Aircooled VW South Africa

Why the change of heart Vader? I think Bratjie just played you like a fiddle. Bratjie I follow your thread with great interest, well done

Update after strip down and inspection

I will lay out as Fault, cause and remedy,

Problem: Sudden excessive engine breathing
A while ago after a few boosted runs I discovered that the engine was breathing excessively,
At first I initially thought that the engine needed a proper breather system as explained to me by Bugger
But at closer inspection I found that something else had gone wrong,

Fault:
Number four piston had broken a ring land as can be seen in the pictures below,

Cause:
A sequence of events had caused this to happen,
Firstly we had been boosting way too much for the standard pistons to handle, I have been warned about this
by a few members on the forum that knows their stuff, but stubborn and incuisitive as I am, I
went ahead and boosted 1 bar anyway, it was just too good experiencing this for me to follow
their advise and it sort of slipped from my mind, that's one problem.
Then I found that at some stage the pipe to the wastegate actuator had torn thus causing the
Turbo to overboost, I didn't pick up the overboost immediately propably by being over confident
with the results I experienced that I neglected watching the boost guage as frequent as I was
supposed to.That could've caused the broken ring land.
The engine was overheating but I didn't think it was too much, I didn't have all the nescessary cooling
tins installed and all the heated air sucked back into the engine compartment causing the fan to just
keep flowing hot air over the sleeves all the time and the intake also sucking hot air into the induction system
rendering the charge cooling system ineffective also, I did not install any kind of temperature monitoring devices.
Lastly the ever dangerous detonation, due to the excessive heat and pressure this could've destroyed more components
than just breaking the ring land on one piston, I could'nt pickup on the tell tale sounds of detonation but I'm pretty
sure that it was present.
Lastly, after installing the electronic ignition I did'nt ensure max timing advance to 24 deg only, instead it advaced under acceleration to
over 30 deg, but I left it that way - stupid move? ya!

Remedy:
I installed a new piston and new rings on the remaining three pistons, installed the cooling tin under cylinder heads and
also modded up the cooling tin around the turbo and the area around where the crank pulley sits, I will have proper tin made up to ensure
more effective seperation between the underside of the engine and the engine compartment, hopefully I will have a lot more cooler air entering the
engine compartment,
I will ensure max timing advance does not exceed 24deg total, no vacuum line attached,
I removed the boost controller ensuring that I dont exceed factory set .5 bar boost, good move? - I think so
I will need to install a bigger charge cooler radiator and also a bigger reservoir, I may have too little water volume wich causes it to pass through
the cooling system too rapidly causing it to not have enough time to cool down before entering the charge cooler again.
As advised, external filtering and oil cooling must be plumbed in to ensure better efficiency under boost. Thx's to all who advised me on this during the build

I have not adhered to many of the requirements for a turbo build but alas, I went ahead and tried it my own way, it's an expencive and time consuming
way to learn but I guess sometimes I just jump into things and learn on the fly,

A word of advice to other builders going it alone in their garages? When the guru's dish out advice - DON'T take it lightly, do it your way but listen to
the important stuff! Really, you miss a step - you'll be sorry

Lastly just keep having FUN

Here we go again, shamefully I need some more advise, could'nt pick up anything on the web for this,

All the pistons looked like they were washed clean at the bootom side of each piston, could this be due to oil after overheating or a fuel issue?

Just waiting for the battery to recharge so I can start her up again later today

what is your deckheight?

Tony Z wrote:what is your deckheight?

Had it at2.25 including spacer to drop comp ratio, now at 1.75 no spacers bringing the CR back to approx to 7:1

that huge deckheight is the wrong way to decrease your CR.
The clean spots on your pistons are from the fuel pooling there and not getting into your combustion area like it should. Clean spots on your pistons or heads mean rich areas and dark spots mean lean areas. How dark is dark? Darker than normal I suppose, but you can clearly see your clean spots.
Which is why I asked the question about your deckheight.... the closer deckheight will help to mix the mixture better. I would take yours down to 1.5 if you can. It wont do that much to your CR but that said (7.1:1), a better mix will resist detonation better than a lower CR with a poor mix.....

O yes, and a non counterweighted crank at 8000rpm like on your video has minutes of life left. Non-counterweighted crank shouldnt spin above 4500rpm. I used to take mine to 6000 in my 1600 (90hp) occasionally, but I knew I was damaging it. Just so you know.... If you can keep the revs below 5500 you will be doing the engine a favour. If you happy to break it, the rev it and enjoy it.

Big deck height will actually make the engine detonate as you are messing with the squish. Personally I would leave the compression standard and boost it 0.5 bar. This will give you about the same power as before (1 bar) with the efficiency of a stock engine. eg. more power, less fuel consumption. I have seen this time and time again as we do a lot of opel corsa turbo conversions.

As for ignition timing... with the high compression 24 degree might be a little too much. I would look at investing in a MSD 6btm module with boost retard. The msd module will give you nice timing for responsiveness and then retard the timing as the boost comes in.

The stock pistons are actually stronger than you think... the damage you got was from detonation and not bad piston quality. Any piston will break if you get constant detonation.

Cooling the intake charge will also help a lot. Invest in a inter cooler!!!

For high boost you can make a fuel mix with some bigger jets. eg 50/50 mix of methanol and 95 pump fuel. The methanol helps with cooling and adds octane. (But you need to retune it for the mix)

So we started her up yesterday morning and took her for a nice long drive, first fitted one heat range cooler NGK plugs, she ran very sweet below boost, very crisp and nippy, now boost comes in a lot sooner and as previously said, we kept it at .5 bar boost, still pulls like a beast but I didn't want to push her too hard, today to work and back she was very nippy and responsive all the way with no boost, put the foot down and here comes the power , immediately, no more smoke and no breathing, engine cool to the touch and still running 95 unleaded.

The missus will be driving her to work for the rest of the week and I'll change oil once again for about the fourth time and reset the valve clearances over the weekend, then we'll go and see what she can do,

till later,

Ps: 4agedub, i have a charge cooling system installed

sweet. Did you tighten up the deckheight?
Good work, let us know how she does.

Tony Z wrote:sweet. Did you tighten up the deckheight?
Good work, let us know how she does.

Yup, removed all the spacers and found an average deck height measured at four points on each piston to be appr 1.7mm, I would hope this is not too tight and considering .5 bar boost isn't too tough on the engine, maybe want to up the boost sometimes to maybe .7bar just for some fun

1.7mm, I would hope this is not too tight

Normally the piston only starts touching the head at around 1mm deck height at high rpm. As for compression... did you measture the combustion chamber cc?

4agedub wrote:

1.7mm, I would hope this is not too tight

Normally the piston only starts touching the head at around 1mm deck height at high rpm. As for compression... did you measture the combustion chamber cc?

I didn't do the physical measurement but assumed that as standard as I only ported and polished the inlet and exhaust ports, I used 51cc in my cfm calculations.
Anything you can advise me on?

Thx's,

With 1.7mm deck height the compression is 7.52:1. Which is fairly low already.

With that kind of compression I would say it's safe to boost to 0.8 bar over JHB atmospheric pressure. (83kpa + 80kpa = 163kpa. So only 0.6 bar over coastal pressure). BUT, you need a good ignition system with boost retard.

4agedub wrote:With 1.7mm deck height the compression is 7.52:1. Which is fairly low already.

With that kind of compression I would say it's safe to boost to 0.8 bar over JHB atmospheric pressure. (83kpa + 80kpa = 163kpa. So only 0.6 bar over coastal pressure). BUT, you need a good ignition system with boost retard.

Valid point, but alas Ignition systems and " boost retard" is utterly my weakest point, what do we have locally that could help me understand and utilise a system like that, I've heard a lot of MSD systems but have very little experience of ignition systems.

PM me, I might have a cheapish alternative.