slpleadIn the classic baseball flick Bull Durham, Tim Robbins’ character – the young pitcher with a “million-dollar arm and a five-cent head” – justifies his insistence on throwing fastballs by simply saying, “I want to announce my presence with authority!”

That philosophy largely sums up the impetus behind SLP’s Loud Mouth lineup of exhaust components, which has been one of the most popular aftermarket systems for the ubiquitous fourth-gen Camaro and Firebird. In fact, the story behind the Loud Mouth’s development and production dates back more than 15 years, while the systems for LS-powered F-cars didn’t actually arrive in the market until after the fourth-gen cars had already gone out of production.

If you’re doing the math in your head, you’ve figured out that it hasn’t been quite 15 years since the fourth-generation F-body production run ended, though. That’s because the Loud Mouth was originally developed – ahem – for the Mustang.

Making Some Noise

SLP had always been about GM vehicles, but we couldn’t ignore the size and strength of the Mustang world. – Kevin Woodruff, SLP

“SLP had always been about GM vehicles, but we couldn’t ignore the size and strength of the Mustang world,” says Kevin Woodruff, who has been with the company since the early years. “And while we had exhaust experience with F-cars since the company’s started, not to mention the Pontiac Firehawk and Chevrolet Camaro SS OE vehicle programs, we were simply unknown in the Mustang community. It was at a time when the Flowmaster 40-series seemed almost like a factory option on those cars and the consensus was we would need to come out of the gate really strong, with a revolutionary product no one could ignore.”

Simplicity at its finest. The stainless steel Loud Mouth resonator was SLP’s exhaust shot that was unmistakably heard ‘round the performance world.

Simplicity at its finest. The stainless steel Loud Mouth resonator was SLP’s exhaust shot that was unmistakably heard ‘round the performance world.

The straight-through, resonator-type design of the Loud Mouth “muffler” was it. It was bold, brash and undeniably loud. The true “authority” of the car might have been up for debate at the drag strip, but when it came to announcing it, the car was audible from a few blocks away.

By the time it was clear the Loud Mouth was a success with Mustang owners, we were looking to change up our lineup for F-bodies. – Kevin Woodruff

As for SLP, the company had boldly announced its presence in the Mustang world, but it was obvious the Loud Mouth concept was one that would also resonate (pun intended) with F-body enthusiasts.

“By the time it was clear the Loud Mouth was a success with Mustang owners, we were looking to change up our lineup for F-bodies,” says Woodruff. “We had been doing our ‘two outlets on the left’ systems for years and it was getting a little dated. The trend was definitely toward outlets on the left and right sides of the car and we thought the Loud Mouth would be a good choice for that.”

A cutaway of the Loud Mouth resonator shows much there is – or isn’t – to it. It’s essentially a straight-through design with a 3-inch inlet/outlet and a 4-inch body diameter. The body is 18.25 inches long.

A cutaway of the Loud Mouth resonator shows how much there is – or isn’t – to it. It’s essentially a straight-through design with a 3-inch inlet/outlet and a 4-inch body diameter. The body is 18.25 inches long.

Interestingly, the first Loud Mouth system for the fourth-gen Camaro didn’t debut on the market until 2003 – about a year after the car had gone out of production. That didn’t dampen demand in the least, as the LS1 cars were still in stride as the affordable performance car of choice for GM enthusiasts.

One of the challenges of building an aftermarket exhaust for the 4th Gen F-body cars is the somewhat odd stock exhaust routing. The stock manifolds merge very close to the front of the car into a single stream, feeding a large longitudinal muffler at the back of the car with dual tips.

SLP had also revised the earlier, all-welded design of the exhaust system to a modular design that used strong, leak-preventing torque clamps, but that were easy to remove, allowing the car owner to change the original Loud Mouth resonator with the slightly tamer-sounding Loud Mouth II muffler if so desired. It features a wrap around the perforated pass-through pipe, toning down the exhaust note considerably.

This look at the Loud Mouth fourth-gen system shows that, in comparison to a conventional exhaust system, the Loud Mouth is essentially a straight-through system with no muffler. That’s the key to its performance advantage and take-no-prisoners sound quality.

This look at the Loud Mouth fourth-gen system shows that, in comparison to a conventional exhaust system, the Loud Mouth is essentially a straight-through system with no muffler. That’s the key to its performance advantage and take-no-prisoners sound quality.

With the same dimensions as the original Loud Mouth, the Loud Mouth II muffler is not as loud as the original Loud Mouth – but it could never be described as quiet.

With the same dimensions as the original Loud Mouth, the Loud Mouth II muffler is not as loud as the original Loud Mouth – but it could never be described as quiet.

That’s not to say the Loud Mouth II was quiet by any measure, but it was certainly less obtrusive to passengers in the car and wouldn’t necessarily incur the wrath of neighbors during a 6 a.m. start-up on a Sunday morning.

The guts of the Loud Mouth II muffler show the difference between it and its louder sibling: A perforated flow tubed wrapped with a ceramic material. It does a good job of cutting down on the in-car resonance that girlfriends and wives get fed up with the original Loud Mouth resonator.

The guts of the Loud Mouth II muffler show the difference between it and its louder sibling: A perforated flow tube wrapped with a ceramic material. It does a good job of cutting down on the in-car resonance that girlfriends and wives object to with the original Loud Mouth resonator.

“The modular concept is the true hallmark of the Loud Mouth series,” says Woodruff. “Rather than scrapping the entire system and installing a new one – or even hack-sawing off a welded muffler and replacing it – the Loud Mouth system allows you to simply unbolt the resonator or muffler and bolt in the new one, whether you want it louder or quieter.”

Love Thy Neighbor

For those looking for even a quieter sound, SLP’s PowerFlo system offer a, oh, let’s say more “mature” exhaust note. It incorporates a pair of more conventional mufflers, but still offers the easy clamp-on installation of the Loud Mouth resonator or Loud Mouth II muffler. In fact, the Loud Mouth resonator stays in place and the PowerFlo mufflers simply install downstream in the exhaust system, just ahead the exhaust tips.

Not everybody wants the full-on Loud Mouth experience and that’s why we offer a range of choices. – Kevin Woodruff

“Not everybody wants the full-on Loud Mouth experience and that’s why we offer a range of choices,” says Woodruff. “Even after you’ve used the original Loud Mouth resonators for a while, you may find yourself in a few years with a baby seat in the back or a new house in a neighborhood that’s not as friendly to basically an open exhaust system – and that’s where the modularity of the system makes it easier and more cost-effective. Rather than a $1,000 or more for an all-new system, you simply spend a couple of hundred bucks and an afternoon to swap out the resonators.”

 

For an even quieter exhaust – make that less loud – SLP offers the PowerFlo conversion for the Loud Mouth system. It adds a pair of conventional mufflers that the company says reduces sound levels by 6 dB at idle and 9 dB at 2,000 rpm. That may not sound like much, but it’s a significant reduction.

For an even quieter exhaust – make that less loud – SLP offers the PowerFlo conversion for the Loud Mouth system. It adds a pair of conventional mufflers that the company says reduces sound levels by 6 dB at idle and 9 dB at 2,000 rpm. That may not sound like much, but it’s a significant reduction.

The finishing touch for a complete Loud Mouth system is a set of tips and SLP offers a variety – all of them in polished stainless steel.

The finishing touch for a complete Loud Mouth system is a set of tips and SLP offers a variety – all of them in polished stainless steel.

One thing all of SLP’s exhaust systems have in common is stainless steel material and in-house construction. It’s been that way from the very beginning.

“Exhaust systems have been a specialty of ours from the company’s early days as an emissions-legal performance parts manufacturer,” says Woodruff. “We’ve got it down to a science.”

This shot of a PowerFlo-equipped Loud Mouth system shows how the mufflers and the original resonator are incorporated. With the conversion kit, the PowerFlo muffers are installed after length of the exhaust outlet pipes are cut off. SLP also offers a complete PowerFlo kit with the Loud Mouth II muffler and pre-kit outlet pipes.

This shot of a PowerFlo-equipped Loud Mouth system shows how the mufflers and the original resonator are incorporated. With the conversion kit, the PowerFlo muffers are installed after a length of the exhaust outlet pipes are cut off. SLP also offers a complete PowerFlo kit with the Loud Mouth II muffler and pre-kit outlet pipes.

Indeed, all of the exhaust components are made of stainless steel and that goes for SLP’s F-body headers, as well. In fact, the company has been making F-car headers just about as long as they’ve made anything.

The headers were originally developed as a compromise-free, racing-inspired equal-length design. They represented a marvel of engineering prowess, but they weren’t exactly street-friendly because, frankly, they hung down too low.

The header design evolved by necessity into a more conventional long-tube design that delivered a performance benefit without ground clearance problems – even on slightly lowered cars. And in true long-tube fashion, they deliver the biggest power gains in the mid-range and upper rpm levels.

SLP’s long-tube headers feature 1.75-inch primaries and 3-inch collectors, and feature a standard, polished aluminum-ceramic thermal barrier coating inside and out. Compared to the company’s tuned-length headers, the longer, full-length design optimizes power output at higher rpm. SLP says they’re designed for a drop-in installation, too, and in our experience that’s pretty much the case.

SLP’s long-tube headers feature 1.75-inch primaries and 3-inch collectors, and feature a standard, polished aluminum-ceramic thermal barrier coating inside and out. Compared to the company’s tuned-length headers, the longer, full-length design optimizes power output at higher rpm. SLP says they’re designed for a drop-in installation, too, and in our experience that’s pretty much the case.

Joining Forces

Another of SLP’s signature exhaust components is the freer-flowing Y-pipe that mounts between the factory exhaust manifolds and catalytic converters. The 2.5-inch stainless assembly replaces the more restrictive, factory-installed flat-tube Y-pipe. SLP says it’s good for up to 10 horsepower.

Another of SLP’s signature exhaust components is the freer-flowing Y-pipe that mounts between the factory exhaust manifolds and catalytic converters. The 2.5-inch stainless assembly replaces the more restrictive, factory-installed flat-tube Y-pipe. SLP says it’s good for up to 10 horsepower.

SLP, which was acquired by ROUSH Industries in 2013, manufacturers the majority of its exhaust components at its suburban Detroit factory, along with some at a Canadian facility. The fixtures for welding the components have been with the company for years, but the equipment to produce them has been revamped or updated since coming under ROUSH’s umbrella a couple of years ago. That meant moving them from SLP’s former headquarters in New Jersey to the Motor City.

“It’s all good with the changeover,” says Woodruff. “It’s like your favorite pizza maker moved to a new location, but took his seasoned pizza pans and recipe with him. All that’s really changed is the address – the ‘pizza’ is still as good as it ever was.”

They’ve also expanded their menu in the new location, adding components for the fifth-gen Camaro – particularly supercharger systems. With ROUSH’s considerable experience manufacturing supercharger systems, the synergies are natural and mutually beneficial. That’s helped SLP retain the OEM-level of engineering and manufacturing quality on which their reputation was originally built.

SLP offers complete exhaust kits from the headers to the exhaust tips that also incorporate high-flow catalytic converters. They feature a high-metallic substrate design with a 200 cell/inch honeycomb. For the tight confines of the fourth-gen F-body engine compartment, SLP also offers a cut-down spark plug socket that makes it easier to remove the plugs. It is especially handy when trying to work around the more bulbous primary tubes of headers.

Exhaust systems, however – and the Loud Mouth series specifically – continue to constitute SLP’s bread and butter.

“We’ve sold literally thousands of systems for fourth-generation F-bodies alone,” says Woodruff. “I couldn’t even guess right now how many we sold overall, because enthusiasts adapt the resonators to vehicles we don’t even offer kits for. Again, it’s the modularity of the design that makes it stand out. They build the rest of the system around the resonators to get that unmistakable sound.”

As a staple of the F-body performance world, the Loud Mouth series unquestionably announced SLP’s presence with authority. They’ve kept throwing those fastballs ever since.