popping at wot

[Todd King]

     Went to the 1/8th mi drags last night. Car ran quite well for its 
     maiden voyage with the new equipment, although a few problems 
     surfaced. Main problem is I still have trouble getting the car off the 
     line, and the prob is exagerated by the new larger turbo. Some other 
     people with similar setups do very well (1.5's or better in the 60') 
     but so far the technique escapes me, plus the car is rich (safer) down 
     low and throughout the pass which doesn't help. So it went a best of 
     96.6mph in the 1/8th last night BUT the "Jato assist" did not come on 
     until at least 150' out (that's about 1/5th of the darn track!). Once 
     on boost the car absolutely wails- hang on!. It went a 7.8x with a 
     best (?) 60' of 2.1x (*hanging head in shame*). Just some rough 
     estimation shows it would have gone 7.3 at around 98 (at least) had I 
     been able to make a full pass on boost and get even a 1.7 60'. This is 
     roughly a low 11 at 123mph or so in the 1/4 by my guesstimates, which 
     is right about where it should be given a half decent 1.7 60' and a 
     full pass under boost, which is set conservative for now due to lack 
     of fuel pump capacity. For my car at 3650 lbs w/ driver the 10 sec 1/4 
     mi threshold is crossed when I reach 100mph in the 1/8th mi. But 
     anyway my question to the list concerns the other problem seen. A 
     fairly common snafu for these cars when they start going fast is 
     "popping" at wot during a pass. Mine started this on the second pass 
     last night. It's not like a "backfire"; more like just a misfire with 
     maybe some pop back into the intake, though it's hard to tell; people 
     just call it "popping". But it has been found that a "cure" is to 
     disconnect the cam position sensor (CPS) after the engine is running, 
     which puts the car into batch fire mode (from sequential). Sure enough 
     this totally stopped the popping and I was able to continue on. Now 
     the question is- why? So far nobody knows. There have been some vendor 
     studies that concluded that the amount of fuel delivered between the 
     two modes does not really change; this is supported by no change in O2 
     voltage between the two modes during a run either. Note that nothing 
     shows up on the scantool data during the popping; things look normal. 
     One of the fast guys claims that the CPS is bad when this occurs and 
     replacing it will cure the problem but this is disputed. ANY thoughts 
     on this are greatly appreciated; email me private if you don't want to 
     use up list bandwidth.
     
     Todd       todd_king at ccm2.jf.intel.com