DD GT3 RD

So went today and checked all the levels. Spot yesterday wasn't flat enough. Re scaled in a flat spot....much more balanced. Sorry for the mess up


With less than 1/4 tank of gas


And with me in the car

chuck911

Much better. Are these your scales then?

TRAKCAR

Not bad at all, great cars!

DD GT3 RD

Friend's scales I used

1analguy

They really did do an amazing job. The car is wider, longer, stiffer, more refined...and still noticeably lighter than the 997.2.

Over in the Corvette camp, we had all of the C7 launch hype about how they sweated blood over every additional gram that went into the car. They switched the frame to aluminum, switched to carbon fiber for large portions of the body, etc...and wound up well over 100 lbs heavier than the steel-framed C6. The lightest available C7 is now 200-300 lbs heavier than a 991, and it's tighter inside...with no back seats!

chuck911

Yeah, its a joke. The worst offender I've personally experienced was the Viper. 3400 lbs and there's hardly any room inside. Me and the guy I was instructing, we were crammed in there shoulders touching each other and the doors, legs all cockeyed crooked, feet crammed into this tiny space between the wheel well and the firewall. Helmets rubbing the headliner. Porsche somehow manages to make a light weight supercar with real useable cabin space, superb visibility in all directions, that's all-day comfortable and comes with plenty of storage space for multi-week trips for two. At 3150 lbs. Incredible.

008

Interesting. My first race car was a Viper built from a street car. With a full cage and a fully useable interior I was right at 3200 lbs. that was with a the old iron block as well. Remember the motor in the Viper is twice the size of the 911 and that's the heaviest single component. This last gen is a bit of a disappointment but that's mostly because the engineers weren't allowed to focus on weight reduction because Fiat mandated a protection of the F12 that required a gap in power to weight to any other car in their stable.

1analguy

The 991's weight is even more amazing when you consider that its engine is by no means a "light-weight". In a recent interview, a Porsche engineer (can't remember which one, but I'm sure you guys would recognize his name) stated that the 991 "has a 270kg lump hanging behind its rear axle". That's roughly the same as the current Chrysler HEMI V8...which has an iron block! The C7's LT1 is about 130lbs lighter, and the Corvette is still a lot heavier. I think it was actually Porsche, not Chevrolet, who was sweating blood over the grams.

chuck911

I've heard similar. They make the lighter car, they have every reason to make the lighter engine, yet they don't. It does seem strange. The only thing I can think of is there must be some inherent disadvantage, in terms of use of materials, in the flat six design. Its probably just a lot easier to make the more cubic shaped V8 light and strong, and with water cooling that's probably more efficient as well. Remember the flat six was initially air cooled, which in those days its shape was an advantage.

Even if I'm totally wrong though the fact is Porsche continues using a heavier design. One or two likely reasons. The for sure reason is because the flat six has such a low center of gravity. Look at a cross-section of a 991, the centerline of the crankshaft is almost on the same plane as the centerline of the axles! That's low! The other reason, its an inherently very smooth running design. Smooth running tends to equate to long life. But mostly I think its because it puts the weight down so low that an extra hundred pounds or so becomes a lot less important.

008

The big difference in weight of the engines is a pushrod design vs dual overhead cams in the heads. There are advantages to both but torque and power production per liter is easier with the latter so you can use a lower displacement engine.

1analguy

"Power per Liter" only has meaning in bench racing. Displacement is empty space. By definition, it weighs...nothing. Unlike all the extra cams, valves, etc. that are required to extract good power from a small-displacement engine, it adds comparatively little bulk or mass.

There's a "chicken and egg" thing going on here. Porsche wrings a lot of power out of comparatively little displacement because they have to. The European tax structure has artificially forced them into it. Getting the kind of power that they do requires a lot of added bulk and mass on their chosen flat six configuration...hence the disproportionate weight and physical size of the engine when compared to a larger-displacement, yet lighter-and-equally-smooth pushrod V8.

The different power characteristics of the two approaches makes declaring one design or the other to be "superior" rather difficult, but the lighter weight and gut-wrenching, pavement-rippling off-idle torque of a pushrod V8 does make it rather difficult to dismiss the design out of hand as being "inefficient"...

008

I agree, but for displacement weighing nothing. Increased displacement means a larger block, pistons, connecting rods, crank shaft, case, etc. The empty space is demised by the parts around it which are larger by necessity to increase displacement.

A smaller engine producing more power is one way to define efficiency but there are others. As I said both designs have their pros and cons and I'm not saying one is better than the other.

chuck911

I've always wondered why Porsche and other Euro car makers place so much emphasis on specific output. One RL'er said he got to talk with a GM engineer who was totally perplexed why Porsche (or anyone else) would care about specific output. If power, torque, mpg, weight and size are good then who cares if displacement is 3 or 6 liters? Well, now we know: GOVERNMENT!

All these years getting stomped in a straight line, consoling ourselves with being better at everything else, when we could have had it all. But no. Government got in the way. It figures. It so totally figures.

1analguy

All true, and yet a 7 liter Chevrolet LS7 V8 encompasses less overall volume and substantially less mass than a 3.8/4.0 liter GT3 engine, while producing similar power and more overall torque. Its simpler method of aspiration far more than negates any mass gain due to increased displacement. Even the much-touted lower center of gravity of Porsche's flat six is compromised by the physical reality of having to mount the engine high enough to allow clearance for the exhaust and the oil sump that they've oddly chosen to place under the engine. That LS7's crankshaft can be mounted quite a bit lower because there's almost no sump under it, while the engine's "V" configuration provides natural clearance for the exhaust.

Don't get me wrong; I love Porsche's cars just the way they are, and I'm not suggesting that they should start buying their engines from Chevrolet...I'm only suggesting that their cars would perform even better if they did. A 991 GTS at under 3000 lbs with GT3 (or better) power and near-981 weight distribution is an interesting proposition, no?

008

Yep, but I do love a motor that can spin to 7800-9000 rpms which you can't get with pushrods. When I had a cayman s and an e92 m3 I dreamed of having that incredible V8 in the mid engine chassis.