Description

This is a pair of (2) Patented VRP XV4 ‘Tuner’ Pistons with Valves and Hardware.  We have developed the VRP ‘Tuner’ Piston to be the ultimate ‘tuneable’ piston for RC Racers. Each piston has 20 individual dimples for the normal holes. Below is a chart where the holes are numbered like a clock, so they can be used as a way of drilling the piston with holes from 4 to 10 holes. These are just a suggestion. There are many possible combinations. 3 Hole, 7 Hole, 12 Hole, etc. Use a high quality drill bit set like the VRP Piston Drill Sets. And finish the job with the VRP Piston Chamfer Tool. The Return holes are 1.2mm, and with the 4 different upper washes allows for a good range of adjustment.  The ‘Tuner’ Pistons use the same rubber valves and washers as the VRP ‘XV4’, so everything is interchangeable. And we have listed the pistons by themselves so racers can easily have undrilled sets ready for tuning at the next race. Just swap the hardware over!

Tips:

1. Over-all flow – The total number of holes X the sum of the hole diameters determines Over-all Flow. The actual calculated number compared to calculated numbers from other drill patterns help build a range and determine any given pistons flow. This number is not exact, (were looking for easy) but it will greatly help differentiate one piston from another.

2. Hole Sizes – The hole size greatly influences pack and the timing of when it kicks in. A smaller hole will pack much sooner than a larger hole. And it usually takes more smaller holes to get over-all flow. And the opposite is true for larger holes. They pack later, and usually need less holes to get over-all flow. Pistons with different sized holes will pack smoother than a piston with all the same holes. This is because each hole packs at a different time, and that spreads the pack out.

3. Hole Thickness- Most Pistons are right around 2.55mm thick. So the holes going thru the piston are also about 2.55mm long. This length of the hole affects pack. The longer the hole, or thicker the piston, the more time it takes the oil to flow thru the hole in an organized way, and thus produces what we feel as pack. Some pistons are 2mm thick. These are usually called ‘Thin’ pistons. They take pack out. And conversely, a 3.0mm thick piston produces more pack. You can reduce the hole length by using the VRP Chamfer Tool and beveling the holes. This in effect reduces the hole length and reduces pack.

4. Return Valve Holes – The VRP Piston valving is patented because it is by far the most efficient way to do the return. In full scale motorsports, all chassis have compression and rebound control. And the VRP Piston gives you this. The original research showed that the average return rate for most full scale motorsports (and SX especially) was right around 7% faster return than compression. And that’s what the Xv4 Pistons are valved too (red upper washers). This is a great all around rate. But some conditions, like super rutted, would benefit by more return, or if the track is very high grip and smooth, less rebound is needed. So I suggest starting with 1.1mm to 1.2mm return holes.

The VRP Team will use 1.0mm and 1.1mm additional holes in the 10th and 8th pistons to soften the low speed dampening, while not affecting the high speed pack. The very small holes only flow at low speed. They essentially ‘lock up’ under high speed dampening. This gives the buggy more grip because the suspension will absorb small imperfections in the surface.

One idea that helps racers a lot is this: Your running the front suspension ‘into’ bumps and ruts, ….and your ‘dragging’ the rear suspension over bumps and ruts. So there is a big difference. Mainly, the front takes more pack, and the rear takes less. So keep that in mind.

For the best holes – Lay Piston flat on table, use hand drill. Drill a 1mm pilot hole, and then the final hole size. Use the VRP Chamfer tool by finger to finish holes. If using a dremel, be careful. Use low speed.

*Important: The VRP ‘XV3’ Pistons are designed to have a washer under and over them. It is important to run washers and that they are correctly installed. Each set of pistons is supplied with a Washer Hardware Pack to make sure you have what you need to install them.