Interesting SVX Article

[Jamsvx]

Hi Harvey

I remember that pub where you, your wife, Blake and I sat around discussing SVX's and you were explaining the 3 rather than D - never had a problem with mine and with the ATF cooler, that was piece of mind - never did get around to fitting the Dakota Digital gauge though

Saw a Pagani Zonda between two F40's in a dealership window here in London last night so am feeling better for being sans SVX!

James

[oab_au]

Originally Posted by Jamsvx

Hi Harvey

I remember that pub where you, your wife, Blake and I sat around discussing SVX's and you were explaining the 3 rather than D - never had a problem with mine and with the ATF cooler, that was piece of mind - never did get around to fitting the Dakota Digital gauge though

Saw a Pagani Zonda between two F40's in a dealership window here in London last night so am feeling better for being sans SVX!

James

Gidáy James, yes I remember that day. Blake and I were having a quick run up Macquarie pass, and there was this 'crazy' in a Toyota Camry, trying to go with us Driving one handed, with a camera out the window. Talk about a nutter.
Oh, shiz, Bernice just reminded me, that was you!!

All the best Mate.
Harvey.

[Chiketkd]

Originally Posted by Rotorflyr

Got this e-mail from a buddy of mine with a link to the following article
Linky

It's a pretty favorable article, thought all of you might enjoy the read

One observation...

The UK, OZ and JDM SVXs use the 'superior' VTD trans which we keep hearing about on these boards. However, I've never seen a review on one that had a 0-60mph time of under 8 seconds (1/4 mile (400m) times are also in the 16+ second range).

Several mags in the USA, were able to run low to mid 7 sec times with the transfer clutch awd system in our 4EATs with 1/4 miles times in the 15's.

What gives? Is the VTD equipped trans heavier, or is there a greater power loss to the wheels in that trans?

-Chike

[Weebitob]

That is also something I have been thinking for some time ever since reading specs on SVX in the UK, which are probably JDM ones that were imported. I always assumed that a VTD system would weigh less, even though I have very limited knowledge on this. But perhaps the 0-60 times are lower as well because not only would the center diff in a VTD system be larger but since it uses torque converters to send power to both wheels while the US ones use a system that still has a more direct way to send power to the front, (I do not completely know what it is or what I am pretty much guestimating so could be nice if someone can help fill me in on this one.) So I am guessing that because of that perhaps the is not as much whp or torque initially generated at the front wheels, which might account for more balanced handling, perhaps more capable of going at slightly higher speeds (I still want to know if a governorless US SVX can reach 175mph , just curious) and less wear on the transmission itself. Of course I am pretty much guess this, so can someone please link an article or type something up on how the VTD system works and perhaps even looks because I can't find article on it.

So please help someone who wants to know why but is clueless to exactle how?

[svxistentialist]

What you say sounds sensible Harvey, and I drive around town, in fact many places besides town, in 3.

Interesting that someone is advising to keep away from the Manual button. I wonder what is the reasoning for that?

I distinctly remember Trevor arguing the opposite, saying his missus drove with the Manual botton engaged, as it made town driving less stressful, less changes. With the high torque engine, I would be inclined to agree with Trevor.

If you drive around town in 3, with Manual on, then the car will start in 2 and fairly quickly select 3. A very smooth way to drive.

From experience, I drove Plum for more than a year with a problem in the tranny, it started and drove in 3 all the time[limp-home mode]. It did not cause heavy consumption, and the only real problem I had was you could not leap quickly into fast moving traffic on roundabouts from a standstill. So I reckon the Manual mode in 3 could be very low stress in the city.

Anybody have an opinion on this?

Joe

[svxistentialist]

Originally Posted by Chiketkd

One observation...

The UK, OZ and JDM SVXs use the 'superior' VTD trans which we keep hearing about on these boards. However, I've never seen a review on one that had a 0-60mph time of under 8 seconds (1/4 mile (400m) times are also in the 16+ second range).

Several mags in the USA, were able to run low to mid 7 sec times with the transfer clutch awd system in our 4EATs with 1/4 miles times in the 15's.

What gives? Is the VTD equipped trans heavier, or is there a greater power loss to the wheels in that trans?

-Chike

Good point Chike.

I have 4 cars with the VTD type, and have no experience of your US type.

My guess, [and it's only a guess] is that your type is more friendly for the drag race start you fellows like to compare over there. I'd say the full-time VTD is probably a better drive on twisties, being closer in spirit to the power distribution the Impreza rally cars use. I find with our type, there is not enough power to break traction for a quick start.

This means one of two things; the two computers ECU and TCU, are programmed to pull back or reduce power so that components are not broken. Some of this reduced power could be ignition retardation, and some could also be lost, turned into heat, in the differentials. The car is terribly reluctant to spin the wheels no matter how brutal you treat it.

So where does the power go to?

Maybe your US one is able to spin the wheels a bit and aid fast take-off times?

That's my theory anyway, I don't for a minute believe weight has anything to do with the differences.

Any takers?

Joe

[Earthworm]

Did yours have the ECU bead to crush?

[svxistentialist]

Do you mean my JDM, David?

I have never done any mods on it, other than installing the additional tranny cooler.

Joe

[Earthworm]

Originally Posted by svxistentialist

Do you mean my JDM, David?

Yes, I was wondering if non-USDM SVX's have the bead/acceleration control issue.

See the Acceleration Control TSB on http://svx-iw.com/ if you want more info.

[svxistentialist]

OK, I see what you mean.

This proves I was right, does it not? The ECU holds back on the power, and if you complain enough about it, they will break this component which presumably disables the "logic circuit"

Interesting.

Is there any information on how often tranny repairs are required on cars that have had this "bead crush" modification?



Anybody care to take a bet on whether the early press cars had this bead crush modification, before the press were let loose in them?

Yes, that's what I would suspect also.

Joe

[Earthworm]

Mine was crushed before I bought it.

[Chiketkd]

Originally Posted by svxistentialist

This means one of two things; the two computers ECU and TCU, are programmed to pull back or reduce power so that components are not broken. Some of this reduced power could be ignition retardation, and some could also be lost, turned into heat, in the differentials. The car is terribly reluctant to spin the wheels no matter how brutal you treat it.

So where does the power go to?

Maybe your US one is able to spin the wheels a bit and aid fast take-off times?

That's highly plausible Joe. In that video of the VTD equipped SVX doing the slalom in the wet against a 300zx, didn't they say the awd system Subaru developed helped maintain better control in slippery conditions by reducing power???

I know several awd systems like the Mercedes 4matic and Volvo's awd reduce power to the wheels whenever wheel slippage is detected. As a result, people who try to drag race the S60R always complain about the crappy launches they get when the ECU cuts engine power.

The simpler transfer clutch awd system in our cars never reduces power when slippage occurs. Personally I've spun all four wheels on my car on numerous occasions and I know of one s/c SVXer who can spin all four at will for several seconds!

-Chike

[svxistentialist]

This is interesting, guys.

Graham in England is working on having his supercharger ready for the SAE show in July. In his case, he already has a 5 speed installed, so there should be no tranny problems.

I am planning to install the same or similar system in mine, but I want to retain the auto.

And my auto is the VTD type.

I'm just wondering what will have to give if the ECU tries to reduce power to the wheels, and there is a lot more power there than the Control Unit is expecting to curb?

We'll find out soon enough I suppose. Harvey has always maintained the 4EAT should be better at handling the extra grunt a supercharger will supply. I expect I will have to monitor torque transfer with a select monitor thingy, and if it looks like the logic control circuitry is creating havoc, then I'll seek & destroy anything remotely resembling a bead.

Joe

[oab_au]

Originally Posted by Weebitob

That is also something I have been thinking for some time ever since reading specs on SVX in the UK, which are probably JDM ones that were imported. I always assumed that a VTD system would weigh less, even though I have very limited knowledge on this. But perhaps the 0-60 times are lower as well because not only would the center diff in a VTD system be larger but since it uses torque converters to send power to both wheels while the US ones use a system that still has a more direct way to send power to the front, (I do not completely know what it is or what I am pretty much guestimating so could be nice if someone can help fill me in on this one.) So I am guessing that because of that perhaps the is not as much whp or torque initially generated at the front wheels, which might account for more balanced handling, perhaps more capable of going at slightly higher speeds (I still want to know if a governorless US SVX can reach 175mph , just curious) and less wear on the transmission itself. Of course I am pretty much guess this, so can someone please link an article or type something up on how the VTD system works and perhaps even looks because I can't find article on it.

So please help someone who wants to know why but is clueless to exactle how?

These are a couple of drawings that I did, to show the difference in the two types of AWD.

The Transfer type, is a front wheel drive box, with a TCU operated clutch to drive the rear wheels.

The VTD uses a compound planetary gear set, that uses different size sun and planet gears, to divide the torque, in the ratio set by the gear sizes. It uses an TCU operated clutch as a Limited Slip unit, that prevents either front or rear wheel spin.

The drive comes in the front sun gear, to drive the compound planet gears. The planet gears are mounted on the carrier that drives the front wheels through the transfer gears. The rear sun gear is driven by the other half of the compound planet gears, to drive the rear wheels. The Limited Slip clutch is connected between the carrier and the rear sun gear. Any difference in wheel speed over 20%, is detected as wheel spin, so the TCU applies the clutch to move more torque to the other wheels.

Under normal driving conditions, the whole gear set revolves together, as a solid unit, the gears don't rotate against each other. The only time that they rotate, is when there is wheel spin.

Now the hard part. Although the gears don't rotate, with each other, they still divide the torque. A set of gears, are only a set of revolving levers, so even though they don't revolve, they still divide the torque by the differential leverage, of their diameter.

Harvey.

[Chiketkd]

Harv,

Great diagrams. One question though, do you see any reason why the VTD equipped SVXs had 0-60mph results in the 8 second range while the US transfer clutch equipped SVXs got results in the 7's???

Do the extra sun gears in the VTD box cause higher drivetrain losses?

-Chike