Ramming has no damage type. This has been tested many times by me and other players (including as noted already in this thread!)
Damage type is entirely a function of fitting a weapon. All known current weapon damage types and splits (together with a tested one) are in my all weapons thread here:
https://forums.frontier.co.uk/showthread.php/246086-Official-FDev-Damage-Stats-for-Every-Weapon
In the absence of a damage type, damage is absolute, i.e., unaffected by shield or hull resistances to thermal, kinetic or explosive damage. There are at least four absolute deliverers of damage, being collision, heat, phasing and 60% of plasma.
Sys pip resistance is entirely separate to all other damage modifiers and really should have a different name to 'resistance' to avoid being confusing.
It reduces damage by 60% at 4 pips. The old testing by Cmdr StarLightBreaker linked above was amazing but was superseded in 2.2.03 or 2.3 (I forget which) when Sys pip damage reduction was buffed to be linear.
In short, Sys pip reduction now works as follows:
4 pips: 60%
3 pips: 45%
2 pips: 30%
1 pip: 15%
0 pips: 0%
With corresponding intervals for half pips.
Sys pip reduction is applied after all other modifiers and is multiplicative (i.e. cumulative) to what has gone before.
Hope this helps!