I playing around with mostly stock Super_AUJP No CCE V3. My car is 91' LB9 with 150k on it. The only "mods" are K&N, air foil, ported and siamesed plenum, tune up, and flows. Im only getting knock(2-4 counts) at 4300rpm -4700rpm at WOT. At WOT in any situation knock will only come in at 43-4700rpm. Im running 93oct and i went ahead and lowered the Main SA -2*. No difference. So now i have the Main SA raised 4* total with a Max SA of 46.41. No diffence. I still get the same knock. How should i go about determining where its detonation or some type of mechanical knock?

Thanks

 

By the time u see detonation, it is already too late.

Too much timing or too litle fuel, usually before the time u actually see it register on the knock sensor

Look for a lean spot before the detonation occurs and/or try pulling a couple degrees of timing from the point of detonation to a few load cells before it.

Yank the plugs and look for dark speckles on the plug.

later
Jeremy

 

I pulled 4* from 4300-4700rpm and no diffence. I never though about adding it to the cells before or checking for lean spots. Thats why im asking. Thanks alot Jeremy. Oddly i changed the oil today and no knock! Im currently building a new motor so this one is my tuning gerbil until i can get a good grasp on what ill need to do on my new motor. Should i check the accuracy of my KS by tapping the motor while reading the knock counts?

Thanks, Brian

 

This is my VE table. Since i have a K&N tb mount, airfoil and ported plenum, do you think with the VE dropping between 4000rpm and 5200rpm might be causing this? Lean spot?


100 KPA

74.61
74.61 5200rpm
76.95 4800rpm
82.81 4400rpm
88.67 4000rpm
91.41 3600rpm
91.80 3200rpm
88.28 2800rpm
81.64
78.52
77.73

 

Do you have a WBO2 and the ability to datalog? You could easily determine if the VE falloff is occuring too agressively/too soon with a WBO2.

Otherwise, try changing the VE table at 100kpa to something like this and see what happens:

100 KPA

74.61
78.xx 5200rpm
82.xx 4800rpm
86.xx 4400rpm
88.67 4000rpm
91.41 3600rpm
91.80 3200rpm
88.28 2800rpm
81.64
78.52
77.73

Probably would help to pull to around 4800 then shut off the engine and do an immediate plug reading at that point to get an idea of AFR if you don't have wbo2.

i'd also suggest not running so much global SA, even if you have the higher octane fuel. the old iron heads GM used on our motors just don't need or deal well with lots of extra timing.

only real way to determine the minimum timing you need for best performance is some type of performance measuring device - dragstrip, gtech, whatever. and you do want to aim for minimum timing needed to get max performance.

 

are you just getting a few counts or is it actually turning into a bit of retard? A few random counts here or there isn't a huge deal.. infact I don't see anyway how the knock sensor can't avoid picking up a few nth order vibrations that match the freq its looking for.

If your actually pulling some timing than I would look into possilbe causes.. One would be how fast your timing comes in there.. Also always look a cell or two before when dealing with this type of thing