Garen

All of us bank on a little bit of luck when tracking our cars ... and, for the record, Rick IS a good driver.

Suspension tuning. Setting up a 2WD 993tt will be different than an AWD version. Plus, there are many old-school 930's with 500-600 HP that are every bit as quick (or quicker) as modern turbos. Just go and see Peter Carrol's car at Mosport, arguably one of the hairiest tracks still around.

An earlier post of yours eludes to having tried the 2WD mod, and having gone back. I was wondering how well the chassis was setup in 2WD mode, and if maybe that's what gave the car an ill-handling character.

In the end, to each his own. I voted 2WD. Just rebuilding the VC & getting the front diff to work as intended can cost as much as a bunch of track days, and there is little debate as to which avenue of spending cash will make you faster!! Your opinion may differ

-Garen

Essexmetal

Jimmy,

I agree with you that you have removed weight from the front but less weight on the front wheels does not always translate to less grip. 911’s by nature will understeer and whether it is a decreasing fuel load or 100 lbs. of driveline not there it’s the vehicle dynamic that I use to make sure the front gives me all the turn in and mid corner transition I need. The car is not bad and I do not notice the lack of the drivelines mass. That said I tend to like a loose set up so if it oversteering hopefully it is not understeering at the same time. As it relates to going to RWD I think that by the time people get to velocity that exacerbates the understeer to a higher level they should be at the stage in there driving ability to control it.

As to my noting the trap speeds it was as a point of reference to the overall speed on the track (not look how fast I can go) and the only time I have a chance to actually look at the gauges, wet or dry. That straight turns into one mother of a fast right hander and to be repetitious the 993 has outstanding rear mechanical grip on that sweeper wet or dry.

I worked for a driveline company that invented the VC and has been the a leader in engineering AWD systems for practically every auto manufacture and regardless of the strong understanding of what a “real” AWD system can do for vehicle dynamics the group was certainly always split into the 2wd verse AWD battle when it came to track applications. So ultimately it boils down to personal choice. Problem is for someone with a 993tt do I take the chance and hope I like it. My choice was an easy one. The VC was toast.

Rick

Jean

I am interested to know the result of the shootout between Viperbob and JJayB, both are very good drivers and have highly tuned engines, so it would be an interesting comparison.

As to 2WD vs. 4WD, it has been discussed so many times, each has is own experiences, my own is that I would not go back to 4WD, 2WD is much more predictable than (our) 4WD, and therefore safer and faster in my books. Under wet conditions, on slippery surfaces and bad roads, for a DD and some spitrited country drives, 4WD is safer I bet.

As to weight bias, given where the front diff is located, low and in the center, the impact on mass transfer is negligeable. Changing from a BMW to a Porsche requires certainly an adaptation to the driving style, but if you drive a Porsche 911 and change the still weight bias around, you will not know you did...What more mass transfer than a passenger in your car? Heavy, high CG, on one side of the car, etc.. do you change your driving style, or has your car become dangerous to drive?? I doubt.

Keep your car in 4WD mode if you drive on the streets only and in wet conditions mainly, or if you go to the track very occasionally for a DE. If your car ownership is more track oriented, a 2WD setup is truly a great modification...but do it right. I do not agree at all to it being any more dangerous to a 4WD setup, it does require some practice in very highly powered TTs and some carefulness when tires are cold.

fredcalero

Bought the shift box and factory RS short Shift components from Viper Bob!

Going to do the 2WD conversion with Ricks help.

Now I can vote ....thanks for all the input.

JJayB

Actually it was Toby (TB993tt) who went to the dark side and came back. Slick roads and 800 Nm of torque was the reason I believe.

I have owned,driven and raced RWD 993's and the given the reasonable power levels I think there fine. Double the horsepower and torque and there not so fine.
All the arguments for conversion to RWD are emotional and subjective. The best engineering company in the world decided based upon testing that AWD was better and they wanted to keep customers not kill them so they engineered a superior handling car. Now I'm being told by a bunch of non engineers on the internet that RWD is superior!

fredcalero

How do you know some are not engineers?

Maybe some even work for race teams.

Perhaps some even work for automotive companies that design 4WD systems.

Many here like me dont know much. Thats why I ask questions.

chris walrod

Well there does appear to be strong arguments to both sides of the AWD vs. RWD argument.

There are folks here who do work in vehicle engineering, design as well as high end race car engineering and manufacturing.

I attended a racecar vehicle dynamics seminar late last year and this very topic surfaced somewhere on day two of the three day meeting.

Ideally, a AWD chassis would have a constant power differential between the front and rear wheels. In other words, the power split would be constant and as a result offer the most predictable power delivery 100% of the time.

Now we all know this isnt entirely possible as there are differential actions between the inside and outside tires or differential grip due to mass shift, weight jacking from caster at steering lock inputs etc. Even non-linear power curves (boost) will effect forces on each tire.

I guess what I am trying to say is with viscous coupling being temperature sensitive, I am not sure how linear or predicable absolute power delivery can be with the system we have in the AWD 993? Cold, dont we get ~5% of front drive? What is it hot? And, what is considered hot to viscous fluid? Once the car is 'warm', how consistent is the VC in these cars? If you ultimately get 35% front drive, does it stay at this amount throughout a session? Or does it really rely upon heat at each corner exit?

I have all of the bits to convert my car to RWD and time willing plan to do so. I DO NOT like the way these AWD 993's drive. I am not sure I am one that pushes a car hard enough to really enjoy any advantages the AWD config offers.

JJayB

Well I know there are a few becasue I have PM from several.

"Jimmy, I can't believe that the DNA from 6 speedonline has now infected Rennlisters. Unless one is building an all out racecar, the AWD clearly out performs the RWD in the 993tt applicaton. If they don't get F..M"

"JJayB, I have a PHD in physics but my BS was in engineering, and I spent some time with an IMSA race team in the late 80's. The thought of AWD was something we dreamed about in order to put the power down. BTW, I have a 993tt and that's why I bought it".

"Jimmy, I've been following the thread on RWD and AWD. I AM an automotive engineer working for one of the big three (until Fiat buys us). I believe you are totally mistaken has to your belief on superior handling on AWD. Although, I've only worked on the cup holders for most of my career, my training on the internet has taught me that 1000 monkeys typing on a key board somewhere in the universe are capable of duplicating a Shakespearean play if given enough time.
So if enough people convert their AWD to RWD it proves it is superior." believe in the power of the internet"

TB993tt

JJay, can't believe this old chestnut is up for discussion again

For road use in typical Northern European conditions ie damp roads much of the time and cambered, bumpy roads, 2WD is managable with stock torque output. As torque nears 600NM it starts getting hairy, 700NM is dangerous and 800NM is bloody frightening.
I ran mine in RWD with 800NM and because of the nature of road surfaces being cambered and lumpy, even with a proper LSD (45/65), trying to manage the torque was not possible. MOD500 tried my car out like this and literally the first time the boost hit in second he nearly went into the hedge.

I spent a while looking into traction control systems to make the 2WD usable but none was available. My 997 GT2 has 680NM and in the dry one can see the TC/SC flickering away in 2nd, 3rd and 4th gear when deploying the torque on the road, this is with 325 section rears and only 680NM !!!

In contrast when the 4WD was reinstalled the car tracked much straighter, I believe on a heavily tuned car the visco is always nearer its critical temperature so there is always some transfer of torque to the front - the car was still scary but so much safer and ultimately much more fun and in straight line acceleration was hardly affected, the AWD is pretty efficient....

An old anecdote but for newer users - A customer of RS Tuning had a beautiful white 993 GT2 race car which I saw being refurbished at their premises, fresh 640hp/830NM Secan engine and because the customer struggled with traction they were installing a 996tt AWD system at massive expense, all the improve track performance....

2WD is a joy in the steering and feel department and with sub 600NM I would probably go for it again, it makes the car feel so light....

I will not comment on what Jean says, I mean driving a 700hp/800+NM 2WD on the track - the guy is insane
I think the consistent dryness of the track surface and extreme (torque sapping) heat probably helps him keep it on the black stuff ?

Spartan

Says another monkey on the internet

Jean

Wow you have not gotten us used to comments like these towards your fellow Listers with a different opinion JJayB… talking about emotional and subjective opinions, yours certainly qualifies.

The counter argument to yours is that according to your logic, Porsche engineers therefore decided then to kill a number of Porsche customers instead of keeping them, by going 2WD on the sportier 996GT2, 997GT2 and CGT? Please.

Those 2WD production 911s have their own target customers, who have the same profile as the customers that are on this board wanting to experience a nimbler (and faster) car, proof is this poll, I would not have expected more than a 5-10% opinion pro-2WD. This 2WD conversion is not intended at the 90% average Porsche user, who loves the securing understeering nature of the stock car, but to people who like to push their cars a bit more and get more driving satisfaction.

As to it being dangerous, we can hardly qualify the return from the dark of Toby as a precedent, or can we? He has one of the most powerful 993TTs on this board, I think it was 2 seconds faster in 60-130mph vs. your Andial, and his carefully tuned engine goes to 1.4 Bar delivering insane torque figures, now try driving the way he drives in UK’s cold weather, damp and slippery roads, and I call it insanity. Is 4Wd safer in these conditions? You bet. And this is what I said in my first post here.

Throwing a blanket statement about 2WD being dangerous “full stop”and whoever says differently is a moron (in different words) is frankly disappointing. I for one consider the 4WD system to be much more dangerous for me, under my driving conditions, than the 2WD system, I simply do not want any unexpected changes in traction or balance in my car when I am at the limit, so I qualify as one of the bunch of internet non-engineers.

As to objective arguments of 2WD vs. 4WD (993TT 4WD) in the dry, I have plenty of them over 4 years of driving both my stock 4WD 993TT and my modified 2WD 993TT on the street and track, do any of the PM fellows who gave words of wisdom in private also have them? It would be great if they join the debate with their experiences.

chris walrod

We all know the scrap rate, so to speak, of supercars. In this case the CGT. We see them wrecked on-line all of the time, same for Enzo's. Do you think the scrap rate would be any less if these cars were AWD?

Keep in mind these two cars are very neutral in mechanical balance or fore-aft grip.

Spartan

Let's keep this thread going with each individuals own experience for and after switching to 2wd (and back if thats the case) and not get into flaming one another

Regardless if this has been discussed in the past this is a healthy discussion for new and old owners alike

TB993tt

I would have to say IMO an unequivocal yes there would be less trashed CGTs if Porsche had developed it with an AWD system. The CGT is a beast with snap power oversteer and only traction control with mega torque (throttle response) at any revs. The CGT is aimed at a specific enthusiast who should know what he is getting into...... the "Porsche turbo" starting at the 993tt is Porsche's mainstream model which is built to include less experienced drivers and the AWD system is a big part of this, even moreso in the 997tt, this can be thrown around in any weather with abandon, exactly what Porsche were attempting to produce... those wanting the purer helm and the OMG moments can buy the GT2.....
Leading on from that the 2WD in the 993tt is just giving some of that GT2 pureness to the mainstream 993tt. I am all for it, just don't go mad on the torque

fredcalero

Spartan,

I asked Viper Bob what he thought of 2WD since he seems to be a good source of the parts needed for the conversion.

I hope he does not mind me quoting him directly.

"The 2WD is MUCH better.... Saves weight, and frees up the car to handle better. Car feels more like a go kart without the AWD. I have done lots of these, and none of the customers changed back....

Hope that helps Fred.

Bob"