Why the engine so far forward?

November 7, 2006 1:06 PM

AutomobileFilter: I was looking at a few cars in the office parking lot and I couldn't help wondering -- why are Audis and Subarus designed with the engine so far forward? I've heard that both these brands of cars generally have the engine placed in front of the front wheels. Is there a technical reason for this, or does it come down to legacy engineering?
posted by clevershark to travel & transportation (11 comments total)

Technical reason: the engine is mounted longitudinally. You can: put the engine ahead of the front wheels so the front wheels' drive shafts come out the side of the transmission (Audi, Subaru); you can put the engine behind the front wheels and therefore the transmission ahead of the engine (Citroën DS19/DS21); you can develop some monkey motion and put the engine above the transmission, with the drive shafts coming out the sides of where the oil pan would be (there's some exotic that does this).

A Subaru backing up has its engine, transmission and (front) wheels in the same alignment as a VW bug has going forward.
posted by jet_silver at 1:19 PM on November 7, 2006

Cool! thanks!
posted by clevershark at 1:59 PM on November 7, 2006

To go with Jet Silver's explanation: the engine is moved forward to give more passenger room. The art of this in the automobile world is called packaging.

Some Saabs (not sure if that's what you mean by exotic) have a flat horizontally opposed engine with the engine above the transmission.
posted by Mitheral at 2:06 PM on November 7, 2006

Well, yes and no. My Subaru has a flat six (aka boxer) which is a horizintally opposed engine and there not mounted longitudinally.
posted by fixedgear at 2:33 PM on November 7, 2006

...therefore...
posted by fixedgear at 2:33 PM on November 7, 2006

Also, Subaru licenses technology from the VW-Audi group, so design similarities are not a big surprise.
posted by b1tr0t at 2:36 PM on November 7, 2006

ALL Subarus have boxer engines (four- or six-cylinder), which are not mounted transversely.
posted by Kirth Gerson at 5:29 PM on November 7, 2006

By "longitudinally" do you mean with the crankshaft in line with the front-to-rear axis of the car? If so, the Subaru engine is mounted longitudinally. My Audi's engine was an inline four, and was mounted transversely, but that was years ago..
posted by Kirth Gerson at 5:38 PM on November 7, 2006

Some non-Quattro Audi's are offered as less expensive front-wheel-drive models. The engine is placed slightly in front of the axles because the transmission sits transversely between the engine and the driver so the axles aren't at an excessive angle. If anything, the axles just reach downward a little from the transaxle. They should have to reach down AND backwards, straining the CV joints and reducing the range of usable motion in those joints.

Subaru's design emphasizes the low placement of their boxer engine to promote a low center of gravity (better handling) as well as a certain amount of passenger safety (the engine will drop beneath the cabin in the event of a serious collision). I guess the unique engine design, as well as the packaging of their transmission and all-wheel drive components (transfer case, etc) sets the engine a little ahead of the wheels.

But the reality is that the engines in these cars (or any car, for that matter) is only very slightly in front of the front wheels, if at all. Since many cars on the road are front wheel drive, the combination of motor and transaxle is mostly balanced over the wheels and any unbalance is the result of the intended driving dynamics set up by the engineers. Most usual (not high-performance) front-wheel drive daily-driver passenger cars are set up so that if you drive them really hard, they'll understeer rather than oversteer. I mean, the front wheels will loose grip and the car will plough rather than the back wheels loose grip and spin the car out. Understeer comes on gradually and noticably and is quickly solved by backing off the gas or applying some brake. Oversteer comes on very suddenly and the car is usally out of control before the driver can react appropriately. Oversteer is also much more the beast that dwells within the more powerful rear-wheel drive vehicles like a Crown Victoria and is less likely to crop up on something smaller like a Jetta.
Anway, car manufacturers don't want people getting too rowdy and hurting themselves with their products so they design their cars with a little understeer to sort of nag at you and prevent you from bawling your car all over the place. A few suspension tweeks and making the car balanced a little more nose-heavy does the trick pretty well.

Also, if you're wondering why these engines sit so far foward based just on a casual assessment of vehicle front end length rather than an observation of actual under-hood engine placement, I'll bet that most of what you're seeing is just crumple area and cosmetic styling. In most new cars, there's a solid few inches of space between the radiator and the very front of the grill. The way they pack the junk in under the hood, the bonnet of the car could be much shorter in general (look at the 2006 Honda Civic for instance) but many car buyers look at a short hood and get the impression that the car is necessarily insubstantial or there's not enough car between them and any potential accident they might have.
posted by Jon-o at 7:28 PM on November 7, 2006

Yah, longitudinal orientation means the crank axis is parallel with the direction the car moves. Some of the '80s Audis had transversely mounted engines but it is a bitch to get all wheel drive (AWD) with a transverse engine. Since both Subaru and Audi make a big deal of AWD, they compromise their designs in that direction. Therefore they tend to make their mountings longitudinal with the attendant forward mounting of the engine.

Offhand I can think of only Hondas that *might* have transverse engine mounting and AWD.

Alec Issigonis' original Mini design really made the transverse-engine / front-wheel-drive concept work. The Mini was all about efficient packaging. You give up a lot in packaging when you make the engine longitudinal, but there are a whole bunch of second-order compromises that get annoying when power goes up - like torque steer. Therefore, you will find that transversely-mounted engines are usually associated with lower engine power. When the power gets much above 200 HP, engine orientations tend to be longitudinal.
posted by jet_silver at 7:50 PM on November 7, 2006 [1 favorite]

Dodge minivans with AWD were transverse, they have a T off the final drive to drive a vicous coupler. Very slick as the transmission isn't changed, just one of the axle housings which bolt on.
posted by Mitheral at 7:30 AM on November 8, 2006