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Some time ago I decided to address the problem of recurring exhaust system cracks  by install a new exhaust system. Larry Vetterman, founder of Vetterman Exhaust, suggested that a four pipe system would be more robust than my current four into two crossover system, as each pipe would be completely independent, with no connection to pipes from other cylinders. I was also considering a four-into-one system, but his performance tests of various configuration systems suggested that the four pipe system might yield a slight performance increase over the crossover system I have and the four-into-one system (more test results). I would have thought that a four-into-one system would be the fastest of all, but repeatable flight test data trumps theory every time. Decision made - a switch to a four pipe system was in order. I decided to get this done before next spring, to avoid any interruption of the good weather flying season.

I pulled the trigger in November, and asked Clint Busenitz (the current owner of Vetterman Exhaust) to make me a system. He was familiar with my recurring cracks, having repaired it twice (the third repair was done in the Ottawa area). He offered to build this new system with thicker than normal pipe at the cylinder flanges, as this is the area most likely to crack.

The new exhaust system arrived just before Christmas. Each cylinder pipe has a slip joint and a ball joint to allow the tail pipes location to be adjusted. The four pipe system also comes with a two pipe heat muff - this oval shaped thing fits over two adjacent pipes, and is reported to put out lots of heat. I also hope to resuse the heat muff I had installed on the #1 pipe, near the cylinder.

 


We had a short spell of warm weather over the last few days, so Saturday I removed the old exhaust system, and Sunday I started the installation of the new one.

The first big task is to drill the holes for the EGT probes. The probes should all be mounted the same distance from the cylinder, on a straight section, and no closer than 2“ to the cylinders. On my previous exhaust system those criteria drove me to put the probes 5” from the cylinders, which is farther than ideal. The EGT indications were always slow to respond to mixture changes, and I attributed that to them being a bit too far from the cylinders.

This new exhaust system has bends in slightly different locations, which allowed me to put the probes 2.5" from the cylinders. I wanted to be able to reuse the existing EGT probe wiring, which somewhat restricted the available clock angles on the pipes - some clock angles would require longer wires, and there wasn’t much slack available to do that. With the closer position to the cylinders, I also needed to be careful not to chose a clock angle that would have the protruding end of the EGT probe interfere with the lower spark plugs.

Stainless steel is a bit tricky to drill, and any round surface risks have the drill bit move around before it starts to cut. I fabricated a small drill guide from a piece of aluminum bar with a hole in it. I used two hose clamps to hold it in position for each hole. This worked a champ, after I acquired a suitable drill.

My hangar rechargeable drill with keyless chuck proved inadequate to the task. No matter how hard I tried, I couldn’t get the keyless chuck tight enough to keep the drill bit from spinning in the chuck once it started to cut into the stainless steel. I went to three different hardware stores in Smiths Falls today, looking for a cheap corded 3/8“ drill with a regular keyed chuck, like the one I had at home. No luck - lots of drills with keyless chucks. The only ones with keyed chucks were expensive ones aimed at professional contractors. I settled on a not so cheap 1/2” hammer drill, as I could use one of those. The hammer function can be turned off, and it did a perfect job on the exhaust pipes.

I was quite relieved when I had all four EGT probes mounted, and the hole locations proved satisfactory, with no interference between the probe ends and anything else.

 


Here is a bottom view of the four pipe system.

I need to install the supports for the tail pipes and the heat muffs. I also must rework the support for the breather tube, etc that exit in the middle of all the pipes - they are just hanging there at the moment, as they were connect to the support for the tail pipes on the previous exhaust system.

 


Left side.

 


Right side.

 


A cold front went through overnight last night, and it will be much colder over the next few days. I’ll switch my efforts to the fuel tank leak repair, as that work is done in our basement.

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