A few car questions....

[loic2003]

Originally posted by: Zenmervolt

Originally posted by: Sunrise089
Advantages of rear engine vehicles (and mid engine, since the engine is still behind the driver and no vehicle other than Porsche 911 is actually read-engined)

-better breaking
-less power loss
-better at the limit handling
-easier to have a neutral to rearward weight bias

Whoa, whoa, whoa there.

Rear engine cars do have better braking (note the spelling).

They do not have noticeably less power loss than other cars, this is more dependant on transmission internal design, not so much on engine and drivewheel layout. Losses on my 951 are less than 10% and it's front engine/rear drive. That low of a driveline loss is less than most front engine/front drive cars.

They most DEFINITELY DO NOT have better at-the-limit handling. RWD cars are EXTREMELY prone to sudden snap oversteer and are notoriously twitchy at the limit. Mid-engine cars a also very twitchy at the limit because there is a very low polar moment of inertia and thus very little keeping the car from snap-spinning. The safest, easiest, most predictable, and best setup for at-the-limit handling is front engine and rear transaxle, this distributes the weight evenly in both ends of the car making it very difficult to spin.

It is NOT easier to have a neutral weight bias with a rear engine. In fact, it is easier to have a neutral weight bias with a front engine (by relocating the transmission to the rear) than it is with a rear engine vehicle. You are correct regarding mid-engine setups though.

ZV

I disagree on some of your points.

I agree that potentially a rear-engined car could have better braking as more weight will be over the rear wheels which usually make up a much smaller percentage of the overall braking.
Twitchiness and snap oversteer are a given, although later models of Porsche have fancy suspension and of course the usual electronic wizardry which has limited this very much and you can drift one fairly comfortably these days.

As for the most predictable and effective engine setup for handling, it's surely got to be the mid engine rather than the front engine as you suggested. Having the engine in between the axles makes most sense, and allows for much better handling. If you don't believe me, check out the cars that are of the mid-engine/RWD/4WD setup: F1 cars, indy cars, supercars (eg GT40, most/all? Ferraris, Lambo, Bugatti, etc etc) even the fastest porsches are mid-engined.

If you believe that a front engine setup is fastest, I wonder why all the race cars (that are by nature, designed to be as fast as possible) have gone for a mid engine setup. Naturally race cars designed on road cars (eg touring, rally) are stuck with front engines.

Your axle and transmission will weigh significantly less than the hefty engine.

Another point to consider is that for handling you want the engine to be a close to the COG as possible. Kind of hard to describe, but if you imagine two chunks of metal, both weighing say, 20Kg. One is a very long shape, like a 2x4 but maybe 3m long. It has a pivot dead center. The other piece is a tall, thin-ish cylinder with an axle right in the center of the cylinder. If you imagine trying to spin each of the pieces one way then the other you'd notice that the cylinder with all the weight very central would be much easier to turn.

If they are both turning at 1RPM, the outer edge of the long piece of metal is going to be moving a lot faster than the cylinder. Bringing it up to speed will take more energy.

Not sure if that comes across too clearly, but basically you need the heaviest weight to be as central as possible, and not spread out. You'll see that in proper race-bread vehicles, even the suspension is brought in close to the COG to facilitate this.

Edit: a simpler example would be to imagine holding a 2Kg weight in each of your hands. If you imagine holding your arms out (ignoring the stress of holding them out) and trying to spin around on your feet, and then holding the weights in close to your chest and doing the same. Holding things tight and central makes it easier to turn....


enough of the analogies already!

 

[Fenixgoon]

Originally posted by: AMCRambler

Originally posted by: funboy42

Originally posted by: Kalvin00
Another point is that if the exhaust is under the car, guess where the exhaust goes when youre stopped? Yep, right up and into the cab.

WHAT they dont want you to die of CO2 poisoning?

Lol at CO2 poisioning. You mean CO poisoning. MON-oxide, not DI-oxide. Can you even get CO2 poisioning? Having too much CO2 and not enough oxygen in your lungs is called suffocation I think. Although that is effectively what carbon monoxide poisoning is. The CO bonds with the oxygen in your lungs and makes CO2 and you starve for oxygen. Poisoing is really a stupid name for it altogether!

if you breathe only CO2 will you die? absolutely!

 

[Evadman]

Originally posted by: AMCRambler

Originally posted by: funboy42

Originally posted by: Kalvin00
Another point is that if the exhaust is under the car, guess where the exhaust goes when youre stopped? Yep, right up and into the cab.

WHAT they dont want you to die of CO2 poisoning?

Lol at CO2 poisioning. You mean CO poisoning. MON-oxide, not DI-oxide. Can you even get CO2 poisioning? Having too much CO2 and not enough oxygen in your lungs is called suffocation I think. Although that is effectively what carbon monoxide poisoning is. The CO bonds with the oxygen in your lungs and makes CO2 and you starve for oxygen. Poisoing is really a stupid name for it altogether!

Yes. Read up on Apollo 13.

 

[jagec]

Originally posted by: Zenmervolt
The disadvantage of a rear engine is horrible handling (with rear drive) and lower traction (if rear engine and front drive).

Yeah, we all know about those horrible-handling Porsches...*sigh*

Originally posted by: loic2003
If you believe that a front engine setup is fastest, I wonder why all the race cars (that are by nature, designed to be as fast as possible) have gone for a mid engine setup. Naturally race cars designed on road cars (eg touring, rally) are stuck with front engines.

Your axle and transmission will weigh significantly less than the hefty engine.

Another point to consider is that for handling you want the engine to be a close to the COG as possible. Kind of hard to describe, but if you imagine two chunks of metal, both weighing say, 20Kg. One is a very long shape, like a 2x4 but maybe 3m long. It has a pivot dead center. The other piece is a tall, thin-ish cylinder with an axle right in the center of the cylinder. If you imagine trying to spin each of the pieces one way then the other you'd notice that the cylinder with all the weight very central would be much easier to turn.

Actually, for straight acceleration (drag racing), you DO want your engine at the front. But for better handling, MR is the way to go.

 

[Zenmervolt]

Originally posted by: loic2003
As for the most predictable and effective engine setup for handling, it's surely got to be the mid engine rather than the front engine as you suggested. Having the engine in between the axles makes most sense, and allows for much better handling. If you don't believe me, check out the cars that are of the mid-engine/RWD/4WD setup: F1 cars, indy cars, supercars (eg GT40, most/all? Ferraris, Lambo, Bugatti, etc etc) even the fastest porsches are mid-engined.

For a race car, yes, mid-engine is best. However, this doesn't work for road cars because of the twitchiness experienced at the limit. It's faster in the hands of an expert, but much more dangerous in the hands of an amateur. And that's all I was saying.

The safest, easiest, most predictable, and best setup for at-the-limit handling is front engine and rear transaxle

Nowhere in there do I say that it's the fastest. Just that it's safest, easiest, most predictable, and best. Now, I can see where one would take "best" to mean fastest, but I didn't mean it like that, I meant it in the sense of safety, ease, and predictability being worth more than merely "fast".

The very attributes that make a mid-engine car more nimble (low polar moment of inertia) also make it unstable at the limit and much more prone to snap-oversteer than a car with a front engine/rear transaxle (high polar moment of inertia).

As far as your comment regarding the weight of the engine versus the weight of the transmission, it's irrelevant. Corvette C6: 50/50 distribution by virtue of having a rear transaxle. Porsche 924/944/951/968: 50/50 weight distribution by virtue of front engine/rear transaxle. A car with a front engine and rear transaxle can easily be made to have 50/50 weight distribution, while it is very difficult to do the same in a car with the transmission bolted directly to the engine.

But that's neither here nor there. The basic point is this: I never said that front engine/rear transaxle was the fastest. Only that it was safer, easier, and more predictable, all of which make it the best in the hands of 99% of the world's drivers. The inherent instability of the mid-engine design make it faster at 10/10ths, but also much more of a handful. An average driver will not be able to take a mid-engine car to its absolute limits. A car with a front engine/rear transaxle layour is benign and predictable even at 10/10ths, albeit slightly slower than mid-engine configurations. However, an average driver can comfortably take a front engine/rear transaxle car up to its absolute limits.

ZV

 

[jagec]

Originally posted by: Zenmervolt
For a race car, yes, mid-engine is best. However, this doesn't work for road cars because of the twitchiness experienced at the limit. It's faster in the hands of an expert, but much more dangerous in the hands of an amateur. And that's all I was saying.

ZV

I agree, but who cares about lousy amateurs?

 

[Zenmervolt]

Originally posted by: jagec

Originally posted by: Zenmervolt
The disadvantage of a rear engine is horrible handling (with rear drive) and lower traction (if rear engine and front drive).

Yeah, we all know about those horrible-handling Porsches...*sigh*

The 911 is generally regarded as one of the most dangerous cars for a non-professional to drive. There are countless stories of snap oversteer introducing amateur drivers to the laws of physics and, not rarely, to large and immovable objects. The 911 is OK up to about 7/10ths and gets rather seriously dangerous between 8 and 9 10ths.

And for the record, the 944 Turbo easily bests the equivalent year 911 Turbo on the track, despite the 944 weighing more and having less power.

And about drag racing, actually, you want your engine and drive wheels in the back. More weight on the drive wheels means more available traction. The 911 Turbo is arguably the best design in the world for a straight-line 0-100-0 competition since the rear engine improves weight transfer both under acceleration and braking.

ZV

 

[jagec]

Originally posted by: Zenmervolt
The 911 is generally regarded as one of the most dangerous cars for a non-professional to drive. There are countless stories of snap oversteer introducing amateur drivers to the laws of physics and, not rarely, to large and immovable objects. The 911 is OK up to about 7/10ths and gets rather seriously dangerous between 8 and 9 10ths.

*shrugs*

I just figure that people who buy sports cars should take the time to learn how to drive them. If not, they should stick to their Volvos.