Pinging/detonation when at high boost (3S-GTE)

[MWP]

Hi all,

I have pinging/detonation problem when on high boost (~18PSI) at ~3500RPM.

Timing at that point is pegged all the way back at 10deg adv (the minimum itll go).
Fueling is good at around 12:1 AFR's (measured with wideband).
Fuel is Mobil 98ron.

Any ideas as to what the problem might be?

Im competing in a hillclimb this weekend... would be great to have it sorted by then.

[takai]

Hotspots in the cylinder?
Blowing out the valve on overlap and blowback from the manifold?

[StuC]

carbon buildup in the head maybe? Try putting some suby spray through it when hot, give it a thrashing and see how it goes.

[thechuckster]

what are your air-temps when it does this? or does this happen regardless?

[MWP]

Hotspots in the cylinder?

Possibly... As Stu recommended, ill put some more Subie cleaner through it.
Its been about 8 months since i did it last.

Blowing out the valve on overlap and blowback from the manifold?

No idea about this one. I gather testing for it would be rather difficult?

what are your air-temps when it does this? or does this happen regardless?

Seems to happen regardless.
The IC does an awesome job, GM air-temp sensor placed just before the TB, says that on boost, temps are almost at ambient.
Though sometimes i question that sensors (or the MT's reading of it) accuracy.

[thechuckster]

The IAT should be the other side of the TB? mounted where the CSI used to be would be ideal for a stock 3SGTE intake? no idea whether is reliable advice but that's where the MSefi folks suggest it go.

However, if you're using a GM sensor and calibration table to suit, they're fairly accurate.

[3jcelica]

Are you sure its pining and not the turbo surging?

Too much retard can result in high EGTs

[MWP]

Really?
Surging and pinging sound similar??

[thechuckster]

high EGTs will also manifest as boost coming on earlier than usual.

[hemi twofifteen turbo]

with that amount of boost i'd bring the air fuel down to 11.5 at least. This will cool the cylinder slightly. 3500 sounds about where your torque peak is, and is where peak cylinder pressure is, and thus where the problem will be most evident. I would keep it around 11.5 to 11.8 AFR max on WOT. If your running a relatively small rear wheel you've probably go a lot of back pressure in your ex manifold also which doesn't help with cylinder temps /heat/detonation.

[JZA70 R]

so its an audible ping or is your ems detecting knock? / engine light flashing?

[MWP]

Its a Microtech, it dont care about knock
Its very audible.

[JZA70 R]

you could try octane booster, help troubleshoot the problem.

can you lower boost? fatten up AFR's?

[MWP]

I think first test will be a tank of BP 98, instead of the Mobil 98.
See if its just the Mobil fuel which is the problem.

Then ill give Subie cleaner a go, then try lowering the AFRs a bit.
I dont have much fuel left to play with from the stock injectors though.

[The Last Streetfighter]

What spark plug gap are you running?