DirectScan and Knock Question

[Lhorn]

I've been trying to figure out a knock problem for a while and have started using DirectScan.

1. Does real knock go away if you keep your foot in it? Reason I ask is that looking through a bunch of files I've made, I always start to get knock (usually starts at a fraction of a degree then increases to up to 6-7 degrees, usually much less) which quickly goes away and I finish the run (foot to the floor) with zero degrees. It always comes on about 30-34 MPH.

2. How do you tell when knock appears on a shift? As above, I start to get knock at about 30-34 mph, while the RPMs are still rising. Several DS frames later I see the drop in RPM that to me indicates a trans shift. Is the trans shift indicated exactly at the point that the rpm drops?

(O2 look OK, FP rises apporpriately, BLM's/INT about 124-128, Hotwired Walbro 340, FP 43 lineoff....did I miss anything?)
Thanks

T+ with LS1 MAF
50# injectors
TT street chip for 93 octane
Boost limited to about 13#
Otherwise stock

 

[Lee Thompson]

Maybe a little help

Yes, you can tell when the trans shifts by looking @ the file. From peak RPM (start of shift) to when RPM starts to rise again--should be around 5-7 frames. I would guess the knock you are getting is in the chip program--going leaner @ that point (I know 000 about chip stuff). May need to show your file to a chip guy. Best of luck.

 

[ijames]

DS will show when the shift begins, when the pressure in that circuit is high enough to trip the pressure switch but probably still not quite high enough to start moving servos and clutches, so the shift and rpm drop usually happen 3-7 frames after the switch lights up in ds. The stock chip was very conservative about how fast it readvanced the timing after getting knock retard, so if you got any knock retard in a pass you might not ever get back to zero degrees of retard by the end, even if the detonation had stopped long ago. Most street chips are more agressive, but still take 1-2 seconds to ramp the retard to zero after the last knock is detected. Race chips are usually maximally agressive and put the timing back immediately. The tendency towards knock is rpm dependent - most likely to happen at the torque peak and since we normally only pass through that rpm during spoolup in first gear, on each shift the rpms drop down closer to the torque peak and the possibility of knock goes up, then as the rpms climb the tendency drops, so yes, you can keep your foot in it and have the knock stop. When pushing the limits of octane it is quite common to get a little blip of knock (say 1 esc count and hopefully no more than 1-2 degrees of retard) within maybe the first 10 frames after the rpm minimum on the 2-3 shift. From experience, much more than that and you aren't going to be going faster so turn it down, be safer, and run the same times. My goal is always zero esc counts and zero retard, and my whole "career" has been pushing 93 octane. 30-40 mph is what, the top of first gear but still well before the 1-2 shift rpm drop? Thats kind of an odd place to get knock since with your stock turbo the boost should be all the way up well before that. Now, I do see that you are running a tt chip, and he uses the maf signal to determine when to dump in all the wot fuel, so look at the maf values during your pass and make sure that you have the boost up enough to get to at least 250. Triggering on the maf is a great way (okay, I'm biased ) to get both good spoolup fueling and good wot fueling, but if the boost is set right at the threshold or below it then things don't work right - this may be one of those odd cases where you can cure knock by cranking it up a little .