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BMW "Airhead" Mufflers




ASSEMBLing a Slip-On cone engineering Conical Merge Collector

While our Merge Collectors were originally designed as a weld-on collector, they can be converted to a slip-on collector without a great deal of additional work.

Choosing a collector begins with your header tube diameter.  We assume that the primary tube diameter you are using is appropriate for the size of the engine and the primary use of the vehicle.  We offer several choices in collectors and transition cones to fine-tune your performance by tailoring the collector to match your needs.  A couple of considerations will be what your vehicle is being used for (street, road-race, drag-race, etc) and also if there are any space constraints.  Our Merge Collectors are designed to use a choke point that accelerates the exhaust gas flow and a transition expansion cone attached to the outlet of the collector.  This pairing creates a low pressure pull, continuing the exhaust gas acceleration and promoting the scavenging process.

In this example we have a dedicated drag car with a 600 cubic inch normally-aspirated engine, running NOS and producing in excess of 1200 hp.  The new header being built has a final outlet of 2.50”.  The builder needs to run a muffler in their class and want a 5” final outlet to match the muffler he has chosen. 

Whether to run mild steel or stainless steel is left out of the decision process here, both would use the same parts, just a different material.  To make it easy we are going to assume they have chosen to go with mild steel.

Since we are building this as a slip-on collector, we start by selecting slip couplings that will fit over the 2.50” primary tubes. The slip couplings have an outside diameter of 2.625” so this means that we will use a 2.625” collector body.  The collector body will slip just over the slip couplings and because of the overlap have a nice tight fit that makes it easier to weld as well as being a very strong weld joint.  Based on the builders specifications we have chosen a 4.50” collector outlet, 2.625” merge bullet vanes to match the collector and a 4.50” x 5” – 13 degree transition cone that works well on a high horsepower drag car.

Parts List, per collector:
Main Collector Body (CL4-263-45-MS) x1
Merge Bullet Vanes (B-2625-MS) x 4
Merge Bullet Assembly Jig (TO-CL4B)
Slip Collector Couplings (CN-CLSC-2625-MS) x 4
13 Degree Transition Cone (TR13-4550-MS) x1
Slip-On Collector Assembly Tool (TO-CA4-263263) (recommend, not required)
Slip-On Collector Header Alignment Tool (TO-CA4-250263) (recommend, not required)
Collector Retaining Tabs (FL-SCB-FT) x 4

Fabrication Steps for Slip on Collector

  1. The Slip-On Collector Header Alignment Tool properly aligns your 2.50” primary tubes to match the 2.625” centerline of the slip-on collector. Using this tool helps ensure that there will be enough room between the primary tubes for the slip collector to slide smoothly into place without binding.  It also makes a terrific focal point to use in fabricating your header primaries, just decide where you want the collector to eventually end up, tack the tool in place, and then build your header toward the tool. 

  2. Start with assembling the Merge Bullet Vanes.  Stack four of the vanes together and drop the Bullet Assembly Jig over the top of the bullet vanes.  Pull it down nice and snug and tack weld the bullets together and remove the assembly jig.  Repeat for second collector.  (TIP:  Some builders like to leave the bullets tack welded and proceed to the next step, doing the finish weld at the same time they weld the bullets in place).  Bullet Vanes can be finish welded then grind/polish as you see fit.

  3. Take the Slip Collector Couplings and use the Slip-On Collector Assembly Tool to get them nice and square so your collector will neatly align to your header without binding.  Tack weld the couplings together so that they stay aligned.
  4. Place the welded Merge Bullet Vanes atop the Slip Collector couplings and weld in place.  Make any cleanup grinds at this time BEFORE you weld the collector onto the slip couplings.
  5. Now that everything is cleaned up, weld the collector body onto the slip couplings.  (TIP:  Build up a small section of weld in the low area where the tubes join to make the collector easier to weld in place without having to backfill.
  6. After the collector body has been welded to the slip couplings, weld your transition cone onto the collector outlet. You may also want to weld a piece of straight tubing to the transition cone to aid in attaching either mufflers or turnouts.
    The final step is welding on some type of retention tab to keep the collectors from being forced off.  We offer several different styles but the most popular for this application is a flat overlapping tab.

NOTE:  The pre-sized Slip-On Collector Couplings are only offered is sizes to fit for 2” OD primary tubes and larger.  You can still easily create a slip-on collector for smaller diametersby utilizing 18g tubing that is .125” larger than your primary tubes.  Simply cut your own couplers, (usually lengths of about 2” long work great), making sure the tubes are round and without burrs.  Then just follow the same steps detailed above.  This can easily be done on 5-1, 4-1, 3-1 and even 2-1 collectors.

Consider your needs and you make the call!



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800.795.5535  • 714.828.3580  • Fax: 714.828.6942