kiggly
Supporting Vendor
- 318
- 185
- Feb 17, 2003
-
Ann Arbor,
Michigan
I've been a bit sparse on the forums lately for adding in tech data, although the last year has produced gobs of information. Over the next month I'm planning to post up a pile of combustion-related data. This past year has been pretty exciting for us from a technical point of view. The drag car has been on methanol since the start of the season. Many little lessons have been learned there, but the main one is the fuel change wasn't a magic bullet for the car's knock issues. Pending some testing for final confirmation with a header change, that is now root-caused as reversion and chamber residuals. The last dyno session with some smaller cams showed slightly less knock on the cylinder pressure metrics, but the plugs now started coming out without any speckles at all. Previously they always were peppered up.
During the last session at Force Engineering on Halloween morning, we were able to get it sorted to 817whp on their mustang dyno. We did run into a couple hiccups with the tune on the smaller cams. I was running it open loop initially, but noticed the midrange was way leaner than desired, to the tune of 20% off target. The AFR was just on target up top, at about 0.62La. I enabled the closed loop in the Haltech Elite for the full range and immediately figured out just how much of a screwed up step was in the map. It added in about 18% fuel and immediately afterward pegged the wideband rich at 0.55La. Going through the fuel used, I think it was in the high 0.4x La range. The 0.2sec swing from dead-on AFR to dead-rich was too fast for my settings on the control loop and really just the fault of a crappy map. The car immediately broke up rich. I didn't think much of it until processing the combustion data.
When processing the data, I found that it flashed over combustion to the intake manifold and slowly burned into the chambers. Combustion in the manifold is dead slow compared to in the chamber. It burns so slowly at the 9k range that it will take multiple engine revolutions to finish burning all the air and fuel in the intake. When this happened, it also breathed clean air into chamber #4, but then began burning before the intake valves closed. Immediately at valve closing the cylinder pressure began to rise quickly. Normal combustion pressures were in the low 3000psi range and this single cycle was up in the 5500psi range! This nearly doubles the stress on all the parts and it was all just caused by a misfire. There was no audible backfire or anything, this sounded like a normal break-up. The parts all look good, FFWD's Cylon rods and Wiseco 1400HD's lived through this and don't appear to be damaged upon teardown and inspection.
Here is the golden nugget, there are 3 normal combustion cycles, one with relatively intense knock. There is the single flashover and preignition cycle, and there is the cycle after the flashover where it has elevated intake manifold pressure due to the backfire and no combustion because the fuel and oxygen was already spent during the backfire.
So, lift if it misfires or this might happen - particularly on methanol:
This also explains why cars sometimes blow rods through the block if you stay in it during misfires. I've seen others have that happen a couple or three times.
Thanks,
Kevin
During the last session at Force Engineering on Halloween morning, we were able to get it sorted to 817whp on their mustang dyno. We did run into a couple hiccups with the tune on the smaller cams. I was running it open loop initially, but noticed the midrange was way leaner than desired, to the tune of 20% off target. The AFR was just on target up top, at about 0.62La. I enabled the closed loop in the Haltech Elite for the full range and immediately figured out just how much of a screwed up step was in the map. It added in about 18% fuel and immediately afterward pegged the wideband rich at 0.55La. Going through the fuel used, I think it was in the high 0.4x La range. The 0.2sec swing from dead-on AFR to dead-rich was too fast for my settings on the control loop and really just the fault of a crappy map. The car immediately broke up rich. I didn't think much of it until processing the combustion data.
When processing the data, I found that it flashed over combustion to the intake manifold and slowly burned into the chambers. Combustion in the manifold is dead slow compared to in the chamber. It burns so slowly at the 9k range that it will take multiple engine revolutions to finish burning all the air and fuel in the intake. When this happened, it also breathed clean air into chamber #4, but then began burning before the intake valves closed. Immediately at valve closing the cylinder pressure began to rise quickly. Normal combustion pressures were in the low 3000psi range and this single cycle was up in the 5500psi range! This nearly doubles the stress on all the parts and it was all just caused by a misfire. There was no audible backfire or anything, this sounded like a normal break-up. The parts all look good, FFWD's Cylon rods and Wiseco 1400HD's lived through this and don't appear to be damaged upon teardown and inspection.
Here is the golden nugget, there are 3 normal combustion cycles, one with relatively intense knock. There is the single flashover and preignition cycle, and there is the cycle after the flashover where it has elevated intake manifold pressure due to the backfire and no combustion because the fuel and oxygen was already spent during the backfire.
So, lift if it misfires or this might happen - particularly on methanol:
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This also explains why cars sometimes blow rods through the block if you stay in it during misfires. I've seen others have that happen a couple or three times.
Thanks,
Kevin
