New Lungs For The Z400

By Andrew Schear

Improving Performance With K&N Engineering and Muzzy's Exhaust

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% increase in horsepower over 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, engineers at K&N maintain that airflow is increased while simultaneously being smoothed out by the pleated design of K&N filter. More air is great, but not at the cost of increased turbulence according to K&N. Similarly, by removing the restrictive stock air box lid in lieu of a K&N PowerLid, massive amounts of air can be sucked into the air box 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 included 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 trashing 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 4-stroke road bike expert turned ATVer Rob Muzzy for a full titanium exhaust system. Utilizing a larger diameter titanium head pipe, oval titanium muffler and USFS approved spark arrestor, the Muzzy system no doubt 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 located in Riverside, California. To our surprise, the stock Z made 29.8 horsepower at 7,000 rpm and 23.7 pounds of torque at 6,200 rpm. A marked improvement over the previous model year, 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 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 in order. So, with the help of K&N PowerSports engineer Charlie Tissen, we jumped up to 165 main jets, shimmed the needle .025 richer and moved the idle/air mixture screw from 3/4 open (stock setting) to 2 1/2 turns open. While this was ideal for our Z, altitude, fuel type and weather can drastically affect jetting, so keep an eye on that plug! Alas, the power had 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 liked riding the stock Z, but it was lacking the throaty aftermarket exhaust tone we've become so 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.

The Muzzy TI system fit like it was original equipment. It even reused the factory Suzuki heat shield, always a plus when thinking about the charred skin alternative.

The K&N replacement High-Flow Air Filter took 5 out of our 60-minutes of installation time. Take note of the pleats used to smooth out airflow. The cotton-gauze wrapped with mesh can be cleaned as often as needed with the K&N ReCharger kit.

The K&N PowerLid fit just as well as the stock plastic lid. Using only the lid and replacement filter will require a 160 main jet and slight adjustment of the air fuel ratio. You'll also notice a slight hum resonating from under the seat, we thought it was cool.

Everything was complete down to the K&N PreCharger, used to help keep your filters clean when riding in foul conditions. One hour of wrenching time for 11% more power...a sweet deal if you ask us.

Source

K&N Engineering, Inc.
1455 Citrus Ave.
Riverside, CA 92507
951/826-4000
www.knfilters.com

Muzzy's Performance Exhaust
62910 Peerless Ct.
Bend, OR 97701
541/385-0706
www.muzzys.com

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