Since the introduction of the Suzuki LTZ 400, enthusiasts have begun to think differently about the 400cc ATV market. They've realized that with a few quick bolt-ons, they can have neck-snapping power and the ultra-light weight of a sport quad, without insane engine mods or a lean wallet.
By combining K&N's High-Flow Air Filter/PowerLid combo, Muzzy's Titanium Exhaust System, and a little JET work on the dyno, we woke up our Z400 to the tune of 33 rear-wheel horsepower, a whopping 11 percent increase in horsepower compared with stock.
We'll be the first to admit that the engineers at Suzuki have done an A+ job with the '05 Z400. Unfortunately, due to environmental restrictions, the engine gurus at Suzuki are required to detune the machines for the showroom floor with conservative jetting and restrictive exhaust.
How It Works
By replacing the stock foam filter with a K&N replacement filter, the engineers at K&N maintain that airflow is increased while simultaneously being smoothed out by the pleated design of the company's filter. More air is great, but not at the cost of increased turbulence, according to K&N. Similarly, by removing the restrictive stock airbox lid in lieu of a K&N PowerLid, massive amounts of air can be sucked into the airbox without degrading air quality. Acting like a giant prefilter, air is now routed through the PowerLid instead of the restrictive intake snorkel. As more air is introduced, more fuel must be added. For this reason, the K&N kit includes larger main jets and a recommended idle/air-mixture adjustment. Contrary to popular belief, running no air filter can actually hurt performance, not to mention trash your engine's internal surfaces.
While adding more airflow is always an improvement for power, reducing backpressure makes your intake efforts that much better. To improve exhaust flow, we turned to road-bike-expert-turned-ATVer Rob Muzzy for a full-titanium exhaust system. Using a larger-diameter titanium head pipe, an oval titanium muffler, and a USFS-approved spark arrestor, the Muzzy system improved exhaust flow while weighing in 15 pounds lighter than stock.
Under The Wrench
The first thing we did was baseline our Z400 at K&N Engineering's dyno facility in Riverside, California. To our surprise, the stock Z made 29.8 hp at 7,000 rpm and 23.7 pounds of torque at 6,200 rpm. A marked improvement compared with the previous model year, it is no doubt due to the larger carburetor and improved cam profiles.
In less than an hour, we removed the stock foam air filter, stock lid, and exhaust, and we replaced them with the appropriate K&N and Muzzy components. With no tuning whatsoever, the air/fuel ratios were lean to say the least. With an air/fuel ratio of 17:1, some serious jetting was called for. With the help of K&N PowerSports engineer Charlie Tissen, we jumped as high as 165 main jets, shimmed the needle 0.025 inches richer, and moved the idle/air-mixture screw from a 3/4 turn opening (stock setting) to 2-1/2 turns. While this was ideal for our Z, factors such as altitude, fuel type, and weather can drastically affect jetting, so keep an eye on that plug. Alas, the power arrived with 96 decibels of thunderous roar, just at the legal limit for most recreational areas in the lower 48 states.
Just The Facts
We enjoyed riding the stock Z, but it lacked the throaty aftermarket exhaust tone we've become accustomed to. It was starving for air and fuel - two things we quickly fixed with the K&N filtration and new jetting. The bottom line: We love the sound, and the performance increase was quick and easy.
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Muzzy's Performance Exhaust