| Re: Track results, AFR heads |
Subject: Re: Track results, AFR heads by Josh on 2009/9/8 18:00:30 Here's my best attempt at explaining the poor 60 foot times: First, my physical limitations. I have a titanium femur in my left leg from a motorcycle accident. The damage to my leg is/was pretty severe, and while I have near normal function, the finesse associated with gently yet quickly slipping the clutch is difficult for me. The fine motor skills in my leg are less than perfect, and you can imagine the impact that has on drag racing a stick shift car. Large movements, clutch to floor and back out for example, are still as quick as ever; but fine motor control has suffered. Even with this limitation, I've been able to go mid 1.8's on street tires with my C4. With careful throttle control, and doing what I can with the clutch, on street tires mid to high 1.8's eventually became the norm. As I made mods, and increased power, wheel spin became more an more difficult to control. I tried drag radials, and while the hook was tremendous when compared to the street rubber, I found myself either bogging from leaving at too low of an RPM, or spinning. Once in a spin, if I lifted off the throttle at all the tires would bite and pull the motor down, causing a bog. In the end, I was only able to get the same mid 1.8's out of drag radials, but it was much harder on the car because I had to come out at a much higher RPM. In the past, before the leg, I had great luck with bias ply ET streets. I got some for this car, and have liked them thus far. The only problems I have had are all breakage related. The grip from the tires is tremendous, and applying power suddenly (in a clutch drop scenario) with tires that do not spin is a great way to find the weak link. Anyway, I digress... My launch technique is as follows: -Burnout, stage. Stage as shallow as possible. -4,000 RPM in first gear, clutch on the floor. -Release clutch in as controlled a manner as possible and squeeze throttle to the floor. What happens is that I let the clutch out too quickly. The process would look like this in storyboard form: -Clutch is released quickly, accelerator is on the floor. -The car lurches forward, tires do not spin. -The car has moved 3-5 feet, and is now traveling at ~10 MPH. -The clutch is out, and not slipping. The tires are not slipping either. -Since the tires are going 10 MPH, and there is no slip in the drive train, the engine is going to be pulled down to an RPM that equates with 10 MPH. -The engine bogs to whatever RPM equates to 10 MPH. -The motor recovers, and starts to build RPM again. I could correct this with a bit longer clutch slip, a slight amount of wheel spin, or more torque/horse power. The tune is exacerbating the problem because: -When the RPM comes down, it falls to a point where the timing backs off from 32 degrees. At 2700 for example, I want to say there is only about 20 degrees of timing in the tune. This kills the power at that RPM, and really limits the engines ability to pull itself out of the bog. I can help this issue with tuning by maybe pulling some fuel out at the appropriate point, and adding timing. This is something I have yet to do with this combo. In other C4's that I've raced (all MAF cars) I've never experienced the bog that I get in my car. I do the same launch technique, and go mid 1.7's without an issue. With some seat time in one of these cars, mid 1.6's would most likely become the norm. If I can correct the tuning issues, and let the engine more successfully pull itself out of the bog, I can start to make adjustments to my technique to correct the issue. The adjustments to my clutch pedal action are difficult, but not impossible. Like I said, the times will come around, it'll just take me some time to dial in the car, and dial in my leg. |
