Think this thread just saved me $600+. I was just looking at those $700 mufflers.
Yeah, no catback is worth more than $200 on a Lotus. There's just not that much material there, and mufflers and pipes size directly to horsepower produced, because horsepower in turn correlates directly to fuel and air burned in an Otto cycle engine. If you're paying more than $200, you're enriching somebody instead of improving your car with the difference.
If you do a little quick math using the most optimistic numbers (2 litres for a 2ZZ, 9000 RPM, 100% VE) you get the grand sum of 9000 litres/min = a bit less than 320 CFM. That's it. The world is full of inexpensive, decently made mufflers meant for half a high performance 5.7+ L V8 that will work very well indeed on a 2ZZ ([email protected]
= 301CFM) . The hardest part is packaging, but Lotus was pretty generous with space behind the engine, so it's not that bad.
Yes, you need higher flow if you have a supercharger. The math isn't any harder, and there are still plenty of cheap mufflers that will do the job.
I went through a version of this excercise on my Corvair van with a warmed-over engine back when. Stock replacement mufflers were restrictive, expensive and an odd shape. I wanted to retain the stock mounts and form factor because of bodywork. Some quality time with the Walker catalog found the OE replacement muffler for a six-cylinder Ford Granada. What was probably an unpleasantly restrictive muffler for a 250 CI low-perf engine was the hot tip for a 164 CI higher-perf engine. Sounds great, too (yes, I have gotten compliments), because the muffler dumps straight out the back of the van with a 6" long tailpipe. Cost? About $50 all up including tubing adapters and clamps. Now admittedly, it's not stainless steel, so will rust out every 50k miles or so, but it's a 1965 collector van, so 50 k miles is 15-20 years.
Exotic money for mufflers for exotics is not a new thing - my father tells me that an Abarth muffler for his Fiat 600D (which was the same part as on a Fiat-Abarth Zagato 750, among other things) was something like $150 in 1963. He went with a custom welded header and glass pack instead, changed the glass pack every year when it started getting too loud, and bought a new set of Pirelli Cincuratos (which did more for the car than any muffler) with money to spare.
Note that this has nothing to do with header/collector/cat selection, which is pretty close to optimized on the NA 2ZZ, but has room for improvement on supercharged or highly tuned engines, as BOE's research