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Old 01-01-2002, 20:53   #1 (permalink)
Can't get enough of it!
Join Date: Oct 2001
Location: Perth, Western Australia
Posts: 382
confused Vct, Irs, Lsd???


Now's the time to make myself look like an idiot :crazy1: ...

I have this cool car (as mentioned, AUII, XR6, VCT, almost all the options) but I'd like some explanation of what VCT, IRS and LSD is.

Now, before you get all hot and bothered ("Geez, man, give the car to me, I'll appreciate it more!"), let me say that I have a basic, laymans understanding of LSD. I know what VCT and IRS stands for, but little more than that <gulp>.

What I'm interested in knowing is a basic explanation of what they do and why they're good stuff in a 2 wheel drive (you can see that the LSD explanation was given to me by a 4WD owner).

I've read the thread on VCT vs HP and found the 3800rpm comment interesting. Does that mean that the habit I have of upchanging at about 3000-3500 is wrong? Should I be driving it 'harder'?

Now, if anyone wants an explanation of ABS, I can help there! :s6:

Thanks in advance,

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Old 01-01-2002, 22:28   #2 (permalink)
Australian Falcon Member
Join Date: Jun 2001
Location: Perth, WA
Age: 33
Posts: 663
Ok, i'll give all three a shot :)

first, the LSD. A differential is intended to allow power to the wheels. However, under cornering, one wheel must turn faster, while the other must turn slower (try pushing a wheelie bin around a sharp corner, and watch the wheels, you'll see what I mean). However, to cut costs and weight, many manufacturers put an 'Open' differential into a vehicle. Simply put, when enough power is put down, the wheel with the least traction begins to spin, as in doing a burnout. In differential terms, this is called Slip. A Limited Slip Differential is exactly that, it limits how much slip occurs between the two wheels. The wheel with the most traction ends up getting the most torque, this type of diff is really good for street use. Just dont put one into a front-wheel drive car, cos that makes it a pig to drive..

VCT - Variable Cam Timing. IIRC the Falcon Six's VCT setup retards the cam timing by 10 degrees after the engine revs exceed 4000rpm. From my understanding of it, what happens is that when the engine revs exceed 4000rpm, the engine retards the camshaft timing 10 degrees in relation to the crankshaft position, which allows a better higher RPM cylinder fill. Unfortunately, it also retards the exhaust timing, being the Falcon's head is still an SOHC design. This feature should be better when the Falcon comes out with a DOHC head.

IRS.. The AU Falcon uses one of the very best IRS designs featured on a sub $50,000 mass-produced car. To use one scenario of IRS in use, imagine you hit a pothole going through a corner, with one of your rear wheels. If it were with a live rear axle, the other wheel must move proportionately to the wheel that hit the hole. This will affect your car's handling, since if one wheel dips a few centimetres, then the tyre on the wheel on the other side of the vehicle must change its camber to accomodate the other wheel's movement. With IRS, each wheel is able to act independantly of each other, so even if one wheel does hit a pothole mid-corner, chances are the vehicle will not be adversely affected by that one wheel's movement.

hope this helps!
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Old 01-02-2002, 17:06   #3 (permalink)
Can't get enough of it!
Join Date: Oct 2001
Location: Perth, Western Australia
Posts: 382
Thanks Discokin6,

That does help. Okay, all you other closet rev-heads, how about it? Want to put your own interpretation on it?


BTW: I checked this morning, I tend to change-up at 2000 - 2500 RPM.
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Old 01-02-2002, 21:46   #4 (permalink)
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Join Date: Sep 2001
Location: ACT
Posts: 594
just another note on irs,

one of the most important areas in designing a well handling and smooth driving car is "un-sprung weight". that is, the weight of all the components (wheels, brakes, diffs etc.) below the springs. the lower the un-sprung weight the less innertia it has when it is pushed up by the road. therefore it won't bounce the car as much when going over bumps etc. irs reduces the rear un-sprung weight considerably by removing the diff from the equation.
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