First RWD Impala spy pics?

[MonaroSS]

First RWD Impala spy pics?

OpEd by MonaroSS

This may well be the LaCrosse prototype being used as a mule for Impala underpinnings.
Or perhaps it's a secret Alpha Platform mule - see post 48.

http://www.leftlanenews.com/gm-four-...prototype.html

At the above link at leftlanenews.com is a story entitled; "GM begins testing turbo four-cylinder engine in large cars". But is there more to this story?

They suggest, "According to a check of the prototype's license plate information, the car is registered to Saab and was built by Holden. The car is also listed as having a 260 hp engine four-cylinder — the type GM officials have hinted might show up in the Pontiac G8 and other large cars."

However I have a different speculative opinion. I gave an undertaking to Bob Lutz not to divulge any secrets he my let slip to me in emails we exchange, but this does not cover my suggestions to him. Six months ago, when the whole "will Impala be RWD or FWD" was being discussed widely I sent Bob a suggestion. I said that if I were him I would challenge my engineers that if Zeta and EPII are so flexible then why can't Impala be offered both as a FWD/AWD transverse engined vehicle AND a longitudinal engined RWD vehicle.

He never commented on the idea, which was not unusual, as I had asked him not to tell me any secrets. But the above story made me wonder, when I saw this prototype was built by Holden who are responsible for GM's RWD car programs. If Bob took my suggestion and asked Holden if they could blend some Zeta RWD into the EPII platform then Holden would be the one to build it from an EPII LWB FWD prototype sent to them, which would happen to be the Buick Invicta/LaCrosse platform (being clearly longer than the Opel Insignia sedan) and likely the closest thing GM has to a running Impala prototype mule at the moment.

So besides my suggestion to Lutz, the spy info that Holden built this prototype when they only really do RWD and do test in Sweden (note that a Buick running around Holden would look REALLY odd), what else is there to tell us more.

Well we have photographs of the car at speed, which can help show us if it is FWD or RWD by its dynamic attitude in cornering, accelerating etc. So let’s look:

(You can see larger pics at the link above)

Pic 1. Here the car is under heavy acceleration, as the track is flat without bumps to cause the front lift. Now, while the nose can rise on a FWD car, the clear gap between the fender opening and top of the front tire shows the front rise that normally is the response found in a RWD under heavy acceleration. Furthermore, a close look at the large picture shows that the driver’s left hand with a watch on it is over top dead centre of the steering wheel, which means he is applying opposite lock. And the angle of the front wheels confirms that this car is powering around a left hand corner with the tail hanging out in typical RWD fashion. Yes you can do this with a FWD car too if you simply go fast into the corner and give it a Scandinavian flick. But test drivers seeking real world feedback would be more likely to be conducting conventional driving styles and that means understeer on FWD and oversteer on RWD.



Pic 2. In this pic we see the car in a fast corner and generating sufficient forces to cause body roll, yet one would expect the turn angle of the front wheel to be greater than shown, as FWD cars tend to scrub or understeer in such situations. In stance this car looks more like a Holden Commodore powering through a corner.



Pic 3 & 4. But the real odd picture is this. FWD cars hard charging through a corner can unload the inside front wheel and spin away power, but they more often lift the inside rear wheel off the ground. Here we see clearly that the inside rear wheel is firmly planted and it is the front wheel that is off the deck. This is common with a RWD car powering through a corner but almost unheard of with FWD. These traits are even more clear on the large pics. Have a look and judge for yourself.





There is precedent for offering both transverse FWD and longitudinal RWD in the same car. MG Rover did it with the I4 and V6 FWD Rover 75 that was also sold as a RWD fitted with a Ford 4.6 V8 in the MG ZT 260. See pics below. But they did it ad-hoc as an afterthought. It would be much easier and cheaper to build in the capability from the get-go so you have one set of stampings across the platform range.

See story here with TopGear Video: http://www.zt260.co.uk/main.htm



So if the Impala will be offered with both FWD/AWD and RWD, then the turbo 2.0 I4 makes sense as the first engine to test given CAFE and a manual box should be a given when you go to the trouble of changing the drive train for a sporting character - why be half hearted. But will there also be a V8? There would be no reason why not, except that GM may want to discourage this for CAFE reasons. I would expect a RWD DI 3.6 V6 as the top RWD engine for a while with perhaps a V8 in very limited numbers later on a range topping Chevy Impala Coupe.




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[Joevette]

maybe, but a turbo 4 in the buick is a good idea too, doesnt it put out almost the same power that the grand national did back in the 80's?

[5 watt]

the gap between the front door and wheel say no.

[zabolots]

Although FWD & RWD on the same platform is not without precedent (Chrysler considered it for the LH platform when Bob was there but didn't follow through due to costs), I highly doubt GM would even bother investigating something like that for the next gen Impala.

It is strange that a FWD mule would have been built by Holden and then tested in Europe and I can't really come up with an explanation for that.

[mikmak]

Originally Posted by 5 watt

the gap between the front door and wheel say no.

I think you sort of missed the whole point of MonaroSS spiel. As a bizarre coincidence, I have been thinking about this of late. How does the drive go to the wheels in a FWD and can it be rearranged to send the drive aft? There are plenty of FWD/AWD cars that can transfer most of their drive to the rear, should conditions or driver input deem it appropriate. The impreza has this function via centre differential control and there certainly isn't any reason aside from tradition that would prohibit it. The downside would be a less flattering weight balance, though this concern wouldn't be so detrimental with a lightweight I4 hanging out front. It would also make that extra length out front pretty redundant, though fits in with the streamlining of floor stampings etc.

I certainly couldn't disprove the theory, though my experience in seeing a FWD car with such a long wheel base undertaking this level of driving, is obviously limited. Forget the front wheel arch gap (the first thing I noticed too) and see if you can come up with anything else! You would have to admit that Holden building a FWD car is like Oshawa building a Lada Niva.

[mikmak]

Hmmm, perhaps something to do with a next gen. Holden and the XWD system?

[ChevyRules]

So it is a RWD Impala made to look like the new Buick LaCrosse? Could it possibly they're testing an AWD system?

[johnstarnes]

The doorsill reminds me of what we saw in the Invicta spy pics.

[FenwickHockey65]

So these are pictures of what could be a RWD Impala but with a LaCrosse body?
Interesting.

[2648562]

It's certainly possible. Video would be more telling. But unless this car and it's driver are much, much larger than they appear I don't see how anything more than a 4 cylinder could be mounted longitudely (sp?). And the likelihood that General Motors would be developing a large RWD car without a V8 in mind is pretty unlikely.

[Kamshaaft]

I haven't got a clue, whatever it is looks very out of character for something built by Holden / on a Zeta platform. Assembled by Holden factor workers maybe. My money is on it being Front wheel drive.

EDIT: I can't read at 2am very well :/

- It's got a round badge, maybe a decoy.

- The styling (not proportions however) looks similar to modern Caddy styling

- Axle is very far back, typical of a FWD configured car.

It's cornering dynamics just make it more puzzling. Maybe it's AWD.

[I-Love-Pontiac]

^Yeah. Unless GM has some kind of voodoo engineering going on, they wont be putting a RWD V8 in that. Which means it almost definitely wouldn't be for an Impala.


Now I wonder how scalable EPII is. Maybe this is the beginning of a small RWD.

[MonaroSS]

Originally Posted by mikmak

The downside would be a less flattering weight balance, though this concern wouldn't be so detrimental with a lightweight I4 hanging out front. It would also make that extra length out front pretty redundant, though fits in with the streamlining of floor stampings etc.

Actually the weight balance would be considerably improved. I've done some diagrams. The fact that FWD cars generally have a few extra inches of space between the front wheel arch and the front door is only because they can. Without the packaging constraints on the positioning of the front axle line with a RWD only design you generally mover the wheels forward to obtain a better front to rear weight balance which favour putting more weight on the rear driven wheels and less on the steering wheels. But it is not the only fact over weight distribution nor the most important or indeed necessary at all.

Below the diagrams show the centre of mass for the engine (red), the gearbox (blue), the differential and drive shafts to the wheels (green) and the battery (yellow).

It is self evident that even by putting a longitudinal engine into a platform designed primarily for transverse FWD engine placement, then engine centre of mass, even though forward of the front axle line, is still further back than if it were mounted transversely. Yes the engine could be further back from the front axle line in a RWD only design, or rather the front wheels could be moved forward, but the better weight balance gains are still there.

However, more important than the small rearward shift of the engine weight in a longitudinal layout comes from dramatically moving back the centres of mass for the gearbox, differential and drive shafts and the battery. Yes the battery could be moved to the trunk in a FWD car but it isn't as you in fact want more weight on the front driven wheels, but with a RWD version the battery can have an alternate trunk placement.

Remember that EPII was designed for AWD from the get-go so it already was to have a transmission tunnel and rear drive diff and drive shafts capability anyway. To go that step further and make a purely RWD version simply means beefier rear diff and drive shafts and a larger hump for the transmission under the front centre console. The rest is engine mounts and engine connections.

I think these diagrams clearly demonstrate how much more the driving dynamics could improve with a RWD configuration, even in a platform optimised for FWD.

[johnstarnes]

I just hope and pray the next Impala is genuinely creative and brave, perhaps with some heritage cues updated for the 21st century, a real head turner like the '65 was when it came out, and not some lame rebadge of a Holden like the Grand Prix wannabe "G-8"!

[I-Love-Pontiac]

Or maybe it's just a very good FWD chassis. And they are over correcting for the abomination known as EPI

+ YouTube Video