe can only be mated to an exhaust manifold designed to accept the ring. I don't think the welded cat flange end is supposed to be mated to a manifold end designed for a ring, but I think it actually does fit, although with less contact area, and you would use the flat gasket. I'm sure others will correct me where I'm wrong here.
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Dave -940's, prev 740/240/140/120 You'd think I'd have learned by now
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