Check out Jared Lesher's AX Pro winning, Supercross chasing HP powered YZ250 on MXA youtube video
Jared Lesher's HP-Powered YZ250 Featured on MXA!
Motocross Action Magazine recently featured a stunning YZ250 built by Michael Shaw for Jared Lesher, and we're excited to share the details! At HP Race Development, we've been hard at work refining the engine combo to deliver the power and performance needed for Pro Supercross racing. We've learned a great deal in a short amount of time, pushing the limits of this two-stroke machine.
Engine Tuning for Supercross Performance
Our YZ250 build utilizes a GET CDI, allowing us to experiment with different ignition maps to achieve the ideal balance of responsiveness and over-rev. We've discovered that Supercross racers spend surprisingly little time at peak horsepower. The goal is to have the bike lug down low, deliver aggressive acceleration, and continue to pull strong well past the peak. Even minor adjustments to the ignition curve and powerjet function can significantly impact the bike's feel on the track. Jared can notice as little as 1 degree of timing change!
Cylinder Head Development with Phathead
We're grateful to Luke at Phathead for providing a billet cylinder head, which has been instrumental in rapidly testing different head inserts to optimize both feel and overall power characteristics. It's interesting to note that we ultimately landed on a low compression combo for Supercross, but the ability to quickly swap inserts has allowed us to run a higher compression setup for Jared's Arenacross races.
Porting Refinements for Smooth Power Delivery
Regarding porting, I've made subtle modifications to our standard package, focusing on maximizing power as the powervalve opens while minimizing any abrupt hit. Our initial setup resulted in a hard-hitting power delivery that was difficult to control on jump faces. Jared described it as "liking to be lugged," and after further investigation, we understood that he wanted to avoid the sudden snap. To address this, we adjusted the relationship between the main exhaust port and auxiliary exhaust ports to create a smoother powervalve opening transition. If we continue to develop this engine, we'll explore wider powerbands in addition to increasing overall power. We also have a special request in with FMF, hoping they can help us with a custom exhaust.
Wiseco Piston Choice
We're using a Wiseco piston—it's not a standard YZ250 piston but it allows porting modifications that the OEM piston doesn't. We value its performance and overall durability, especially the single-ring design.
Carburetor and Jetting
The carburetor is stock size, equipped with a STIC metering block. We find its throttle response and over-rev capabilities unmatched. Jetting remains fairly consistent due to the indoor stadium environment, but Michael uses an iPhone app to monitor Relative Air Density and fine-tunes as necessary.
YZ250 Performance Enhancements
Flywheel Weight Benefits
A flywheel weight was added early in the Supercross series, and it has made a significant difference. We highly recommend this modification for all YZ250 owners, as it improves power delivery. Even in the demanding conditions of Supercross, it has proven to be beneficial.
Addressing Start Issues
Starts have been a challenge for Jared, as he's struggled to keep the front end down. This wasn't anticipated, but it's a significant issue. We are developing a prototype product to help with this for the remaining rounds. If we can get him a good start to qualify, we're confident that his riding ability will secure a spot in the main event, marking the first two-stroke in the premier class since 2006!
Support Jared Lesher's Supercross Journey
Be sure to follow Jared on social media and reach out to him if you'd like to support his racing efforts. He's achieving remarkable results with the support of dedicated individuals and companies.
Frequently Asked Questions
What CDI unit is used on Jared Lesher's YZ250?
Jared's YZ250 utilizes a GET CDI, which allows for fine-tuning of the ignition maps.
Why is a lower compression head used for Supercross?
A lower compression head provides a more manageable power delivery for the tight and technical Supercross tracks.
What does a flywheel weight do for the YZ250?
A flywheel weight helps smooth out the power delivery and improves traction, making the bike easier to control.
What is the purpose of the STIC metering block in the carburetor?
The STIC metering block improves throttle response and over-rev, contributing to better overall engine performance.
What prototype part is HP Race Development working on to help Jared Lesher?
HP Race Development is working on a prototype product to help Jared keep the front end down during starts.