Review on 🚀 Dorman 674-164 Exhaust Manifold Kit Compatible with Chevrolet, Geo, and Toyota Models - Boost Performance! by Dante Black

Cast iron exhaust manifolds often crack, original or non-original. If you don't allow enough downtime for the exhaust to warm up (especially in cold weather), cracks can and do occur. Fast driving after a cold start contributes to cracking. The cracks allow air to be drawn into the exhaust stream and can be seen by the O2 sensor as a lean mixture, which in turn causes the car's computer to add fuel when the engine doesn't really need additional fuel. A good way to tell if the crack is large enough to cause this is to look at the reading of the intake O2 sensor (engine fully warmed up) with a scan tool (or digital voltmeter) at idle. Then spray carburetor cleaner (flammable) directly on the crack. Do the same for about 2000 RPM. If the O2 voltage rises every time you hit the crack with a spray, the manifold should be replaced. Any air drawn into the exhaust before the O2 upflow can reduce fuel economy without setting a trouble code. The casting I received was actually more powerful than the stock Toyota Corolla's casting. 4 inlet ports and one outlet port. The pipes were also slightly larger than stock and smoother, so there are no limitations with this header. 4 different donut sockets were included. to cover every application and decent looking graphite gskt. per cyl. on the head side, as well as two new distributors for tube bolts and nuts. worth your money.