Your latest project isn't going to get very far without an exhaust system, but while a lot of builders are happy to tackle many aspects of a build, exhaust fabrication seems to be one job that often gets farmed out to muffler shops. However, with the availability of mandrel-bent tubing, there's no reason why homebuilders can't fab their own systems.
We were invited along to MagnaFlow's R&D facility to see how the crew built a custom system for the Cruisin' for a Cure event giveaway roadster, and figured it'd be an ideal way to pass along some tips, while at the same time see how a custom-bent stainless steel exhaust was made.
MagnaFlow doesn't fabricate one-off systems in its general course of business, rather the team designs and builds prototype systems for musclecars and late-models before offering such systems for sale. Sure, the computer-controlled bender and tube scanner shown here are beyond almost everyone's reach, but Dan, one of MagnaFlow's fabricators, started piecing together the system from a number of pre-bent sections, just as you or I would, before it went all high-tech, resulting in one-piece multi-bend sections of tube. Starting with headers already installed, and a selection of bends, here's how it came together.
With the Sanderson headers...
With the Sanderson headers installed on the motor, Dan's first task was to use this angle finder to determine the angle of the first bend in the system, taking into consideration clearance for the steering and oil filter.
You can see from this angle...
You can see from this angle just exactly how close the header is in relation to the steering shaft.
Here's another angle showing...
Here's another angle showing the clearance issues as the first section was going in. As well as the steering, the brake booster bracket and trans body were in the way. The exhaust system has to snake its way past all of these obstacles.
The chassis crossmembers included...
The chassis crossmembers included these tubes through which the exhaust could be routed, ensuring maximum ground clearance. Dan mocked this section in place before tacking it to the previous sections. This completed the first part of the system, as there will be a joint here to enable the finished system to be assembled.
Before bending any tubing,...
Before bending any tubing, Dan installed a flange on the header.
Dan tacked the pipe to the...
Dan tacked the pipe to the flange using a MIG welder and then measured and trimmed the next section before tacking that in place.
Once the various sections...
Once the various sections were welded, this trick piece of equipment was used to "read" the tubing. It transferred the dimensions and bends of the tubing to a computer which told this machine where and at what angle to fabricate a duplicate from a single section of tubing. Much of MagnaFlow's work is prototyping exhaust systems, and this machinery can reproduce the prototype as many times as required once the initial pattern is produced.
The guys at MagnaFlow do this...
The guys at MagnaFlow do this all day, every day, and have a selection of pre-bent tube and leftover bends that can often be utilized. For the first section of our exhaust, Dan used a 90-degree bend and formed a flare on the end, which will be welded to the flange bolted to the header.
Here's the view from the rear....
Here's the view from the rear. Note how Dan fabricated the pieces to ensure the system ran parallel with the ground, or, more accurately, the rack.
Here's the tacked-together...
Here's the tacked-together pattern next to the single-piece version. Neat, huh? Of course, you won't have access to such equipment if you're making your own system, but there's nothing wrong with cutting and welding sections of tube. Just make sure your cuts are square.
The exhaust will be mounted...
The exhaust will be mounted to the crossmembers, so Dan drilled and tapped them to accept a 7/16-inch threaded bolt. These fabricated hangers were bolted to the crossmember using neoprene bushes that will eliminate any vibration and transference of exhaust noise into the chassis. Note the temporary use of the bushes to center the exhaust in the crossmember tubing.
Even with all the automated...
Even with all the automated machines, Dan used this tubing cutter to ensure each cut was square on the tubing, making mating two sections so much easier, with no gaps. It's much the same as a brake-pipe cutter, only much larger.
With the midsection of the...
With the midsection of the system mounted, the tailpipes were all that remained. As this car runs an IRS, Dan elected to run these so they exited below the differential.
Dan used a piece of box section...
Dan used a piece of box section steel to ensure the tailpipes were the same height, while also ensuring they were of equal distance from the car's centerline.
Here's the complete stainless...
Here's the complete stainless steel system mounted in place. You can see how neatly the exhaust system is tucked up out of harm's way. In fact, the lowest part of this car is the oil pan!
This neat bracket was fabricated...
This neat bracket was fabricated to mount the tailpipes on the forward side of the differential, again using a neoprene bushing.