HPI Sprint 2

I finally had a chance to dive it, I dropped the traxxas VXL system in it with a 28t pinion and it's not bad. I think I need better tires and I need to do something with the diffs and suspension, it's all over the place under heavy throttle....torque steer like a mofo! Once I mod a few things I think I can learn to like it.

I had a Sprint 2 Sport, and couldn't even fit a 2s in it without loosening screws and cramming it in there. However, with a Castle Sidewinder and Castle 4600kv, it was a screamer!

I have been running the car and it's starting to be fun but needs a little more work. The first problem I corrected was the front drive belt rubbing the motor (with a smaller pinion) and the battery, the belt actually ran through the top part of the battery compartment. I can't take credit for the mod, I found all of the info posted by a member named Marv on RCTech, he created a thread called "Making a silk purse from a sow's ear" and it has a ton of info about this car. After reading his mods and seeing his pics it seems like HPI might have made some changes might have been done to this kit but they are very slight. The first thing I noticed was that my dogbones don't have much slack, not even close to needing anything to help them stay in the cups. A few other minor things that I will post if I find it necessary.

I added a belt guide under the front drive belt that raises the belt just enough that it doesn't rub the motor or battery, some trimming on the top plate is necessary afterwards. Marv's mod says he used a 18x3mm screw for this but that was a little short on my kit, to get a full nut on the screw would require a 22x3mm screw. I dug in my screw pile and found a 25x3 screw, two 6x3x2.5 bearing, and two 8x3 washers. You want the washers to be a little bigger than the bearings so they act as a belt guide.





The top plate had to be trimmed where the red arrow is pointing

Steering slop is not uncommon in rc's but on this car it's a little different from what I have seen with other models. On this car the right side is what consider normal and acceptable, the left side is another story. While driving at a slow speed trying to adjust the steering trim I could actually see the left side (drivers side) tire wonder and make the front of the car shake a little. I found two things causing this, the capture ball cups on the Ackerman rod and slack around the steering post on the left side. The cups looked to be causing most of the problem so that is the first thing I worked on. This was a simple and very easy fix, replace the ball and cups with ball rod ends. The steering is noticeably better, I can easily hold a straight line now! I will mess with the bearings in the steering post but I haven't decided exactly how I want to do it yet.

Before


After