The exhaust manifolds in the 2.5L Fiero are found in several other GM cars but the manifolds in the 2.8L Fiero are unique. Unfortunately the 2.8L manifolds are prone to cracking and leakage. Repair by welding or replacement with used exhaust manifolds are the only options with a 2.8L engine (other than aftermarket performance headers or exhaust pipe modifications). If you are willing to make customized exhaust piping, manifolds from many 2.8/3.1/3.4 engine will bolt to the Fiero heads. Note that the Fiero manifolds are stainless steel.
That said, there is one set of cast iron exhaust manifolds that will bolt to the 2.8L Fiero which requires only minor modification to the downstream exhaust piping. These are the manifolds from the 1989/90 Grand Prix Turbo (Turbo ONLY). The Fiero Y-pipe requires bending to match the manifolds and this can be done using a vice and a 2" pipe for additional leverage. A benefit of using the Grand Prix manifolds is reduced noise in the cockpit.
A company called AM Autoparts (am-autoparts.com) lists a new manifold for the Fiero 2.5L engine for about $100 (March 2010) with free shipping.
Exhaust Manifold Bolts, 2.8L
We'll say it up front: Replacement bolts for the 2.8L exhaust manifold are available as Dorman Part No. 03411. It is a set of 10 studs with locking nuts for Ford V8s. Typically available at auto parts stores - ask for them by number.
Pontiac 6000 '83-91 2.5L Pontiac Astro '85-90 2.5L Olds Calais '85-91 2.5L Camaro '82-86 2.5L Chevy Celebrity '83-90 2.5L Buick Century '83-92 2.5L Olds Ciera '83-92 2.5L Chevy Citation '83-85 2.5L Firebird '82-86 2.5L Pontiac Grand Am '85-91 2.5L Olds Omega '83-84 2.5L Pontiac Phoenix '83-84 2.5L Pontiac Safari '85-90 2.5L Buick Skylark '83-91 2.5L Buick Somerset '85-87 2.5L
We have read that the exhaust manifolds in the 1990-1993 S-10, S-15, and Blazer will fit the '87-88 Fiero 4 cylinder engine but we have not been able to confirm this.
Chevy Lumina Car '90-92 2.5L
Exhaust Kit (flange, gasket, bolts), 2.5L,'84-88 Help! 03126 Exhaust Manifold, 2.5L, '87 Manifold Plus 674-101 Muffler, all years Walker 40094 Left megaphone tip Walker 35866 Right megaphone tip Walker 35867 Exhaust hanger springs Walker 35722, 10 reqd Left exhaust tip hanger Fiero Store 60189 Right exhaust tip hanger Fiero Store 64158 Catalytic Converter rodneydickman.com