MicroSquirt.com read only forum (Jan.15,2018)

Ive been keeping to the safe side of 12:1 up to 15psi but have started to notice a noise that might be knock. Ive heard knock in many non-turbocharged engines but no a boosted one. The stock ecu is controlling timing and doesnt feel to be pulling the advance but it sounds something like someone has put something in the way of the flow of intake air - like when you get a high pressure garden hose and stick your finger in the stream about 12 inches from the nozzle. A sort of rushing noise a bit like a leak, which is what i searched for first. Nothing really like when you get 'pinking' on old cars that sounds like erratic ball bearings bouncing around, but then this engine is a whole different beast from the ones im used to.
It comes on full boost (or as low as 12psi) but not on part throttle, only when i go >60% roughly. It happens at 3500rpm+ and i can turn it on and off, so to speak, by backing off the throttle and back on again with no apparent change in acceleration - obviously at an over-throttled point.

I dont want to melt/smash pistons so im being a little cautious around this area, but i cant make my mind up if its knock or just the noise the engine makes on full throttle lol, maybe opening the throttle fully at that boost level hits a harmonic somewhere.

Thoughts welcome!
J

Maybe an idle to book and hour on a rolling road and have someone who`s used to listening for Knock have a look at it?

Mine knocks quite badly over 7 degrees ignition 12 pis at 2000 rpm (WOT) loaded up in 4th gear, sounds like the classic ball bearings in a paint can though.

Could try Boris`s knocksense module and rig it up to the MS to log knock?

I'm gonna check my plugs for any scary signs then take it to a RR for a blast and see how it goes. Tad pricey, theres very few 4x4 rolling roads in the UK and they charge a premium for the pleasure of telling you bad news
Roughly $100 US for a single power run.
J

I normally do club rolling road days, 2 runs for £25, when the car was on K-jet I took it to Steath Racing and they only charged £55 for 1 1/2 hours of rolling road setup!

I`ve looked down the plugholes to check the condtion of the piston tops before, at least it gives you an idea..

Thats fairly cheap, if i can get to one i'll give it a shot.

Strange how its throttle position related and not map/revs related specifically. Same MAP, same revs and it turns on and off with throttle position. Only think i can think is the AFM thats controlling the timing is swinging open more, but i was under the impression that after 10psi its jammed open anyway, which is why i was seeing mentally rich mixtures before.

J

Maybe time to go spark on the MS, then you know exactly what spark degree is being used at all times?

i tink youre right, and knock and boost control.

Oooh, im wondering if its actually the variable intake opening. Hmm, could do with an LED to watch that.

It sounds nothing as obvious as http://ken-gilbert.com/wrx/knock.wav Certainly isnt 'stone thrown on ice' sort of noise.

some stock computers calculate timing by the percieved load the engine is under. The less load, the more timing. Depending on how things are working, its very possible that the computer is sensing a low load situation at that particular point and jacking the timing way way too high.

This is a very common problem on EEC4 systems when people use the calibrated MAF sensors for example. The MAF sensor is "fooling" the computer to adjust for the bigger injectors, to get the right amount of fuel, but in the process of fooling the computer, the computer always thinks its a low-load and and pings unless you lock the timing (remove computer timing adjustment)

Umm its not at a low load position - its at full chat, just with throttle fairly open. It stops if you ease off the throttle slighly. I'm fairly sure my timing is set by the AFM as i mentioned, which should be locked at full whack by 10psi (normal approx max boost).

I'm wondering if its the second runners on the intake opening and allowing more air to flow, changing the induction noise, or worse closing them. The toyota variable induction system opens the second intake ports past 3800ish rpm under load to give better torque low down while not restricting the upper end. It also changes under knock conditions but i cant remember if it opens or closes or the theory behind it lol.