Knock..

[keithmac]

I`ve been running my supercharged 16v for a while now but I still can`t seem to get reasonable timing without it knocking/pinging. At the moment I`m running 7 degrees advance from 1500 to 3000 rpm just to get rid of the knock, any higher and it`ll start to ping.

At 2000 rpm my MAP is around 170kpa, static compression is on the low side of 9:1, even water injection can`t irradicate the ping. Never really see MAT`s over 50c, and it`ll knock even at 35c or so.

Running MS1 v2.2 extra, 029q, Distributor on next cylinder mode, AFR`s are 11.5:1.

Can anyone throw me any ideas?

[Dr.Hess]

I ain't no expert on boosting, but I have a boosted non-MS motor and I've been following other people for a long time.

How much boost are you running? 9:1 is fairly high compression to be boosting. I would just guestimate that anything over a half-ish BAR is going to be difficult to maintain.

[PSIG]

Hmmm... offhand your setup sounds fine for boost assuming no other weird mods. Every engine combo has its limits but I see your frustration with this one. A few Q's:

Is the ping/knock suddenly rather heavy or barely perceptible to start?
Does it ever ping under 100kpa?
Are you sure your 'readings' are each accurate(timing/AFR/MAT/etc)?
Are your spark plugs showing the same indications (ping/AFR/heat/etc)?
With the wastegate forced open - does it respond like it should (although relatively sluggish) with normal timing?

David

[Moonsteel]

I`ve been running my supercharged 16v for a while now but I still can`t seem to get reasonable timing without it knocking/pinging. At the moment I`m running 7 degrees advance from 1500 to 3000 rpm just to get rid of the knock, any higher and it`ll start to ping.

At 2000 rpm my MAP is around 170kpa, static compression is on the low side of 9:1, even water injection can`t irradicate the ping. Never really see MAT`s over 50c, and it`ll knock even at 35c or so.

Running MS1 v2.2 extra, 029q, Distributor on next cylinder mode, AFR`s are 11.5:1.

Can anyone throw me any ideas?

You've got the same motor as me, I don't remember it pinging last time I was out.
You've got a smaller pulley than me eh? (68)

[PSIG]

With the wastegate forced open - does it respond like it should (although relatively sluggish) with normal timing?

Oops... was thinking about another VW turbo project If it uses a bypass a small (or no) pulley can be used for testing.

[keithmac]

It`s on a 68mm pulley now (65mm was even worse, but faster ) , I`ve eradicated the ping but I`m down to 7dbtdc up to 3000 rpm, car never knocks off boost (30 to 40 dbtdc).

I had a play with the water injection and it makes a big difference to the power, but no real difference to the knock.

I`ve got it up to 14 degress at 6000 to 7000 rpm, but I haven`t had chance to test it yet, an unmarked police car, Volvo S40 ruined my test track yesterday .

Plugs look fine, a little rich if anything but that`s down to daily driving and relitively high warmup corrections.

I have a feeling it`s to do with the dizzy being driven off the cambelt (through the inlet cam) causing the timing to wander, but DIGI1 uses the same system with no ill effects?

It`s not horendously loud but it was definitely knocking.

Moonsteel, would you mind posting/ pm`ing your spark table?

[PSIG]

Some silly things to double-check - Correct cam and crank timings with proper belt tensioning. Well seperated and crossed plug wires (under boost they try to crossfire) with low resistance through the connectors verified. Correct disty phasing. Correct sensor polarity. No carbon traces, moisture, tracking or cracks in the disty cap and rotor.

Those (and others) can all affect timing and knock under boost conditions. Any other weird symptoms?

[Moonsteel]

It`s on a 68mm pulley now (65mm was even worse, but faster ) , I`ve eradicated the ping but I`m down to 7dbtdc up to 3000 rpm, car never knocks off boost (30 to 40 dbtdc).

I had a play with the water injection and it makes a big difference to the power, but no real difference to the knock.

I`ve got it up to 14 degress at 6000 to 7000 rpm, but I haven`t had chance to test it yet, an unmarked police car, Volvo S40 ruined my test track yesterday .

Plugs look fine, a little rich if anything but that`s down to daily driving and relitively high warmup corrections.

I have a feeling it`s to do with the dizzy being driven off the cambelt (through the inlet cam) causing the timing to wander, but DIGI1 uses the same system with no ill effects?

It`s not horendously loud but it was definitely knocking.

Moonsteel, would you mind posting/ pm`ing your spark table?

I'll dig it up when I get home, it's by no means perfect, but I didn't knock.
Max boost for me was 182 kPa @ 7000 rpm
I'm using 2 ABA head gaskets, so I think my compression is higher than yours as well.

A side note, when you say water injection makes a big difference to power, how so?

[keithmac]

PSIG some good suggestions there, cam and crank (including inter cam timing on the chain) is fine, I`ve used a pegged vernier pulley to correct the timing to stock, I`ve made a set of carbon core leads for the car - was the same with the Beru VAG leads, New dizzy 3k miles ago and a second set of caps (2nd hand though..) .

I did think at one point it was due to the full stainless exhaust getting hot and igniting unburnt fuel, but I`ve head knock before n/a and it sounds the same..

Moonsteel, I had the WI kicking in at 40c IAT and before this the car felt 'dull' to give a better description, when the WI kicked in it felt a lot crisper and more powerful, I`ve now set the IAT to 20c for water injection and it seams to liven the car up no end.

The wideband was triming the AFR to 14.7:1 on the last MOT and the emissions log cam out at exactly lambda-1 so I presume the ZT-2 wideband is reading fine (checked the display with what MSLVV reported).