Since I have an IO-320 engine for my Cozy, one of my considerations is to optimize its performance via all available means. Tuned exhaust for automotive applications has been around for years and is growing into the general aviation and experimental arena. The problem is space inside the engine compartment and the cowls. I spent some time in talking to tuned exhaust business owners for a set of tuned exhaust for the Cozy MKIV. I even paid Burns Stainless to calculate the optimal length and design for our exhaust system, using their custom software. All in all, I received an 'estimate' of what the length should be, but with no guarantee because they have to use a bunch of assumptions (or the lack of factual data) for the calculation. I either spend ~$2,200 for a custom exhaust with questionable performance or $500 and stay with the Plans, using the extra room for the oil cooler. I decided to stay with the Plans exhaust.
Installing the Exhaust System
I bought my standard exhaust from Custom Aircraft Parts and it arrived within a week - they have it pre-made, in stock. The exhaust pipes fits easily with no issues, but I had to bend some of the fuel lines out of the way - just for clearance.
I cut out the exhaust holes in the cowling (as shown). I was told there should be 1" clearance around the exhaust. I shall wait until I figure how long the exhaust pipes should be, then I'll open up the holes accordingly.