HPI Sprint 2 Drift/Sport front motor conversion Mod tutorial

Since getting my Sprint, it has been constructed and deconstructed more times than I can count. Considering how cheap they are as rollers or...

Since getting my Sprint, it has been constructed and deconstructed more times than I can count. Considering how cheap they are as rollers or second hand, I thought it would be worthwhile creating a separate guide on converting the chassis to a front motor. For drifting, having the majority of the weight as far forward as possible makes the chassis less wild and a lot more predictable.

Tools required

  • Screwdrivers
  • Pliers
  • Allen keys
  • Drill
  • File/Dremel (optional)

Optional parts required to complete the build

  • 2 rods (ideally threaded)
  • Shot as possible rod ends
  • Wide angle CVDs (optional)
  • Sponge/small o-rings (optional)

For the process on this guide, the front will be regarded as whatever end is holding the front one way (purple) diff. I would recommend cleaning as much as you can at this stage and also swapping out the bearings for some metal shielded ones. I purchased mine via rcbearings.co.uk who sell a kit dedicated for the Sprint.

Had some sort of container(s) available or screw each screw back where it is destined to be otherwise you will lose track of what needs to go where. I learnt that the hard way...

If you are running any sort of countersteer, you will need to either go back to 50/50 or read my countersteer at the end. My mod guide will not cover the battery mount installation as I did not complete this step.

I will be going from this

To this

First, just teardown the chassis and give it a good clean
Next, remove all the steering and suspension components till you are left with the diffs and supports. Swap them around but keep the orientation as they are. If you flip the front one way, it will become useless. All of these holes will line up no problem.

Both front and rear assembled including suspension and steering hubs

At this moment in time, all of the current holes remain the same. No new holes need to be made to support the mount swaps. Here is where you will need to decide what you want to do. I decided I did not want too many extra holes and wanted to use what I could.

Since on my setup, there was not going to be a way of sliding the battery in sideways like before due to the belt being in the way (as tight as it can be due to countersteer), I chose to have the servo closer to the motor meaning a shorter steering rod was needed.

One hole was already there so I used that as a guide of where my servo is going to be. The second hole rested on the ridge and so made my next hole directly there. No measurements of this as it is going to vary from servo to servo or how you wish to mount.

Next would be worth fitting your motor in as you need to find a pivot point for your steering. I found that it is best to have it inline with the motor as below. Drill a hole and then screw it into position. Don't place it too close to the motor otherwise you will not have enough clearance for maximum lock in one direction over another and don't mount too close to the edge.

Use the steering knuckle with the silver threaded base. You can then go ahead and connect it up with a short rod and rod ends. Be warned that depending on how you mount this short rod, your suspension on that side may not allow for full travel so experiment more.

Then use a longer rod end setup to connect the steering pivot to the servo. Here is the setup after I swapped the motor mount plates over. Note if you swap the motor plates over, some of your screws maybe too show due to the plates are not countersunk on each side. Here, I just chopped up the second arm and used it to extend. (will tidy that up)

Sadly I do not have many photos from this stage but use your imagination. To now connect the steering between wheels, you need to frabicate a long rod+rod ends as below

With the above photo, that is a basic setup and offers NO ADJUSTMENTS to your toe in/out so make sure your rod is a little longer and trim as required.

In theory, that should be it. I mount my battery using velcro and runs alongisde the rear belt. This stuff is heavy duty so only a few patches are required. Trust me, it is stupidly strong stuff! If you are able to mount your servo and ESC elsewhere, you can run the battery mount in the original place and have even better weight balance.
Other than that, your conversion should be complete. Its not that hard to do, just requires you to take your time and do a bit a day. You could invest in the wide angle CVD's to help with the lock or just fit in some (start with one each side) on the one way diff cups or use some sort of sponge. That will allow you to use the standard dogbones without the risk of them popping out.

Not much that needs to be done since I have got it figured out (kind of). I have to thank Cali Drift Tech for their support here. My original cs kit came from them and I would buy from them again. They can sell you the cs kit for the Sprint in normal (rear motor) or reversed (front motor)

For 1.5 cs
- Use the standard rear diff
- Use a 15T pulley for the rear (tensioner can be used)
- Use a 10T pulley for the front
- Standard belt for the rear
- Purchase this belt for the front (3mm Pitch, 56 Teeth, 168mm)

For 1.8 cs
- Use the standard rear diff
- Use a 18T pulley for the rear (belt maybe tight but will be ok)
- Use a 10T pulley for the front
- Standard belt for the rear
- Purchase this belt for the front (3mm Pitch, 56 Teeth, 168mm)

Please note that it is all experimental so before making holes etc, check everything and take your time! Your results may require further adjustments so make sure you are ready for the project. It is worth it overall and found it is a much more enjoyable chassis. 

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