ypshan

Is there a site that I can read up on the pros and cons of the different placements of the engine?

I am interested to learn more about the benefits and draw backs of the Porsche rear engine design.

Thanks.

Minis-are-slow

Personally, the only advantage I can see with the rear engine design of Porsche/air cooled Volkswagen, is space-saving considerations. It's well-known that due to the rear engine, 911's tend to spin like a top. That's why the all-wheel arrangement was adopted on the turbos as I understand it. I feel that the mid-engine configuration of the 914/boxster is best for handling.

offroadr35

i don't think there is any question that mid-engine is ideal for a sportscar. Porsche has done an amazing job of compensating for what i feel is an inferior weight distribution.

-Steve

ypshan

I talked to a 914 driver once and he indicated that mid-engine cars have all the weight in the center. It's beautiful when you are under control. However, when you starts to lose it, you spin easily.

A front engine rear transmission car like the 944 would have most of the weight near the front and the rear. So it won't spin as easily.

Also if mid-engine is more ideal, how come Porsche has won so many races against all the competition?

JasonO

Kick me if I'm wrong, but aren't alot of racing Porsches midengined?

I thought that the GT1 of the 90's, despite being called a 911, was actually mid-engined...

Bob Rouleau

The rear engine is not all bad. It makes braking more efficient because the front tires do not overload as badly as a FE car. It also allows earlier or greater acceleration out of a corner because of the better grip on the rear tires. The 911 moto is slow in, fast out. Rear engined Porsches have an outstanding record in racing. The notion that the rear engine placement is "bad" is not correct. It has its strengths and weaknesses like every other engineerng compromise.

JeffES

Depends on how far "into" auto design you want to go.
A simple site is "howthingswork dot com" - gives the basics. For really good insights, you'll need to hit the printed page - read anything by Paul Frere on the topic for some great insights, and there are several books on driving sold by the Robert Bentley company.
What you'll discover is that each configuration has tradeoffs - the real interest is in how each layout has been handled by different companies.
J

Trojan Man

Well you got me on this one - I was always told that the rear engine design was superior to front engine for taking corners and that it is extremely difficult to fishtail a 911.

I have only spun out once on the track when my PSM & ABS were shut off and I trail braked hard into a corner.

That being said, the one time that I drove a standard Boxster, I was surprised that it could corner as well or better than my Turbo w/ techart coilovers. Mid Engine is definitely the best!!

JeffES

Trojan,
Whoever told you that is F****ing nuts! You wanna have some fun, find an early 930 with some wear on the tires - it's only slightly easier to spin a Cuisinart than the 911 (up to the 993 - then they sorted it out).

That being said - with a good level of skill, a driver can do what Bob said above, and be very, very fast indeed. In my experience, it's easier to spin my Boxster than the current 996.
J

Minis-are-slow

"In my experience, it's easier to spin my Boxster than the current 996"

Is your 996 awd such as a 996Turbo?
If so, that would explain why it's harder to spin then a 2wd boxster.
Not that I'm saying anything that evreyone doesn't already know.

ypshan

Is this the reason why 4wd on a 911 makes it harder to spin out:

On a rear heavy car, the centrifugal force is larger in the rear so the car is likely to over steer in a corner. The front wheels of a 4wd car are pulling besides turning so they are more likely to give and thus more likely to under steer. The two factors balance out and you have a better handling car.

I've heard people talking about 4wd is safer but slower. Is the above the reason?

Carlos from Spain

Like Bob says, each has its advantages and disadvantages. But if we are talking about strictly handling and without getting into RWD vs FWD vs AWD combinations, the mid-engine design comes closely followed by the rear engined, last in line is the front engined.

The advantage of the mid-engine is not the more balance weight distribution since they all are rear-weight biased around 40-60 just like the rear-engine (for handling you want rear weight bias, for grocery shopping you want 50-50 or even front bias: Front engine-FWD), the advantage is its low polar moment of inertia since the mass is closer to the center of the car, unlike the rear or front which is towards the ends of the car (like a dumbell) this enables the car much more agility in turning thats why it easier to spin it when you loose it too.

But have you seen many mid-engined cars with two rear seats? so the next best solution for a 2+2 seater car is the rear engine which while having higher polar moment of inertia like the front engined, it has more balanced weight distribution upon braking than the front engined and better grip upon acceleration due to rear weight bias. Its just that its a bit more difficult to drive and getting used to since its pivot point is more rearward than the front engined or mid engined so it tends to oversteer (with the common lift-off oversteer, etc) rather than the safer understeer, thats why some people fear it and not something that would appeal to mainstream market/manufactures besides not being that practical for multipurpose cars in its packaging, but nowadays with more consevative suspension designs, PSM, and AWD ect. the 911 is basically idiot proof and still has more personality than a front engine. You can't ask for anything more (well, actually, a stiffer and weight saving aluminum chasis, LSD compatible with PSM and more agressive suspension/chasis setup wouldn't be a bad start for the 997 )

Lets remember though than a car's handling characteristics are much more than engine placement so we are talking about small differences in the overall picture (drive, suspensions, chasis, aerodinamics, tires, differentials, steering, weight, electronics, and on and on...). For example, a front engined FWD car like a Mini Copper S Works can out handle a mid-engined & AWD Diablo VT going down a tight & twisty canyon



But, rear engine? can't be that bad if the rear-engined 911 is the most succesful racing platform in the history of motorsport

Jared W.

Haven't you ever heard the saying "Porsche rear engine. A horrible idea brilliantly executed"?

The pre-964 (964=1989 C4 and up) cars are a little tricky. Because the weight is in the rear, once you lose traction, the inertia just keeps pulling you around....

But, starting with the 964, Porsche began to set up the suspension to handle more neutrally. My 964 is much easier to handle when the rear end goes out than the 1988 and earlier models. My Dad's GT2 is even better (although the 456 hp makes it tricky sometimes to keep the traction to the rear wheels. That's another story).

It has been said before: under power, the rear of the car is "pushed" down, providing great amounts of traction, as long as you don't over-do it and spin the tires. This is why, when exiting a turn, you can put the power on much earlier in a Porsche: the weight of the engine, combined with the pressure of acceleration, keeps the tires connected with the road.

ebaker

Porsche has kept the rear engine design because the public wants the 911. It's what sells. They tried to ease into front engine but the sales were poor.
My 928 felt much more stable at fast highway speeds than my 996TT. The 928's high polar moment of inertia is much more confidence inspiring at high speed whether cornering or going straight. Mid-engine low polar inertia cars feel more nimble because they can pivot more quickly. In an autocross or hairpin curve you want mid-engine, in a bumpy 100mph corner you want a car with a hi polar moment.
Another point to consider with a tail heavy car. The 911/996's performance is limited by the size of the rear tire. A 50-50 weight distribution car have less load on the rear tires and can make use of large tires front and rear. A 3400 pound corvette or 928 has about 1700 pounds on it's rear tires, the 996TT h has about 2080.

ypshan

Does Porsche publish the weight distribution of their cars?