TomTomTom

As far as I know, the RSR has a 4.0l engine, but I could be wrong.

If it in fact has a 4.2l engine, there are some explanations:
1) They just can do it. And 4.2l means more power. If the WEC allows it, why not?
2) The RSR is actually not completely "no budget". The development of the mid-engine RSR was actually rather expensive for GT sport.
3) Adapting the race engine for 4.2l is something completely different than getting a new engine certified for the road.
4) In the end both engines may be "related" but they are still completely different animals.


If Porsche can bore out the GT3 engine to 4.2l they probably would do it, as the 4.0l is probably rather max'd out right now. If not, they just give the RS the same drivetrain as the regular GT3 and use more aero and more track focused suspension to differentiate.

GrantG

I think they just need to make a crankshaft with 5% more stroke (unless room for more bore) and add few more parts. Not that difficult for them.

Guest89

The RSR has a 4.0 liter 9A1-derived engine.

(1) WEC GTE homologation allows manufacturers to utilize naturally aspirated engines up to 5.5L displacement (e.g., Corvette) and forced induction engines up to 4.0L displacement

Current configurations:

Aston Martin: 4.5L NA 8 cyl
Corvette: 5.5L NA 8 cyl
Ferrari: 3.9L TT 8 cyl
Ford: 3.5L TT 6 cyl
Porsche: 4.0L NA 6 cyl

Nota bene: BMW races the M6 GTLM in the North American IMSA series, which borrows the rulebook from WEC GTE. IMSA allows BMW to compete with a car that is NOT homologated for GTE; the car utilizes a 4.4L TT 8 cyl engine.

Porsche had the opportunity to develop an engine with a larger swept volume, but they chose not to.

Also recall that Porsche could race any engine they want to in the variety of one-make GT3 Cup series around the world. Would be a perfect place to trial a 4.2L flat six in a race environment. But they chose not to.

What do Rennlist PTS and deviated stitching enthusiasts know that Porsche Motorsport just can't figure out when it comes to building and warranting a street flat six with displacement > 4.0L???

(2) I understand that there are budgetary considerations for everything that Porsche does, and your comment highlights my argument. The development of an all-new mid-engine 911 RSR was expensive. The program enjoys significant resources that they chose to deploy toward other avenues vs. ... developing a flat six with displacement > 4.0L.

(3) Yes it is completely different. But I'd wonder why they couldn't get it done in a Motorsport application if it came to the road car only... Recall 2014 991 GT3 fire debacle.

(4) Of course they are entirely different engines. The RSR engine would cost as much as a 991.2 GT2 RS if they would sell you one, which they won't.

I think they will continue doing what they've done in the race cars (even since 997 days). Keep the displacement at 4.0 liters and keep cranking the redline up while giving more aero, tire, brakes, etc.

gmgracing

Cough cough...

porscheflat6

wow looks and sounds amazing

porscheflat6

agree with your points

TomTomTom

I think the main reason for this is "Balance of Performance".

Why waste millions of dollars for a new engine and then thanks to the 50hp more, you have to take a smaller restrictor or more weight in the car...

I think your points are all valid but we have to understand that "race engines" are never "street car engines" - even the CGT engine needed some major adaptions (and had many fires during testing...).

It does not make too much sense to "show case" the engine....

All those "motorsport derived engine" stuff is marketing in my mind; but hey, I only spend in the street car engine development

JCtx

Supposedly, the 4.0L engine is maxed out at the bore, so any increase in displacement would have to be in stroke, which means less revs. With the previous GT3 fiasco, I don't think Porsche wants to push the envelope and risk having an unreliable engine. But the reality is if they want more power, and want to remain NA, it'll have to grow in displacement at some point. I'd like to see a reduction of weight instead. With the stratospheric prices charged for the GT2 (without a motorsport engine), it should have had a C/F tub IMO. It's hard to build a reliable NA engine if you push more than 125HP/liter with a 9K redline, but we'll see soon enough what Porsche has up its sleeve.

usctrojanGT3

Maybe they'll build the non-limited production .2GT3RS 4.0L and then do a limited numbered run of 4.2L...sorta like they did with the 997. Just throwing that out there....

GrantG

More stroke doesn't necessarily mean less revs. They just stroked the 991.2 GT3 to 4.0L and kept the redline at 9k. I think the bottom end of these motors is really strong. And adding stroke to 4.2L and keeping 9k redline will certainly make for some high piston speeds, but it might be within the engineering limits for this motor (if bore is truly at a max - and I'm not 100% sure that it is).

rosenbergendo

AP mentioned the 4.0 had seen over 600hp at over 10k revs. So they could just tune up the 9a1.5 in the .2 GT3.

Mvez

That's my thought. With the new solid valve train, they can add power pretty easily without more displacement. But honestly, who cares? If it's 4.0 or 4.2, it's still going to be great.

JCtx

The issue is not if it can be done (it obviously can), but how long it'd last. Remember it's a street car. At 9K on a 4L engine, you're already pushing the envelope on reliability, solid valvetrain or not. Same 9K rpm on a stroked motor would probably need stronger internals. A new longer block to accomodate a 4.2 with larger bores on a rear engine platform is probably a no-no as well. As somebody said, not much room to move on a 911 anymore. They'd have to go mid-engine, just like it happened with the RSR, even when Porsche refuses to call the RSR mid-engine. So guess Caymans are not mid-engine either, even when in both cases the engine is forward of the rear axles. Will be interesting to see what direction Porsche decides to go. But seems like the 911 platform is truly maxed out now.

Guest89

Torque is one key benefit of more displacement, ability to turn lower revs can help with wear and fuel economy, which can be meaningful over 24 hours of 80%+ WOT at Le Mans.

What were they going to do? Build a bespoke 991.2 run out edition carbon tub for a few thousand cars, max? How would that investment amortization make any sense? It would fundamentally alter the construction, engineering, and production of every single aspect of the vehicle. Porsche uses the parts bin to differentiate the 911.

It's not like a substitution on a restaurant menu FFS.

The RSR does not have a CF tub FWIW.

The quote to which the two of you are referring is attributable to FSW (unless AP said something similar):

I interpret his quote as referring to the race engine in the RSR, on an engine dyno, without the fitment of sonic restrictors utilized ostensibly to equalize performance through BOP. I believe that that the GT3 R (ie GT3 / GTD spec) redlines at 9,400 RPM (from memory); the RSR redlines well north of 10,000 RPM in current race trim.

As a side note, the change in exhaust layout came after one of the cars burned during 6 Hour race at Silverstone over Easter weekend, despite the heat shielding atop the diffuser - if I understood the crew chief correctly (was during a support race when we discussed).

(Excuse the typical Andrew Frankel speculative blather, pertinent part bolded)

https://www.autocar.co.uk/car-news/m...-design-change

MeanMachine

Will they offer a manual gearbox like they did with the GT3?