C4s " characteristics"

[peterfrost]

I have just joined the forum and gone through the post.
I run an 03 boxster s and 03 C4s.
-running in-I think youve got it spot.
I make a point of driving off asap and selecting a gear which holds rpm at 2500rpm whilst the engine comes up to temperature.
-oil consumption-mines at 3500 mls ,I think I used about 3/4 litre of oil(I had an oil /filter change at 3000mls.
I' ve found all the cars give an accurate correlation between dipstick and dash but only if the car is level and has stood a while .If you take the first reading from the dash countdown its usually a bar lower.
I invite comments on some difficulties:
My clutch felt OK at first but suddenly the pedal needed more effort /travel -OPC sorted this by bleeding and said the problem was air.
Unfortunately the problem re-occurred and has been bled again.
Its not got the extended travel but still feels a bit inconsistent to me.
Lot stiffer than the boxster S
Anbody had this problem?Seems much more likely to be slave cylinder problem to me.
Oil pressure-I was at the Ist combe track day when I noticed a dramatic fall in oil pressure thro' the chicanes. For me and my limited skills its about 5000rpm in 2nd gear.
The drop was from nearly 5 bar down to 3 bar which slowly recovered on the straights.
Needless to say this moderated my driving.(others had not experienced the problem)
Like Mr Cooke I have the 345hp 03s engine which having driven a couple of std cars certainly offers a lot more at the top end although it sacrifices a bit circa 3000 rpm .
I returned the vehicle to the OPC and had the precautionery oil/filter change(the oil had
got a bit black during the track session) they also checked the fault memory without finding anything.
I then tried the car on a lightly used open r' about and could repeat the problem.
I again contacted the OPC and agreed to bring the car back and take out a mechanic(sorry-technician).
The day came and it rained,it was damp to wet but the car repeated the problem.
It was agreed to refer the matter to Porsche.
I returned the car and the OPC had then been advised to remove the engine sump and check the oil pick ups for cracks.
This investigation was done and they found no faults so they tested the car with a manual oil gauge(along with another C4s and C2)they all did it I was told.
I was not convinced and received a letter from Porsche stating it was standard practice to carry out the dismantling AND " it is a characteristic of the vehicle that the oil pressure will be regulated during cornering"
Confusing is' nt it that they would get them to take it to bits when they knew it to be normal?
Apparently Porsche GB gave the 1st instr and Germany the 2nd.
Naturally I was' nt happy.The OPC then took me out in a 1700ml press C4s (with pccb brakes!)on pirelli rosso' s and nailed it to 5000rpm 2nd gear and with the extra grip again got the oil pressure to drop to 23/4bar.
Its not very nice to be pushing the car asking for power and the only thing stopping keeping the metal apart goes on holiday!
So there we are- they C2,C4 and C4s all do it and they reckon its OK(piston cooling is from 1.8bar)
Handbook says " approx 3.5bar at 5000"
I was a bit mislead because I had a session with bernard at Chobham and neither of us could get rthe C4S demonstrator to do it(but it did have n/std wheels with spacers)
I also asked a lot of people in the trade and they had no knowledge of it.
OPC says I' m the first one to spot it?
Any comments?
I read the blurb and thought these dry sump /track proven designs would be free from this.Seems its the return of oil via the swirlpots that limits flow.

 

[Gary Bullen]

As there are not that many 996 C4S cars around it might be worthwhile posting your comments on the USA site www.funcarsonline.com 996 forumand see if they have experienced this problem. Wish the OPC' s wouldn' t always say " you' re the first person to have this problem" . It always makes me suspicious!

 

[Diver944]

ORIGINAL: peterfrost

I read the blurb and thought these dry sump /track proven designs would be free from this.

I am probably wrong and have no experience of 996' s but am sure I have read in a magazine or online somewhere that the 996 is the first flat six engine that Porsche have produced that is NOT dry sumped.

The GT3' s and Turbos are, but the standard Carreras are not. I' m quite happy to be proved wrong because you know how reliable some of these websites are

 

[Mark_Bennett]

The GT3' s are not based on the same engine as the 996.

The 996/Boxster engines are described by Porsche these days as " semi-dry sumped" [&:]

 

[Guest]

Hi Peter,
Your oil consumption is about the same as mine (just under a litre after 4K).

No issues with my clutch. The travel, feel, and biting point are pretty much the same as new, and is consistent. I can' t compare it to a Boxster, but I wouldn' t describe it as heavy at all.

I don' t watch my oil guage, it tends to be behind the wheel rim for my seating position. I check it after starting and from time to time when going along, but not normally when going round a corner.

5000rpm in 2nd is about 50 mph. If I can find a suitable large roundabout I will try to see if I get the same thing. I' m going into hospital tomorrow for a minor operation, I' ll try to do it in the morning, but even so it' ll be a few days before I can get back to you.
I don' t have the engine upgrade, though, but I don' t think that matters since I don' t believe the oil system is changed.

On the Porsche website, all 911 models are described as dry-sumped (see excerpts below).
The GT3, Turbo and GT2 have an external oil reservoir. The Turbo and GT2 have 2 pumps in each of the heads and a 2 stage scavenge pump in the sump to send oil to the reservoir. The GT3 has 1 pump in each head and a scavenge pump in the sump.

However, the C2, C4, C4S have no external oil tank. Two pumps send oil from the heads (one in each head) to the sump, where a third pumps it around the engine. This is not my understanding of the definition of dry sump! I thought it meant that the sump was not used as the oil reservoir.
The oil goes via the two swirl pots. Maybe this is how they claim it is dry sumped, since the oil does not go directly from the sump to the oil feed points.
I could understand that the swirl pots could affect oil throughput, but why this would cause such a sudden effect at a certain speed, I' m not sure. It depends on their orientation and the whether they work like mini-cyclones.

I don' t believe there is an oil cooler on the C2, C4, C4S to affect the flow. I think on the others there is a oil/water intercooler, so the water circuit is then used to avoid having another radiator (but I am not sure of this).

I have included a piccy of the oil system from the GT3 (the Turbo page shows the same picture, but the turbo is supposed to have two oil pumps in each head).
I have also included a picture of the C2/C4/C4S engine (on the left) and the GT3 engine. The GT3 engine has the exhaust system attatched, the plastic intake ducting dominates the regular engine, but the pully centre aren' t the same, but these are for the ancilliaries.

It mentions in my handbook (p.6) that the fitting of racing tyres (e.g. slicks) for sporting events is not approved by Porsche. I presume this is not in the GT3 and GT2 manuals, don' t know about the turbo.
Very high cornering speeds can be achieved with racing tyres. The resulting acceleration values would jeopardise the adequate supply of oil to the engine. They refuse to accept any liability for damage occuring as a result of non-compliance.
I take this to mean that the standard oil system is OK for road tyres. With the 295' s on the C4S, and with the sports suspension, it could be that the margin is reduced, hence the issue you have seen, but that the values should still be OK. I would have thought that 3 bar was still plenty to ensure adeqaute oil provision.


As to whether the engines are different, it depends on what you mean by engine.
The cyclinder block appears to be the same for all 996 models, C2 to GT2. All are 3.6 litres, I believe they have the same piston diameter and stroke, the oil ways and water channels are most likely the same. From an economic standpoint, I wouldn' t have thought they would have multiple castings.
The differences occur in the inlet manifolds, head design, the cam profiles, the valves, the con-rods and balancing, and the oil management.

With the Carerra power upgrade the modifications include a new alloy induction manifold, cylinder heads, exhaust manifolds and camshafts, as well as revised engine management software.

In theory, I think a C2 engine can be converted to a GT2 engine by changing various bits. Aside from the block, quite how much is the same, I am not sure. Indeed G-Force Motorsport can do this for you for £17K.
I think I read on the GT2 the bores are Nikasil coated, but I don' t know if this applies to all 911' s (I would think so, since the alloy bores would wear too much).


=========================
C4S blurb (same as C2 and C4 pages)

Dry-sump lubrication ensures a reliable oil supply, even under race conditions, as well as helping to cool the engine.

Because today' s 911 engine is water-cooled, the quantity of oil required has been reduced significantly. As a result, the oil reservoir can now be accommodated within the engine, and there is no need for an external oil tank.

The oil is pumped from each of the cylinder heads directly into the sump, from where a third pump supplies it to the lubrication points in the engine.

While performing this circuit, the oil passes through cylindrical containers, known as swirlpots, where it is defoamed. This process ensures optimum lubrication, while maintaining the oil pressure required for the hydraulic tappets to function properly, a factor that is extremely important in terms of both performance and emissions.

Each piston crown is sprayed with twin jets of oil from the main supply, a solution that also helps minimise engine temperatures.

This system ensures a reliable supply of oil to both banks of cylinders, even under extreme lateral and longitudinal forces. In race conditions, that means unrestricted access to the car' s considerable power reserves.

An electronic oil indicator enables you to monitor the oil level without stepping out of the car. A conventional dipstick can also be found in the engine compartment.

===================
GT3 blurb


The dry sump lubrication system on the new 911 GT3 ensures a reliable supply of oil under even the most demanding g - force conditions.

... Each of the two cylinder heads is equipped with an oil scavenge pump driven by the corresponding exhaust camshaft, which, together with the two - stage pump in the crankcase, transports oil direct-
ly from the cylinder heads into the external reservoir.

The pumps are designed to create underpressure conditions in the crankcase. This reduces resistance on the pistons, thereby increasing effi-
ciency and thus power output.

A third pump in the crankcase supplies the lubri-
cation points in the engine with oil sourced from the external tank.

The result is consistent and reliable lubrication of the entire crankshaft assembly as well as each of the two banks of cylinders, even under the extreme gravitational forces encountered on the racetrack. Since all moving parts are lubricated at all times, the system helps extend the life of the engine.

=============================
Turbo blurb

Dry-sump lubrication with a separate oil tank contained within the engine ensures a reliable supply of oil to the 911 Turbo engine - even in the longest of high-speed corners.

Two oil scavenge pumps in each of the cylinder heads and a central scavenge pump in the crankcase return the oil quickly and efficiently to a separate oil tank. This configuration ensures that the oil level remains as high as possible at all times. A sixth oil pump supplies the lubrication points in the engine directly. Oil is defoamed by means of an oil separator integrated into the oil tank.

The oil level can be monitored from the cockpit using the onboard computer included as standard in the 911 Turbo. This solution is not only cleaner and more convenient for the driver, it is also more accurate than a conventional dipstick.

 

[peterfrost]

Thanks guys for your thoughts-I do not think it would be an issue with me if
I had been originally told they all do it. as instead OPC' s and others had said they were not aware of the characteristic.

Gary-you refer to C4s,it happens to all M96 engines and the previous 3.4litres I would imagine.(excepting the original 996 power upgrade did include an additional scavenge pump which was omitted from the 03s engine.
Its true when the 3.4 was introduced OPC' s were warned about non-standard tyre set ups negating warrantees.
The GT3,GT2 and turbo are completely different and exempt from this effect for sure.
I do not think I want to export the issue to US,they' ve got enough problems with sales as it is and I am not seeking to damage the brand.
Fact is Porsche are saying its OK so that will have to do me.
Had the characteristic been confined to the C4s then yes you could have said the turbo
running gear is a mis-match and dynamically too good for the engine,but I' m assurred this is not the case.
Interestingly when the telegraph reviewed the car sun 17/5 stephen bayley writes " :the only limitation ,one imagines,on cornering would be the effects of centrifugal force on oil supply"

Stuart-be careful on the highway,you' ll be going quite close to the limit and at speeds not anticipated if people are joining the r' about.Yes it is about 50-55mph @5000.
The reason I chose that was it corresponds with the h/book pressure and eliminates any
varicam effects.

 

[Kevin Cooke]

Peter,

Interesting, I' m normally to busy concentrating on line to watch oil pressure thru corners.

I presume the maximum ' g' will be felt at high speed corners like Fordwater at Goodwood. I' ll try and keep an eye on the oil pressure gauge when I' m at Silvertstone in July.

My track day tyres are Pirelli Corsa' s and the grip level is very high, I' ll check the handbook but I thought it contained the same statement as the Boxster regarding fitting of slick tyres for the track invalidating the warrenty, there is for sure wording regarding no speed events before 3,000km and certainly no caution on the warrenty about only using Porsche approved tyres. If my engine goes pop on a track day due to oil starvation I' ll be looking for Porsche to pick up the tab.

I' ll report back after my next track day.

Regards

 

[peterfrost]

Kevin,
I will also be at Silverstone.see you there.
I' ve only done Goodwood in a boxster,I do not think Fordwater would do it.
It was when we were at Combe(Ist track day when you were there)on the chicane) before Hammerdown that it was worst.
I think I would keep stumm about sticky tyres!doh too late.
peter

 

[peterfrost]

I have received an e-mail from Porsche GB " Whilst we recognise your comments that if the characteristic had been known to the dealership,investigations wouldn' t have needed to be made,we would still have to confirm that the process of ensuring that components were not presenting an issue would still have been taken."
I don' t know what it means,talk about keep digging when your in a hole.
Why can' t they make mistake!
Annoyed me!
I think they are saying even though the car was behaving normally they would still have taken it to bits just to make sure!

I have asked if they' re going to do it to all of them!
peter

 

[Helen Goff]

Peter,is this the dai_lemma reincarnated????

 

[ianbanneville]

Re the clutch problem, this is probably no help whatsoever, but anyway... I had a problem with my clutch pedal and a new pedalbox was fitted under warranty.

I had an odd feel through the pedal that made it feel as though it was attached to a dry cable under strain... stiction I guess you would call it. Made it feel awful in traffic!

Of course there is no cable... and one C2 I tried was the same. The guy at my OPC also reckoned my pedal was heavier than normal. The replacement cured it.

Regards

Ian

 

[peterfrost]

Ian,
re-your clutch,sounds like you describe mine,which OPC sorted it for you?
peter

 

[peterfrost]

helen,
No I am sadly not dai_lemma reincarnated,just a coincidence.

peter frost

 

[Helen Goff]

don' t be sad peter your name sake joined this forum as a respectable(ish) chartered Building surveyor.and is now a half qualified hairdresser and part time pheasent breeder.

be warned thats what this forum can do to you!![]

 

[peterfrost]

Helen,
Yes I can see just what you mean
peter

 

[ianbanneville]

(In reply to Peter re clutch)

It was sorted in Guernsey. The most difficult thing was trying to describe the problem! [] Another way I would describe it is like a " dry bush" in the pedal assembly. [8|]

Unfortunately on RHD cars most of the dashboard and interior has to come out (LHD the pedal box slides out but the heater matrix is in the way) so I thought long and hard about whether or not to go ahead.

Regards

Ian

 

[Guest]

I watched the oil pressure carefully on Monday.
I was driving quite hard but did not notice what you described.

What I did notice was that the pressure was consistently higher than the 3.5bar at 5000, more like 5. I get 3.5 much earlier.
I noticed the needle moving around a bit even when going at a steady speed, e.g. when going over bumps and taking minor deviations. It moved by +/- 0.25 bar at most.

Although going round a roundabout at 5000 rpm, I did not see the issue. Do you need to go round a whole turn or is 270 degress enough? Should you be right on the limit as well? Perhaps I was not cornering hard enough.

I drove it again today, but aside from a couple of traction control interventions, can' t go too mad round corners till I get the stitches removed and the bruising dies down [][] At least I am now off the tablets (you can' t drive for 48 hours after an anaesthetic and 3 out of the 4 tablets they gave me had warnings about driving) []

 

[peterfrost]

Stuart,
Thanks for your observations.Yes 5000 rpm will give 4>5 Bar,with a nicely warm engine.
The minor fluctuations you describe are more likely to be the variocam adjustments I guess,these are done and dusted at +4500 rpm under load.
To achieve the " characteristic" pressure drop you do need to get it dialled in with the front close to the limit and balanced with some throttle,as the turn in increases with the throttle and the " G" forces increase the pressure drops to 2.75-3 bar.
On the track I experienced it at abrupt changes ie chicanes rather than prolonged turns.
I can assure you it happens but with traffic I would' nt advocate trying too hard.
Regarding your comments on handling/track days.
I urge you to give it a go,your' ve got a fabulous and very forgiving car.I' ve done a couple and theyre great fun with no pressure.Its not racing and you go at your own pace.
Handling-yes I know what you mean,its not oversteer or slip because the PSM would intervene. Like you I found I would miss apex' s and the car will run wide when I first drove it gently on the road.Its the 4 wheel drive overun and not enough power.
I do' nt think I could do now,its second nature to hold a bit of power on,it disappears on the track when its just a matter of grip.
In fact I tried a turbo (they only had a tiptronic which I don' t like)general view-it seemed softer than the C4s to me,sure a bit more torque but not really as exciting.
Less tramlining on pirellis than my continental.
I put this turbi into manual mode and stuffed it into a couple of corners @ 3000rpm.Guess what it over-road dropped a gear to 4500 ish mid corner and powered round with perfect balance.Clever thing but who wants to be a passenger holding the wheel.
But at least its telling you how to do it.
peter

 

[Guest]

As I mentioned to Kevin Cooke elsewhere, I want to do a track day to find how hard I can corner on a smooth surface. I was strongly considering Silverstone since it has some nice straights, I have a reasonable idea of the layout, places seem to still be available and it is not far from me.
However, I have just had a couple of lumps chopped out of my lower back due to an infection. I don' t know if I will be able to make it, since it is only 3 1/2 weeks away. I would like to be in top condition. The rest of the PCGB events are pretty booked up and/or a bit of a trek. I see the quack on Thursday, and if things are looking good I will make a decision at the weekend (assuming any places remain that is).

 

[peterfrost]

Stuart,
Best of luck with the quack.
If you can make Silverstone I,m sure there will be newcomers like me and tuition available.
Thought a bit more about your 270 deg?360?
I had it happen after 180 deg,I think it unlikely to do it on one corner either on the track or road, as its seems to be a cumulative effect when a deficit builds up due to reduced flow back from the swirlpots.
On the track it takes about 3-4secs (I' d guess) of straight and level to recover to full pressure,on the road the recovery seemed quicker to me.
You really need an observer and driver to do it safely so I would' nt try.
peter