When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I assumed smaller engine + more parts = overall the same.
All the Flat-6 9A1 motors weigh about the same from 2.7 to 4.0 liters. In the case of the Boxster/Cayman where they are downsizing from NA Flat-6 to turbo Flat-4, you would be correct. Hopefully, they'll actually shed weight. In the case of the 991, there is no weight advantage in going from 3.8 to 2.9 (or whatever), if they are staying Flat-6 (which it seems they are). Only added parts (turbos, intercoolers, plumbing, beefier drivetrain to handle the increased torque, better cooling, bigger brakes/wheels/tires, possible AWD on all turbo models?).
All the Flat-6 9A1 motors weigh about the same from 2.7 to 4.0 liters. In the case of the Boxster/Cayman where they are downsizing from NA Flat-6 to turbo Flat-4, you would be correct. Hopefully, they'll actually shed weight. In the case of the 991, there is no weight advantage in going from 3.8 to 2.9 (or whatever), if they are staying Flat-6 (which it seems they are). Only added parts (turbos, intercoolers, plumbing, beefier drivetrain to handle the increased torque, better cooling, bigger brakes/wheels/tires, possible AWD on all turbo models?).
And the case could be made that a 4.0 liter motor made from the same case as a 2.7, all else being equal (same oil pumps and con rods and crankshaft material and number of main bolts, etc.) would weigh LESS than the smaller 2.7, because it has bigger holes in it. More air, less steel.
No, larger diameter piston and cylinders would weigh MORE. That's pretty simple geometry.
The 9A1 does not have cylinders (of various sizes) bolted on like the old Mezger - they all share the same block (crankcase halves and 3 cylinders all one piece). There are bigger holes for the larger bore pistons. The crankshaft probably weighs slightly more on the larger motor, but the difference is negligible.
No, larger diameter piston and cylinders would weigh MORE. That's pretty simple geometry.
LOL, do you think they still screw jugs onto the case like in 1963?
They take a solid block of aluminum and they drill six holes in it. Then they partially fill those holes with pistons and con rods, but they mostly leave them open -- just air.
So if your "holes" amount to 4 liters, that's a good bit more air than the same block with holes that amount to 2.7 liters.
All in theory, of course; in reality they most likely beef certain components up for the larger displacements, perhaps have another oil pump, grind a larger crank, maybe bigger valves, etc, and I would bet the larger displacement MA1 motors actually weigh a little bit more than the smaller ones for that reason -- because all is not actually equal between them.
In fairness, they did do that up until 2012 for the top models (997 RS 4.0 was the last, I think).
With all due respect, the Mezger M64-derived engine in question doesn't have anything like the separate piston assembly of the air-cooled cars (and old VWs.) I have one sitting in my garage right now, a Turbo with an M96/70S (GT2) motor. It utilizes a one-piece cylinder head assembly (for each bank), with a one piece cylinder assembly (per bank). Yes, there are of course six separate drop-in cylinder sleeves or liners, but to the point of our friendly discussion, going with larger cylinders just means you drill larger holes in these one-piece cylinder assemblies.
Of course, this is all just banter -- it doesn't really make a 4.0 liter lighter than a 2.7; I'm just pointing out that the post-air-cooled motors go together differently than the old ones did, even when it's the M64-based model (Turbos and GT cars.)
Cheers!
Best picture I could find online -- scroll down to the exploded GT3 motor pictures.
Can someone explain why turbos are generally heavier?
So as noted, the extra stuff (exhaust plumbing, turbo, wastegate, high temperature and pressure rated intake, intercooler, additional cooling capacity, etc) adds quite a lot of weight. However turbo engines also increase the weight of the engines themselves, largely because they generally turn at lower revs. Lower revs for equal power means each ignition creates substantially more force, and thus every component needs to be beefed up to resist those higher forces. Outside the engine itself there are further weight increases that are often overlooked- since turbos generally produce more torque, they require transmissions with higher torque ratings which in turn weigh more.
In street cars it's neck and neck between turbos and NA in terms of power to weight ratio for the engines, and it generally comes down to how much attention is paid to weight savings.
Some examples of engines of similar generations come from BMW:
The 272 hp BMW N52 (3.0L normally aspirated) makes .76 hp per pound. The turbo version of the same engine found in the BMW 1M increases power to 335 hp, but weight is up too, the result being a nearly identical .77 hp per pound. The normally aspirated 4.0 L V8 from the M3, on the other hand, makes a substantially better .93 hp per pound.
Within Porsche most engines have pretty poor power to weight ratio, likely a result of sharing common parts and hence being overbuilt. The 2.7L engine in the Boxster weights very close to the same as the 3.8L X51 engine in the Carrera GTS as is shares most parts, but it makes nearly half the power. At the pointy end, however, things get decent: the Turbo S manages 1.16 hp per pound, one of the few Porsche engines better than the Z/28's pushrod V8, which incidentally also outperforms every BMW engine above. However both pale in comparison to either the Carrera GT's 1.28 hp per pound, or the 918's mighty 1.97 hp per pound. Putting this into perspective, if Porsche swapped out the Turbo S engine for the 918's, the turbo would both gain nearly 50 hp and lose 175 lbs from the back of the car.
As you can see, power to weight ratio generally improves as power climbs and engines get newer, so it's a little misleading to compare engines of different generations or outputs. However within motorsports some good examples can be found.
F1 V8 engines were an extreme example of a lightweight normally aspirated package: they were required to weigh over 209 lbs by the rules, and were also capped at roughly 750 hp with revs. Despite the rules the result was 3.6 hp per pound, and their low torque meant that gearboxes could also be spectacularly light, around 80 lbs for a seven speed.
The new turbo F1 engines are smaller and make less power, but they are roughly 100 lbs heavier than the old ones, both because of hybrid units but also because the lower revs and higher torques generated mean parts have to be beefier.
Bottom line high power to weight ratio engines of either type can be built, but head to head there are more examples of lightweight normally aspirated engines than turbo ones. With everything going turbo this will likely change, but this is generally due to movements of the market rather than engineering fundamentals.
^^ Great analysis. You must have had to do some digging to get the weights on all those engine set-ups. And yeah, as much as I hate to admit it (I have a running feud with my Corvette-loving-and-owning brother) the LS motors in modern Vettes are amazing powerplants for both their weight and their packaging size.
So as noted, the extra stuff (exhaust plumbing, turbo, wastegate, high temperature and pressure rated intake, intercooler, additional cooling capacity, etc) adds quite a lot of weight. However turbo engines also increase the weight of the engines themselves, largely because they generally turn at lower revs. Lower revs for equal power means each ignition creates substantially more force, and thus every component needs to be beefed up to resist those higher forces. Outside the engine itself there are further weight increases that are often overlooked- since turbos generally produce more torque, they require transmissions with higher torque ratings which in turn weigh more.
In street cars it's neck and neck between turbos and NA in terms of power to weight ratio for the engines, and it generally comes down to how much attention is paid to weight savings.
Some examples of engines of similar generations come from BMW:
The 272 hp BMW N52 (3.0L normally aspirated) makes .76 hp per pound. The turbo version of the same engine found in the BMW 1M increases power to 335 hp, but weight is up too, the result being a nearly identical .77 hp per pound. The normally aspirated 4.0 L V8 from the M3, on the other hand, makes a substantially better .93 hp per pound.
Within Porsche most engines have pretty poor power to weight ratio, likely a result of sharing common parts and hence being overbuilt. The 2.7L engine in the Boxster weights very close to the same as the 3.8L X51 engine in the Carrera GTS as is shares most parts, but it makes nearly half the power. At the pointy end, however, things get decent: the Turbo S manages 1.16 hp per pound, one of the few Porsche engines better than the Z/28's pushrod V8, which incidentally also outperforms every BMW engine above. However both pale in comparison to either the Carrera GT's 1.28 hp per pound, or the 918's mighty 1.97 hp per pound. Putting this into perspective, if Porsche swapped out the Turbo S engine for the 918's, the turbo would both gain nearly 50 hp and lose 175 lbs from the back of the car.
As you can see, power to weight ratio generally improves as power climbs and engines get newer, so it's a little misleading to compare engines of different generations or outputs. However within motorsports some good examples can be found.
F1 V8 engines were an extreme example of a lightweight normally aspirated package: they were required to weigh over 209 lbs by the rules, and were also capped at roughly 750 hp with revs. Despite the rules the result was 3.6 hp per pound, and their low torque meant that gearboxes could also be spectacularly light, around 80 lbs for a seven speed.
The new turbo F1 engines are smaller and make less power, but they are roughly 100 lbs heavier than the old ones, both because of hybrid units but also because the lower revs and higher torques generated mean parts have to be beefier.
Bottom line high power to weight ratio engines of either type can be built, but head to head there are more examples of lightweight normally aspirated engines than turbo ones. With everything going turbo this will likely change, but this is generally due to movements of the market rather than engineering fundamentals.
Great, simple explanation. Thanks. I guess Porsche is the king of "perfecting" the turbo. The obvious downside aside from the character of the turbo engine is the change in handling of the cars if you add 200 lbs. I know the Turbo is an amazing car, and I've yet to drive one, but it seems like to handle the added weight and maintain amazing handling, a lot of technology is used that detaches the driver from the car. Again, I base this totally on journalists and what people have said about things like PDCC on this forum.
There seems to be so much anxiety about the 991.2. I'm sure it will be amazing, but maybe less "pure".
There seems to be so much anxiety about the 991.2. I'm sure it will be amazing, but maybe less "pure".
If someone was previously in the market for a Turbo, it is a great turn of events (most of the character and performance for much less money). But for NA adherents, hopefully they will keep the GT3 and possibly the GTS as their NA stalwarts.
01-29-2015, 05:03 PM
