We often times are asked about the billet head kits that are available from the aftermarket. So, here’s the deal. The OEM engine configuration has to assume you might run into some bad gas somewhere along the way, and they have to assume you might be running the sled at -40 degrees, or all the way down at sea level. They have to plan for most any and every eventuality you might encounter, trying to keep your sled running and not having to pay for (expensive) warranty claims.
That means they intentionally leave some performance on the table for you to make use of. If you can run good quality premium fuel, you will be good. If you are not riding at super cold temperatures, you should be good. And this is the big one; if you are not running at sea level, you should be good. This is why most performance shops will offer different compression levels of their head kits, to best match the elevation you will be riding at. Example, if you have a stock sled that has safe compression levels for sea level operation, buy you always ride at a higher elevation, you can safely increase the compression with a head kit and make more power. Safely. Add to this your ability to run premium (higher octane) fuel and you are safer yet.
Another benefit of the head kits is they will often times give you increased cooling capacity, and more cooling capacity is always a good thing when we’re talking about high-performance two-stroke engines. This is even more true when you have also made other mods (exhaust, intake, porting) but even with a stock engine that is being asked to perform hard it is beneficial. Anytime your engine coolant temp starts to get hot, these new engines with all of their smart electronics will start to pull back the ignition timing and you lose power, quickly. Installing a head kit typically keeps the engine running cooler with more power, a win-win for sure.
The high performance head kits will be carefully designed to improve the squish band, dome angles and overall compression. Where an OEM is held back by the almighty EPA and emissions requirements, the aftermarket head kits can go after the power left on the table (or in the computer) and give you significant gains in performance. Typically a high elevation head kit will increase the compression by 20 pounds and give you a healthy 8-9-10 HP gain, where the lower elevation head kits (lower compression than the high elevation heads) will give you more like 4-5-6-7 HP gains, all assuming use of premium pump gas. Both versions are known for their ability to give you great low end grunt and hard pulling acceleration. It all depends on the exact engine and how well the stock heads were designed, as some sleds will see bigger gains than others, but the shop you work with should be able to give you a good indication of what kind of gains are typical for each given engine.
Even if you want to leave the rest of the engine entirely stock, installing a billet head kit is a time-tested and proven method of extracting some great gains out of your sled, usually costing right about $500. Problem is, if you’re making more power you will want to tweak the clutching to make use of the new power, as the added power will pull whatever weight you have in the clutch far easier. That is how you know you’re making more power after any mod; it pulls the stock clutching so much easier, you have to throw more weight at it or ramp up the helix angles to keep the RPMs in check. Again, the shop you get the head kit from can steer you into the proper clutching changes to get the added power down to the ground.