Sporadic detonation

[bazibbo]

I'm slowly getting my 1914 turbo running nicely, and its all starting to come together.

I'm still getting some sporadic detonation that I need to get tracked down before I break something. I'll get some data logging done this next week or so, so I should have some better information for you all, but for now, and advice or thoughts would be appreciated. I can take the car for a good long ride out with no issues, but then, if I take things steady for a time, maybe a long run along a motorway at 65mpg or so, then I often get the detonation when I start to push the car again. a good example would be the 10 miles up to a local suspension bridge with tolls, I often get detonation as I accelerate (sportingly) away from the toll gates. Odd.

One thought would be that oil builds up somewhere and only gets blown into the intake when the boost builds - thus reducing octane and detonating. might be, but I only had the turbo rebuild 500 miles ago.

I'm not seeing bad AFRs on my wideband as it happens either, but then a quick glance at the AFR isn't data logging is it.

Here's a pic I'm sure you'll have seen before, either in this car, a 1302s or my earlier 1200 blue bug - but no thread should be without pictures!




and in place...


Spec:
1914 EFI chargecooled turbo
around 8:1
1914
counterbalanced 69mm crank
bugpack 110 equivalent
044 cnc roundports 42 x 37 valves and I think they're 63cc
350cc injectors
VW Speedshop SP1 manifolds
DPR8ea 9 NKG plugs

in tank walbro pump
Chargecooled
Turbosmart 45mm wategate
dual dawes type MBC

DTA S40 ecu
Innovate MTX

Think thats it.

I'll be aiming to datalog using the tried and tested way of pointing a camera at the laptop screen, with the AFR gauge next to it, whilst shouting a commentary out, which has worked before and should give me most of what I need, air temp, AFR boost. I think I can record on the S40, but not download anything, so maybe a few screen dumps.

Any pointers to watch out for? thoughts or ideas guys?

ta

[madmike]

Maybe just bed fuel? I know nothing about F.I. but I'd try better fuel, if it's still an issue it's ignition,perhaps

[66brm]

Heat soak? Do you have a temp sensor for iat, after the intercooler?

[bazibbo]

Maybe just bed fuel? I know nothing about F.I. but I'd try better fuel, if it's still an issue it's ignition,perhaps

I should, fingers crossed, be ok with fuel madmike, it been happening for quite a time and I've had a lot of tank fulls of fuel. I always use the same branded garage and the same Shell V-Power @ 99 RON. Not certain if the UK RON rating is the same as the US one.

Fuel delivery though... I can't collect fuel pressure data at the moment, but I should be able to see and log AFR changes

Oh and before I forget, I run 10 psi normally, retarding to 21 degrees. Could probably give it less retard, but I haven't had chance to test things.

Around 14psi when I want to go on a few 'run what you brung' days, or when I feel the need - retarding to 20 degrees there.

[bazibbo]

Heat soak? Do you have a temp sensor for iat, after the intercooler?

I can log IATs 66brm, so I'll have a look at them after a slow cruise and normally.

[bazibbo]

Sometimes my logging is shouting ' what does it say now!' to the wife...

[66brm]

The thing I would be looking for would be an increase in iat, I'm not sure how your cooler is setup but it may not be transferring enough heat/ recirculating heat on longer drives. Just a thought anyway, as to your datalogging techniques, well if it works.....

[madmike]

on the wife comment

[bazibbo]

The detonation seems to come on fairly early as the turbo first starts to kick in, I'm not noticing it when I get over 3500 or 400 rpm.

The cooler should be performing, it got a new upfront radiator last year which should have been a huge improvement. It might be worth me insulating the two water pipes in the engine bay - guesswork until I can give you a few IATs though.

I daren't wrap the exhaust though, my last one, a CB Hideaway rotted away in days after it got wrapped

Turbine wears a hat normally though

[buguy]

I wonder if pulling a bit more timing would be a precaution at this point 'til you have actual numbers. Detonation is pretty scary stuff.

[bazibbo]

I maybe ought to do, but I'm not convinced timing is the issue ( though it'd obviously treat the symptom )

95% of the time I have no issues, in fact I think I'm pulling timing because of this issue only. I'm sure I should be able to comfortably run more than 21 degrees at 10psi, on a chargecooled injected car.

I might be retarding to disguise an issue

Or it might all go bang buguy and I'll regret not retarding it more

[buguy]

Yeah I don't know that timing is the issue. I just thought pull timing to be safe so you don't do any damage.

[RJVolksperformance]

The detonation seems to come on fairly early as the turbo first starts to kick in, I'm not noticing it when I get over 3500 or 400 rpm.

You say it has 21degrees timing at 10psi, is that on the whole ignition map rpm range? are you using the dta boost compensation to pull timing, if so have you checked its actually that timing on boost?
It sounds like you get det down low and I am thinking it has more timing down there?

cheers Richie

[bazibbo]

Hi Richie

Yep, I'm using the basic version of the manifold pressure compensation, keeping it as broad brush strokes, and pulling 6 degrees out everywhere at 10 psi.

So before any compensation...

1000 - 11 degrees
1250 13.5
1500 15
1750 17.5
2000 21
2250 24.5
2500 26.0
2750 27
3000 onwards 27 degrees

I also add few degrees under 90 kpa and lower.

So 3000 at 10psi is 21 degrees after compensations, but Im going to get some real figures this weekend and double check what's happening and where

I'll also try and replicate the conditions where it starts to detonate and see if my basic data logging can pick up anything.

[bazibbo]

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!)