996 Turbo RMS

[raviramyead]

I have a frend who is considering buying a 996 turbo. Has there been any instances of RMS failure on the turbo or is this purely a C2/4 Boxster issue?

 

[NicD]

996 Turbo and GT3 are based on the GT1 motor, and doesn't seem have this "feature"

 

[gaxor]

I can confirm, RMS failures are not an issue with the Turbo - different engine

 

[glenn mcmenamin]

Nic,

Are you sure about turbo engine being based on GT1 engine ??

I thought that lump was specific to the GT3, and my turbo sounds nothing like my GT3 !!!




Gary,

How you getting on with the wheels/tyres i sold you ?


G.

 

[NicD]

Glenn,

not a wind up, I hope and someone else will fill in much more detail.

What I remember, the only way they got financial sign-off on the engine was to use it in both the 996 Turbo as well as the GT3.

 

[Guest]

Here are some details. To fully understand I need to provide some more detail on the M96/03 engine(3.6l) (which evolved from the M96/01 3.4l) but I don't have time to do this now.


996 ----------------------- GT2 ----------------- TT --------------- GT3 Mk1 ------- C2 (3.6)

Engine type --------------- M96/70S ---------- M96/70 ---------- M96/76 -------- M96/03
Cylinder bores ------------ Nikasil ------------- Nikasil ---------- Nikasil ---------- Lokasil
Bore x stroke ------------- 100 x 76.4 -------- 100 x 76.4 ----- 100 x 76.4 ----- 96 x 82.8
Capacity (cc) ------------- 3,600 -------------- 3,600 ------------ 3,600 ---------- 3,596
Compression ratio --------- 9.4:1 ------------- 9.4:1 ------------ 11.7:1 --------- 11.3:1
Valve gear ----------------- Variocam plus-----Variocam plus- --Variocam ------ Variocam plus
----------------------------------------------------------------------- Helical ramp type
Valves (4 per cylinder)
Diameter Intake/Exhaust -- 37/32 ----------- 37/32 ------------ 41/35.5 --------- 40.2/34.5
Valve lift Intake/Exhaust -- 10 & 3/10 -------- 10 & 3/10 ------- 11.5 / 10.5 ----- 11 & 3.6/10
Timing variation angle
Intake/Exhaust degrees ----30/0 -------------- 30/0 ------------- 25/0 ------------ 40/0
Valve opening duration at
1mm lift Intake/Exhaust -- 210&116/212 ------210&116/212 - --243/234 -------- 232/234
Connecting rods ----------- Steel -------------- Steel ------------- Titanium ------- Steel
Max. power PS ------------- 462@5700 -------- 420@6000 ------- 360@7200 -- ---320@6800
Max. torque Nm ------------ 620@3500-4500 - 560@2700-4600 370@5000 ----- 370@4250
Max. revolutiopns rpm ----- 6,750 ------------- 6,750 ------------ 7,600 ---------- 7,300

Twin mass flywheel -------- Yes ---------------- Yes -------------- Yes except CS-- Yes
Clutch diameter mm ------- 240 --------------- 240 -------------- 240 -------------- 240

Gearbox type -------------- G96/88 ------------ G96/51 ---------- G96/50 --------- G96/00


Note:
Valve lift has two numbers, since you have two cam profiles with Variocam plus on the intake (not GT3).
I don't have details for the GT3 Mk2.
The details for the GT2 are prior to the upgrade about 12 months ago (current one has about 11 bhp more).
Don't know what the X50 does for the gearbox, it is supposed to be strengthened, but I don't know the type number.


The GT3 was developed from the first evolution of the 996 Cup car, used from 1998 onwards. It is homologated in the FIA GT3 class and is the base for the 911 GT3R and 911 GT3RS racing models (and also the GT3RSR).

The 3,600cc twin cam, 24-valve, M96/76 engine of the GT3 is closely related to the turbocharged unit used in the GT1 which won at Le Mans in 1998, except that it is atmospherically aspirated through a two stage resonance intake system, similar to the installation in the 1994-95 M64/05 engine (993 engine, 996 C2 installation is similar, TT and GT2 do not use resonance system).
The other important differences (to the C2) are a 100mm instead of 95.5mm bore, a crankshaft (plasma-nitrided as in the racing engine) providing a 2mm longer piston stroke of 76.4mm (as in the M64 air-cooled engines), different camshafts with variable timing on the intake side and a higher 11.7:1 compression ratio.
Compared with the nitro-carbide treatment of the M96/01 and /02 (C2 3.4 manual and 3.4 tiptronic) and M96/03 (3.6), the plasma nitriding process of the crankshaft ensures a deeper hardened layer and a higher torsional resistance.
The variable intake cam shaft timing is not obtained by a special chain tensioner, as in the M96/01. A conventional, hydraulically operated helical ramp system is used. The intake camshaft is advanced or retarded, as on the M96/01 (the M96/03 uses a variant of the M96/76 Variocam plus (more compact version) which varies both intake and exhuast timing).
In this engine the intermmediate shaft driving the camshafts and the oil pump is gear driven and all four hollow camshafts are driven by duplex roller chains from the rear end of the engine.
As in the racing versions, titanium con-rods and big end bolts are used, which save 150g each, or 26%, and are good for upto 9000 rpm.

The GT3 mk1 was produced in two almost identical series from autumn 1999 to the end of 2000. In all 1,858 cars were made, excluding the racing versions which were continued after the end of production of the road version. In Europe GT3 models had to be registered before 1st January 2001 because they do not meet Euro 3 emmision regulations. (I don't know what they did for the mk2 to overcome this.)

The crankcase, cylinder blocks and wet Nikasil liners are identical for the M96/76 and M96/70.
Except for valve sizes, the cylinder heads of the M96/76 and M96/70 are the same.
the GT3, TT and GT2 have a separate external oil tank for the dry sump in front of the engine, rather than having it integrated into the crankcase.

The aluminium 8-bearing crankcase without the cast-iron main bearing supports of the M96/01 engine, is similar to the crankcase of the M64 air cooled engines.


The M96/70 engine powering the 996 TT was developed from the Le Mans racing engine, but it has smaller turbochargers, different camshafts and bore and stroke dimensions, identical with the GT3's M96/76 giving a capacity of 3,600cc. In contrast to the M96/76 and the racing engine, steel connecting rods are used, identical with those on the 993 turb, the comparatively low governed limit of 6,750rpm making the use of expensive titanium rods unnecessary.
As in the GT3, the valves are closed by twin spings (C2 is single springs), but the valve sizes are different. (For the GT3 I think two springs are used due to the rec limit, in the TT the springs are needed due to the air pressure from the turbos).
The standard turbos, with incorporated waste gate, are the same as the those used on the 993, except the flange is different, and are located closer to the exhaust ports (I believe).
The variocam plus allows for variable intake valve lift and timing.


The GT2 was developed as a turbocharged sister model to the GT3, but is largely based on the TT.
The main reason Porsche does not offer an RS version for racing (in the international GT2 class) is because the rear-engine layout does not allow the car to develop sufficient ground effect to be competitive in major international racing against possible future mid-engined competitors specifically designed for racing.
The M96/70S engine differs from the turbo's M96/70 engine only by the use of slightly larger turbos (I think these are the same as for the X50 upgrade).
The higher boost pressure (up from 0.85 to 1 bar) requires more efficient intercoolers (again I think these are the same as for the X50).
The variocam plus allows for variable intake valve lift and timing, same as for the turbo.


In general, whilst on the surface things seem quite similar, the more you dig, the more differences between the models you find. Some are quite subtle, but there has to be some justification for the price differences between the models (it isn't all just marketing).

 

[glenn mcmenamin]

Jeeeeesus Stuart !!!


I've got a headache after reading that lot !!!!

Thanks for the info though.

So, do we say the engines just share some common parts then ?

G.

 

[Guest]

Basically, GT3 and TT have same crankshaft, cylinder liners and cylinder blocks.
The heads are the same design, but the valves are larger on the GT3. Both use 4 camshafts, but the TT has the dual profiles of the Variocam Plus for the variable lift. The mechinism to cope with the timing advance differs between the two.
GT3 uses titanium con rods, TT uses steel (unless you get it tweaked, then with the rev limit higher you can go faster).
I don't know if the GT3 crankshaft and the TT are the same, I would expect the TT to be stronger (and heavier).
Chains and intermediate shaft design is the same on GT3 and TT, but I am sure they are different from the C2.
Intake system is different for the GT3, using the resonance system for better cylinder charging (2-3% more power I think), whereas TT just has pipes with turbos forcing the air in - no resonance needed []
Engine management systems are different, since boost pressure, charge temperature, traction control, etc. aren't an issue for the GT3,
Exhaust systems are different. GT3 uses a 30mm shorter cats with 3 exotic metals instead of 2 as in the C2, TT plumbing is competely different to C2, but quite similar to 993 TT.
Camshaft covers are aerodynamically optimsed on GT3/TT to improve airflow.

Engines on all cars are angled at 2 degrees (I think) to give some mild venturi effect for better stability.

 

[Guest]

So, do we say the engines just share some common parts then ?

Sorry, forgot to answer the question:
TT is a GT3 with turbos and intercoolers from 993, plus change the cams and swap the con rods. All big bits are the same.

TT gearbox comes from 993 GT2 G50 variant, GT3 is similar I think. C2 has a different box altogether, designed for the 996.
GT3, GT2 and TT can have all ratios, bar 2nd, changed, if you're bored and have some money to waste.

 

[glenn mcmenamin]

Stuart,

With all this said i have a theory !!!!

My Turbo cab produces 420 BHP and my GT3 380 BHP, the high figure
of the GT3 is partly due to its high revving ability i think ??

So, if the Turbo could rev to that figure by having the Titanium/lighter bits fitted, then
it could produce near 500 BHP ?????


G.

 

[Guest]

Yes.

The tuning companies get up to 750 bhp, by increasing boost pressure and squirting in more fuel, so peak torque rises from 560 Nm (or 620 for X50) to 700-800. The highest I have seen is about 850 I think.
They also raise the rev limit After changing the con rods) and change the engine fuel mapping. Then you get 750 bhp.

Power is just force x distance, so the higher the force (torque) or the higher the distance (revs at which the force applies), the more power you have.

Getting 750+bhp costs you £40K+, so it is not cheap. (G-Force said a rule of thumb is about £100 per bhp, I seem to remember.)

The low rev limit of the TT is just down to Porsche taking a conservative approach, and also their philosohpy of giving max boost at low revs, so you get mid range torque rather than top end power, which is more useful on the road.

Bhp is not the whole story - for the McClaren F1 the power of the car 627 bhp (I think) was a consequence of the torque they wanted. Given the weight, to get a certain acceleration, they wanted a certain torque, so the power was just a result of that - at least that's what Gordon Murray claimed.

 

[NicD]

Stuart,

fantastic detail!

Serious question, do you type your answers in each time, or do you have a copy you can copy and paste from?

 

[Guest]

Most posts I just type off the top of my head.
The longer ones (of which there have only been about half a dozen, the one above and two about 997vCorvette), I type in notepad since I can save it, then if the PC crashes half way through or the post fails I don't lose it, then just cut and paste. (I use notepad since it has no formatting embedded, wordpad or word has formatting that is a pain sometimes).

I don't have an archive of prepared answers though, just a couple of books and reasonable memory.

I wanted a 911 for about the last 18 years, but didn't think I could afford it or justify the cost. I bought a C4S by accident 2 years ago, without really knowing what all the models were. I had planned to become full knowledged up before buying, but it went a but wrong. I read all the magazine articles on them for 20+ years, but wasn't an anorak. I then thought I ought to read about what I had actually bought and what I now have.
I would like more detail, but I will either need the workshop manuals or to take one apart.

 

[NicD]

Stuart,

you give what I would consider to be definitive answers, a great amount of detail, just to enlighten.

I applaud you and wish you a great Xmas break

Hope to meet you in person at some stage - you share a similar taste in cars with Jeff (Admin), and me and Ali - it was a toss up between a GT3 or a TT, but for a variety of reasons (not least, the lower cost) the GT3 won out

 

[Guest]

I've seen you, so I know what you look like, but I have a low key approach []

I struggled to decide between GT3 and turbo, but due to the day-to-day usability and lack of track usage, the turbo won out.
GT3 pace complete with kitchen sink - best of both worlds.
"Less is more" is OK, but "more is more" is better []

 

[NicD]

Stuart,

please introduce yourself next time, I would like to meet you (though I too have a low key apprach, not so much a public person)

 

[Guest]

Nicked this from AMD's website (www.amdtechnik.com)
(996TT X50 produces 1.8 ft-lbs/cu-in @ 6000 rpm, turbos are a different kettle of fish [], hence the fudge factor applied to turbos of 1.4 if memory serves, to give equivalent performance. This is why Porsche used 2.14 litre turbo cars for competition in the 3 litre class.)
(3,600 cc = 220 cubic inches )

Horsepower and Torque:

Power is the rate at which work is done. When the engine torque is turning the crankshaft and power is being delivered, the resulting horsepower may be expressed as:

hp=2*pi*t*rpm/33000

which can be simplified as

hp=t*rpm/5252

where: hp = horsepower, hp
t = torque, ft-lbs
rpm = engine speed, revolutions per minute


This is a great formula. Basically it says that if you can keep the same amount of torque, then the more rpm you can turn, the more horsepower you get!

That's why Formula One and CART and IRL engines all turn incredible rpm. The faster the engine turns, the more power it can make (when it's properly tuned to operate at that speed).

Consider for example: a normally aspirated internal combustion engine typically produces about 1 to 1.5 ft-lbs of torque per cubic inch when it is properly tuned to operate at any specific rpm. With a 2 litre (1 litre is about 61 cubic inches) engine, producing 1.5 ft-lbs of torque per cubic inch, you would expect to get about 180 hp at 5200 rpm... but you will get a whopping 415 hp if you can get it to run at 12,000 rpm.

The 3.5 liter IRL engine is reported to produce about 650 hp at 10,700 rpm. That would be about 1.5 ft-lbs per cubic inch.

The Ferrari 3.0 liter Formula One engine is rumored to produce about 860 hp at 18,500 rpm. That would be about 1.33 ft-lbs per cubic inch.

And at the other end of the rpm spectrum, one model of the 360 cubic inch four cylinder Lycoming IO-360 aircraft engine produces 180 hp at 2700 rpm, which is 0.97 ft-lbs per cubic inch.

In general, production automobile engines that have a broad torque band will produce about 0.9 to 1.1 ft-lbs per cubic inch. Highly tuned production engines, such as the Honda S2000 or the Ferrari F50 are in the range of 1.1 to 1.3 ft-lbs per cubic inch. Highly tuned race engines such as NASCAR, IRL and Formula One are often in the range of 1.3 to 1.5 ft-lbs per cubic inch.