When fitting custom exhaust pipes, the most important thing to remember is that clearance is king and flow is secondary. Some compromises will undoubtedly need to be made to clear floorpans, driveline components and suspension pieces. This article focuses on fitting an exhaust system using pre-bent pipe, though a good mandrel bender is, of course, preferable for top-end work.
How to fit Custom Exhaust Pipes
Plan out your exhaust system. Assuming the pipes are already out of the car, one of the best ways to plan an exhaust system is to use flexible aluminum dryer duct. The 4-inch diameter pipe will allow you to contour the pipe to the bottom of the car while ensuring that you always have at least half an inch of clearance.
Cut the ducting into 4-foot sections.
Run the sections of pipe along the route you wish to use, securing them to the bottom of the car with duct tape. Make sure to try and replicate the angles of the tubing sections you wish to use.
Mock up the entire system from front to back, making sure to clear the rear axle by as much as possible. It might be a good idea to fit the mufflers in the locations you wish to use first, so that you know where to terminate your pipes.
Remove the template sections from the bottom of the car, being careful not to bend them out of shape.
Compare the template sections to the tube sections you have, or use them as a guide to buy the ones you need.
Cut the tube sections you need, making sure to leave about two inches of excess for trimming and slip fitting.
The tubing you cut should kick out parallel to the ground. Trim the tube about 5 inches back from the turn, leaving room for the slip joint.
Work your way back from the front to the muffler, securing the exhaust system with no more than the expanded slip fittings. Install whatever emissions or sound-deadening equipment you desire in the straight sections of pipe.
Tack weld the sections of pipe together on either side of the tube.
With the wires attached, place the O2 sensor on the head tube, making sure to leave plenty of slack in the wiring. Make sure to place the O2 sensor in an accessible position for future replacement.
Weld exhaust hangers to the floorpan and top of the pipe, with the two pieces connected.
Remove tack welded system from car.
Weld all around pipes to secure them together. Use exhaust putty if needed to seal joints, but a good weld is preferred.
Drill hole for O2 sensor where marked. Use a bit that just allows the O2 sensor’s sampling tip to fit through with a minimum of clearance.
Thread the O2 sensor onto the bolt, and inset it into the hole.
Very briefly tack weld the bolt onto the pipe. Don’t overheat the bolt, as this will cause damage to the sensor.
Grease the O2 sensor stand-in bolt, and thread it into the nut.
Finish welding the nut to the pipe.
Install the finished exhaust system into the car.
- Moderately Challenging
Things You’ll Need
- Assortment of pre-bent tube segments. At least two 45 degrees, four 15 degrees, two rear-axle kick-ups and a few assorted angles.
- At least 20 feet of straight pipe
- Mufflers of your choice
- Catalytic converters of your choice
- At least six universal weld-on exhaust hangers
- Exhaust clamps
- Lug nuts sized to fit oxygen sensor
- Mig welder
- A full set of 3/8 ratchets
- A full set of wrenches
- Flat head screwdriver
- Floor jack
- 50 feet of 4-inch aluminum dryer duct
- Duct tape
- White grease pencil
- A bolt the exact size and thread pattern of the O2 sensor
- High-temp grease
- The finished exhaust system should bold straight in, but have a second set of hands to help you tweak the assembly, since it will have warped a bit with the heat of welding.
- Never attempt to use galvanized pipe for exhaust systems. Welding galvanized pipe releases dangerous and potentially lethal gases.