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So, they kept the same stroke as the 4.0L but increased the bore. This means we should keep our high 9k redline. The 3.8L became a 4.0L with more stroke - this time we can keep the crankshaft and rod length and change just the pistons (maybe even more compression to go with new injectors seen in the Speedster). 200cc only implies 5% more power and torque, but a bit more compression and better breathing (ITB's) could bump that slightly.
I think ~530ps and 365 ft-lbs would be possible in GT3 (and >545ps for GT3 RS).
That is exciting.
The only reason I would upgrade my current GT3 would be for a future NA-only GT3 with a significant bump in torque. I didn't think Porsche would ever make a bigger NA engine, but a 4.2L NA GT3 with >355 ft-lbs of torque would be very tempting!
Guess that takes care of all the naysayers that said Porsche couldn't/wouldn't build a 4.2L flat six.....
The aftermarket has been building 4.4+ liters for a while, and clearly Porsche could have gone to 4.2 earlier if they wanted to. Currently going past 4.2 doesn’t seem to make sense for them however with the possible exception of chasing fuel economy through lowering revs.
Assuming the RS gets a derivative of this engine (seems almost guaranteed) the 104.5mm pistons will equal the biggest Porsche has fit to a street car (the 968 used 104mm standard and 104.5mm rebuild pistons). Technically Porsche could also fit 105mm or larger pistons- the aftermarket has and they can take out additional material between the bores before they have thermal issues. Unfortunately they can’t get to 107mm without serious thermal stress, and that would be required to use bore and move up to 4.4 liters and the next displacement break under endurance racing class rules. A 4.3 liter engine is uninteresting to Porsche as is would be handicapped in its class, so a 105mm bore while possible isn’t likely unless it was combined with more stroke. Longer stroke would limit revs and thus is less interesting.
Thus this 4.2l makes a lot of sense on the 9A1, and I’m betting the next RS gets an epic engine. Given ITBs I suspect that with headers and exhaust in place of a particle filter it’s good for 600+ real hp on pump gas once the ECU is cracked.
The path from that point forwards for Porsche looks a lot less clear. ~105.5 x ~83.5 seems unlikely to me, but...
The aftermarket has been building 4.4+ liters for a while, and clearly Porsche could have gone to 4.2 earlier if they wanted to. Currently going past 4.2 doesn’t seem to make sense for them however with the possible exception of chasing fuel economy through lowering revs.
Assuming the RS gets a derivative of this engine (seems almost guaranteed) the 104.5mm pistons will equal the biggest Porsche has fit to a street car (the 968 used 104mm standard and 104.5mm rebuild pistons). Technically Porsche could also fit 105mm or larger pistons- the aftermarket has and they can take out additional material between the bores before they have thermal issues. Unfortunately they can’t get to 107mm without serious thermal stress, and that would be required to use bore and move up to 4.4 liters and the next displacement break under endurance racing class rules. A 4.3 liter engine is uninteresting to Porsche as is would be handicapped in its class, so a 105mm bore while possible isn’t likely unless it was combined with more stroke. Longer stroke would limit revs and thus is less interesting.
Thus this 4.2l makes a lot of sense on the 9A1, and I’m betting the next RS gets an epic engine. Given ITBs I suspect that with headers and exhaust in place of a particle filter it’s good for 600+ real hp on pump gas once the ECU is cracked.
The path from that point forwards for Porsche looks a lot less clear. ~105.5 x ~83.5 seems unlikely to me, but...
What are you talking about regarding endurance racing class rules?
GTE limit is 4.0L displacement for forced induction; 5.5L displacement for natural aspiration
Seems if you are looking to add significant torque this isn't the way forward for a road car. Small KERS boost will annihilate a 4.2l with probably 580hp and over 500tq.
What are you talking about regarding endurance racing class rules?
GTE limit is 4.0L displacement for forced induction; 5.5L displacement for natural aspiration
Up until 2017 the FIA used a table defining displacement vs intake restrictor diameter and vehicle weight for Balance of Performance. That has gone away in GTE in favor of adjustments based on actual performance data collected. That method is great but challenging for other series to implement, and many still rely on legacy BOP tables like the one below, which as of 2017 in Le Mans included a 4.2l class (the table below is a prior year).
This is why Porsche engines have all traditionally been slightly under a round number in terms of displacement. If this type of BOP table goes away entirely Porsche would be free to ignore these displacement limits, but I’m not sure if many of the other series Porsche would like their cars to eligible for can easily eliminate the tables- many don’t have enough cars of a given type or the data acquisition and analysis available.
Up until 2017 the FIA used a table defining displacement vs intake restrictor diameter and vehicle weight for Balance of Performance. That has gone away in GTE in favor of adjustments based on actual performance data collected. That method is great but challenging for other series to implement, and many still rely on legacy BOP tables like the one below, which as of 2017 in Le Mans included a 4.2l class (the table below is a prior year).
This is why Porsche engines have all traditionally been slightly under a round number in terms of displacement. If this type of BOP table goes away entirely Porsche would be free to ignore these displacement limits, but I’m not sure if many of the other series Porsche would like their cars to eligible for can easily eliminate the tables- many don’t have enough cars of a given type or the data acquisition and analysis available.
This new car will race in 3 series: FIA WEC, IMSA, ELMS
Neither WEC nor IMSA apply the older form of BOP, but I can’t say for sure regarding ELMS
This new car will race in 3 series: FIA WEC, IMSA, ELMS
Neither WEC nor IMSA apply the older form of BOP, but I can’t say for sure regarding ELMS
But remember- if history serves as a guide these engine dimensions will form the basis for nearly all Porsche 911 based competition engines going forwards, from the street GT3 and RS through to Cup cars on up. It makes sense that they’d choose an architecture competitive across the widest range of applications, and there really isn’t any reason not to given that there is no real advantage to going larger in WEC the way that BOP works.
Do you see another explanation for constantly stopping a few CCs short of a round number on all Porsche’s competition engines?
But remember- if history serves as a guide these engine dimensions will form the basis for nearly all Porsche 911 based competition engines going forwards, from the street GT3 and RS through to Cup cars on up. It makes sense that they’d choose an architecture competitive across the widest range of applications, and there really isn’t any reason not to given that there is no real advantage to going larger in WEC the way that BOP works.
Do you see another explanation for constantly stopping a few CCs short of a round number on all Porsche’s competition engines?
I see what you mean, and they’ve done that for awhile. Why not push it all the way to a round number, though?
I hazard that the reasons for going larger on the GTE car are torque/drivability, fuel consumption, stress (lower max RPM?).
The cup car could have an outboard V8 if they wanted it to - it only officially races in one make races.
There is much greater latitude for GT3 class engines - witness the 6.2L NA V8 Benz engine (where the road car has a 4.0L TT V8).
Last edited by Guest89; 07-06-2019 at 09:12 PM.
Reason: Typo
I see what you mean, and they’ve done that for awhile. Why not push it all the way to a round number, though?
I hazard that the reasons for going larger on the GTE car are torque/drivability, fuel consumption, stress (lower max RPM?).
I think the question is why bother to stop where they did, just below a round number?
There is likely no technical limit at 104.5mm bore. There are limits around both maximum piston diameter and clearance between bores, however neither of those have been reached at this displacement. Other street cars (Corvette LS7 for example) run significantly less clearance between bore and cylinder wall thickness, ditto piston diameter. So if displacement helps fuel economy, etc, why not go slightly further? Why not use something more like the 105.4mm bore the aftermarket has been putting into the Mezgar for years for example?
Porsche doesn’t stop just below round numbers on many of its street cars. The 2.7 liter 981 Boxster got 89 x 72.5 for 2.706 for example, or the 997 Carrera S 99 x 82.8 for 3.824 Liters. However those engines were never meant to go racing, and the GT cars are different:
996 GT3 100 x 76.4 = 3.600 liters
997.2 GT3 102.7 x 76.4 = 3.798 liters
997.2 GT3 RS 4.0 102.7 x 80.4 = 3.997 liters
991.1 GT3 102 x 77.5 = 102 x 77.5 = 3.800 liters
991.2 GT3 102 x 81.5 = 102 x 81.5 = 3.996 liters
992 GT3 RS? 104.5 x 81.5 = 4.194 liters
So all at or just a couple CCs under a displacement class break, and if you increase any of the last digits to the next number up they’d be slightly over. I’d suggest that’s no accident, and you need only to look at the various rules books for a strong hint as to why. A hypothesis certainly, but one that makes sense (to me anyway).
07-06-2019, 12:37 PM
