Sporadic detonation

[RJVolksperformance]

Retard is..

120 kpa -1 degree
130 kpa -1 degree
140. -2 degrees
150 -4
160 -4
170 -4
180. - 6
190 - 7
200. -7

300. - 15 ( you never know!)

You know those figures in dta manifold pressure compensation are percent not degrees?

[bazibbo]

There's a tick box in 'general engine settings' for 'advance compensations in deg not %'

I used to run percentages but my brain can't get round the figures as fast as it should.

[RJVolksperformance]

There's a tick box in 'general engine settings' for 'advance compensations in deg not %'

I used to run percentages but my brain can't get round the figures as fast as it should.

Ok cool, I have always run it in percentages


cheers Richie

[RJVolksperformance]

Couple more thoughts then

Have you confirmed map sensor reads same as actual boost?
Does it do it when engine and water in intercooler is still cold? or just after a few miles ?

What is afr when it starts to det? might be a little to lean just at the rpm it starts to make boost?

[Piledriver]

How well is the engine compartment sealed from the exiting hot air?
From the picture, its... not, although a valiant attempt was made on the passenger side.
(I realize some parts were removed for the picture)



Recirculating hot stale air is deadly to an ACVW, esp at idle.
If there is ANY path for used hot air to recirculate, it will.

I have proposed a few times a ~horizontal engine compartment divider that goes from the top of the fan housing to the deck lid and seals...usually as a rain tray.
If it fit really well, it could keep the hot and cold sides separate as VW did, something is basically required.
That combined with decklid standoffs (and maybe someting at the sides) should prevent anything but cool air from getting at the fan, and it would be invisible from the outside.

You could try it with plastic cardboard perhaps, cuts with scissors, I used it for my AC condenser ducting to make a pattern and it fit/worked so well it stayed.
Holds up great as long as it doesn't get too much heat or sun.

[madmike]

Or drive it like it is all open just to check

[bazibbo]

To be fair, I've not helped because I stick up picture of the engine whilst it was in bits Piledriver. Its by no means perfect as the turbo gets in the way, but it's usually like this...



I think you were referring to the drivers side though

and the boot lid is also further vented behind the bumper like this:



Ok, taking onboard your advice, I've had a morning driving around sunny Lincolnshire with a mate and his GoPro. sadly the GoPro wouldn't pick up the AFR gauge, but we checked things manually.



Some figures:

Todays weather: Sunny and 16.5 degrees (61f)

Intake Air temps 41 degrees at 9psi boost ( seems to stay around 40 all the time ) ( 106f)

Oil temps around 85-90 degrees ( 185 -195 )

Chargecooler water temp, just for interest, around 28 degrees, measured at the reservoir near the fuel tank, not in the engine bay.

MAP matches on the boost gauge and the PC interface - both reading 9psi.

There's no detonation at 10 or 14 psi until the engines done at least 10 miles. It starts to appear as the oil temp rises to 85 deg C, and I guess as the inlet temps rise.

AFR at 10 psi is around 11.5 but can rise to nearly 12.

On the short testing trips, I could easily loose all the retard at 10psi ( its actually irritatingly 9 psi, I discovered ) and run it at 27 degrees and it was totally detonation free, and 5 extra degrees adds quite some performance.


I think it could be something to do with my Air Temperature Compensations Technically I understand that physics dictates that you pull fuel for higher temperatures. I remove some fuelling, but not as much as the 'set to standard' button that forms part of the DTAs sotware.

Air Temperature Compensations ( air temp - Fuel Comp %, as a minus figure )
20 deg 0
25 deg 0
30 deg -2%
35 deg -3%
40 deg -4%
50 deg -6%
60 deg -8%

So I wonder if this is the culprit. I'm going to try it as '0' but I could even add a little bit as it gets warmer.


I think I've covered all your suggestions, I've got more data if needed. How does 40 degrees sound for IAT? Other than raising the filter a bit and adding more insulation, I can't do much. I might duct tape all my tinwear leaks.

Any thoughts guys?

[Piledriver]

Looks great, actually.
The shot with bits missing just concerned me.

What fan belt? Is that a doghouse fan/housing etc?
The wider doghouse fan wants the wider late 11mm belt...
But you may just be getting a bit of old fashioned heat soak...

Note that fuel also gets less dense but at a much lower rate...
Its only about 6% from -40c to 40C, if you had a fuel temp sensor.
(mine is part of my ethanol % sensor)
I was surprised how hot it gets while circulating.

Less fuel/std gas law setup isn't going to improve the det issue, but may help normal running.

[bazibbo]

Yep, doghouse with the oil cooler in place. Blocked off heater outlets, though I might try drilling a half inch hole in them.

It's not the wider, squarer fan housing. Belt is 9.5 x 905, so I might have a look into the 11mm belt.

Intake air temp is about 106 f in US currency

[Dan Dryden]

It goes against physics, but have you tried spraying more fuel at higher temps?
The fuel evaporates and helps cool the intake temp.

[bazibbo]

Just set it all to zero Dan, but I'll add a bit if that doesn't work.

Those few extra degrees don't half pack a wallop

[blue thunder]

What cam are you running? Too mild a cam can cause a high dynamic compression ratio at low rpm's and can cause detonation when temperatures rise due to heat-soak.

[bazibbo]

To be honest, I don't know what cam it is.

I never got the chance to get an engine built to specs, but I've slowly built it up from a mix of used and new parts. Though I had a decent engine builder put it together.

We think it's something along the lines of a 110 or mild bugpack, but it's certainly pretty tame.

[Dan Dryden]

Have you had a chance to look into this any further?
Interested to know if / how you've resolved it.

[bazibbo]

Sorry, I've been a bit slow with this.

So I'm pretty certain that it was the reduction of fuel over 40 deg C. Whilst I haven't done many miles, I appear to have lost the detonation.

I've started to look at lowering the intake temps a bit, firstly I'm insulating the charge cooler water pipes - not expecting great gains from this.

I did buy some deck lid standoffs, but to be honest I don't like the look.

So, so far, all looks rosy - thanks.