|Power Increase Over Stock:||10-50 WHP|
The Mk3 Supra Turbo responds very well to a more free flowing exhaust than what Toyota specified for this car. The 7MGE, however does not see the same immediate benefits and I will not spend any time discussing exhaust for the NA engine at this time.
Factory exhaust on the A70 NA is approximately 2” in diameter and the Turbo is approximately 2.25-2.5”. This flows well enough for factory power and yields a nice, smooth, quiet exhaust note. If you want to free up some power in a 7MGTE car a full turbo-back exhaust is probably your best first step. Most other modifications won’t help much with the factory exhaust continuing to restrict flow. There are a few components of the system which need to be swapped out. A simple “Cat-back” exhaust isn’t really what you want here for an actual power increase. You need to free up flow on the entire system. That involves the Turbo Elbow, Downpipe, Catalytic Converter, Resonator, Muffler and all the piping in between.
1 Elbow and Downpipe
The downpipe attaches to the turbo and in the case of the CT-26, the wastegate. The factory system on the A70 Turbo has a cast iron “elbow” to connect the downpipe to the turbo. This elbow is the first offender. There are a few options to replace the elbow alone, but I would STRONGLY recommend to replace the elbow AND downpipe with a new downpipe which mounts directly to the turbo. Many of the better downpipes are set-up this way and if nothing else it will save you weight over the heavy cast elbows. Downpipes are offered in a couple varieties.
Bellmouth – Which have a big common opening for the wastegate and the regular exhaust flow
Divorced – Which have separated flow paths for wastegate and regular exhaust flow that either combine later down the flow path (Recirculated) or which dump the wastegate to atmosphere (non-recirculated). Non-recirculated are generally not road legal and will be very loud any time the wastegate opens. Toyota utilized a divorced recirculated in their Group A cars.
Both of these options have great power potential and the choice between the two depends on your preferences. If you live in an area with no concerns for emissions or road legality and you want the raw, loud roar of your engine every time you “boost” then the non-recirculated divorced may be a good choice. If you want a more refined, legal set-up then go with a recirculated divorced or bellmouth set-up.
2 Catalytic Converter
The factory converter is an old, restrictive part of the system, but its importance in keeping our air clean and your engine sound smooth shouldn’t be overlooked. New ceramic and metallic cats are very efficient and are available in high flow varieties that wont restrict flow to any noticeable degree. “Test pipes” are available for track use, but should never be used on the street. Not only do most engines, including the 7M get raspy and cheap sounding without a cat, they also pollute like crazy. Good high flow cats are only $100 so don’t be a fool a run without one in your quest for extra power.
The next component in the exhaust system is the resonator. This is designed to lower the exhaust level and keep droning to a minimum. The factory resonator is baffled just like a muffler. It’s effective in regards to noise, but doesn’t help the system flow very well. Aftermarket resonators are available in many different designs that help to lower drone and do not restrict flow. You can run without a resonator if you don’t mind the exhaust drone. If you’ve got $100 to spend on one it is a good investment in your sanity on long drives. If you’re building a track car I wouldn’t bother with one.
Similar to the resonator, this quiets the exhaust system. This is the final component and will have the largest affect in the system’s noise level and tone. Larger openings here will tend to give a lower growl and will obviously be louder. Youtube and Streetfire are full of thousands of exhaust videos. Search around and find one that fits your preferred style and tone.
As mentioned earlier an exhaust system is probably the first worthwhile modification in the quest for power on a Turbo mk3 Supra. It pays off quickly and allows other modifications to show their true potential. Before you do anything else to raise the boost on the turbo or fine tune the engine go ahead and explore some full exhaust options.