Johnny G Pipe

Hi fellers
Ruaridh's recent post ('a bad idea brilliantly executed') set me thinking, that I wouldn't really sound convincing, if I were asked the above question.

Maybe a stupid question, but in my experience it is important that stupid questions at least receive answers.. because as we all know putting an aircooled engine where the air don't reach, AND hanging it behind the back axle where it will always want to overtake you, is definately A Bad Idea, which would need some brilliant thinking to make it A Good One.

So is it all a traction thing? - no wheelspin on takeoff.

A handling thing? - light steering feel, and when used correctly it can slingshot the car thru and out of a corner

A traditional thing? - beetles had it, so why not continue it, all the way through to a 10 billion bhp gemballa 996 TT (not a lot else in common with the bug, admittedly)

A noise thing? - engine in slipstream

A comedy thing? - you can smilingly put your shopping /groceries into what everyone assumes is the engine compartment

Just wondering....

Adrian

Dear Johnny,
Traditional. When you are onto a good thing stick to it. The story is much more complicated than this really but think VW Kafer, think miltary. vehicles. What was lying around in Austria and Germany after WW2. What was available to work with, and you will begin to see why things happened the way they did. The first 356 was mid engined, the next one was rear engined and the rest was history,
Ciao,
Adrian
911C4

joey bagadonuts

The following excerpt was taken from the July 2002 issue of Automobile magazine. The piece was a sidebar to the cover story which compared five current model supercars from Lamborghini, Ferrari, Aston Martin, Mercedes-Benz AMG and Porsche. To demonstrate the superiority of the 911’s rear-engine design, the magazine’s tech editor compared the 3,600-lb Turbo to the Aston’s 4,000-lb Vanquish:

“Static distribution in the Aston Martin is 52/48 percent (front/rear), not far from the alleged 50/50 ideal. The Porsche, on the other hand, shines its rump at that standard with only 38 percent of its mass supported by the front wheels, leaving 62 percent for the rear…

All five cars are capable of accelerating at 0.6g. In this gas-pedal-down mode, the tail-heavy Porsche’s rear tires are pressed to the pavement by more than 2600 pounds—a dynamic load distribution of 26/74 percent. The same acceleration rate in the Aston loads its rear tires with less than 2400 pounds, a dynamic distribution of 41/59 percent. Even if the Porsche didn’t have all-wheel-drive to pass its 414 horsepower to the pavement, its rear tires are less susceptible to fruitless meltdown (spinning during acceleration) than the Aston’s. Dynamic distribution is why.

A heavy (static) rear bias is even better for braking, where a 50/50 dynamic distribution is desirable because all four tires are hard at work. Assuming a deceleration rate of 1.0g, well within the capabilities of all five cars, the “unbalanced” Porsche wins again by a wide margin. Its dynamic distribution is 60/40 percent versus the Aston’s 74/26 percent. (Temporarily swapping the Vanquish’s wider rear boots to the front would have shortened stopping distances, but we didn’t attempt that.)

And what about cornering? That’s a sticky wicket … Instead of solving complex equations here, the best insights come from turning the steering wheel and heeding the seat of one’s pants.”

Cupcar

JB's Post is interesting in that it covers the advantages of the rear engine design well. The article quoted leaves the cornering issue a "sticky wicket". When Porsche or any other company builds a real racing car, as opposed to a modified production car, they unstick the wicket with a mid-engine design. Note that the latest greatest Porsche Carrera GT is mid-engine. The low polar moment of a mid engine design can't be ignored.

The main reason for rear engine is tradition. In marketing the 911 as somehow better than the Boxster in design, Porsche has capitalized on this traditional value. Put equivalent engine and rear suspension in a Boxster and it would be no contest. Porsche has put lipstick on the pig, but hey I drive one!! <img src="graemlins/icon107.gif" border="0" alt="[icon107]" />

Dick Dawson

I think from a "best handling road car" point of view front engine/ rear wheel drive wins hands down.

That is a different question to most grip or best racecar set up! Certainly mid engined cars always used to be renowned as a bit tricky at the limit!

My understanding of why Porsche chose a rear engine was purely for the desire to have real 2+2 accomodation , as opposed to the laughable 2+2 opposition (try getting into the back of a Lexus SC430 for a laugh!).

The practical result is a car that has luggage room, a sensible driving position and reasonable acess to the engine.

I think the odd character traits the rear engine adds give the car its character, which brings me back to my start the "best" is not always the most likeable.

Christer

I don't know the reason but I will second that there is much less mass transference to the front under heavy braking and of course the traction is second to none. This in my view suits my driving style. When driving a 97 M3 last year I would always brake too late and get loads of understeer as the front got around 70% of the weight bearing down on them - whilst trying to break for the apex. Change my stylle? Never!

Let's not mention lift-oversteer. Having said that, the only car so far that has actually caught me out on any kind of oversteer was my BMW320 a couple of years back. I couldn't feel it go at all.

Cupcar

No question different layouts for different goals and what is good at the track may not work as well in the snow or on the road with luggage.

If Porsche put the GT3 engine,gearbox. suspension and brakes in the Boxster they would have my business for a pure sportscar though. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Mueller

Cupcar,

Dream on buddy, the factory will never build such a car for track use....it would dominate the 996 too much....

It would be one sweet ride however

Cupcar

Mueller-

Sweet dreams are made of this kind of this, who am I to disagree, everybody's lookin' for something....

You are right Porsche would never build it because they are locked into the 986 is "less than" the 996 box, too bad. BTW, if'n Porsche would ever make such a Boxster, it would have to be a coupe for me to be really there with the money. <img src="graemlins/yltype.gif" border="0" alt="[typing]" /> <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

joey bagadonuts

[quote]Originally posted by Cupcar:
<strong>it would have to be a coupe for me to be really there with the money.</strong><hr></blockquote>

Agreed. The folks at Ruf have already put together high-powered Boxters with 3.4 and 3.6 liter engines, but somehow the rag top doesn't provide the right mix--for me at least.

Emanuele Ferry23

Putting the engine on the back can't be defined a "bad idea". Rememeber that vehicle dynamics is a relatively recent discipline. In the early 30's, when the VW was developed there were only qualitative ideas such as "put weight on the back if you want to increase oversteer" and oversteer has always been considered preferrable to understeer by drivers. As a matter of fact the degeneration of oversteer is a loss of adherence on rear, non directional wheels which leaves still the possibility of controlling the car (you must be very quick and skilled indeed). This for sportscars. In Italy, when the 911 was developed in 1964 the most popular cars were FIAT 500 & 600, with engine and gearbox on the back. In a meeting at the university Dr.Ing Dallara (producer of chassis for Indy cars) said that FIAT engineer Giacosa was inspired by Porsche's works. I think there was also an economic reason: transaxles and transverse engines weren't so popular and putting an engine+gearbox+differential block on the rear was more economic than putting an inline engine on the front, driving a shaft thru the length of the car and putting differential on the rear. (99% of sedans of the period were this way).

pig4bill

Most of these answers look way too complex. I think it's a simple as the fact that the 356 was rear-engined, and it made things a lot easier to make the new car the same way. Not to mention less of a chance in alienating the Porsche loyalists. They've tried a few times to get rid of it. I've got an old road test on the SC where they say Porsche is convinced the SC will be the last 911, and the 928 and it's progeny will take up the flag.

Ruairidh

[quote]I think it's a simple as the fact that the 356 was rear-engined, and it made things a lot easier to make the new car the same way. Not to mention less of a chance in alienating the Porsche loyalists. <hr></blockquote>

Which I think brings us back to Adrians point about tradition and I also believe the initial reason for the 356 configuration was the influence of the VW (what was the VW Kafer - was that the original pre-WW2 Bug?) which gave rise to the "bad idea, brillantly executed" thought - 165mph car with the engine hanging behind the rear axles is great for traction but those laws of physics don't half catch up with that rear engine and short wheelbase fast in the =twisty bits and that is where I think the Porsche engineers have done a great job...

Incidentally that tradition thing is one of the reasons I like 911's. I like the fact that my car shows its direct lineage from this car of 50 years ago (the clipping is from the Autocar of 10-19-51) and yet is still one of the fastest cars on the road.

If you compare the Autocar clipping with my avatar you'll perhaps see what I mean.




Ciao

R