Green tune AFR and Timing AnalyisÖ.
Some time ago during a discussion about AFRs and Timing the topic of more/less boost, effect of AFR, and effect of ignition timing came up. While I was on the dyno last week working on one of our project STIs, I did some playing around with a few of these variables. I was primarily interested to see the direct effect of AFR on the resulting torque, and how that played into both EGTs and ignition advance.
The tune was done on Timís STI, 92 octane pump gas, FP green, the usual Perrin goodies (TMIC, Injectors, BigMaf, etc). I wanted to focus on changes in wheel torque with the same boost level.
I started off with a few baselines, which all netted about the same peak hp and torque (about 340hp, and 285 trq). The map I started was pretty conservative on timing and fuel, with AFRs in the low mid 11s.
As expected, taking a degree of timing away, and taking off about .5 AFR of fuel netted a noticeable change:
Red is baseline, blue is fuel removed and timing removed.
You can see in this graph that midrange torque was improved, especially above 5000 rpm.
Here you can see how the AFR was leaned out a bit, averaging around 11.7 or so, up from about 11.3.
Timing was decreased about a degree, a bit less in a few spots.
Boost was the same for these runs.
Those changes resulted in a good gain, so letís see where it goes If I add a bit more timing back in.
In these, Blue is baseline, Red is timing added.
You can see in this graph that midrange torque jumped up a bit, but the upper end lost some, and most places are nearly the same.
Here you can see how the AFR was about the same.
Here you can see Timing added. The timing at 5000 netted the most gain, while the rest of the timing didnít help much.
Last but not leastÖboost was the same for these runs.
Sure enough, in this case, the slightly leaner and less advanced map made more torque then the more advanced map with more fueling. As I continued the tuning, I pushed both the fuel and timing more. As AFRs got passed 12.0, there were no gains and power, and knock was eaiser to get. The timing was already pretty well dialed, and adding more timing added no more power, and eventually knocked. Even at the highest advance, adding fuel back in (down to about 10.9:1) resulted in now more power. EGTs were almost identical in all of the runs as well, except at the very lean side(12.5:1), where they grew to almost 1700. Most of the runs were right at 1600F after a 4th gear pull. (even at 12:1)
The next task was to work at a lower boost, and see if additional timing combined with the right pressure would yield more power. Unfortunately, this particular Green has the wastegate door turned a few times to keep it shut at high boost, so less boost then about 20psi isnít possible. Once I get another Green based car up on the dyno, Iíll collect and post some more data. As it is, I have 47 pulls, complete with UTEC logs for each to go thru.