Published on November 17th, 2022 | by Joe

Yamaha YFZ450R Big 3 Engine Upgrades, Dasa Exhaust, Fuel Customs Intake, and PEP Stock ECU Reflash Test:

More power, Broader Power Curve, and Better Throttle Response for the YFZ450R!


Most sport ATVs ever produced enjoy significant horsepower gains by addressing the Big-3 engine upgrades. The Big-3 refers to utilizing a freer flowing exhaust, air intake system, and the necessary jetting or fuel mapping changes to match the increased airflow. More stringent EPA restrictions have made things a bit more complicated with the introduction of an Air Induction Systems (AIS) on Yamaha’s sport ATV models. It injects air from the intake into the exhaust to help burn off any remaining fuel that made it past the combustion chamber causing some minor backfiring  under deceleration. This and the accompanied leaner running condition at lower RPMs left 2014 and newer YFZ450Rs with an occasional minor hesitation or bog at lower RPMs when you crack the throttle. This becomes far more pronounced with a freer flowing exhaust or intake without the proper tuning and mechanical setup to match.  For this YFZ450R Big-3 Test, we’re pairing up a Dasa Racing exhaust, Fuel Customs intake, and a PEP Tuning ECU reflash in search of getting the most performance possible out of the engine, while keeping it  simple and relatively affordable.

Fuel Customs has been the leader in modern sport ATV intake design for some time. Testing many of the top exhaust systems on the market with their air intakes on different machines, Fuel Customs helped us pick the exhaust for our Raptor 700R Big-3 Test a while back. Fuel Customs has a few aftermarket exhausts they recommend for the YFZ450R with Dasa Racing producing one of their favorites due to their performance, construction, and ease of maintenance. PEP Tuning tells us that the DASA Racing exhaust and Fuel Customs intake are the ultimate combination for the YFZ450R, so we knew our intake, exhaust, and tuning solutions should work perfectly.  Also, all of the products used in this upgrade project are made in the United States, not China.

Test rider, Evan Hartzel, races cross country on a pair of YFZ450R’s, giving him a good amount of experience on lightly modified Yamahas.


The Big-3.5 Engine Upgrades

AIS Block-Off Kit


The first step in getting your 2014 and newer YFZ450R running its best is blocking off the air induction system. Our test had an air induction system block off kit from 38 Motorsports installed. It helps eliminate the backfiring under deceleration, eliminates the clutter of the AIS, and is necessary for proper tuning with an air fuel sensor.


Dasa Racing exhaust


Dasa Racing Exhausts are handmade in the USA. Beautiful tig welding is used throughout, befitting of a high-end performance exhaust. The head and mid-pipe feature 304 stainless steel construction with an aluminum silencer body and end cap.  The end cap and mid-pipe bolt to the silencer body using Allen screws instead of rivets for easier repacking or replacing individual parts.  Billet silencer mounts add both looks and strength to the exhaust. The silencer and Dasa logo are available in a variety of colors to match your machine. We opted for the white and blue color scheme for a light, fresh look. A billet end cap adds to the exhaust’s aesthetics.

The exhaust’s expanding multistep design is said to allow a greater expansion of the exhaust gases for a broader powerband without sacrificing peak horsepower. According to Fuel Customs, the Dasa Racing Exhaust adds around 7-8 peak horsepower. Sound output is 102 DB at 4,500 RPMs, which should be legal at most tracks according to Dasa.

DASA is now offering a new AMA edition exhaust, designed to meet the AMA’s 96db limit for racing. It is currently available with a polished silencer body only, but that could change as availability increases. They also offer a shorty version with a 4” shorter silencer body offering a touch more peak horsepower and acceleration at the expense of being rather obnoxiously loud. They’re typically used for Drag racing or TT Racing on a closed course.


Fuel Customs Intake 


Fuel Customs’ intakes and air boxes are constructed of Rotary mold plastic. They feature a tapered design and increased volume in search of improved throttle response, horsepower, and torque across the RPM range. The harder material is said to increase the intake pulse improving every aspect of performance. Paired with a good aftermarket exhaust, they’re said to add 9-10 HP with the intake adding an additional 2 HP at peak and 5-6 HP in the over rev while reaching peak torque faster.

Their intakes are available with and without an airbox, which adds some added protection against splashing water and flying debris without affecting horsepower, so we always utilize Fuel Custom’s airbox with their intake.

Fuel Custom’s Airbox Intake System comes with their eight-layer, high-flow K&N style filter, utilizing Fuel Custom’s own proprietary material with four additional layers for a greater level of filtration. An Outerwear pre-filter is included for added protection and reduced maintenance. We’ve asked for it and now Fuel Custom is offering foam Outerwears for their filters. They promote it for mud and wet conditions, and run dry. We’d oil it up a bit for added protection against fine dust and silt, but your machine will run a little richer.


2014 and newer kits offer hook ups for the air induction system. If you are running an AIS block off kit like us, you can order the intake for the older models for a cleaner install.


PEP Tuning Reflashed Stock ECU


PEP Tuning is a subsidiary of legendary PEP Suspension. They specialize in all things tuning for the YFZ450R from aftermarket ECUs from Vortex and new AIM ECU, to piggyback controllers like the Power Commander V and Auto Tuner, to reflashing your stock ECU.  PEP Tuning started providing programming for the YFZ450R’s stock ECUs in the Pro Stock Class at the ATV MX Nationals, due to stock bikes running extremely lean from the factory. From there, they created tunes for basic mods like removing the airbox lid, running different filters, and adding aftermarket exhausts.  The ECU reflash is best suited for trail riders and racers wanting to stick to the Big-3, according to PEP.


For around $350, including shipping, the stock ECU can be retuned for fuel and ignition timing.  Premium piggyback programmers, like the similarly priced DynoJet Power Commancer V, add features like raising the rev limit, setting the throttle position sensor, and auto tune capability with the addition of DynoJet’s add-on Auto Tune module. Piggyback tuners are a little more complicated to wire up, and you’ll be hooking up a laptop computer for tuning or sending different fuel maps to figure out the best one for your machine’s setup.  From there,  an aftermarket ECU provides the added ability to tune injection timing, fan-on temperatures, turn off tip over sensors, adjust starting parameters, idle RPM, plus launch mode, various ignition curves, and traction control capabilities. Skies the limit are what can be done with an aftermarket ECU.  However, they cost around $800 plus tuning. PEP says nothing provides the throttle response of an aftermarket ECU, but you have to decide if your needs justify the investment.

For a practice or local race machine, we decided to go with the least expensive and least complicated option and had PEP reflash our stock ECU. They have fuel mapping and ignition timing specifically for the DASA Racing exhaust and Fuel Customs intake in addition to other popular exhaust systems. A couple weeks after sending ECU off, we had it back. It plugged right back in and was ready to go without the ability to alter the tune.


Other Important Details


The Trimbles typically use Maxima Racing products to maintain their machines. Prior to testing,  our YFZ450R received a fresh oil change. The Trimbles run Maxima Premium engine oil for practice purposes and Maxima SynBlend on race days where the quad gets pushed harder with less time for oil changes.  98 octane pump gas was used to prevent any gains from running boutique race fuel.

For handling that can keep up with the increased engine performance, a set of adjustable Teixeira Tech CXC upper A-Arms and a Precision Racing steering stabilizer were previously installed.  See our review of the Teixeira Tech CXC upper A-Arms for more on how to improve your YFZ450R’s handling.


The Test


Testing took place on a private motocross track. Test rider, Evan Hartzel, races cross country on a pair of YFZ450R’s, giving him a good amount of experience on lightly modified Yamahas.

Cold or warm, the freer flowing YFZ450R fired up quickly; our first positive sign from the PEP reflashed ECU. On the track, the YFZ ran pretty flawlessly. Throttle response was good regardless of RPM. We were impressed with how much fuel we could dump with the throttle while lugging the engine at lower RPMs with none of the bog YFZ450Rs are claimed to suffer from. This proves to us that a great running YFZ450R has more to do with the tuner than the tuning device, although as we’ve noted, piggyback fuel tuners and aftermarket ECUs can unlock even more performance.  The only time the engine ever bobbled mildly on the track was on crushing jump landings where we tried to pin it after landing instead of landing on the gas.

The Dasa Exhaust combines beautiful construction with a big bark and the horsepower increase to match.  We certainly felt the difference compared to the stock exhaust, with notably more power available at all RPMs, especially from the midrange up.

Dasa is responsible for building some of the fastest ATV race engines around and we know of other motor builders who happily recommend their exhausts. Whether you’re uncorking your stock engine or building a monster race motor, the Dasa Racing exhaust for the YFZ450R is pretty hard to beat.

Evan’s YFZ450R has been raced with different aftermarket exhausts in conjunction with a Vortex ECU, which should add performance, and yet, according to Evan, “It doesn’t feel as powerful as the YFZ450R we’re testing here.”  Getting the most out of the Big-3 engine upgrades is about balancing intake , exhaust, and tuning. Evan’s YFZ lacks the freer flowing Fuel Custom’s intake, which made a difference in power we could easily detect compared to the stock intake.

Overall, the YFZ450R feels more unstoppable and stall proof at lower RPMs, although it still needs to be kept in the midrange and up to make serious power. Midrange power is notably stronger feeling racing out of turns with a welcomed increase in top-end power and over-rev on long straights. It’s certainly faster and easier to ride at either a casual or race pace.




Rid of restrictions, free flowing and fine-tuned Yamaha’s YFZ450R delivers an easily detectable increase in performance and fun. Working with well-respected aftermarket company’s products that admittedly play well together, we were confident in running the Fuel Customs intake, Dasas Racing exhaust, and PEP reflashed ECU together and were very impressed with the results.


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