That is Bosch terminology for a notch or helix cut on the leading edge of the plunger. It varies start of injection. Because it is recessed from the top of the plunger it can ,in effect, ONLY retard injection timing. Timing is set in the middle of the notch so you have a minimum amount of static advance. On either side of the notch it will advance from the MINIMUM spec of static timing. But the top (leading edge) of the plunger is not variable, and the notch effectively retards timing, hence retard notch.
lol. Nope. You are following the internet blanket myth of the 215 retard notch that only can retard. As mentioned, when set-up by someone that knows what they are doing, the 215’s can advance 6 degs. Seth builds most of the pumps I sell nowadays & before that I marketed the PDR Stupid Pump that guys like Fletcher, Scott Vorhee’s Big Bad Dodge etc put up the numbers back in the day.
Some info quoted by Seth:
"If the pump is pinned at 10.5mm rack travel, which lands at the lowest (flat) part of the upper helix. So when we pin the pump at 13* btdc and it is set on the engine at TDC, this is how the
rack travel equates in static timing on the engine (dynamic follows closely too)
0 to 5.5mm- no port closure
6.0mm- 16.5* btdc
6.5mm- 15.5* btdc
7.0mm- 14.5* btdc
7.5mm- 14* btdc
8.0mm- 13.5* btdc
8.5mm to 16.0mm- 13* btdc
16.5mm- 13.5* btdc
17.0mm- 14.5* btdc
17.5mm- 15* btdc
18.0mm- 16* btdc
18.5mm- 17* btdc
19.0mm- 18* btdc
19.5mm- 18.5* btdc
20.0 to 21.0mm- 19* btdc
In factory form, the pump never gets past 14mm, so it only retards timing, that may be where the internet theory came from. With a stock rack plug, it only achieves 19.5mm rack travel. The way I set them up when I max/balance them they reach the 6* advance right at 21mm and no less.
0 to 10.5mm of rack travel, not idle to half throttle. Those are two completely different things. In stock form these pumps idle between 6-7mm, zero boost fuel is 10-11mm, and full fuel is 13.5-14.5m of rack travel.
The groove in the top of the 215 plunger lies in the middle of the plunger and comes into play in the middle of rack travel (10.5mm). In a static test, the timing is retarded as you move from 0 to 10.5mm, then it is advanced from 10.5mm to 21mm. However, static timing doesn't tell the entire story. To advance timing using the plunger, you must lower lift to port closure, which hurts high end performance more than the timing change would help."
So please educate yourself on the notch/helix & stop spreading false info that the 215 pumps & others plungers that have the notch/helix can only retard timing.