The exhaust system on a motorcycle serves three functions.
Symmetry. The 4-cylinder KZ-1000 engine can be viewed as two twins sharing a crankshaft.
The inner two cylinders form one twin, while the outer two cylinders constitute the other.
Thus, in a 4-into-2 exhaust system, the outer headers should merge, and the inner headers should merge.
This is not the way the stock exhaust system is configured.
Flow. Exhaust tuning is a significant factor in engine performance.
To ensure high torque across the RPM range we follow these principles:
The resulting exhaust system is perfectly symmetrical, unrestricted, and well-tuned for a broad power range.
It looks good, runs good, and sounds good.
|Stock KZ-1000 Exhaust|
| This is the stock exhaust configuration for the KZ-1000 Police motorcycle.
It is ugly, inefficient, and doesn't sound good.
We retain the stock header pipes. The outer two must be cut off from the mufflers.
|The Cass-1000 Exhaust System|
| This is the redesigned exhaust configuration for the KZ-1000 engine.
This section fits under the bike, between the four stock header pipes and two H-D mufflers.
It is two-dimensional in that all of the pipes lie in the same plane.
The four 1 5/8 OD exhaust pipes have a 30° bend and slip over the 1 1/2" OD header pipes.
Two 1 3/4 OD tailpipes (not shown) have a 40° bend and slip into the mufflers.
All joints are welded.
The centerline spacing between the two inner headers is 5.0 inches.
The centerline spacing between the two outer headers is 12.2 inches.
These spacings keep the header pipes parallel and vertical.
The centerline spacing between the two mufflers is 15 3/4 inches.
Pipe Size. 16-gauge steel tubing has a 1/16" wall thickness, so it's OD is always 1/8 inch larger than its ID.
The stock headers are almost exactly 1 1/2" OD, so they slip nicely into 1 5/8" OD pipe.
The 1 5/8" OD tubing slides into the 1 3/4" OD pipe, and that slips neatly into H-D mufflers.
1 3/4" OD 16-gauge tubing with a 1 3/4" ID flange on one end is stocked at auto supply stores (Auto Zone, Advance, O'Rileys, etc.).
1 5/8" OD 16-gauge tubing is available in the fencing section at Home Depo in 5' and 10' lengths. They call it "Line Post."
Tuning. The series of transitions from a 1 3/8" ID header (1.48 sq. in.) into two 1 3/4" ID mufflers (4.8 sq. in.)
produces a stepped increase in cross-sectional area that sends negative pressure pulses back up the pipes
toward the exhaust valves. This improves exhaust scavenging and horsepower across the RPM range.
Further, the unequal length headers help to avoid flat spots in the torque curve by increasing the number of different RPMs at which the system is "tuned."
| This is a cardboard mock-up of the collector.|
Unlike the design above, this one has a short space between the outer exhaust pipe inlets and the outlets.
This collector is made from eight pieces of 1 3/4" OD pipe.
Four 1 3/4" OD inlet pipes merge into the collector at a 30° angle.
Two 1 3/4" OD outlet pipes exit the collector at a 40° angle.
|The Pieces that Make Up the Collector|
| The two-focus collector above is made from seven pieces cut from 1 3/4" OD 16 guage tubing.
Two pieces are required for everything except the center section.
The center section is cut off at 15° on the left and 75° on the right, as shown.
The two inner exhaust pipe inlets are cut off at 15° and 60°, as shown, and welded to the center section.
The two outer exhaust pipe inlets are cut off at 35° and 75°, as shown, and welded to the center section.
The two tailpipe outlets are cut off at 35° and 50°, as shown, and welded to the center section.
These pieces can be rough-cut with a bandsaw or miter saw and finished on a belt sander or a milling machine.
Making the Collector. The easiest way to make the pieces is to cut them on a bandsaw and true them up on a belt sander.
Use an 18-tooth-per-inch metal-cutting blade and 120-grit sandpaper.
Not only must the angles be correct, but the cuts must meet in the exact center of the pipe.
and must be perpendicular to each other.
Most of the pieces are simple because one end is cut off at 90 degrees, and their length is not critical.
These pieces can be sanded down until they are right at one end, and then cut to length with a chop saw.
The 75° cuts are difficult because the guides on most bandsaws, miter saws, and sanders won't go beyond 45 or 60 degrees.
The center section is the most difficult opiece to make because it has two 75° cuts, and it's overall length is critical.
Further, for the center section, the cuts at either end must be in rotational alignment with each other.
| This is a breadboard that is used for constructing the collector.
It is made from 1/2" plywood that comes laminated with white Formica on both sides.
A full-size drawing of the exhaust system is glued to one side.
A piece of transparent plastic protects the drawing.
1/4" holes are drilled at the locations of the saddle clamps, with tinnerman nuts underneath.
The saddle clamps are held in place by countersunk 1/4" by 1" flat-head screws.
They hold the pipe pieces in place while they are fitted and tack-welded together.
Then the assembly is removed, and the welding job is completed.
The design shown here has no space between the inlets and the outlets, for a smoother flow.
| Each tailpipe slips into a collector outlet and has a single 40° bend.
Each muffler clamps over one of the tailpipes.
The hanger bracket supports the muffler bracket.
|The Finished Bike|
|This is a KZ-1000P with H-D mufflers. Click to see the other side.|
|This KZ-1000P has longer tailpipes to place the mufflers further back.|
| You might find a Harley-Davidson muffler in one of three conditions.
In stock mufflers the gasses flow into the outer chamber, then into the outlet chamber.
Some mufflers have had the diverter punched out to allow straight-through flow.
Others have the weld cut out, allowing removal of the inner baffle for unrestricted straight-through flow.