Technical information: lower turbo downpipes

We've taken a close look at many aspects of our turbo kits recently. The lower downpipe is one of them. Here are the results.

The casting/downpipe combination was retained to allow backwards compatibility for our existing customers and because of the strength advantage over fabricated units. The new design fits any FM turbo car that is equipped with a cast or fabricated upper section (as shown at left). We built some adjustability into the downpipe to help compensate for production variances in the earlier designs (the middle and right parts in the picture) but depending on the severity of the misalignment it may not be enough. More on the casting in another tech bulletin. It is not directly compatible with the 2004-05 Mazdaspeed MX-5 turbo car.

To start, we built a jig from a stock downpipe and mounted it to the back of an engine/transmission/subframe combination. This ensured the flanges would end up in the exact factory locations. It also let us work out the routing without having the body of the car in the way. Once that was done, final tweaking was performed on a car using our rapid prototypes of the manifold and turbine outlet casting. The result is a downpipe with large amounts of clearance on all sides as well as maximum ground clearance. Anyone who has ever driven a car where the exhaust contacts the steering column or subframe will appreciate this.

The new piping is made of polished 304 stainless steel. Even the laser-cut flanges are stainless. This is the same material we use for our exhaust systems and it gives the downpipes the same long life. Long enough, in fact, that we can offer a lifetime warranty on these parts just like we do on our exhausts! It's the last downpipe you'll ever buy.

The pipes are cut and bent on a massive CNC (computer numerical control) pipe bender for consistency and accuracy. Due to the accuracy of the process, we were able to remove a heavy, expensive flex joint that was also a potential failure point. In fact, we cut the number of welds in the piece from 11 to 4. This not only cut down on possible inaccuracies but also smooths out the airflow inside the pipe. We even cut down the weight by nearly a pound. Naturally, we left a bung for a wideband O2 sensor as well as the factory one. The manufacturer keeps a known good piece on hand so they can check the jigs at any time as part of the quality control process.

The two-piece design has a number of advantages. The biggest one is for 1990-93 owners. We can provide the 1.6 upper section with a 1.8 lower, allowing the use of a 1994-97 catalytic converter. This removes a major bottleneck caused by a 2" flange in the system, while still retaining compatibility with all factory and aftermarket parts. It's also easier to ship, cutting down on shipping costs.

The two pieces are joined together with an Accuseal clamp. This 430 stainless clamp has a special block to ensure even clamping forces and prevents any leaks or pipe distortion. A typical cheap U clamp will not only crush the pipes, it will also rust and may even need to be cut off.

The best part is that we've managed to cut the price of the part nearly in half. The new lower downpipe is only $219.00 with all the stainless steel hardware included. They're available immediately.
1990-93 downpipe
1990-93 hybrid downpipe (1.8 cat)
1994-97 downpipe
1999-05 downpipe