[soutthpaw]

I knew I read it somewhere, It was in the infamous 80E thread at PSN posted by Swamps.

"Firehunter: higher altitude = less dense air, which in turn means lower cylinder pressures and temperatures during the compression stroke, delaying the start of ignition. Advancing the injection timing under these conditions allows the start of ignition to begin at a more "optimal" point in terms of crank-angle than if the timing was left at a more retarded setting.

About 4 years ago Tadd (now Elite Diesel) and I got together at his old shop in Alamosa, CO (7500' Elev.) for a week of cylinder pressure testing and tuning on his dyno. We provided the truck with a fully built engine and everything on it and he provided the tuning, pressure transducer and scope. When I returned to Nashville (500' Elev.) I found that I had to pull 5-10* of timing out of the timing table we developed.

Aggie: Exactly--the injection delay table allows the start of injection, but even more so the start of ignition, to occur at the desired point in the engine cycle regardless of temperature or ICP pressure.
The pressure exerted on the injector intensifier piston is a function of the ICP pressure minus the pressure drop through the poppet valve. Higher viscocity oil resists flow, giving a greater pressure drop, so you end up with less pressure on the piston."

I dont think I added more than 4 degrees anywhere on the high altitude timing over what Bill had as sea level.. but I did change the high altitude maps to match his sea level maps then tweak from there... I want to wait and see what Bill's comments are on the the topic before getting to carried away. On a side note, I noticed when I tried doing a straight copy and paste I got similar aberrations to the map images on that thread that Bill posted... and the anomaly was on the copy map not the map I pasted too... Interesting, no? Then it would give an program error and shut down some of the time.


OH, I didn't compare that file you posted the image from to the stock map so I need to take a look when I get a chance.. Also got my Bluetooth keypad today so that will make working with the 3D maps nicer..