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Robertb
Dijon


Joined: 01 Sep 2003
Posts: 7120
Location: South Oxfordshire

2002 Porsche 996 Carrera 4S

PostPosted: Thu Feb 01, 2018 11:23 am    Post subject: Reply with quote

One thing I've never understood is the idea of a closed deck... isn't the cooling done via channels around the cylinders? If these are 'closed' then how does the coolant get about?
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 16515
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Thu Feb 01, 2018 11:40 am    Post subject: Reply with quote

Only the top of the deck is solid, ie. The liners are like a top hat and provide more support at the top where all the 'explosion' happens. Lower down is still cooled 'open deck' style. Suppose its a trade off against strength and cooling.
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EddieCRX
Trainee


Joined: 30 Jun 2014
Posts: 89
Location: Paris


PostPosted: Thu Feb 01, 2018 11:44 am    Post subject: Reply with quote

Are they using a machined interfaced fit support to close the deck?
I used this method in my race car, from 190hp to 600+ but on stock sleeves in my case.
 



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Robertb
Dijon


Joined: 01 Sep 2003
Posts: 7120
Location: South Oxfordshire

2002 Porsche 996 Carrera 4S

PostPosted: Thu Feb 01, 2018 12:35 pm    Post subject: Reply with quote

alex yates wrote:
Only the top of the deck is solid, ie. The liners are like a top hat and provide more support at the top where all the 'explosion' happens. Lower down is still cooled 'open deck' style. Suppose its a trade off against strength and cooling.


Ah cheers, that makes sense, particularly looking at the pic above.
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8319
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Thu Feb 01, 2018 2:18 pm    Post subject: Reply with quote

Good write up Alex and nice to have Hartech let you evaluate their new capacity engines. I assume you could have got more info but it sounds like the day was slightly overwhelming to take everything in.

The closed deck is just top hats fitted to the top of each bore letting coolant still flow around the cylinder walls. I had them fitted on my standard bores on one side that didn't have Nikisil liners fitted, come as standard if you do have Nikisil liners fitted.

See my top hats below,




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bazhart
Approved Trader


Joined: 20 May 2009
Posts: 955
Location: Bolton Lancashire


PostPosted: Thu Feb 01, 2018 2:48 pm    Post subject: Reply with quote

It was good to spend some time with someone that knows their stuff and get out for a drive!

Thanks various contributors for answering most of the questions for me.

The standard engine suffers because they made the engine bigger with a new type of cylinder bore surface that turned out to be less reliable than other previous solutions and then combined it with a softer piston coating - which made things worse. The more powerful the engine and the more that performance is used - the shorter they last.

We machine out the whole cylinder and replace it with a new one from Aerospace Alloy with a Nikasil finish (recognised as the best on the market and as used in GT3, turbo and all air cooled 911's for decades).

The standard cylinders are only connected to the outer casting in the centre (like holding a tube in your hand half way down) leaving the top and bottom free to move and distort.

True closed deck supports top middle and bottom and we do this with our replacement cylinders and yes all in machined interfaces.

The basic block is the same sizes it was when the first 2.5 Boxster engine was built so as the bores increased so the coolant space diminished. By using all alloy new cylinders with ribbed externals we have both increased cooling surface area and heat transfer - so no problems with cooling and we have been making and supplying these for 15 years now.

The cars run very well prior to re-map but we have re-mapped them for oversized engines to be on the safe side.

The bottom ends are reliable enough to take 3.9 cc and we do this (as already stated) with 100mm diameter pistons.

Because the time available to "suck in" air reduces in a straight line as the revs increase most engine designs have a kind of breathing limit at peak revs and create max torque lower down where their is more time to fill the cylinders.

An oversize engine exploits this benefit creating much better torque in the lower and mid range and better throttle response but at the top end max revs it is only a little more powerful because of the breathing limit. This makes a fast reliable engine.

I am preparing a long (and if I say it's long watch out) report on why torque accelerates engines and why a broader power-band (that you get with an oversized engine) will out perform a standard capacity one with typical tuning enhancements like porting, exhausts, re-maps etc,

Probably a month or so away yet but will answer all such questions and explain a few other issues.

We do not provide bhp figures as they are too easily adjusted by others but will eventually provide comparative graphs std to oversize. I prefer comparative road tests and the press will inevitably gets there hands on some to try.

There is a lot of new production to get in stock to handle the anticipated demand so although we are building some at the moment I think there will then be a delay before we can run the 2nd batch (while we work on standard rebuilds that are booming).

Our main effort has been in quality and reliability (as the performance just sorts itself out).

Thanks for coming over Alex - the 4 litre Gen 2 will perhaps be the next test drive!

Baz
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EGTE
Imola


Joined: 06 Jul 2015
Posts: 830



PostPosted: Sun Feb 04, 2018 12:30 pm    Post subject: Reply with quote

Now that's the one I want to see!
 
  
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Ghianightmare
Spa-Francorchamps


Joined: 25 Apr 2017
Posts: 343
Location: Dublin


PostPosted: Fri Aug 02, 2019 1:04 pm    Post subject: Reply with quote

Having clocked up a few hundred miles of spirited driving with my manual 3.9, I feel it appropriate to add my first hand experience to this thread.

The car is completely transformed. My 3.6 engine had been rebuilt 14,000 mile prior to me buying it and it was a good strong engine - albeit with a dodgy valve seat - and therefore I feel I am comparing a fresh 3.9 to a fresh 3.6.

The surge of power the Alex mentioned is very much there from 3,000 rpm. However my 3.9 engine has more torque from 2,500 than a standard engine had at its maximum - which is 260lbs and it pulls effortlessly in 4th from 2,000 rpm and it just keeps pulling as far as I am happy to go at this point which was very briefly to 6,500. It is a beast.

Where before in the 3.6 i would primarily use 3rd when driving b roads, no I can just leave it in 4th, and have a very useable power band.

I had a 991.2 GTS for a few days in the Swiss Alps last year. It is a fantastic car. Power whenever i needed it and with 450bhp it was beyond my capability. I loved every minute of it. I was dreading getting back into the 996 afterwards, but I was pleasantly surprised that I didn't judge my 996 based on thew 991 experience.

The driving experience in my 996 3.9 elicits the same smile as driving the 991. Power when you need it, the engine roars beautifully and doesn't sound like it is being overworked. It is a very useable power. It is just fantastic. I am delighted. I recommend.

P.S. While it is hard to judge the fuel economy due to the spirited nature of the driving I have to do to run it it, I think the fuel economy is a tad better when cruising...I will report back in a few months.
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