Odd dip in top of torque curve, ideas?
08-06-2009, 11:03 AM
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Odd dip in top of torque curve, ideas? Car is C5 Z06, AFR205's, 22x? cam, long tubes, no cats.
I had my car on a dyno yesterday for the first time. The first pull was with the tune from the shop that built the car. It had too little fuel and too much timing, IMO. It was 13:1 and 28 degrees all the way across at WOT. As you can see on the attached dyno, the car was soft on torque and had an odd dip in the powerband from 5900-6400rpm. The car did not show any knock and maintained 28 degrees straight across the entire pull. So, for the second pull I wanted to add some fuel to bring it around 12.5:1 and pulled timing back to ~24 degrees through the middle and 26 degrees through the top. The timing change brought the torque back up to around 395 and drastically increased the curve all the way across, but the AFR didn't respond to my PE table changes. I glanced through the tune and didn't see any reason for it to not be entering PE, but it wasn't. Anyone notice anything weird that might be keeping it out of PE? I didn't want to waste my dyno time, so I just went ahead and started adding fuel in the MAF table. I was able to richen it up no problem from there. I played back and forth trying to clear up the drop off in high rpms. I tried all the way down to 12:1 and 20 degrees timing and all the way up to 12.9:1 and 27 degrees of timing, no change and all of the curves were very tight to eachother through that section. Never once did I see a single degree of knock retard and it was always running exactly the timing that I was commanding. I just cannot figure out what this dip is stemming from. Does anyone have any idea what could be causing it? I feel that if it hadn't fallen off right there, horsepower should've peaked maybe another 10whp higher. My bigger concern, though, is that I am not sure why it is laying over right there and I don't want something to creep up and bite me with a hurt motor.
I have attached the dyno chart with a couple of runs for comparison. Run 1 is 28 degrees through the top, 13:1, run 5 is 24 degrees, 12.4:1 through the top.(hard to read, I know, I am trying to get electronic versions. The higher curve is run 5), the base tune (run 1), and the pull 5 tune. Unfortuantely, I do not have any of the data logs. :-( I can tell you, though, that spark didn't do anything unusual and you can see AFR.
Oh, and don't mind the 2-4k rpm range, I know it needed more fuel and would've picked up a ton of torque, I was just not paying any attention to it and focusing on that dip in the top end. I did end up fixing that fueling after I left. Again, it wasn't hitting the PE table, so I had to fix it through the MAF.
Ideas?
I had my car on a dyno yesterday for the first time. The first pull was with the tune from the shop that built the car. It had too little fuel and too much timing, IMO. It was 13:1 and 28 degrees all the way across at WOT. As you can see on the attached dyno, the car was soft on torque and had an odd dip in the powerband from 5900-6400rpm. The car did not show any knock and maintained 28 degrees straight across the entire pull. So, for the second pull I wanted to add some fuel to bring it around 12.5:1 and pulled timing back to ~24 degrees through the middle and 26 degrees through the top. The timing change brought the torque back up to around 395 and drastically increased the curve all the way across, but the AFR didn't respond to my PE table changes. I glanced through the tune and didn't see any reason for it to not be entering PE, but it wasn't. Anyone notice anything weird that might be keeping it out of PE? I didn't want to waste my dyno time, so I just went ahead and started adding fuel in the MAF table. I was able to richen it up no problem from there. I played back and forth trying to clear up the drop off in high rpms. I tried all the way down to 12:1 and 20 degrees timing and all the way up to 12.9:1 and 27 degrees of timing, no change and all of the curves were very tight to eachother through that section. Never once did I see a single degree of knock retard and it was always running exactly the timing that I was commanding. I just cannot figure out what this dip is stemming from. Does anyone have any idea what could be causing it? I feel that if it hadn't fallen off right there, horsepower should've peaked maybe another 10whp higher. My bigger concern, though, is that I am not sure why it is laying over right there and I don't want something to creep up and bite me with a hurt motor.
I have attached the dyno chart with a couple of runs for comparison. Run 1 is 28 degrees through the top, 13:1, run 5 is 24 degrees, 12.4:1 through the top.(hard to read, I know, I am trying to get electronic versions. The higher curve is run 5), the base tune (run 1), and the pull 5 tune. Unfortuantely, I do not have any of the data logs. :-( I can tell you, though, that spark didn't do anything unusual and you can see AFR.
Oh, and don't mind the 2-4k rpm range, I know it needed more fuel and would've picked up a ton of torque, I was just not paying any attention to it and focusing on that dip in the top end. I did end up fixing that fueling after I left. Again, it wasn't hitting the PE table, so I had to fix it through the MAF.
Ideas?
