Questions about Transversely Mounted Engine & Torque steering

"zeontestpilot" (zeontestpilot) 05/06/2014 at 11:12 • Filed to: question

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Here is a rally mustang as a 'thank you' for looking.

First off, I want to say thank you to everyone that answered my !!!error: Indecipherable SUB-paragraph formatting!!! !!!error: Indecipherable SUB-paragraph formatting!!! yesterday. I enjoy learning more about cars, and since I'm new to the magical car-world, I genuinely feel oppo is the best place to ask car questions since it is a gathering of gearheads and I can get straight answers. So here are my next questions.

My first question is this, what is a transversely mounted engine? I looked online, I couldn't find an answer that I thought was suitable or plainly spelled it out. From what I gather, it is the placement of the engine for fwd cars. But, is it where the engine is off to the side, so the transmission can fit in the engine bay as well?

My second question is about torque steering. I took my car to the shop the other day (a '08 pt cruiser, I know, I'm sorry), and they said I had torque steering. I knew my car couldn't drive straight, but I didn't know what it was called (like I said, I'm new). The question is this; I thought you needed a big, powerful engine to get torque steer, don't you? Or is torque steering inherited with all fwd? On a related note, I saw something online that said torque steering happens when you have a transversely mounted engine, is this true?

I'm trying to understand my car more. When something goes wrong I like to know why its wrong, so I can approach the issue with some basic idea of whats going on. This helps grows my knowledge of the internal workings of a car, plus helps prevents me from getting swindled by a mechanic.

Thanks in Advance.

crowmolly > zeontestpilot 05/06/2014 at 11:19

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A transversely mounted engine is one where the crankshaft centerline is parallel to the "front axle". Or in other words the engine is side-to-side in the engine bay vs a longitudinal engine where it's front to back.

Transverse:

Longitudinal:

Regarding the transmission, usually it's a transaxle like this picture illustrates:

I do not know why the mechanic said you had "torque steering" as that seems like a misuse of the term.

Sethersm > zeontestpilot 05/06/2014 at 11:20

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Answer to question 1: A transversely mounted engine has its crankshaft running sidey-sidey instead of fronty-backy.

zeontestpilot > crowmolly 05/06/2014 at 11:24

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That's what I thought too, about the torque steering. I watch Top Gear (uk) a lot, and in one of the episodes they mentioned a fwd car had torque steering because of the big engine. They never really mentioned or emphasized torque steering until that point. So I assumed it was with bigger engines; not a 2.4L, 4 cyl, gas guzzler.

crowmolly > zeontestpilot 05/06/2014 at 11:30

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Torque steer is something transverse engine FWD cars can have, but it's more of a driving sensation than an attribute that a particular car has vs. one without it.

zeontestpilot > Sethersm 05/06/2014 at 11:30

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Correct me if I'm wrong, but the front to back would be a longitudinal engine, right?

zeontestpilot > crowmolly 05/06/2014 at 11:32

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A driving sensation? Like having the car pull left and right while driving?

crowmolly > zeontestpilot 05/06/2014 at 11:37

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The first gear part is all you need to see.

You can tell a Finn but you can't tell him much > zeontestpilot 05/06/2014 at 11:43

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Looks like your question on transverse mounting has been answered pretty well.

Like someone mentioned, the way the mechanic used the term torque steering seems to be incorrect. Torque steer is inherent in FWD cars, but is generally less noticeable in less powerful cars. Torque steer causes the car to want to steer to one side when you accelerate hard. For example, when taking off from a stop light and you hit the gas hard the car will pull to the right and the steering wheel will try to turn that way too. In cars like the Mazdaspeed 3 it can be pretty significant, but in most cars it isn't too bad.

zeontestpilot > crowmolly 05/06/2014 at 11:45

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Well, I guess maybe I don't have that then, at least, mine isn't that violent. My car, while driving above 50, the wheels *for lack of a better term* lazily drifts off to either the left or right, at a 80 degree angle, which would put me off the road or into the next lane if i didn't correct it.

crowmolly > zeontestpilot 05/06/2014 at 11:49

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That sounds like an alignment, steering system, and/or suspension problem. PT Cruisers have torque struts, maybe that's what your mechanic meant?

zeontestpilot > You can tell a Finn but you can't tell him much 05/06/2014 at 11:50

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Yeah, its becoming apparent that torque steering isn't the issue I'm having. Which bites because I would of had a name to go with the issue.

BoxerFanatic, troublesome iconoclast. > zeontestpilot 05/06/2014 at 11:57

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Torque steering is an effect that when applying throttle, and then the engine applies torque to the driveline and front wheels, the force applied to one front wheel is greater than the other, to the degree that the torque being applied to the wheel and tire against the ground gets transferred through the wheel and tire into the suspension hub assembly which causes the front wheels to try to turn themselves through their steering arc, sending that torque action backwards through the steering system, all the way back to the steering wheel in the driver's hands.

It only applies when the engine is trying to power the front wheels, and usually with high-torque applications. It would be far more likely to happen and be pronounced on a Turbocharged PT Cruiser than a lower-torque standard PT cruiser, but it is a function of any torque being applied, and transferred back into the steering system.

A steering issue that is constant, is much more likely to be a steering or suspension issue otherwise, possibly a broken part, or simply the suspension alignment that has gone out of spec, even from just hitting a pot-hole or other obstruction.

The effect is largely due to the differing lengths of the axle shafts between the transaxle's differential outputs, to each wheel. The transaxle is offset to one side of the car, due to the engine layout, and so the differential output is closer to one side of the car than the other. One of the axle shafts is shorter than the other. Those axle shafts have a certain amount of torsional rigidity, but torque will try to twist the steel of the axle shaft, and put stress on the joints. A longer axle shaft will naturally twist with less torque input, or twist further with the same torque input, compared to a shorter shaft that is more rigid. The tire at the end of the side with the shorter shaft will retain more of the engine's torque than the off-side with the longer shaft. The longer axle shaft will absorb some of the torque in that twisting action.

Some cars and trucks use that torsion effect on long steel rods as torsion bar suspension, rather than coiling those steel rods up as coil springs. Same effect, but used on purpose, rather than a side-effect.

It is only related to transverse front-mounted engines (typical front-wheel-drive layout) due to that asymmetry. Longitudinal drivelines tend to have symmetrical axles, the same length for left and right axle shafts, whether talking about a pickup truck with a live-axle in a rigid axle tube, (the inner axle shaft is still vulnerable to twisting, but they both twist at the same rate, being the same length.)

Subaru markets Symmetrical AWD... a longitudinal AWD drivetrain with symmetrical axle shafts, on both front and rear axles, that doesn't torque-steer. Subaru's 90's era FWD cars deleted the rear section of the driveline, and still had symmetrical front axles. There are very few other longitudinal FWD drivelines similar to that.

Mid-engined rear-drive cars with transverse drivelines (FWD system moved to the back of the car, basically... MR2, Fiero, Fiat X1/9, Lancia Scorpion, Lancia Stratos, Ferrari Dino, etc... Not Porsche/VW boxer drivetrains, which are longitudinal.) have similar torque disparity issues with unequal-length axle shafts, applying different amounts of torque to the rear tires... but the rear tires don't usually steer, so the suspension resists and stops the twisting action feeding back through the suspension, and torque differences on the rear axle are usually less pronounced, and usually only result in one of the rear tires losing traction earlier than the other, and spinning.

zeontestpilot > crowmolly 05/06/2014 at 12:03

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It could be. The place that informed me was Firestone Tires. My normal mechanic couldn't find anything wrong, on two separate trips.

On a related note, what is torque struts? Sorry for the fifty questions. When you mentioned it i quickly googled it, but for some reason no one likes to spell it out or put a simplified definition online about it. From what I discovered, its either a mount between the engine and the transmission, or its a mount that has something to do with the rear end of a car. Or am I confused and these are the same things?

PushToStart > zeontestpilot 05/06/2014 at 12:09

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It looks like other people have answered your question about what a transverse mounted engine is, but it doesn't necessarily have to be on a FWD car. Some mid engined cars (where the engine is placed in between the axles, typically behind the driver) are transversely mounted. For example, the Ferrari 328 has transversely mounted engine, but years later, when Ferrari replaced the 328 with the 348, they made the engine longitudinal, which it has remained ever since. There are plenty of other examples of this in mid-engined, RWD cars, but those are just examples.

With the engine transversely mounted, from what I understand, it's a little but easier to manage and distribute the weight in a smaller area, so the center of mass is closer to the middle, which improves handling. That said, that doesn't mean longitudinally mounted engines handle poorly, it just makes it more difficult for the manufacturer to get right so the car handles well.

zeontestpilot > BoxerFanatic, troublesome iconoclast. 05/06/2014 at 12:11

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Ha, awesome definition. I was wondering about AWD too. And from what you said about Subaru's setup (longitudinal, symmetrical axles), i really like that design choice. Though I'm wondering how other AWD vehicles are set up now. I don't want you to do all the homework for me, but do you know where I can find/research information about this kind of stuff? None of this has ever occurred to me, so now I wish to research more. :)

zeontestpilot > PushToStart 05/06/2014 at 12:18

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I didn't know that about mid engined cars, so thanks for the knowledge!

I'm thinking I prefer a long hood with a longitudinal mounted engine in it. namely because it won't be a pain for mechanics (or me) to fix something. I remember when my neighbor helped me heat up my car (during this past, bad winter), we popped the hood and he couldn't believe how jammed packed everything was in there. just trying to put a heater near the engine was a pain.

BoxerFanatic, troublesome iconoclast. > zeontestpilot 05/06/2014 at 16:12

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Regarding how All Wheel Drive works, I am not aware of a single source... but HowStuffWorks.com can sometimes be a good start, and then reading about individual cars, or types. But I can go through the main variants below.

Most new AWD cars on the market are basically transverse front-engine, basically FWD, with rear drivetrain additions added, with a third output added to the front transaxle's differential, like a power-take-off. Then either a viscous coupling or an electro-mechanical clutch pack (usually integrated into the rear differential) varies the engagement of the rear axle to assist the front axle. (and the front engine and transmission are usually more centered than that illustration, and the front axle shafts are usually less symmetrical. The rear differential unit is usually more compact, and the rear axles are usually more symmetrical than shown above, but the general idea is conveyed.

Sometimes the rear axle is dis-engaged completely, especially if tuned for fuel economy by reducing drag. Haldex is a primary manufacturer of systems like this, and supplies many different brands, from Ford to VW, and including transverse Audis, like A3 and TT. Transverse Audis still are labeled Quattro, for AWD, but it is actually VW's 4-Motion system, Saab's XWD, and almost all other transverse-based AWD on the market.

Subaru, Audi/Lamborghini, and Porsche, and most longitudinal-based AWD systems tend to use a slightly more involved setup, with a bit of variation for the mid-engined AWD applications.

Subaru and front-engined Audi Quattro have the engine in front of the transaxle. The transaxle houses the transmission gearbox, a center differential or viscous coupling in place of a center differential, and an internal shaft that drives an integrated front differential between the transmission and the engine, usually under, and just behind the clutch on a manual gearbox, or the torque converter on an automatic gearbox. The front differential drives the lateral axle shafts to the front wheels, necessitating that they are behind the engine's center of mass. This is why Subaru and front engined Audi AWD cars are significantly front-heavy. A second output from the center differential, extends back to the traditional rear-wheel-drive style rear differential and axle shafts. Usually with a center differential, the AWD is permanently engaged, and can be front or rear biased, adjustable-bias, or 50/50 permanent bias, depending on the specification of the center differential.

Longitudinal All-Wheel-Drive evolved and advanced (greatly) from typical 4x4 systems in trucks. 4x4 trucks typically have a gear-driven transfer case instead of a center differential, and drive the front and rear axles from that... but in the past they were either fully dis-engaged, or fully locked and engaged, where the front and rear axles could not operate at different speeds, which makes turning difficult if the tires are on a solid surface and can't slip. loose or slick surfaces allow that necessary slip... but a center differential is actually engineered to allow the axles to turn independently at varying speeds, and can be permanently engaged on hard surfaces. More modern trucks and truck-based SUVs are offering a 4WD-full time option, which basically is a viscous coupling inside the transfer case that emulates a center differential, and more resembles AWD... but still having the locked-together 4WD, and low-range reduction gear options as well.

That difference... the ability to or necessity of locking the front and rear axles together with a geared transfer case, is usually the main classification difference between 4-wheel-drive, and other forms of full-time or automatically computer-controlled All-wheel-drive, and why the distinction is usually made between the two.

BMW, Mercedes Benz, Chrysler, front-engined Porsches like Panamera and Cayenne are similar to that (new Macan is actually probably closer to Audi's front-engined Quattro system, like Audi Q5 with the front differential within the transaxle), with a center differential at the output tail end of the transmission, and divert a front-facing output shaft to a 'divorced' front differential that is a separate component from the transmission/center differential unit. To have acceptable weight distribution, the front differential is sometimes even pushed so far forward to be just in front of the engine block, or is otherwise built to drive one of the front wheels via a shaft through the engine's oil sump assembly, with the differential on one side, and another attachment joint for the axle shaft on the other side. This sometimes moves toward the necessity for asymmetrical front driveshafts but not drastically different lengths... and usually these systems distribute at least 50% of the engine's torque rearward anyway, and the torque-steer effect is minimized.

There are some special cases...

Porsche 911 Carrera 4, 4S, and Turbo models with AWD resemble Subaru and Audi Quattro longitudinal drive, just facing the opposite direction, with the engine off the back, rather than off the front axle, with the transaxle directly driving the rear wheels, and the front differential.

Lamborghini Gallardo V10 and Audi R8 V8 and V10 have a similar system to Quattro, with the transaxle behind the engine, and lateral axle shafts for the rear wheels behind the engine, but what would be the rear output shaft, is turned 180 degrees, and sent forward, past the engine block, to the front axle.

Nissan R35 GT-R has an aft-transaxle, like a mid-engined car, but the engine is not bolted directly to the transaxle at the back, it is mounted toward the front of the car... but the engine center of mass is behind the front axle line, for weight distribution... but it also means that there are 6 driven shafts under the car... engine to transaxle, transaxle to front differential, and four axle shafts.

Lamborghini V12 cars, as well as Bugatti Veyron 16-4 actually resemble other longitudinal AWD systems, but facing backwards. The engine is longitudinal, but the belt drives and accessories are at the back of the car, and the transmission and center differential unit are bolted to the engine, facing the front of the car, under the interior cabin. One output shaft goes to the front axle, the other output shaft goes around the engine to a rear differential just behind the engine block, driving the rear wheels.

Racescort666 > BoxerFanatic, troublesome iconoclast. 05/06/2014 at 16:14

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I think this should be a separate post.

zeontestpilot > BoxerFanatic, troublesome iconoclast. 05/06/2014 at 16:43

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You are freaking awesome!! That is an epic answer! :D

HammerheadFistpunch > zeontestpilot 05/06/2014 at 16:52

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Boxer did a great job, I also wrote something up about it a while ago if you want a different writeup

zeontestpilot > HammerheadFistpunch 05/06/2014 at 17:10

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Ha, I remember reading that, it was informative and a very good write up.

But I can't help but wonder, what is the point of awd? Is it just 4wd for cars, but with a center differential so all the wheels can spin at a different speed?

And I've also read that awd is good with traction (and possibly cornering), does this also include dirt roads? I was gonna research more on that question before I decided to ask oppo, but I've found zilch or seemingly biased info on this so far....

HammerheadFistpunch > zeontestpilot 05/06/2014 at 17:19

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its nuanced and books could be written about it, but here is the long and skinny of it. AWD in road biased vehicles has 3 main purposes:

1. to aid in winter/low mu traction situations w

2. to balance tractive forces for less violent weight shifts on high power vehicles when on power (i.e. the chassis is less upset putting 150 hp to 4 wheels at each corner vs 300 hp to 2 rear wheels during acceleration/deceleration events) and to keep power under check (more wheels, better traction for quick acceleration)

3. to sell cars to people in the snowbelt.

From a technical perspective. AWD=Permanent 4WD, the center diff solves the issue of axle bind so you get the benefit of 4wd without the wear and tear of a 50/50 locked split. AWD is great for getting going in slippery situations and can aid in cornering and deceleration if set up right; the idea being that any force applied through the transmission is divided by 4 instead of by 2 means better traction from a start, better management of traction in a corner (less likely that a single wheel will be overpowered and spin) and more force from engine braking applied to the wheels for more balanced deceleration off the brakes.

Did that sort of cover it?

zeontestpilot > HammerheadFistpunch 05/06/2014 at 17:26

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Actually yes it did. Thank you. :)

TwoFortified > BoxerFanatic, troublesome iconoclast. 05/06/2014 at 18:58

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FWIW (as one of the more famous performance AWD cars), The Nissan Skyline R32-34 GT-Rs use a system (called ATTESA) that, as far as I understand, works like the far right image on that small Subaru diagram. It's also worth noting, I think, that the R34 Skyline GT-R used an updated version (I'm not 100% clear on the changes) and the R35 GT-R uses a further updated version. Finally, the GT-Rs aren't the only cars that utilize Nissan's ATTESA tech (but they happen to be the coolest).

webmonkees > BoxerFanatic, troublesome iconoclast. 05/06/2014 at 19:11

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Yeah, if I drive the old Subaru for a few days I definitely notice a different dynamic in the 'motion' of the VW transverse engine. Kind of the way a gyroscope pulls.

With all the extra doodads they put on engines these days that kind of difference might not be even apparent.

BoxerFanatic, troublesome iconoclast. > TwoFortified 05/06/2014 at 19:50

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Nissan ATTESA stands for Advanced Total Traction Engineering System for All-Terrain. E-TS is for Electronic Torque Split, a variable engagement chain-driven and hydraulic-engaged clutch-pack split device, usually between 100% rear drive by default, and 50/50 torque split.

It is a marketing name for Nissan's AWD system, like Quattro is for Audi, and X-drive is for BMW.

I am not sure how much "all terrain" the system is calibrated for with the road-car specification suspension involved in the passenger car lines like Skyline and GT-R; but it has been available in many Nissans, and Infiniti models designated with an X in the name, including what was formerly known as the G37X coupe and Sedan, M_X, as well as Infiniti's CUVs like FX, EX, and JX.

It operates much like the right image in the Subaru diagram, much as BMW, Mercedes-Benz, Chrysler RWD-based cars, and Porsche front engined cars. Technically referred to as a divorced front differential longitudinal AWD system, since the front differential is not part of the gearbox casing, and as such, the transmission is not a transaxle. The torque split device is a computer-controlled clutch pack, more aggressively tuned, in the GT-R applications.

Most Infiniti/Nissan longitudinal AWD applications, like BMW X-Drive, and M-B's AWD systems, (except new transverse CLA-based models) actually are RWD by default, and the center torque split device engages when rear slip is detected... kind of like an inverse of Haldex, which is often FWD by default, with rear assist when slip is detected by the ABS wheel speed sensors.

Part-time AWD systems like that are often marketed as more fuel efficient, due to the capability of being completely dis-engaged when not required, reducing some mechanical drag on the engine's output, but also tend to only be able to react after slip is occurring, not to actively prevent slippage on loose or slick surfaces by being already engaged before slip occurs.

TwoFortified > BoxerFanatic, troublesome iconoclast. 05/06/2014 at 20:02

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Sounds about right to me (not that you need my validation; looks like you know quite a bit more about this than I do). Also worth mentioning (those "updated versions" I glossed over), despite not being traditionally an "AWD" system, the ATTESA ETS-Pro also did rear left-and-right splitting using a fancy rear differential (Active Limited Slip Differential), the ECU, and the ABS sensors (primarily. Looks like they used the G-meter etc as well). The ETS-Pros came on the R33 and R34 V-Specs (which were very rare, race-built models that are, more or less, the stuff of legends).