Why do camaros run rich
Administrator
Joined: Nov 1998
Posts: 71,121
From: Hell was full so they sent me to NJ
Very easy.... that's the way they are programmed at the factory.
When you go to WOT, the PCM drops the O2 sensors out of the loop, and bumps the target A/F ratio up to a value significantly richer than the 14.7:1 that is uses in closed loop for low load/low rpm economy. The target A/F ratio in "power enrichment" mode is calculated from a couple of variables, according to tables in the PCM. Typically, you will see a fairly rich 11.7:1 as the target A/F ratio at WOT. That's is a bit richer than the traditional values of 12.8 - 13.2:1 that are assumed to produce peak power and torque.
Apparenty the factory feels they need an overly rich mixture to protect the engine.
When you go to WOT, the PCM drops the O2 sensors out of the loop, and bumps the target A/F ratio up to a value significantly richer than the 14.7:1 that is uses in closed loop for low load/low rpm economy. The target A/F ratio in "power enrichment" mode is calculated from a couple of variables, according to tables in the PCM. Typically, you will see a fairly rich 11.7:1 as the target A/F ratio at WOT. That's is a bit richer than the traditional values of 12.8 - 13.2:1 that are assumed to produce peak power and torque.
Apparenty the factory feels they need an overly rich mixture to protect the engine.
Administrator
Joined: Nov 1998
Posts: 71,121
From: Hell was full so they sent me to NJ
It not for emissions. Emissions are only measured/regulated at part throttle, "normal" driving conditions (and remember that's "normal" for mom & pop - not for us 
). That's when the PCM operates in closed loop, and maintains an A/F ratio of 14.7:1. That's the point where the combined emissions of HC, CO and NOx are minimized, and provides decent fuel economy.
But 14.7:1 is too lean for power. When it goes WOT, it should be looking for something along the lines of 12.8-13.2:1 for max paower and torque. Some of the people here with good dyno tunes have even found a wider range, maybe somewhere in the low 12's, on up toward the higher 13's.... varies a lot.
But remember, as the engine leans out, it increases the tendancy to detonate. By current production engine standards, 10.4:1 compression is fairly high... and the LT1 is one of the few engines running compression that high. So, I would suspect the factory tries to keep it on the rich side, to prevent detonation. If you get any detonation, the PCM is going to pull a ton of timing, and then put it back in slowly, until it sees knock again. So... you can put in a lot of spark advance, then run it rich to prevent retard and the resultijng power loss, or you can start with moderate advance and run it closer to 12.8:1. Appears the factory chose to push the spark advance up aggressively, and then use a slightly richer mixture to prevent detonation.
All of this is pure guesswork... I haven't the slightest idea what the factory was thinking when they programmed the PCM.
). That's when the PCM operates in closed loop, and maintains an A/F ratio of 14.7:1. That's the point where the combined emissions of HC, CO and NOx are minimized, and provides decent fuel economy.But 14.7:1 is too lean for power. When it goes WOT, it should be looking for something along the lines of 12.8-13.2:1 for max paower and torque. Some of the people here with good dyno tunes have even found a wider range, maybe somewhere in the low 12's, on up toward the higher 13's.... varies a lot.
But remember, as the engine leans out, it increases the tendancy to detonate. By current production engine standards, 10.4:1 compression is fairly high... and the LT1 is one of the few engines running compression that high. So, I would suspect the factory tries to keep it on the rich side, to prevent detonation. If you get any detonation, the PCM is going to pull a ton of timing, and then put it back in slowly, until it sees knock again. So... you can put in a lot of spark advance, then run it rich to prevent retard and the resultijng power loss, or you can start with moderate advance and run it closer to 12.8:1. Appears the factory chose to push the spark advance up aggressively, and then use a slightly richer mixture to prevent detonation.
All of this is pure guesswork... I haven't the slightest idea what the factory was thinking when they programmed the PCM.
Thread
Thread Starter
Forum
Replies
Last Post