Originally Posted by
stanleyw808
Hello icecyc1,
Your tool is indeed very very useful. Thank You very much for sharing to us.
Just last week, I was racing at FEMCA 2018 in Batam, Indonesia, and pitted close together with Mugen Japan Team. Atsushi Hara was one of the Leading Driver on the Qualifying day, although Kyle McBride TQ'ed the race, at the end was Hara San comes out as the winner. An interesting information from the Mugen Team that they are using 8 holes Piston with 4x1.0mm and 4x1.4mm holes. I tried the Piston set at the remaining 5th and 6th Qualification and felt very nice. Low speed felt plush that generate good traction as the surface is relatively slippery but also have a very solid impact damping keeping the chassis not to bottom out.
Now, could adjust the tool so that we could calculate this kind of mix/stager hole Piston Type?
Cheers..
Glad you find the tool useful. Interesting to hear about their pistons. A little tidbit... based on what I had learned using the dyno, I had developed a multi size hole piston a couple years ago. What I had found is that you need the smaller holes to be 1.0mm or less. We used 0.7 and 0.8 mm small holes along with 1.7 or 2.0 mm holes. I did a 3 hole (large) with either 3 or 6 additional smaller holes. What this effectively did was increased the pack ratio, or the high speed damping compared to the low speed damping. Small holes any larger than 1.0mm did next to nothing more than just a basic piston could do.
I have made my own spreadsheet that does in fact predict the damping of these multi hole pistons. Unfortunately, it gets pretty complex and causes me to have to think deeply every time I use it. The basic rules for multiple size holes is to find the damping coefficient for each "set" of similar sized holes, then add them up as though they are in parallel with each other. For example, If one set of holes give a damping coefficient of 0.9, and the other set of holes gives a damping coefficient of 1.3, then combining them you will get 1/(1/0.9+1/1.3) = 0.53. It will always be lower than either one of them.
If you want to try to simulate the tiny hole multi-hole pistons, you can try this: First, take your large holes and ignore the smaller holes to find the damping coefficient for just them. Keep the low speed DC value, say it's 0.9. Also, keep the Impact value, say it's 1.6. In your hybrid pistons, the 1.6 will be your final hybrid Impact DC value. Now, run the same calculation on ONLY the tiny holes, say they give you a DC of 2.2 (because they are so small, they will be very stiff). Now, you can use the equation above to find your low speed damping value: 1/(1/0.9+1/2.2) = 0.64. So, as you can see, the low speed damping was reduced quite a bit by the holes, but the assumption is that the tiny holes "close up" during impact compared to the large holes and effectively don't exist. This isn't exactly true, but it's reasonably close (your impact DC will actually be slightly lower than the large hole Impact DC in reality) So, in summary, if you ran a piston with just the large holes, you had DC values of 0.9 and 1.6 giving you a pack ratio of 1.78. Your hybrid pistons have DC values of 0.64 and 1.6, giving you a pack ratio of 2.5. So, you kept your impact value the same, but you greatly reduced your low speed damping. This should help you keep your pistons stiff for landings, but soft for handling.
I really believe the compromise for off-road damping ratios of about 0.9-1.1 are because you need it for landing, so you compromise the "ideally perfect" 0.67. Increasing the pack ratio allows you to get closer to the ideal range while not having to compromise your landing damping you need.