TB993tt

This is still a popular area of discussion amongst us anoraks and so it should be.

Having done more miles than most with 750+NM going through both 4WD and 2WD I feel pretty qualified to comment on the merits of each configuration:

Converting a stock 993tt to 2WD instantly alters the car's handling, makes it so much lighter on its feet and gives it telepathic turn in. Removal of the 4WD takes ~50kg out ot the car which gives all round benefits.

The downsides start to creep in when one starts to push greater amounts of torque through the chassis which when combined with uneven roads makes for a more dangerous animal. Add in damp or cold conditions and things can get scary on every outing.

My determination is that for cars whose 60-130mph is more than ~10.5s the G forces will be managable and 2WD is the way to go for the perfect 911 driving experience - on smooth roads and on the track you will have a fixed grin with the front end being 200% more communicative - a delight
On compromised roads and slippery/cold conditions you will have to be a little more careful, but with a good LSD and proper geometry/suspension you will be fine and will REALLY enjoy the car.

The trouble comes when one tries to run 700+NM (60-130 in sub 10s) through 2WD. By the nature of turbo torque delivery, it is relatively "un-linear" and if you get a hint of spinning a wheel, the torque will take over very quickly and really try and "light up" the tyres. This can be very dangerous with 2WD.

Another aspect to consider is how and how often you drive your car. If your car is sub 5K mile a year then I guess driving it is for "special days" when you actually want a bit of a scare to keep the adrenalin going
If yours is a daily driver and you use it in inclement conditions a lot then this is where the constant attention becomes draining - flooring it at 120mph on a cold Autobahn and getting wheelspin through 2 wheels is not at all funny - through 4 wheels is still exciting but at least the thing won't kick sideways !

With a full GT2 chassis set up I am certain that the stiffness of the chassis helps considerably in making any loss of traction more manageable - the race GT2s seemed to do pretty well with their 630hp and 800NM torque. Like I said before, this is not the same as driving WOT on bumpy/greasy/cold roads.
I run an LSD, Euro turbo S chassis (includng harder bushings everywhere) + PSS9s.

I recently had the pleasure of driving MOD500's 730NM 4WD 993tt. The steering was pretty horrible, I couldn't believe how it wanted to plough on in the corners..... But.....just how it put the torque down was a revelation. I had completely forgotten (after 15K miles in high torque 2WD) how easy the 4WD made the car to drive fast.
Where my car at WOT would skip over a bump and the spinning wheel would seriously unbalance the rear meaning instant "off throttle" or big moment - MOD's car just felt like the fronts were pulling the car over the bumps, keeping the whole car straight....

Doing a 60-130mph in MODs was so undramatic, just hold the wheel and point it -in contrast mine would be bucking around and felt on the edge wanting to throw you into the scenery all the way up to 130mph.

Another thing which has niggled in my mind is that all of the 993tts which RS Tuning do their 520hp/700NM kits on, they ALL stay 4WD, even the ones which get lightened to 1350kg/3000lbs.
It was particularly poignent meeting a Swiss car nut at RS (owner of multiple exotica and 550hp 993tt 4WD daily driver ) who was having his race 993GT2 (700hp Secan engined) fitted with a 996tt 4WD system (at unthinkable expense).......


This is why I had a s****** at Brad's latest dyno and all the chassis dyno boys musing over his 780lb/ft / 1060NM of torque......... going through 2WD....... I'd like to see that

So when my gearbox decided to call time for the second time in the last 4 years (yes its amazing how quickly they wear when proper torque goes through them ) it was an opportunity to renew the shaft (which was chopped as part of the 2WD conversion) whilst the box was apart, and to go back to 4WD.

The horrible steering is a given but it will be interesting to see how the 4WD affects the performance numbers on my car - I am hoping for 60-130 near 8s still

ACEparts_com

Good timing. There I was, spanner at the ready to disconnect my 4wd. I've never had a problem with understeer yet still felt compelled to do it - the power of the masses eh!

TB993tt

Ace..... You are running under 700NM (60-130 in more than 10.5s) ?

If yes then do it...... I would have no hesitation - the feel of steering has to be experienced (with the 4WD system off) makes it into a different car

Acropora

Sigh... Hand the man his Geritol..

TB993tt

indeed .........

Would have been even funnier if you had accompanied it with a 6s
60-130mph

kennyboy

TB - the only problem with your report is.....you haven't left any room for questions!

Nice insight, cheers.

Stummel

Can't you have an additional mapping with limited torque and slower building of torque?

At least a different throttle programming for bad weather. drive by wire...

AndyT

is the goal here straight line speed ?

viperbob

If I can, I will add a couple of my insights along with TB993TTs into doing the 2WD swap. First, I used a Guard LSD that was set to 50/80. A really good LSD is KEY to now running all the power through the rear end. Second, with more HP (clearly I could not have over 500HP as I was running a stage 4 K24 Hybrid setup with different intercooler, 1.35 BAR, straight thru exhaust, modified throttle body, and more) yes you need to be a little more careful with the gas. I could spin 12 " slicks coming onto front straights in 4th gear. It is just something to get use to. Finally, suspension. I was running Motons with 1000lb rears. I had to up it to 1200 to get the proper set of the car for rear wheel bite on turn exit. The car will try to do more of a squat under acceleration by putting all the power through the rear. A little extra rear spring helped quite a bit.

Now most of my experiences are more to the extreme from a track perspective. On the street where I did drive quite a bit, I never really had any issues related to the 2WD setup.

MOD500

Great post TB.

I think you hit the nail on the head regards the 2WD + mega power would be great for a total pleasure car, but might taint the experience somewhat over time when used daily, especially in the dire winters we have in ol'Blighty.

Having had the privilege of driving TB's car in 2WD and ultimate RS '06 spec, the steering feel was a revelation, plus the front end response was so much more precise as said. I had been thinking for some time about going 2WD myself until upon a straight dry road I floored the blue beast in 3rd at 2, 500 revs or so ..... it was one of those 'can I get off now please, I feel ill' moments as the engine soon ripped through peak torque and lit the rear 315's up with rampant ease

Think going 4WD will allow you to enjoy the car's grunt much more safely on the road, without the fear of going badger hunting in the hedge bottom upon full flexation of one's right foot The rudder in treacle steering feel is a PIA, but a sacrifice worth making for the increased confidence the 4WD will bring?!

I hope there will be no reprisals against me from the 2WD devotees for me (re)showing TB the benefit of 4WD ?

TB993tt

Stummel
I'm sure one of those switchable ECU thingies could be adapted to give a torque limiting map, but part of the fun of a powerful car is overcoming the grip, surely ? with 4WD you can reach the limit (of grip) and not be spat off the road.
A while back I made investigations into traction control (thanks ninemiester for saving me on that one ) and discussed it extentsively with RS - basically not doable with the 993tt.
I feel the new 997GT2 with proper traction control will be and entirely different beast and much safer to deal with more power with power being instantly cut the moment wheelspin is detected - this will make the perfect 2WD 911 IMO -especially if it is switchable for "special occassions"

Kennyboy
I'd like to see more discussion from drivers real daily road experiences with 4WD/2WD
eg. other 2WD tt owners who run lower torque - is the car much safer (as I am guessing) ?


VB, am I correct in saying your car was only used in hot dry climates ? I know Jean's is used in the Mid East (although he has also given it an airing in a wet Germany ) From discussions with Jean I know he has also experienced some scary "bucking" from the rear at high speeds on the highway although his car is now a legendary race competition winner and Jean no doubt can handle his 2WD better than I would ever be able to

Andy T
The goal is to have a Northern Europe climate capable, 8s 60-130mph performance 993tt able to deploy its torque in as safe a manner as possible without having to have the thought "I'll take the other car to work today 'cos it looks bloody slippy" -hence a true ~600hp daily driver

As MOD says I just hope the "rudder in treacle steering feel" does not ruin the whole experience.

PS where is JJayB with the big slice of humble pie for me

Red9

Interesting - I wondered where TB had got to! I would have always thought that the safety margin versus ultimate handling conclusions were always going to be along these lines. Having had both set ups and the unpleasant experience of reversing down the freeway at high speed ( damp) on one occasion and another early morning let off , I have always taken a great interest in other people's experiences.What is interesting is trying to impart your own knowledge onto others and trying to help them avoid potential disasters.Once again-- a very helpfull thread.

kennyboy

So would I - and I may be in a better position to comment on 4WD mode after the weekend, I'll be blatting around Bedford tomorrow.