215 retarding notch

[ISX]

Across the internet, the common myth is that the retarding notch is never used on a stock truck unless you do the rack plug mod (you'll see what I mean by this if you don't already know) which lets the rack go further and into the retarding notch. Because of this, people say never to do the rack plug mod on 215 pumps.

The problem with the notch is that it retards timing at high RPM for emissions reasons. Retarding timing at high RPM has its own drawbacks though, including high EGT and less efficient burn and stuff.

With that said, the 215 pump not only gets to the retarding notch, but is ALWAYS in it. In fact, the few people who did the 215 rack plug mod had more power and boost and everything else. I say few because it wasn't long after that the retarding notch myths came up and people were told it was stupid to do on a 215 pump because it moves the rack further and finally reaches the retarding notch which supposedly retards 4* (haven't tested for actual degrees yet).

So here are PICTURES showing the damn proof, once and for all. This is straight from my 215 pump straight out of my truck which runs fine etc etc. I even took out the delivery valve on barrel #2 to make sure #1 wasn't set wrong (I had messed with it's calibration before).

Here is where it is at idle. Now remember with all these pics that the spill port is not closed until it is completely closed...meaning the very top of the port determines start of injection. So although parts are in the notch, the top part is the determining factor. My retarding degree guesstimates are based on the 4* supposed difference and how far up it was on the taper (so halfway up the taper is 2* retarded...). The green line is the center of the spill port, so match it to the plunger and thats where the timing is regulated. The red line is the edge of where max retarding starts.

Then at WOT with the stock (#2000) plug in.

Then at WOT with the plug removed (max rack travel).

And here is what I am talking about when I mention this plug stuff. The aftermarket one is deeper to allow for more rack travel. You can see it actually goes out of the timing notch and advances timing. Meaninggg the rack plug has nothing but benefits on a 215 pump. As long as you have the boost to match the fueling..

So that explains why the timing is all over the map. If you set the timing and the throttle moves at ALL, since the spill port is right on the taper, any movement causes a timing change. Meaning you ideally want it mid throttle. Now I measured all of this on the 160 pump and it does not bottom out the rack on the stock plug so it has no issues with bottoming out. Though it's 0.005" from hitting

[AH64ID]

And you think the CR stuff is complicated....

[ISX]

It's just this pump of mine lol, the rest have a flat top plunger. There is one thing I just noticed as I measured everything to see if I can actually calculate the degrees. The area past the end of the retarding notch has no helix under it.. The helix stops at the end of the notch. Meaning if you did the rack plug mod, there is no "end of injection", just an end of the stroke So then you can say you are truly maxed out

[Rogan]

That was very interesting, as well as quite informative (as always)..