What so special about our engines?

2.7L or 3.4L what's cool about the flat-6? Of course they sound amazing, and I assume the flat configuration allows for some neat packaging nice and low in the car, but what else makes them truly special versus another 6-cylinder engine out there?

Forged crankshaft and pistons, dry sump lubrication, Lokasil cylinder bore liners, continuously variable intake and exhaust valve timing, cylinder-specific knock sensors, dual-coil valve springs... probably more. This is all very premium stuff.

How are other crankshaft and pistons made? I think this (OP) is a great question. I thought that the engines were hand-made, unlike most other engines. Then I was told by another member on this forum that they are not hand made and are assembled in a similar manner like all other engines.

The engine is not a true dry sump (ask anyone getting oil starvation at the track) and variable timing is not special anymore. Doesn't BMW do that and Honda. In fact, even MINI Coopers now have DFI. PAG is behind the curve. I dont know about you all but I got a 3.4L engine, not 3.2, so I guess mine is "special" Download The Cayman Club - Downloads - The New Cayman and the Cayman S and read about the engine.

Another benefit of horizontally oposed engines is lower vibration - due to the fact that pistons fire at the same time on opposite sides of the engine.

All "Flat" engines whether a Flat 4 in a Subaru or Flat 6 in a Porsche have the added advantage that you can keep the weight low in the car which aids the centre of gravity !!

The motors are basically hand assembled... the parts are pre-picked, and multiple pieces of the same parts are carefully hand-weighed so each motor gets parts that are identical in weight... this is from Porsche's Web site under the "virtual factory tour" section: Highly qualified personnel and premium components guarantee that every engine meets Porsche's high quality standards in terms of performance and service life. The pre-picked components are supplied to the various work stations in picking trolleys for precision manual assembly. Crankcase, pistons, oil suction pipe, water and oil pump, cylinder head, tappets, intake system and wiring harness are assembled with great care to form a finished unit weighing 200 kg. The following hot test is the final step in the engine production process. The engines are first of all heated up to operating temperature and then subjected to a functional test including full-throttle testing. Information in the form of up to 220 parameters is generated in this test of around five minutes' duration. brad

It's interesting to see how much flatter the torque curve is on the 2.7L vs the 3.4L which his a very pronounced rise upwards at 3,800rpm.

What I've never understood is why a Boxer configuration, whether 4 cylinder (like Subaru) or 6 (like Porsche ), sounds so different (i.e. better ) than a V- or I- configuration.

Watch how Ferrari makes its engines beginning at 45 seconds in: YouTube - Ferrari 456 GT - Making of

There's a "flat" engine that you missed. It's the boxer engine in a an R Class BMW . "Flat" engines are great for giving a low center of gravity.

conrods are cracked too! Racing tech! Yaay!

Unfortunately in the sports car world they're not that special. Quite a few others out there a reaching 100hp/ltr specific output which many consider a bench mark of efficiency. There are also many "lower" end models boasting complicated variable valve and cam systems on both the intake and exhaust side. Not to mention large (4+ liter) engines that outspin ours by 1,000+ rpm. As mentioned above, we also have oil starvation issues and accessory drive issues, RMS leaks still seem to be occurring, etc.

Question with regards to the variable valve timing: I notice that if I start off in too high a gear (say 2nd from almost a dead stop) the engine almost always responds fine, it's really hard to stall and it doesn't 'lug, lug, lug" it just pulls away smoothly. Is that variable valve timing looking after me?

No (Unless I'm missing something here about what you are saying) . Go read the Cayman tech documents in the files section. The variable cam comes on about 4200 when you feel the kick. Its like the old saying when the car "is on the cam". You shouldn't be lugging the car in first gear from a stop either. If anything, you'd be lugging it in second gear because the RPMs may be too low.

There are several benefits to the flat engine. Many of them have already been stated but I will recap and elaborate: 1). Lower Center of Gravity If you've ever tried to lift the cylinder head of an engine, you will know that they are very heavy. The cylinder head serves as the top of the combustion chamber. It holds many parts including the camshafts, valves, valve springs, lifters, spark plugs, Vario Cam Plus adjusters and cam sprockets. Though the head itself is made of aluminum, it is very thick and most of the other parts inside it are made of steel. So they are very heavy.​ If we compared the flat 6 to a straight 6 or even a V-6, the location of the heads would be very different. On a flat 6 those heads are down low and their weight lies in the same axis as the car's axles, or center of the wheels. On a V-6 or Straight 6, those weights (heads) are way up high, usually significantly above the center axis of the wheels. When people talk about 'center of gravity' this is what they are referring to.​ When you have a great deal of weight above the axis of the wheels, and you ask the car to turn or change direction, that weight wants to keep going in the direction it was traveling in before you requested a turn. In this situation, that weight will apply a force toward a straight path, which creates a torque inside the car toward the outside of the turn. This is called 'Body Roll'. A flat 6 carries it's weight much lower and therefore contributes far less to body roll than other engines.​ 2. Shorter, Lighter and More Rigid Crankshaft When compared to a straight 6 that has all of it's pistons in one line, a flat 6 has a much shorter crankshaft. Crankshafts are always made of steel so they are very heavy. Removing weight from the crankshaft gives an engine the ability to change speed more rapidly in the same way that replacing your flywheel with a light weight model would. Remember, the crankshaft is all rotational mass.​ Also, because the crankshaft is shorter it flexes less eliminating the need for a harmonic balancer. In comparison, a BMW straight 6 needs a harmonic balancer. A harmonic balancer is a weight connected to the end of the crankshaft opposite the flywheel. It's function is to absorb and resist the natural flex of the crankshaft that is caused by the forward cylinders. The fact that a Cayman does not need a harmonic balancer saves weight and rotational mass.​ Remove the harmonic balancer from a BMW straight 6 and you will quickly learn why it's there. You will not only feel a lot of vibration, but in time the crankshaft would likely fail.​ 3. Natural Vibration Cancellation Because a flat engine's pistons are pushing in completely opposite directions, they can cancel a great deal of their neighbors vibrations. Many in line 4 cylinder engines employ the use of counter balance shafts to achieve this. V-6s and V-8s will realize some degree of vibration cancellation due to their V's, but all pistons are still pushing down so they will still vibrate more than a horizontally opposed engine. Anyone who's ridden motorcycles can appreciated this. A 45 degree V-twin Harley will vibrate like crazy while a horizontally opposed BMW will be as smooth as silk.​ You're friend is mistaken. I've seen them being built with my own eyes, and they are built by hand. Take a real close look at those charts. The marketing folks a Porsche sort of duped you. The torque curves of the two vehicle are displayed using two different scales so that the torque curve on the S would look more dramatic. If you compared them using the same scale you would realize that the curve shapes are near identical, only with more torque across the rev range for the Cayman S. It's all about exhaust valve timing and the number of cylinders. For example, on an in line 4, there is an exhaust valve opening every 90 degrees of rotation. On a V engine the valves open in less symmetric intervals, depending on the angular spread of the V and the number of cylinders. On a flat 6, an exhaust valve opens once every 60 degrees of crank rotation. Piston size, compression ratio and RPM also have an effect on sound, but the standard flat 6 sound is a product of the valve timing and and engine configuration.

Having dual, or varying cams allows for dynamic state of tunes for given rev ranges. In this case providing more torque on the low end. I'm defining "lugging" in this instance as the feeling of little or delayed acceleration in low rpms when you apply the throttle as opposed to just tooling around at low rpms as mentioned in the break in procedure, which is the way I think the op meant it.

Firing order of the cylinders. The VW- Audi VR6 motors are similar so they sound very much like our flat 6's. Most inline 6's are also similar, the engine in my old E46 M3 also had that unmistakable 6 cylinder growl. On the other hand, V-6's are different and thus sound different. Some sound better than others, i.e. the 3.5 liter in the latest Nissan products, but it's mostly the exhaust configuration as opposed to inherent design factors.

Gator Bite, Thanks much for the excellent tutorial .... much appreciated ..... kind of reaffirms why i love coming to this Board :cheers:

another thing special - all flat 6 porsche have crossflow coolant flow... keep all cylinders and combustion chambers at the same, consistent level of temperature. if you take the 335, pump is close to cylinder 1, and cylinder 6 will eventually have big issues (gasket ??? )

I agree with all of the pros given so far about horizontally opposed engines but I think there is one being missed that is really the reason it is used by Porsche . It is the configuration that can be air-cooled most efficiently. While this doesn't apply anymore, I think that is the primary reason Porsche started using them in the first place. Or more correctly, the reason VW used them in the first place and then the first Porsches followed that design.

not only that. a V6 might not fit in the 911 rear, and definitely not in the space given to it by the cayman platform. V8 mid engine - R8 - the mid-engine part is TOO LONG. Flat6 has packaging advantages. Much shorter.

Not only are the connecting rods forged, but they are carefully weighed and matched with others of the same exact weight before they go into your engines as a matched set. This ensures maximum longevity.

Is the flat six a 4-stroke engine?

Yes. All modern automobile gasoline engines use the 4-stroke design.

If that's the case, in order to get the rated engine power of 295bhp, the implied volumetric efficiency for the flat six is 110%. Without forced induction, how can that be possible?

Wow, your questions went from 6th grade to undergraduate mechanical engineering in one post! How did you figure that the CS engine has a volumetric efficiency greater than 100%?

I am also curious how you are calculating horsepower and volumetric efficiency. Math please.

HP = atmospheric air pressure (14.7 psi) x compression ratio (11.1) x volumetric efficiency x engine displacement (207 cu in) x RPM@peak hp (6300) / 5252 /150.8 Substituting hp = 295 will give you an implied volumetric efficiency of about 110%. All other variables are from Cayman brochure. Atmospheric pressure is assumed at sea-level which is pretty standard.

Hawc, Great thread. Keep the comments coming everyone.:banana: I think the low cg of boxster design aids handling. I also think the flat configuration aids the physics associated with rotation and the combustion process. Please correct me!

being a mathmatician for many years and working with a wide range of formulas I have never come across this one. What is the source of this and how does this equate to hp

gr8 thread, I cant stop smiling ________________________ "Sir! We're surrounded!" - "Excellent! We can shoot in any direction!" A good car will get you from point A to point B. A great car... will just get you into trouble!

Hey, the more I think about this thread, the less I think the Porsche motor is special. Good - yes. Special - no. One reason I say this is because I bought a Honda Insight a month ago - a 2002 and I've been looking at it's technology. A few interesting facts about that motor for comparison against a Porsche motor: 1. Forged and carburized rods. 2. Motor can go above stoichiometric periodically, like 20:1 or something. 3. All cylinders are checked and marked at the factory for plug indexing. 4. Variable valve timing and lift (I think it has both) 5. As inline three cylinder motors are not inherently balanced it should use a balancer or such - it doesn't - it compensates for vibration by selectively generating or consuming power through the motor/generator attached to the crank. 6. It uses an exhaust catalyst that selectively captures NOx (produced through lean burn) and periodically richens the engine mixture to react them off. 7. Aside from the motor, the unibody is all aluminum, the body panels are aluminum or plastic, etc I'm saying this not to put the Insight on any pedestal but just to point out technologies that Porsche could still use to increase fuel mileage, power, reduce weight, improve handling, etc

It does have both, along with variable intake technology. I love my Insight... brad

I trust the seat of my pants. ZZZZ on all the other. JMO. More power to those who love math.

Simply amazing. Certainly, no one needs a car built with that kind of precision, but if you can afford it, it has got to be nice! You get what you pay for. Our beloved CS is not built with that kind of obsession to detail, but Porsches are not too far behind in fit and finish and attention to detail. This is why our cars cost so much more than the little econo rockets out there. They may be just as fast, but they sure ain't as pretty or finely built!