Originally Posted by
TRiN
Also thanks
icecyc1 
With the available pistons and oils in my arsenal, your spreadsheet helped me locate an equivalent piston and oil setup with a (slightly) lower speed DC while maintaining a similar Impact DC. I punched in some numbers and boom! I now have multiple 5 hole piston combo's that is within range for me to try out. I managed to test one 5 piston combo over the weekend and it worked great! I was previously using a 6 hole piston setup.
To preface, I also run a HB Racing buggy and staggered pistons front and rear are currently the norm/base in most recent online setups. For example Front 6x1.3, Rear 6x1.4 or Front 5x1.5, Rear 5x1.6 depending on the track conditions. I'm now noticing hybrid pistons being experimented, expanding upon on the existing base shock setups:
Some examples:-
F 6x1.3, R6x1.3/1.4 (3x1.3, 3x1.4)
F 5x1.5, R5x1.5/1.6 (3x1.5, 2x1.6) or (2x1.5, 3x1.6)
An extreme example I noticed using a 4 hole piston combination used on a bumpy track
F4x1.5/1.6 (3x1.5, 1x1.6), R4x1.6/1.7 (3x1.6, 1x1.7)
Using your spreadsheet together with your hybrid/multi-hole piston simulation theory, and focusing on hybrid pistons combinations mentioned above. You may have noticed, there's either an equal amount of 'smaller' and 'larger' holes or a slight variation of it. I would assume the formula (1/(1/a+1/b)) for the hybrid Low Speed DC value remains unchanged, but how about the final hybrid Impact DC value? Is the thought process still the same by ignoring the smaller holes?
Hybrid pistons are definitely more complicated to calculate. The equation I provided assumes you have an equal amount of two different sizes holes, not a 3x and 1y hole pattern. I haven't tested that, but my initial guess would be that it should still work, although perhaps not exactly in that ratio in reality, I really don't know. The reason this equation works in this situation is because the holes act as a resistance to motion, and they are in parallel with each other. In electrical terms, if you have current running through two resistors in parallel, you simply add them up as noted above, to get the overall Effective resistance. That's what we are doing hydraulically, and the dyno results verified that.
When I described the hybrid functionality where you can ignore the small holes for impact, I am also assuming significant difference between hole sizes. You won't get a significant difference between a 1.3 and 1.4mm hole, not enough to create more pack. I think your DC and Impact values would be exactly as the hybrid formula would predict for both, with holes that close in size, you cannot ignore the smaller hole. I believe the only time you can ignore the smaller holes for the impact DC is if the smaller holes are less than 1.0mm (even that big might be pushing that assumption). Larger than that, it's essentially just another hole. I think the holes function sort of like a slender rod, where the length/diameter ratio is critical to it's strength. So, above 1.0mm in a 2.3mm thick piston, the L/D ratio isn't enough to provide a "lock-up" behavior, but less than that, it begins to show those effects. If for instance you have a tapered piston, that L/D ratio would be even less, so it would require an even smaller hole diameter to matter. (A tapered piston behaves the same as a flat piston, but due to the smaller profile, or thickness, it provides less damping, or a lower DC for the same oil, holes, & diameter)