Project [Rotary] FD RX-7: Part 4 – Turbo System


Now that most everything with the turbo system is complete and installed we might as well go ahead and finish out the exhaust system while we're at it. Like I said earlier, we are modifying the old 4″ turbo-back A-Spec exhaust system for this build. Originally the mid-section of the exhaust had a very short resonator in it that was nearly useless, but not long after the initial build of the car this was replaced by a Random Technologies 300-cell metal matrix catalytic converter to make the car more street legal. Adding this didn't reduce the exhaust noise at all, but it did significantly improve the smell of the car…which can get pretty bad on a catless, ported rotary.

The mid-section of the exhaust remains unchanged from the previous 4″ tubing with a 300-cell Random Technologies high flow metal matrix catalytic converter.

Beyond the catalytic converter and the changes to the downpipe to make it work for our turbo setup, the one other change to the exhaust system that should be significant to reducing sound output is upgrading the muffler. Now lets get one thing straight first, this is a full 4″ exhaust on a rotary, it is never going to be quiet. However, with a little luck and some help from Borla, maybe we can make some improvements.

Enter the new 4″ Borla XR-1 Multicore muffler. Here it is pictured next to the old muffler. This is a rotary specific 4″ in/out muffler that should tame a bit of the noise that plagues rotary powered cars. If it doesn't, then I doubt anything will.
Borla XR-1 muffler welded to rear section of exhaust tubing. Also added some tubing to the outlet of the muffler as an exhaust tip to keep any rotary induced flames from catching the bumper on fire.
The rear section of the exhaust mounted up to the car. The factory muffler is so big on these cars that there is plenty of room for the large 4″ Borla XR-1.
Another shot of the exhaust mounted to the car. Good view of the internals of the Borla XR-1 Multicore muffler for anyone looking for it.

There are only a couple of engine articles left for Project RX-7 before we start the wiring and install of the new engine managment system. Next time will be heat exhangers galore as we cool air, water, and oil.



Borg Warner
Borla Exhaust
Earl's Performance Plumbing

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