ENGINE SEIZURES

[bazhart]

Hi Alexw, I think all big capacity 944 based turbos have exhaust flow restriction. This is why most (except perhaps those with extensive head work and large exhaust systems) produce too much mid range torque for a track car or too sudden a boost spike to control out of corners.

You can overcome inlet restriction by more boost but not exhaust. The 16 Valve head has more flow capacity and also provides the opportunity to experiment with negative valve overlap via the variocam adjustment system. There is a difference of opinion over the benefit of this and I don't know for sure what the answer is but I will be finding out when this lot is running OK.

Unusually instead of re-welding the head or block to fit an 8 valve head to a 3.0 block I have adopted a 2.5 block and welded the block to accept a 3.0 16 valve head (because there are deeper coolant channels that I want to exploit to improve cooling).

Once we discover what the answer to the overlap situation is it can then be exploited in later engines that also have a variocam system - like all M96 and M97 engines.

It will take a while to get the whole thing running with stand alone systems and then to experiment with different cam timing etc - but at least it will fill in some blanks in our knowledge that need understanding better.

Baz

 

[barks944]

Baz, I have some software that can extract all the factory map information from the 944's DME. This includes all the ignition timing, fuel, the parameters for cold start. Would this information help you create a base map for your standalone system? Let me know if it would help you. I'm not sure how similar the parameters it would be to the standard 2.5 engine however but it might be easier than starting from scratch?

 

[Lowtimer]

Wouldn't the map they are using on the current 3.0 Turbo be a better starting point?

 

[bazhart]

Any information like that would be a big help to get it running - thanks - although Wayne ' chip wizards did such a brilliant job last time with the 3 litre car - I want to use him for this new one - but I guess he would prefer it to run on delivery - if possible and we do have different camshaft sprocket positions to test out (to alter the variocam positioning - so we may need a 2 stage job @ Waynes - to get it running then for us to change things and test out with our dyno and then get him to refine the chosen result package.

It's going to be interesting!

Baz

 

[944 man]

ORIGINAL: bazhart

I still think the standard gasket is probably best as it allows some distortion of the block to still be sealed - but I agree that for higher boost turbos you need something extra to stop it sliding sideways under pressure.

Baz  

How about a combination of standard head gasket, cut to accommodate Wills rings?

 

[Diver944]

ORIGINAL: 944 man

How about a combination of standard head gasket, cut to accommodate Wills rings?

That's exactly how JMG seal the 3.2's. The rings fit into a groove in the deck of the block and seal the cylinder against the head. A standard gasket has been trimmed to seal the waterways

 

[944 man]

More information here, for those who arent familiar... http://www.ret-monitor.com/articles/950/rings-of-fire/

The internet isnt exactly overflowing with information. I dont think that Ive searched before and the t'internet was a twinkle in Berners-Lee's eye when I first read about them in Cars & Car Conversions... []

 

[bazhart]

Strangely I used to use Cooper sealing rings on the motorcycle race engines (particularly 750 cc Suzuki triples) but could not trace them so resorted to Wills rings this time.

Although we have good enough machinery to manufacture anything special in house - we always try to design things as practically as possible and modify things in such a way that others could manage to maintain in years ahead with as much standard equipment or machinery as possible.

Bearing this in mind - I have machined the grooves in the head to pinch on the standard head gasket (for no more reason than it is easier to then change them and fit a standard gasket especially as the original turbo will be offered for sale soon and it helps the new owner to maintain with standard parts). It also stops the Wills ring damaging/impinging on the block top face (which is difficult to re-machine needing all studs to be removed) and allows some easy re-machining of the head (if ever needed). This should stop the gasket rings sliding sideways - but then I also have fitted 9/16 UNF high tensile studs to increase the head closing pressure - and think it will all work out OK (hope that's not famous last words)! I also changed the head stud system on the older turbo but decided this was a better way forward this time needing even more closing pressures without distorting the block.

When this animal is finished and running Ok it will also be sold on (because it is a little old to be developing this much and we need to move on to newer engine types transferring the information over) and it is important for me to standardise as much as possible to help the new owners wherever they may be in the World. Both cars/engines will be easy to maintain despite the special nature of the designs.

Baz

 

[sawood12]

I'm often surprised deck plates are not more commonly used in conjunction with o-rings. A bit pricy to incorporate but surely a pretty robust solution?

 

[barks944]

What is a deck plate?

 

[blease]

This is very interesting. Can I add a coupla points?
1. I presume these channels that are deliberately blocked by the head gasket are there because the engine is half a 928 and the 928 design needs these channels?
2. Blocking the channels with a perishable head gasket is always going to be a compromise situation, so why not block the channels permanently with some form of plug?

Oh, and 3. Bummer again....only just had my camchain, guides, belts and idlers done and woulda done the gasket too except I was advised it probably wasn't necessary in anything other than a full race engine!

 

[bazhart]

You really should read the article/section 5 before asking all these questions as many are answered there.

For example the reason for the gasket controlling the flow is because the coolant comes in at the front of the block and therefore how else can it get to the back unless the head gasket forces it there? It is nothing to do with any 928 origin. It needs to flow backward to then pass up into the head to pass forward again - or it would create hot spots - which the similarly titled posting on this 968 register shows with a picture of a bad head gasket indicating how it short circuits that planned flow.

However the research into this (to improve the temperature differences in our mk2 turbo engine) and why 996 and 997 3.6 and 3.8 engines (which we imagined were two entirely different issues) kind of merged together and the link made me realise what the potential problem was with the 944/968 head gasket once it deteriorates and creates holes (as shown on the 968 forum).

Baz

 

[blease]

Sorry Barry, I've read back through all the posts on this thread and I'm not sure which article you are referring to. Can you point me in the right direction so I don't ask more nit-wit questions? This is all pretty new to me as a non-engineer enthusiast.

 

[Lowtimer]

It's part 5 off this page:
http://www.hartech.org/buyers.html

If you haven't read the rest, part 2 also has a lot of 944-specific material in it.

 

[blease]

Thanks Lowtimer...a useful steer there. I was unaware of this internet resource. An interesting but slightly depressing read. My 3.4 996 has a ticking noise from the rear of the nearside bank (is that bank 1 or 2??) which, at 85,000 miles makes me think that this is the piston-tilt the article addresses. Ho hum! So now I need to factor in a new 944 head gasket AND a trip to a handy man with a boroscope for the 996!

 

[bazhart]

Hi blease - worry not unless you also have increased oil consumption etc - more than likely a tappet - good luck anyway.

Regarding the 944 - don't forget that my advice is merely a warning of something that could cost you the end of the 944 unless something is done about it - so although it may incurr a relatively small outlay - most gaskets that have never been replaced before will go anyway on the compression side eventually (and can stillk cause damage through overheating when they do) and so having them done a little earlier while protecting the whole car as a viable second Porsche - is not such a big issue looked at in that light?

Baz

 

[JM1962]

Here is a picture of my head gasket removed from my 1985 8V this weekend. I know for a fact that the gasket is at least 19 years old because I work with the previous owner who had the car for 15 years and I have had it for 4, so in all probability it is original. It has started to rot around cylinder no4 but what the picture shows less well is how it has rotted around the other cylinders and become porous, left much longer it would have short circuited the cooling system as Baz described.