An important modification to a turbo charged car is the exhaust. A restrictive exhaust will lead to all sorts of problems, ranging from a loss of horsepower to excess heat build up in the exhaust manifold, and may even end up affecting components like the exhaust valves. Unfortunately for the owners of Celica GT-Fours (All-Tracs), there are no after market downpipes available to replace the turbo elbow, and the main CAT, until now that is. A long time member of the GT-Four mailing list, Nathan Fogg, decided to embark on the design, and fabrication of a 2.5 inch stainless steel downpipe, with laser cut flanges. Since the time that Nathan made his first prototype Passion Automotive has already sold 20 of these units, one of which I had the good fortune to receive. The downpipe sells for U.S. $265.00, not including shipping, and you have the option of getting it ceramic coated. Of course the coating will cost you extra, but I highly recommend it. For more information contact Nathan Fogg at

The Downpipe

When I first opened the box and saw the downpipe, I was very pleased with the quality and finish of it. I had mine ceramic coated, which gave it an almost chrome look. The downpipe even came with a hole taped at the bottom of the pipe to fit a common O2 sensor. This is excellent as it makes hooking up my wide band O2 sensor and an analyser so easy, just remove the bolt that plugs the hole, and screw in the sensor.

Downpipe 1
Downpipe 2
Downpipe 3
Downpipe 4
Downpipe 5
Click on any of the pictures above to see a larger image. If your browser does not support pop up windows you can use the links below the images to view the larger images.
Installation Issues

I would not recommend that novice Do-It-Yourself persons perform the install. Anyone from the average to experienced Do-It-Yourself type should be able to perform the installation. I am not going into any detailed installation procedures, but I will comment on the two main approaches to accomplishing the install. One way is to remove the CAT, and then remove the turbo and elbow as a unit, and then install the downpipe to the turbo, and install the turbo/downpipe combination. The method I chose was to remove the oil cooler, remove the bolts, and bracket for the AC compressor, and push it to the side, then remove the stock elbow. Next install the downpipe, it will be a bit tight, and require some wiggling of the AC compressor to get the downpipe to slip over the turbo studs. Then just bolt everything back up.

There were some minor alignment problems with the downpipe, which is acceptable, because of the extremely reasonable price of the pipe, coupled with the high quality of it. This pipe isn't made by one of the big manufacturers like HKS, or Blitz, and if it was, I'd expect it to cost in the region U.S $500.00 or more, so it understandable that things may not be 100%. One of the problems was the flange at the bottom of the downpipe that attaches to the exhaust pipe flange. They didn't quite line up. I fixed this relatively easily by letting go some of the exhaust mounts, and then drawing the two flanges together by tightening the bolts, then reinstalling the exhaust to the mounts. The joint does not even leak. When I get a chance, I'll still stop by the muffler shop, and just get them to set up the exhaust flange in line with the downpipe flange.  The bottom stay on the downpipe also didn't quite line up with the stay coming off the block, but a little twist with a vise grip easily solved this issue. There is also a point at the top of the downpipe that is supposed to be connected back to a stay that runs from the area of the alternator. However this did not line up at all, so I didn't bother with it. Personally I feel the one stay at bottom is more than adequate. A company in Italy called Super Sprint used to make a 2.5 inch downpipe for the GT-Four, but it was discontinued quite a while back, and their downpipe had no stays at all.


Overall I feel this downpipe is excellent value for your money, and I am 100% satisfied with it. From the time I started up the car after installing it, I noticed how strong the exhaust pulse out of the tailpipe felt. On wide open throttle the exhaust has a deeper note, and the car revs out freely. I have heard all the claims that unless you use a 3 inch downpipe you are wasting your time. I find this to be a false statement, as most of the research I've done on exhausts, seems to indicate that 2.5 inch is good enough for approx. 400 hp. So my recommendation would be to get the downpipe, and change the rest of your exhaust to 2.5 inch, or even better 3 inch.

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This page was created by Dennis Heath.
If you should wish to ask a question about the GT-Four/All-Trac, you can join the GT-Four Mailing List, where I, and many others with GT-Four's, might have your answer. For information on joining go to

Please note that I am not a mechanic by trade, and that any information offered on this web page is free and without guarantee. Should you choose to perform any of the procedures listed on this site, you will be doing so of your own free will, and I will not be held responsible or liable for any damages that might occur from using information obtained here.