996 3.4 on Track Days

crash7 · 12 Feb 2020

MC :floor:

Vbox data makes for interesting reading, at Coombe for instance when in the car I would say that the exit throught the Esses and Old Paddock bend feels high G, the data states around 1G.

The exit of Quarry and Tower dont feel particularly high but the data says 1.2 - 1.5.

Its the mid-speed corners, circa 60-70 mph that appear to pull most force.

While it was a 3.4 I had an ex Super-Cup racer pedal a few laps, cornering force is similar, he was however, unsurprisingly, braver on the brakes!!!

DarthFaker · 12 Feb 2020

crash7 said:
I ran a 3.4 with FVD sump for circa 20 trackdays with no oil starvation issues, this was on sticky Yoko AD08R tyres and cup car suspension.

VBox at Bedford showed max Corner G at 1.3G, Braking at 1.6G - Coombe was simlar with 1.5G & 1.6G.

PCGB 996 C2 racecars run baffled X51 sumps on slicks and also do not suffer issues, some cars, not all, also run accusumps, none-run the additional X51 scavange pump.

When I rebuilt to a 3.7, not due to failure, I added the X51 scavange for extra piece of mind, the only item available from Porsche runs backwards, ask me how I know, as such the pumps are now NLA.

Many track 996's with no modifications at all.

I'd imagine PCGB are running race car oil (that doesn't foam) in their race cars, and probably running 997 straight oil return pipes inside the sump rather than the 996 swirl pots, this solution with the X51 pan is known to be fine. But I'm trying to find a solution that will work with a quality road car oil, if at all possible?

MisterCorn · 12 Feb 2020

We could start a whole new thread on this. As I understand it the swirl pots on the 996 are there for a reason, on the 997 it still uses swirl pots but due to a redesign of the scavenge system they are not located in the sump.

Given how the x51 sump and scavenge pump work, I can imagine that under the vast majority of circumstances they will work very well to cure the issues of the standard sump and lack of second scavenge (which not only contributes to oil starvation but also to possible hydraulic fracture on the tappet chest), however it is conceivable that oil could still build up in the sump away from the pickup over a period of time. Whether this can happen enough to cause starvation in any real world environment is open to question, but it is something that Dammit and I have some ideas for if required.

The worst scenario for the standard system is braking from high speed followed by a high g-force long left hand bend. The scavenge pump helps in both circumstances, the sump helps to some extent, but with the continuous sideways g-force there is a limit to what can be done as some oil is being pumped back in to the side of the sump which is not accessible to the pickup, so even with perfect baffles and trap doors there is a wedge of inaccessible oil.

MC

TV8 · 12 Feb 2020

MisterCorn said:
TV8 said:

At least your friend can run the 'backwards' pump from Porsche, on the Boxster it needs to run on the opposite bank so is correct for this application.

MC

Click to expand...

Thanks - one for him.

Backwards pump and Porsche seems an odd combination to me! More like the TVRs we are both used to

Dammit · 12 Feb 2020

DarthFaker said:
Dammit said:

IIRC the non Mezger GT3's are all running integrated dry-sump, as are all 991 and 992 911's.

It had issues in the M96 and M97, but you can also see a continuous evolution of the concept through the M9X series engines.

The external tank and associated plumbing represents complexity, weight and cost, and it has to be packaged- would be my guess as to why it was dropped by Porsche engineers.

Click to expand...

Correct, the Mezger M96/M97 engines and the 9A1 engines fitted into the GT3 and GT2 cars are true dry sump, so they do offer a proper motor sport engine, but it's a shame they're trying to peddle the Carrera as a sports car where it's probably less track ready than a MX5 in all fairness, I've never heard of anyone blowing a £150 MX5 motor on track and they're running slicks in some series. I know the flat six presents some interesting issues but these cars were never cheap and they're still not cheap even today they're still more than some new cars, I just think it's a poor showing from Porsche.

Despite this though, the chassis, brakes handling and general experience is worth it in the 996, just wish they'd not put a chocolate engine in the car.

9A1 is integrated dry sump, good article here: https://nnjr-pca.com/9a1-engine/

DarthFaker · 12 Feb 2020

I was under the impression the 9A1 engined GT3 and GT2 were true dry sump? correct me if I'm wrong but I thought they had an external oil tank thus true dry sump?

Dammit · 12 Feb 2020

I can't find any reference to a different system for the GT cars.

That's not to say there isn't one- absence of evidence is not evidence of absence, but it'd be a very significant reworking of the 9A1 and I would therefore expect to find some data.

If you find anything please add it to the thread- it'd be fascinating to know that they went that route.

Dammit · 12 Feb 2020

Although with that said a sudden thought and subsequent search for '991 GT3 oil tank" does indeed bring back a Mezger-esque tank, which does point in that direction. More Googling to come.

Dammit · 12 Feb 2020

More Googling done and I was 100% wrong, the GT3 adds an external tank to the system from the Carrera.

DarthFaker · 12 Feb 2020

Dammit said:
More Googling done and I was 100% wrong, the GT3 adds an external tank to the system from the Carrera.

I'm pretty sure the MA1.76 engine in the GT3 and GT2 has a lot of differences from the MA1.03 in the Carrera.

In the same way the M96.01/02/03/05 and M96.76 were very different indeed, but perhaps not to such an extent, ie the .76 is the designation for motorsports derived engines.

Dammit · 12 Feb 2020

It's been interesting doing some research, I hadn't really paid any attention to engines after the M97, so it made the time on the Eurostar pass productively!

DarthFaker · 12 Feb 2020

See attached.. Can see the tank at the rear of the engine.

Dammit · 12 Feb 2020

Forgive the phone format

DarthFaker · 13 Feb 2020

Well there we go! From the horses mouth, regarding dry sump.

I spent a bit of time yesterday on the phone to a well known specialist who shall remain anonymous, they were quite frank about the suitability of the M96 for track use, something along the lines of:

"If you don't want it to blow up and you can't afford the chance of it blowing up, then simply don't track it,. There's nothing you can do to resolve the inherent issues within the M96 for 100% reliable track use, buy a Turbo or a GT3 if you want to track it regularly"

Which I think is pretty sound advice, if your pockets are endlessly deep and you're racing the M96 in a race series such as PCGB I'd imagine a spare engine is neither here nor there.

My funds are not endless, I have a budget and I don't think the cost of a £9-12k rebuild factors into my costings for the odd track day a year.

Dammit · 13 Feb 2020

Did they say what they believe the unfixable inherent issues were?

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