Pure

For this you will need to come first with all 5 engine types.

Make 5 ATV's, each with a different engine type. There are a lot of different brands of engines to choose from. Just make sure you use a different brand of engine in each ATV. Use each of these 5 ATV's on different tracks (preferably sprint tracks) and finish 1st. After doing so, the trophy is yours.

Here, RedEye420 shows how he got it:

"I did three sprint races in the first group. I used the same bike and just changed the engine (manufacturer; sparks, alba, FMF, etc). After the third race it unlocked (since I skipped over the engine it was on and another one I knew I had used)."