Porsche Enthusiasts Club Forum

Haven't driven the car for a week since a 250 mile round trip to OPC Reading. The swirl pot didn't improve anything as I had pressurisation at both ends of the journey and coolant blow out on shut down. This week I bought a new 951 coolant tank and fitted it. I can now see if coolant is flowing into the tank from the main feed pipe or from the vented pipes and if its creeping up to the neck level before blow out. Refitted the week or two old 951 cap

I also bought a borescope as I wanted to see wants in my cylinder bores. Not an expensive one and pics are low res but I think you'll get the picture.

#1 bore honing


#1 piston which is nice and clean with a small pool of oil in the crown


#2


#3


#4


I ran up the engine for 10 minutes to get hot, bleed the coolant, held at 2000 rpm for a minute so it got hotter, allowed to cool before shutting down. No coolant blow back occurs after idling, this usually occurs after a good 30-60 minute drive and getting on boost.

And here's another view of #1, and again with a pool of oil


So just for comparison and idea of dish shape of the pistons


All the plugs have a nice whitish brown tips although the preimeter is a touch sooty. The threads have oil 'lubrication' but nothing further up from the threads.

I did drive at a reasonable speed above the national limit on the M5 up to Reading and did have some oil blowing out the oil separator. This is the first time its happened since renewing the HG 1200-1500 miles ago. Not a lot but a few drips/splashes have come through the K&N onto the inner wing.

Good news, the new coolant expansion tank appears to be working on one drive out this morning. I'll be more impressed if it survives after a longer high speed motorway run. Didn't do this earlier as the roads were awful. Still spins up the rear wheels in 2nd and 3rd gear on full boost/torque on wet roads running 0.9 bar

Bad news is the oil is still pooling on the pistons after I shut down. Just left the car to cool a bit for 15ish minutes before pulling a plug and shoving the borescope down. Interestingly when I started it up this morning there is no smoke from this oil burning off either on start up, idling or blipping the throttle.

I think I may try piping the Purolater back into the fuel metering head unit and see if the suction/vacuum relieves crankcase pressure if thats whats causing the oil on the pistons.

Found the culprit to the coolant issue, a gradual blockage to the vent line inlet on the old expansion tank. When you blow in initially it allows air through and you think its fine (did this numerous times on the car!), but the longer you blow in it slowly begins to close up and finally stops any air through, even under pressure of a bike pump. Hopefully that's the end to my coolant issues. If I add up the cost of an ally radiator, swirl pot, Samco hose, elbows, and finally the expansion tank plus the continual top ups of water wetters and anti freeze, that's be an expensive and painful period I hope over with.

Now onto the new one of oil!!

But at least you now know that you have a cooling system that should more than adequate for the engine.

If you have a little oil pooling on the pistons after switching off is this not likely valve stem oil seals and or valve guides?

It would be if I were not trusting that the refurbed head already had brand new seals and guides bought, paid for and installed. I think its a crank case breathing issue and a improved breathing system is required. Awaiting Jon to chime in with the solution/appointment date for sorting

Had another drive out in the car last night and the cooling is, I hope, sorted despite some high speed and high boost being liberally applied.

I think your breathing for the crankcase is wholly inadequate )

Can't be 100% sure, but I suspect you could do with a revised oil breathing circuit.

I'll be in touch Jon regarding booking the car in with you over the next month or so

Sounds like a plan. Just hope the weather is better than it is at the moment for some road tuning..

Id quite like a go on a dry road, too...

Get in line...

210BHP at 4900 RPM and 0.7 Bar of boost.. This will be quite monsterous at 1.2 Bar of boost which it should be able to do all day long.. In theory, the 924 turbo engine, with its cast iron block should be quite detonation tolerant compared with the 944 turbo block, which means that although I would still avoid detonation, pushing the envelope a bit further, such as to anywhere from 1.4 bar to 2.0 bar is doable.... But I think 1.2 is a nice safe figure, I have tuned 924 CGT's to this point without so much as a whisper of detonation on the knock sensing equipment, and their intercooler is awful compared with the 944 front mount as this car has.

But knowing an engine will be detonation tolerant, (as long as the top piston land is!) means you can push things a bit further without worry of a glitch of detonation will blow the bore wall out as can happen on a 944 turbo thats pushed too far.

1.2 Bar should be a lot of fun! Steve's car is pretty light so will really move with that kind of power (once he regains traction hehe).

How do you improve the oil breathing circuit on a high boost 924 Turbo Jon?

I have an ancient Turbo Technics crankcase breathing kit. I'll try to find the diagram/instructions for it and post it online as they don't sell it anymore - partially because they could no longer obtain one of the valves for it.
The kit uses a funny type of PCV valve that has 3 connections. The crankcase breather hose connects to one. The next runs to the inlet manifold via another one way valve on the way. The last runs to the Purolator oil/air separator (or a catch can).
On their diagram the purolator then connected to the air filter but I had a catch can instead vented to atmosphere through a small filter.

The kit works brilliantly. When off-boost the 3 port valve allows the inlet manifold to create a vacuum in the crankcase and pulls the combustion gas etc. out. When on-boost it closes the previous connection and allows the crankcase to vent to the Purolator or catch can.
You can feel the vacuum if you remove the oil filler cap on idle.

Using this system my engine went from having oil coated inside the intake/charge tube to having none at all. In my first year of ownership the oil breathing was so bad, it would push a bit of oil past the turbo seal and put a cloud of smoke out ON IDLE. It did this even with all the Porsche breathing updates. I know of quite a few other cars that would also push oil past the seal, even though nothing was wrong with the turbo.

I've seen the 924GTS CS cars with the vent on the cam/rocker cover going to the Purolator, then from the Purolator to the air filter. I assume this helps fresh filtered air ingestion. Didn't you also mention a PCV valve used from a Montego? I've heard this mentioned a long time ago and someone even using a similar 3 port valve from a Peugeot model.

I have some ideas to add to the Turbo Technics system to help ventilation when on boost. I'd be interested to hear your experiences with dealing with this.

At the sort of power expected, I wonder whether Steve will wish that he had a little more track width (and length)?

Nope, it's a fun car and not an ultimate lap time track car

Yes, I intend to participate in the odd sprint and hill climb but no intention if being ultra competitive with it. Just want it to be fun, which it is already.

Wes, Several ways of attacking it...

The TurboTechnics kit, I believe, from memory, was the same parts as used in the original Porsche main dealer 924Turbo "In case of emergency break glass kit"

Basicly, back in the early 80's Porsche knew they had a problem with the 924 turbo breather system, and they released a TSB with a parts list of bits and a diagram to improve the situation of 924 Turbo's which were smoking at idle due to the breathers. This was in response to the main dealers constantly sending turbo's back to the factory on warranty claims.

It was never officially a part you could order, as one of the part numbers was extremely different to a Porsche or VW part number... What the dealers were told on the QT was "Get it from a rover dealer", the part was a Montego MG Turbo PCV valve.

But the factory insisted that this kit of parts was fitted to any 924 turbo and re-tested prior to letting letting a main dealer run through a warranty claim on a 924 turbo engine or turbocharger.

The funny thing is, I only ever see these rarely fitted to any 924 turbo's, I partly suspect that subsequent owners or specialists remove them thinking "what the hell is this?"

I also suspect, the turbo technics kit, from memory, was the same kit of parts, and the part they can't get anymore is the Montego MG Turbo PCV valve.

The very best solution is a aircraft inspired exhaust venturi that plumbs into the middle of the exhaust system (if the system is a nice big bore) and then connects to a catch can, with the other side connected to the crankcase breather, as long as your exhaust is not heavily choked at full boost, this system supplies a vacuum to the catch can at all idle and boost situations, as well as venting the blowby gasses into the exhaust rather than through the engine, which in any kit will leave some oil vapour in the intake, and therefore oil residue and contamination to the whole intake and combustion and intake track.

The other alternative would be an atmospheric venting system via a catch can, which is cheap, but dirty and less than ideal.

Negative crankcase pressure is a wonderful thing, and can bring additional power to any engine under any opperating conditions, some of the benefits include..

* Turbocharger oil drain back flow improvement (sometimes worth playing with this and possibly restricting oil flow to tune it)
* Defoaming of engine oil (negative pressure causes forceful extraction of air from the oil)
* Less lower crankcase pumping losses (the denser the gas in the crankcase, the harder it is for pistons to move)
* Improved piston ring spread, especially at lower rpm and better sealing on the intake stroke throughout)
* Improved valve guide and stem seal sealing
* better oil flow throughout the engine
* less likely for even a poor seal or gasket to leak
* Less crankcase windage due to reduced aerodynamic vortex generation

All of which, to be honest, are the holy grail of a fast car, which is why Porsche used this system in Le Mans cars in the 80's

The downside is a single one... Unless your doing the work yourself, its not cheap and your engine needs to have good seals and gaskets to make sure it is efficient.

Ooops.. I just gave away a trick... Oh well, following my health scares, I don't want some of this stuff to be lost, so better in the public domain than being lost.