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bazhart
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Joined: 20 May 2009
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PostPosted: Fri Dec 23, 2011 11:18 am    Post subject: Cylinder Scoring Information Source Reply with quote

The new section 5 of our Internet based buyers guide has now been uploaded (see www.hartech,org buyers guide). You will need a lot of time and probably a headache pill or two if you want to read the whole lot in one go.

It has been written to inform anyone at any level of relevant knowledge (from a non technical owner to an experienced qualified engineer) - that is interested in the problem of cylinder scoring in 996 and 997 3.6, 3.8 and Cayman S engines - what the many contributory factors are and why.

Briefly it covers why it is easy to design an engine so bullet proof that it never ever goes wrong but it would then be very expensive and heavy as a result. With pressures on profitability, low emissions and higher performance - manufacturers have been under pressure to trim designs, weights, costs, emissions and fuel economy while increasing performance - which inevitably moves their products closer to reliability or longevity limits.

This section gradually explains how some systems that worked OK in air cooled 911's and the 944/968 range had small subtle differences when applied across into the M96 engines that individually seemed insignificant but actually pushed each reliability issue slightly closer towards the limit - but insufficient to cause a problem (in other words pretty well perfectly designed for the needs of the modern World). Many of the changes and weaknesses seem also to concentrate the problem on bank 2 (where most of the failures are).

When the later bigger capacity and more powerful versions were built - instead of changing some of those marginal issues to compensate for the additional heat and loads - it seems that they were either left exactly the same or in one case while moving in the right direction for reducing costs - went entirely in the wrong direction for reliability - resulting in engines running so much closer to that boundary - that some - after ageing and with some wear and tear taking place and after experiencing different driving conditions and styles - simply slip over the boundary and become damaged (usually on bank 2).

The scenario is typical of many other historical engines from different manufacturers that following a capacity or performance increase - search out and find the weak spots in a previously reliable design.

Usually a small but significant modification eventually appears on the market to fix the problem - but more often from smaller specialist organisations (that is presently taking place with these engines).

Because this initial engine range was actually so very well designed to run really close to - but still inside those "safety margins" - the increased performance applied to later models without other supporting alterations - has revealed a complex list of contributory weak spots - each even closer to the limits - such that a particular mix of sometimes different circumstances can push the engine over them.

It is therefore a complex problem requiring lengthy investigation and testing, proving good well founded solutions while exposing some other inadequate ones recently coming to the market.

This 25,000 word section explains each issue with both simple explanations and analogies backed up with technical and scientific facts so anyone should be able to grasp the salient points and realise that there are several issues to consider and several modifications that are beneficial during a rebuild and not one simple fix. It also includes further new developments that may help owners avoid the problem.

Before readers start with responding with typical criticism – please remember that I don’t need to write this stuff for my benefit (I already understand it) and furthermore if I spent the same amount of time and effort it took to write this section on promoting our business in other advertising or marketing ways – it would certainly result in greater financial rewards. It has been written to inform others about the problem – what we know about it and what we do about it – to prevent misleading alternatives from confusing owners – empowering them to make informed decisions if they need help or advice.

Although many with more experience would not need to read the whole of it to understand what it contains, I do not intend to respond to any criticism unless every word has already been read.

Best regards and happy reading,

Barry Hart
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bazhart
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Joined: 20 May 2009
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PostPosted: Fri Dec 23, 2011 11:22 am    Post subject: Reply with quote

Sorry correct web address is www.hartech.org
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michelin
Indianapolis


Joined: 28 Oct 2010
Posts: 2382
Location: Liverpool

2006 Porsche 997 Carrera 2

PostPosted: Fri Dec 23, 2011 11:32 am    Post subject: Reply with quote

Appreciated Baz. I will read over Christmas and attempt to understand.
Thanks for taking the time.
Merry Christmas.
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MisterCorn
Dijon


Joined: 08 Jan 2011
Posts: 7331
Location: Nottingham, England

2004 Porsche 996 Turbo

PostPosted: Fri Dec 23, 2011 11:43 am    Post subject: Reply with quote

Yes, great work Baz, I look forward to an interesting read.

MC
 
  
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Tony 991S
Imola


Joined: 27 Nov 2010
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PostPosted: Fri Dec 23, 2011 12:16 pm    Post subject: Reply with quote

Just read section 5 worship
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GT4
Nordschleife
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Joined: 08 Nov 2008
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Location: Hertfordshire and Hampshire


PostPosted: Sat Dec 24, 2011 12:07 am    Post subject: Reply with quote

Baz, what specific benefit (or deficit avoidance) does fitting an additional oil suction line have on the cylinder head of bank 2 (cyls 4,5,6) of an M96 block?

 
  
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bazhart
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Location: Bolton Lancashire


PostPosted: Sat Dec 24, 2011 10:33 am    Post subject: Reply with quote

Sorry GT4 - switching off for a week now - but must admit that while I can always see exactly what the engineers had in mind in modifications to older engines (and agree with them) there are several technical issues like that in the newer engines that without a lot of time and effort to analyse - I cannot see the immediate reason for or benefit of - and often cannot either - after a big effort to understand.

This could be because they know better than me (or possibly the other way around) but the open deck cylinders and the original IMS bearing seals - were in that category - immediately seized upon by me as wrong and later modified by them or designed out in Generation 2 engines - so it seems I was on the right track then.

Within the section 5 (that this post was about) - there are numerous issues exactly in that category - that I have tried to be polite and modest about by not saying exactly what I really think about some of them (reading between lines might help here). It was not intended as a critical post but an informative one - I still love my 997 - great car!

It would be interesting to see what you think the benefits are - I will look into it in the future (and what you made of the section content).

Happy Christmas and by the way - you get a good mention in the section - and thanks once again for that help with the temperature gauge readings.


Baz
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PeterS
Fuji


Joined: 01 Nov 2009
Posts: 9293
Location: Solihull

2003 Porsche 996 Carrera 2

PostPosted: Sat Dec 24, 2011 11:15 am    Post subject: Reply with quote

Thanks for posting, and all the information.

Personally, I am going down the "be sensible with the warming up, ignore the doom-mongers, enjoy my car to the fullest"

If I am unlucky enough for it to blow then I will have no hesitation in bringing it to you for a complete rebuild with all your mods.
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churny
Montreal


Joined: 17 Nov 2010
Posts: 501
Location: Newcastle

2003 Porsche 911

PostPosted: Sat Dec 24, 2011 11:40 am    Post subject: Reply with quote

Hi Baz
As someone who has had the misfortune of scored bores, and benefitted from a rebuilt engine complete with all your improvements i have the following question.

If i have understood correctly and with cooling being such an important issue, would the addition of a third radiator ie gt3 etc be worthwhile.
My car is an anniversary with the x51 engine and the american version had the additional rad, i believe.
 
  
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GT4
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PostPosted: Sat Dec 24, 2011 1:30 pm    Post subject: Reply with quote

bazhart wrote:
Sorry GT4 - switching off for a week now - but must admit that while I can always see exactly what the engineers had in mind in modifications to older engines (and agree with them) there are several technical issues like that in the newer engines that without a lot of time and effort to analyse - I cannot see the immediate reason for or benefit of - and often cannot either - after a big effort to understand.

This could be because they know better than me (or possibly the other way around) but the open deck cylinders and the original IMS bearing seals - were in that category - immediately seized upon by me as wrong and later modified by them or designed out in Generation 2 engines - so it seems I was on the right track then.

Within the section 5 (that this post was about) - there are numerous issues exactly in that category - that I have tried to be polite and modest about by not saying exactly what I really think about some of them (reading between lines might help here). It was not intended as a critical post but an informative one - I still love my 997 - great car!

It would be interesting to see what you think the benefits are - I will look into it in the future (and what you made of the section content).

Happy Christmas and by the way - you get a good mention in the section - and thanks once again for that help with the temperature gauge readings.


Baz


Thanks very much Baz, I read the section (again) last night (having read the earlier version too) with the new lubrication improvements.

I have various aspects to discuss, but the additional jets you have been trialling made me think of the 996 X51 additional dual-chamber oil pump and specifically the bank 2 lubrication service.

Perhaps I will call in the new year (if GT4 doesn't sell, as much as Grant talked me out of a discretionary rebuild, I may just drop her up with you to strip and rebuild her Better...stronger...faster, a la Six Million Dollar Man!)

In the meantime, have a great Christmas Thumb
 
  
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GT4
Nordschleife
Nordschleife


Joined: 08 Nov 2008
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PostPosted: Sat Dec 24, 2011 1:47 pm    Post subject: Reply with quote

churny wrote:
Hi Baz
As someone who has had the misfortune of scored bores, and benefitted from a rebuilt engine complete with all your improvements i have the following question.

If i have understood correctly and with cooling being such an important issue, would the addition of a third radiator ie gt3 etc be worthwhile.
My car is an anniversary with the x51 engine and the american version had the additional rad, i believe.


The Anniversary edition was only ever fitted with the larger Turbo/C4S side rads (any centre rad you will have seen will have been in association with the Tiptronic box, requiring the extra heat-exchanger cooling as with any auto model).

How the cooling efficiency of both compares (triple rad vs larger double rad) is debatable (a simple surface area comparison may suffice, but technically the fact the side rads are mounted at an angle to incident air flow and are obstructed by the A/C condensers makes this comparison more difficult).

In any case, the GT2 models of course had all three (larger Turbo side rads and centre GT3 rad).
 
  
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bazhart
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Joined: 20 May 2009
Posts: 988
Location: Bolton Lancashire


PostPosted: Sat Dec 24, 2011 4:58 pm    Post subject: Reply with quote

Don't mind commenting on this one as I have given it so much though and testing already!

Cooling is much more complicated than people generally realise. It is all to do with coolant speed and cooling air speed really working through different mediums. The thermostat and engine revs between them contribute to coolant speed while the ambient conditions and car speed influence the radiator capability.

If you speed the coolant up - that is good in a total loss system but of course more speed reduces the amount of heat the coolant can collect as it passes through the engine and the time it is in the radiator to cool it back again. If it goes through the radiator too fast there isn't enough time to take out as much heat so it returns to the engine hotter.

However too slow a speed results in a higher temperature difference inside the engine (as the coolant has time to extract more heat) - leaving it to the radiators to have enough capacity to remove the heat afterwards.

Heat transfer is greater if the temperature differences are wider - but then that also means more of a temperature gradient. So if the coolant is slower - while it has time to collect more heat - it is also less efficient as the coolant is heating up and there is less of a temperature difference towards the outlet and less heat can be extracted.

The thermostat being on the inlet doesn't help because it isn't controlling the temperature inside the engine - only as it enters it. If the engine therefore gets hotter - the temperature on the way out of the engine will be hotter (i.e. the top of bank 2 where the scoring occurs). So it is then a question of if the radiators are efficient enough to get that extra heat out before the coolant returns to the thermostat. The thermostat is then slower to respond as it takes longer for the coolant to get to the front of the car and back again - than in a more conventional layout.

I think the main benefit of the extra radiator would be in very hot conditions when the air is too hot to do such a good job as it did when the air was cooler and the thermostat has fully opened but the radiator is unable to remove enough heat - so the returning coolant gets too hot before it even enters the engine.

In conclusion - if the system is well engineered in the first place and extra radiator should only be useful in extremely hot conditions - however - as you already have proven - the engines run hotter than the dashboard gauge suggests (and hotter therefore than engines used to run at) which is why the lower temperature thermostat - tries to compensate and also gives more time for the system to respond before potentially reaching the high temperatures it used to run at.

My experiences with the lower temperature thermostat suggest the system is more stable with higher coolant speeds (as that is what it does by opening the thermostat sooner) and this in turn reduces the temperature gradient inside the engine - so keeps the top of ban 2 cylinders cooler. Indeed in my experience so far my car and both our other test cars run much more consistent coolant temperatures and keep cooler when you floor it (what did you find out - was it similar?).

Baz
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GT4
Nordschleife
Nordschleife


Joined: 08 Nov 2008
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PostPosted: Sat Dec 24, 2011 5:07 pm    Post subject: Reply with quote

The third rad will mitigate heat effects of any excess load use, but only AFTER full thermostat opening.

Although for the standard tstat Porsche may prefer to characterise this by extreme high load uses like racing or use in very hot climes, sadly these high temperatures are also experienced in very normal driving - thus slowly killing the engine.

The low temp tstat thankfully completely changes this.

The rads determine the rate of maximum possible heat dissipation, BUT only once the thermostat is fully open.

So for a GT3 or X51 the low temp tstat is absolutely necessary to get any real benefit of the extra rad (ie in a temp regime PRIOR to one already starting to cook the heads!).

The standard tstat will render extra rads irrelevant below the NINETY NINE °C (205-210°F) fully open temp, the low temp tstat means the third centre rad can now start holding the temp steady or cooler after EIGHTY TWO °C (180-185°F) instead.

Assuming the standard rads are adequate, adding more and more surface area has little or no effect below fully open temp (by definition) as it is the thermostat that is the gatekeeper (obviously this is complicated by the entry mounting of the tstat).

As an analogy, assuming no excessive heat loss, doubling the number radiators in a house will have no effect in raising the room temperature if the thermostat is still set on 10°C.

Change the thermostat to 20° and all those extra rads will now heat the house quicker, but the thermostat always controls the ACTUAL temperature achieved.

The low temp thermostat is the way forward (and Porsche know this: fitting a 130°F/55°C to the racing Cup cars, where performance, and to a degree reliability, take precedence over blanket emissions controls).

Fitted mine over the summer, write-up here:

http://www.911uk.com/viewtopic.php?t=65932

 
  
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churny
Montreal


Joined: 17 Nov 2010
Posts: 501
Location: Newcastle

2003 Porsche 911

PostPosted: Sat Dec 24, 2011 7:34 pm    Post subject: Reply with quote

Thanks for the reply GT4 perhaps you can also clarify the 3rd rad as many sources including adrian streather state it was inc on the anniversary.
Having viewed a few anniversary cars when i was looking to buy one, none of them inc a 3rd rad so i assumed it was a USA spec.
 
  
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GT4
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PostPosted: Sat Dec 24, 2011 8:17 pm    Post subject: Reply with quote

Erm, didn't I specifically reply to that on page one? (the other post is for Baz)

Quote:
The Anniversary edition was only ever fitted with the larger Turbo/C4S side rads (any centre rad you will have seen will have been in association with the Tiptronic box, requiring the extra heat-exchanger cooling as with any auto model).
 
  
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bazhart
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Joined: 20 May 2009
Posts: 988
Location: Bolton Lancashire


PostPosted: Sun Dec 25, 2011 11:47 am    Post subject: Reply with quote

Thanks GT4 - as I often explain - I am not a technical writer just an engineer trying to share knowledge and experience - but I am pretty sure your last post just confirmed what my section 5 says - although probably more eloquently - I certainly agreed with it - so I think we are on the same wavelength.

I have tried to get an even lower thermostat manufactured but so far need to buy several thousand - which I cannot justify - hence the re-balance of the internal flow to compensate.

Both our racing Boxsters - although manual - were selected by us because they were originally built with a third radiator - if that helps confirm our position in arduous circumstances as we expect next season.

Baz
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GT4
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PostPosted: Sun Dec 25, 2011 1:29 pm    Post subject: Reply with quote

See if you can source the 55°C Cup tstat from Porsche "for analysis".

I will ask Porsche Motorsport for details and prices.
 
  
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bazhart
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PostPosted: Mon Dec 26, 2011 10:33 am    Post subject: Reply with quote

Thanks GT4 - I didn't realise they used that rating in the Cup Cars (have not yet been involved with one) however I am delighted with the news because it totally vindicates what I wrote about the benefits of lower thermostat settings for reliability and performance and also the recent enquiry I made for a thermostat to open at somewhere between 55 and 62 degrees for our race cars (which resulted in the huge quantity I could not justify ordering).

I must try and get one of those thermostats and see how to fit in in the race car 1st then a road car for test (we still have one of the test cars with temperature gauges fitted all over the engine).

However it also questions why such a high rated thermostat in the road cars?

A further point I should have made in the section 5 is that as the thermostat controls coolant speed - and as the coolant is branched off through several internal galleries and slots etc - it follows that as the coolant speed changes - the proportions that flow in different parts will actually vary too. Usually this will handicap the smallest outlets (like the slots feeding the cylinders) and benefit the largest holes (like the ones feeding the head which they made larger for later engines) = when the going gets hotter - the cylinders will get even hotter - weird when it appears they already know what to do when they go racing!

Baz
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GT4
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PostPosted: Mon Dec 26, 2011 12:34 pm    Post subject: Reply with quote

Three reasons:

Emissions, emissions and emissions.

Everything else is foregone: power, fuel economy, reliability/longevity.
 
  
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Red993C4
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Joined: 09 Dec 2010
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Location: S. Wales


PostPosted: Mon Dec 26, 2011 2:09 pm    Post subject: Reply with quote

bazhart wrote:
Thanks GT4 - I didn't realise they used that rating in the Cup Cars (have not yet been involved with one) however I am delighted with the news because it totally vindicates what I wrote about the benefits of lower thermostat settings for reliability and performance and also the recent enquiry I made for a thermostat to open at somewhere between 55 and 62 degrees for our race cars (which resulted in the huge quantity I could not justify ordering).

I must try and get one of those thermostats and see how to fit in in the race car 1st then a road car for test (we still have one of the test cars with temperature gauges fitted all over the engine).

However it also questions why such a high rated thermostat in the road cars?

A further point I should have made in the section 5 is that as the thermostat controls coolant speed - and as the coolant is branched off through several internal galleries and slots etc - it follows that as the coolant speed changes - the proportions that flow in different parts will actually vary too. Usually this will handicap the smallest outlets (like the slots feeding the cylinders) and benefit the largest holes (like the ones feeding the head which they made larger for later engines) = when the going gets hotter - the cylinders will get even hotter - weird when it appears they already know what to do when they go racing!

Baz


Before you go jumping to wrong conclusions, keep in mind that:
a) the Cup cars use completely different engines with completely different coolant canal "architecture", and
b) a racing engine's thermostat is virtually only ever closed whilst the car is still in the pit lane and unrestricted flow is called for any time the car is on the track, whereas road cars have to provide for the eventuality of granny driving to the shops in winter weather in cold climates.
 
  
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