fxz

Mooty always the greatest! You re right
and i guess one of the very few with a non fake Mezger Porsche
in your garage

cebe

I will post this question here as it seems relevant to the 3D ...


I am not familiar with the homologation procedures of the GTD series and I was wondering (besides the marketing content of the official press releases by PAG): how much of the internal components of the GT3 R 9A1 engine are really in common with the 9A1 engine in the road-going RS?


Here on the European forums the consensus is that almost zero components are in common besides the bore-stroke measures ... Probably not even the crankcase.
This would bring support to the argument that the 997 GTs are the last ones with a racing based engine.


Difficult to find somebody in the knowledge without some skin in the game, either wanting to inflate the 997 GT prices or the 991 GT prices ...


But I was wondering ... at least the crankcase should be a production component in the GTD class, otherwise they are a prototype as much as a GTLM class RSR ...


Maybe someone on RL can shed some light.


Myself, I own only old AC mezger powered 911s ... so I do not care which GT3 goes up in price because of the alleged "racing connection".


I admit having an RS incoming on week 10, but planning to use it and drive it for substantial km: I suppose the racing results and connection will not make any difference by the time I may sell it a few years down the line: no garage queens for me, thanks.


Looking forward to hear some experts.

Ur20v

Even the 996/997 cases are not the GT1 cases- they are 'based' on them, so very few parts are likely to have any racing heritage from that car- they have heritage in the cups and other classes where 996 and 997's have raced.

Same for every car- hell they have raced BL Austin Maxis, Morris Marina's, Ford Zephers and Anglias etc- I seriously doubt there is a car that has no racing heritage since they first built cars! Simply there is no need to bleet on about it.

JasonAndreas

The 9A1-based RSR will have as much in common with the 9A1-RS as the 997RSR had in common with the 997 GT3. The architecture will be the same but actual common parts will be limited to things like fasteners and ancillaries. That is the way it's always been. ex. MY97 993-GT1

cebe

Thanks for your inputs.

I understand that the 991 RSR is a full prototype and the official bore-stroke number are different from the 9A1 in the roadgoing RS.

I was more interested to hear about the 991 GT3 R running in the GTD class, for which the bore-stroke official number are nominally the same of the 4.0 lt 9A1 in the roadgoing 991 RS.

Homologation info (or a summary) on the GTD rules would be helpful.

cebe

With a little research I found a GTD Technical Regulation (not sure if updated and current to 2016).

In point 6.2.1 it states:
Cylinder block, cylinder head(s), valve angles, number, material and location of camshafts: must remain original, as they are fitted on the production vehicle. The firing order is free.

I am not sure if it really means that a GTD car has the same crankcase and heads from the road-going model, but it sounds like it.

Zulu Alpha

Well that pretty much sums it up then. As per regs it seems that more than just the crank case has to be production.

But yeah, it does look like same as production as I can see from the working as well. It could mean in Porsches case that it is a possibility that it's based off a GT3 RS rather than a bored out Boxter 2.7L if you know what I mean.

JasonAndreas

Porsche always obtains a waiver or play around with a loophole. For example the last 911-GT3R followed the same homologation rules as you described above but as you can see...

Just in time

This probably explains why Porsche went all out with the crankshaft using an ultra expensive manufacturing process.