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Product reviews

PSI Genesis 425cc Big Bore Kit for your 250R

Caution: explicit power for brave adults only!


April 07, 2001
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ImagePSI, known for their potently fast snowmobiles, entered the high performance ATV market over a year ago. Since then, the company has been embraced by some and shrugged off by others. Some ask where were they when ATV racing was stagnant, while others welcome them because they're proud to have reputable companies and their modern day technologies peak into the ATV performance market.

As far as we're concerned, we are grateful that companies like PSI are popping up since they offer new and interesting concepts to our industry. In doing so, they keep existing companies on their toes by offering improvements to their own products. All in all, a win-win for you and I - the consumer.

PSI's big bore 425 is the biggest kit available for one of the the best high performance ATVs ever made, the Fourtrax 250R. The cylinder kit uses a mammoth 86mm piston that is ceramic coated on top and poly-moly on its side for long life. The cylinder has a Nikasil bore to further long durable life. A high volume pipe is definitely necessary to allow the motor to breath to its full ferocious potential. PSI claims that your new R will pump out a whopping 70 plus horsepower. After riding it we don't doubt their claim one bit.

 

ImageJohn Pellan rails on the monster 425R.The unique "Dial-A-Dome" head allows for better cooling capabilities while offering easy adjustments for the different fuels. In other words, you can dial in the compression ration of the cylinder. This is great for using regular pump gas while practicing, then tuning it up to the highest compression setting and using more expensive race fuels come race time. But if you can afford a high dollar state of the art engine kit like this, you can probably afford to run race gas all the time - so you would leave the setting to its highest compression setting.

The kit comes complete with a V-Force Reed cage, aluminum intake manifold with a matching rubber boot and a heavy duty head stay. The sexy looking 10-port Genesis cylinder is supplied with billet water manifolds, O-ring, gaskets, all the needed hardware as well as a detailed instruction guide. The PSI Genesis "Big Air" Carb ($495) and PSI's Exhaust & Silencer System ($400) are not included.

 

ImagePSI delivers new and innovative technology for the ATV. The 425 cylinder head above is one example.The stock radiator does not properly cool the monstrous motor, therefore PSI offers a Hi-Volume-Hi Flow Radiator kit for $375. We went a step further than just modifying the stock radiator. Thanks to Jody Bateman at JB Racing in East Springfield, PA for outfitting the big bore quad with an additional radiator. His set up cooled the motor just fine in the most extreme situations.

This kit does require a case modification so the top end works with your bottom end. It also gets a couple of extra boost ports added to the lower end.

If you're not sure what milling the cases mean, the pictures below should explain the process pretty well. The case mod is also offered through PSI if you or your local dealer are not up to the project.

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