Source: About.com

The after-market for automotive exhaust components is absolutely vast. Summit Racing has over twelve thousand mufflers featured in their online catalog. They list dozens upon dozens of manufacturers in their exhaust department. If you’re building a custom exhaust this incredible variety is a double-edged sword. Having a lot of options is great, but it can make the job of narrowing down your parts selection quite intimidating.

Such was the case for Project Hoondy. When we started our own custom exhaust project we had a good idea of the results we wanted, but only a vague concept of how to get there. We started with deciding what we liked about other custom exhaust builds we had previously admired.

The performance gurus at MotoIQ are a constant source of inspiration for our own automotive ambitions and this time was no exception. They’ve covered a wide variety of killer projects, but perhaps none have stuck with us as firmly as Project V8 RX-7. There are many wonderful aspects to that build, but the exhaust is one of our favorites:

Source: MotoIQ
Source: MotoIQ

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This exhaust utterly embodies MotoIQ’s signature phrase: “Hellafunctional.” A simple design with top-notch fabrication yields a brutally efficient configuration. Despite the raw, straight-pipe construction there is a great nod to serviceability via quick-release V-band clamps. High quality materials provided by Vibrant Performance also ensure excellent durability.

Even with the function-over-form mentality, one of the best things about this exhaust build is the way it looks. The no-nonsense, single-exit, un-polished oval exhaust tip exudes pure motorsport charisma. No chromed up rolled-over tips, no fakery, no styling for style’s sake alone. That’s our kind of visual attitude.

The V8 RX-7 gave us great philosophical inspiration for our own exhaust build, but did little to push us in the direction of any particular manufacturer of exhaust components. The V8 RX-7 has no mufflers, resonators, or cross-over pipes. For ideas on these parts we would need to look elsewhere.

We decided that in order to initially narrow down our selection we would focus purely on sound. From there we would emphasize performance and build quality.

Our quest for the perfect sound took us down a nostalgic road. We grew up spending every weekend of every summer at a small Midwestern drag-strip. The deep burble of a lumpy-cam V8 idling through un-muffled headers is just about our idea of exhaust note perfection. This preference was at odds with the Genesis Coupe’s popularity among the “import tuner” scene. It was for this reason that we looked into products from Flowmaster, Kooks, and others that have more popularity with the muscle-car crowd.

We knew we wanted a muscular burble in our exhaust note, but we knew even more that we did not want drone. Classic muscle-car sound is great, but classic muscle-car exhaust systems tend to employ rudimentary technology such as the venerable “glass-pack” muffler. This old-school tech makes a great noise when you’re on the power, but they can be hell for the driver during a long cruise. Highway journeys and other instances of steady-state driving often induce an endless, intrusive droning sound that can seriously take the fun out of a daily driver. We’d already had a nasty run-in with unwanted noise via a rattling short-shifter on Project Hoondy. That incident was costly and irritating. We were loath to repeat the experience:

This drove us to seek out more modern innovations in exhaust system tech that are popular with muscle-car owners.

We think that Corsa Performance is at the top of this particular food-chain. We’d heard of them in the past and knew that their labyrinth-style muffler baffling was particularly well-known for its effectiveness in reducing drone. In the course of our research we found this excellent article by Chevy Hardcore that greatly expanded our knowledge of Corsa and made us seriously interested in owning some of their products.

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Unfortunately, for the most part, Corsa doesn’t sell their mufflers as stand-alone products. They are only available in pre-made exhaust kits built for specific cars. We contacted Corsa about this and they said that it was because their muffler technology is very effective but works best within tightly defined parameters. The geometry of their mufflers is always tailored to the specific engine it will be paired with. One of their mufflers that works great on one car will be far less effective when moved to a different one.

On one hand this made sense to us, but on the other hand we knew that Corsa produces exhaust kits for engines with very similar configurations to Project Hoondy. After all, they make exhaust kits for the V6 Camaro, Challenger, and Mustang. How different could the muffler geometry be for the 3.7 liter DOHC V6 Mustang versus the 3.8 liter DOHC V6 Genesis Coupe?

Even after bringing this up, sales reps from Corsa did not seem very interested in enabling us to buy their mufflers for off-label use. If we had persisted we might have obtained what we needed from them, but their reluctance caused us to start looking elsewhere.

We really liked the labyrinth silencer technology that Corsa employs. Its combination of low drone and great flow characteristics was what we craved. We focused our effort to try and find a different company that used similar technology. It was at this point we discovered SpinTech exhaust, who’s roots go back to NASCAR in the nineties.

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In 1995 Sterling Marlin’s Kodak-sponsored number four car caused a stir at the Daytona 500. Commentators and fans alike were remarking on the car’s unusual sound.

Through qualifying and the race that followed, it became clear that there was plenty of speed to go along with that sound. Marlin ended up taking the checkered flag at the end of race day:

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Just a few weeks earlier, Morgan-McClure Racing, the race shop that Sterling Marlin drove for, contacted one Mr. Boyd Butler. Boyd had developed some new exhaust technology and had actually been trying to gain the interest of NASCAR teams for quite some time. Until then, nobody in NASCAR would give him the time of day. Many months prior, Boyd had ended up simply placing an ad in Circle Track Magazine and hoping for the best.

That advertisement eventually caught the attention of Mark Giles who was the exhaust system fabricator for Morgan-McClure Racing. He was forever on the hunt for a competitive advantage and decided to take a chance on Boyd Butler’s new technology. Giles and company then confirmed significant power gains with a set of Butler’s first-draft prototype pipes.

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Mere days before the ‘95 Daytona 500, Morgan McClure Racing flew Boyd Butler into their shop where he feverishly developed a new exhaust system for Sterling Marlin’s car. It was the first time Butler had ever worked with oval exhaust tubing, which was a must on Winston Cup cars due to their low ride height. Butler rose to the challenge, netting the team an extra 4.5 horsepower for their race at Daytona.

That extra power advantage contributed to a race win and set off a trend in the NASCAR scene. Boyd Butler was vindicated as he immediately began receiving calls from all the other race teams. Larry McClure ended up signing Butler to an exclusive deal for the season, and then in 1996 multiple teams would adopt the technology. It was from here that Butler earned his nickname “Dr Gas.”

Boyd Butler’s exhaust systems became a staple in NASCAR and from that success grew a full-on aftermarket exhaust company known as SpinTech, which would come to specialize in oval exhaust tubing and produce mufflers based on Butler’s own techniques. The mufflers themselves employ spiral traps to attenuate exhaust noise without drastically reducing flow. The traps work by converting sound energy into heat and their carefully arranged geometry keeps exhaust gas velocity high for good performance.

While this is different in execution and possibly cruder than Corsa’s labyrinth silencers, we found enough similarity in principal to become quite interested in using SpinTech products for Project Hoondy.

That interest grew quickly when we saw that SpinTech offers all of their products in 304 stainless steel, our material of choice for this exhaust build. Then we discovered that SpinTech’s mufflers are made to order and the company will happily fabricate fully custom units upon request at a minimal surcharge. This sealed the deal as the possibility of a muffler made to our exact specifications was too tantalizing for us to pass up.

Given this kind of leeway, an idea of what our custom exhaust system could look like quickly formed:

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If there’s enough length available, SpinTech can make a dual-inlet, dual-outlet muffler with internal cross-flow, eliminating the need for a cross-over pipe. This would drastically simplify the design of our exhaust system. We could use the muffler to make a right-angle bend and also to translate from 2.25 inch round pipe to an oval pipe so we could have bitchin’ oval exhaust tips. A sufficiently large muffler would be quiet enough not to need secondary resonators as well.

A custom SpinTech muffler would be expensive, but it did so many things for us that we would be eliminating a lot of complexity and therefore cost. We settled on SpinTech as our primary supplier of exhaust components, happy that they could provide both our muffler and all the stainless bends, tubing, hangers, and flanges we could possibly need.

We were ready to move forward with our custom exhaust. Sadly, we are not talented fabricators, so we would need help putting it together. Find out who we would partner with for this task next week on Project Hoondy!

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