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Re: 2 Piece exhaust manifold Posted by Gary Stottler [Email] (#1463) [Profile/Gallery] (more from Gary Stottler) on Sun, 18 Dec 2022 06:23:31 In Reply to: Re: 2 Piece exhaust manifold, Johnson [Profile/Gallery] , Sat, 17 Dec 2022 20:31:13 Members do not see ads below this line. - Help Keep This Site Online - Signup |
True on all counts! I believe there were several reasons for the changes over time.
First, the earlier one-piece manifold was somewhat prone to cracking and loosening of the bolts holding it to the cylinder head (cast iron and aluminum expand/contract at different rates with temperature change). This may have been the main reason for the change.
Second, Saab was also "tuning" the 4-2-1 exhaust for best scavenging (power and torque). I think both the pre-75 and the 76-78 manifolds were 4-2-1, but there were tuning differences.
Finally, the advent of the lambda/catalyst system (1977 California, 1978 turbo) went back to a one-piece manifold for better emission control. Saab managed to limit the power loss better than most. I don't know about the non-Turbo cars, but it was practically a feature of the early Turbo manifolds that they cracked between the #3 and #4 runners. The manifold was redesigned in 1980 and the later one is much more resistant to cracking.
All of the downpipes are pretty difficult to find at this point. I think I got the last one in the Saab US warehouse for my '77 EMS (2-piece manifold) in 2009 or so.
Best,
Gary
_______________________________________ Gary Stottler
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