TB993tt

OK so I'm sure many owners think 4WD is the answer to their traction problems and that going 2WD is asking for trouble.

When I ran 4WD with ~750NM/550lb/ft I still got rampant 4 wheel spin as the engine went through peak torque if the conditions were cold and wintery. The difference between 4WD and 2WD is that the 4WD cuts the amount of torque applied (through losses in the torque tube and front diff) and distributes the lesser amount through 4 tyres not 2.

The other big benefit of 4WD is that when the tyres let go the car tends to just spin all 4 in a linear fashion wheras the 2WD (and LSD) will violently snap the back out.

In the current cold conditions we are getting in the UK I am not enjoying myself too much, even with the car pointing perfectly straight the torque seems to twist the chassis when it surges on and "throws" the back end to the side as the LSD tries to do its thing, this is not funny at 90mph.

A run up the same roads at the weekend in a mate's SL55 astonished me at how he just buried the throttle and shot up the road with the rear tyres always at the limit of traction - absolutely staggering considering the conditions !

After talking to our friends who make the Driftbox I am going to have my shop fit one of Race Logic's Traction Control systems. All the info is in the link below but basically it reads wheel speeds from your ABS sensors and interrupts the fuel supply via the injectors to provide seamless traction ?

Well we shall see. It has a 30 day money back guarantee.

Has anyone else considered this sort of thing, I'm told they sell a lot to the 1000+hp Viper and Skyline/Supra crew ?
http://www.racelogic.co.uk/?show=Traction_Control

dbf73

you might want to talk to RS and make sure that the TC system will play nice with the Motronic

NineMeister

Toby,
I'm surprised, this does not sound like you at all. You are the proud owner of an RS Tuning "How Much??" engine running on a fully remapped & optimised Motronic ecu and you are considering risking it all by splicing into a £1000 Porsche engine loom by cutting the injector wires, linking in a £400(?) traction control unit and expect it to run perfectly? My advise is "DON'T DO IT!!" (hopefully you can hear me shout this from home?).

Yes, I'm being serious, I suspect that you will have problems if you go down this route. We could not get the system working properly on a standard 3.2 Carrera engine, and an ex-colleague had issues with it on his supercharged 924 Turbo engine running an Emerald ECU. I have traction control on my 993RS courtesy of the Motec engine management, it works great in the wet but it is very sensitive to set up parameters so it is not something that can simply be plugged in and expected to work straight off, but if you want me to fit Motec for you just call me up.

TB993tt

Thanks for the advice......seriously
Colin, you are so right, this is sooo not like me at all however my car is all but undrivable in current conditions and I want to drive it.
When one speaks to the tech Sales guy at Race Logic he basically says they have sold so many of these units that they don't want to get into debates about how well they work (or not) and that there are certain groups of car people (like us ) who won't even try it. I have emailed a guy who has one fitted to his GT3 for input....
dfarrow
I have emailed RS the question, but if an "experimentalist" like Colin thinks these things are dodgy I can guess the reply from RS

Felix

Ignoring suitability issues I wonder how well it will work in practice. It's one thing to use it for launch control on dry surfaces but as traction control in the wet with mega torque I have my doubts.

A point to consider even though it might be apples and oranges: I've watched a colleague get 45 degrees of oversteer in a BMW 530d turning into a car park in the wet. No diesel spillage, just gobs of torque. He was rather white faced and was adamant the stability control was on and that he gave it some welly but not full throttle. And that's without an LSD. (It's fair to say TD's run unthrottled so the comparison may not be fully valid but I had expected more from an integrated system in a 21st century BMW.) Can the TC really reduce the torque quickly enough? Assuming it does, how quickly does it bring back the fuelling? And is that sudden torque reduction not the precursor to lift-off oversteer?

Discuss!

Kevin

My understanding with the RL system is that is will cut the spark output.. That is how it is limiting torque. I wouldn't worry about your wiring harness. There are places in the connectors that you can apply the taps. The engine harness is extremely CHEAP.. One could fit magnetic wheel speed sensors on every half shaft and run independant "custom" wiring harness.

TB with all of this said, I think that you should consider moving forward with this project. If you made some ground rules to explore all the wiring options without cutting into your $4000.00 wiring harness, I think that you don't have anything to lose..

On a seperate note, Toby have you thought about a reduced output or low torque/boost program on your ECU..

TB993tt

Thanks Phelix and Kevin for the responses.

Here is RS's take on it:
"For the Alzen car we had Porsche Motorsport support for traction control, Porsche had never before had traction control on a turbo race car - we tested a lot on the dyno with restricting ignition - this caused the unburnt fuel to destroy (completely) the insides of the turbos -the pistons also got too hot" (wasn't sure whether he said this was when they tried to limit injection also )

The loom alone for the 996 turbo race traction control electronics is 30K Euro !

They would not discount out of hand the Race Logic approach but said it would not work on the race track.

The 993 turbo electronics do not support any type of traction control, but they fitted a modified 996tt 4WD system to a 993GT2, the system is lighter and the weight is biased towards the front more also with a modified visco clutch they can bias more torque to the front - this apparently worked well with the 700hp 993GT2 but at 38K Euro is probably getting stupid

Looks like the right foot will have to learn more self control

BTW he said they saw the new GT2 and Panamera (sp) last week at Weissach (sp)

NineMeister

On the Motec system I use I tried a random ignition only cut and it simply did not reduce the torque of the engine sufficiently, even when just using launch control (lower rpm limit for standing starts). In the end I had to run with ignition and fuel cut together which sounds a little brutal on the line but did the job nicely. My first experience of the benefit of TC was in the wet at Shelsley Walsh Hillclimb, where the end of the course consists of a 40mph 90 degree right hander then flat out uphill to a 100mph finish on a straight narrow road. In the morning dry session I managed 100.3mph (according to the Motec wheel speed datalogger) across the finish line. After a lunchtime downpour, I turned on TC for the timed runs and had a "leap of faith" for my last run, coming out of the bend and nailing it to the boards. I heard the ignition cut trimming the engine to maintain a fixed % of wheel slip between front & rear along the way and finished across the line at 99.8mph, giving me a class win in the process.
The bottom line is that TC works but it needs a lot of setting up if it is going to get close to an optimum performance, I'm happy to run the Motec system because it is an integral function of the engine management system but I doubt that I would have bothered with a stand-alone package.

What you really need is a 3D boost/throttle control table to cut boost radically when you lift off, but with the torque you have I just do not think that it would work fast enough. Interestingly the later systems employed on the 996 & 997 use the drive-by-wire throttle and simply close the throttle to cut the torque, but drive-by-wire and sports car engines in my opinion should not be used in the same sentence together, let alone engine bay....

Geoffrey

I'll second Colin's experience with setting up traction control. On my racecar with the newer MoTeC, I found I needed to add a g-force channel to the mix to help the traction control become less intrusive and upsetting to the car when activated mid corner. I also have a dash mounted **** to allow the %slip based on the conditions and I have found that helps optimize it for the condition. The latest GT3R TT engine with MoTeC I did has a DBW throttle and MoTeC controlled boost which will make traction control and reaction much better than just ignition and fuel alone as is on my car.

I don't know if I would install a system that was not tied to the engine management system, especially on a turbocharged engine where ignition timing retard can overheat turbos and too little fuel can lean an engine out. I would want a complete system to ensure consistency of all of the systems working together.

The 993s use magnetic sensors for wheel speed that are referenced against a floating ground circuit in the ABS controller. If you tap into the wheel speed sensors with a splice, it disrupts the the floating ground reference and the new device also adds a voltage drop to the signal. There can be some unpleasant consequences to tapping into ABS wheel speed sensors. Simply adding an additional mag or hall sensor to read the 6 halfshaft axle bolts is fine to log wheel speed, but does not have the resolution required for the speed of a TC system (or ABS) which is why OEMs use rings with many teeth (48 on the 993). You would really need to tap the hub carrier and install a second sensor. If you use a hall sensor, it is sensitive to heat and they don't tolerate temps higher than 105c very well.

Colin, with respect to DBW and sports cars, having now done the GT3R TT engine with DBW, I can say it is awesome. The control you can have over the engine irrespective of what the driver's foot is doing is great. Idle control works much better than with a simple ISV. You want the car to idle at 900rpm hot and 1200 cold, set up a MoTeC table and it does it automatically. The engine begins to get hot, use a table and restrict the throttle opening to 50%. The throttle response feels sluggish, you can alter the throttle pedal vs throttle blade relationship so 10% throttle pedal might give you 20% throttle blade. Rember the throttle cams sold for early 944s? It gives you additional control that you don't have with a cable throttle. I don't want to go back to cable throttles. Don't even get me started on variable camshafts...

Red rooster

I used an early version of the Race Logic traction control system several years ago. At that time it was fully intergrated into the DME and used the ABS sensor signals for wheel speed. The set up software was pretty comprehensive and gave a very succesful end result.
I think that the unit on the RaceLogic web page is a more universal sytem to accomodate the huge variety of DME sytems in use today.
It could be helpful to find out whether ignition/fuel or both are used for torque control .

The talk of uprating the viscous coupling characteristic sounds very expensive for little end result ! Those things operate solely on front /rear wheel speed differential . A proper system like 964 C4/959/997tt would be a real solution !!

Colins attack on DBW was amusing ! Maybe he wants carbs back in fashion !!!
We are in the 21st century now , well at least we are here !!!

All the best

Geoff

fc-racer

Hey Toby,

We used the Racelogic system on a Supra producing 500rwhp. It was amazing to just bury the throttle and hear the exhaust crackling as the tires held on at the edge of traction. It's not exactly the smoothest experience, but it was damn fast around a wet track. We often had unusual problems with the Racelogic box with it cutting the ignition when trying to start the car. We eventually wired in a bypass and never did quite figure out why it did that. It was a racecar so we didn't really care

I should note that the setup took forever to get right and even then, when we changed tires to a different brand, we found ourselves having to reset things. It's quite a jolt to run a race-TC equipped car on the track, just planting the throttle is so counter-intuitive!

NineMeister

I wondered if the DBW comment would raise an eyebrow or two. My issue with it is not in concept, just the unbelieveably poor execution of it that I have experienced with DBW on the 996, GT3 and GT3RS. I'm not saying that I can do better, it's just that when I try to drive our stock GT3RS on the edge at low throttle positions in the wet, I often end up lurching around bends when the throttle plate "lag" starts to open up the orifice just as I am lifting off, driving it yesterday in the wet had me sideways at an intersection when the power came in with a jolt. How hard can it be to get it right? My 993 race engine on throttle bodies would not do it and that has 320 degree cams!

Sorry, it's just that all these late model DBW Porsches wind me up with their non-linearity at low rpm part throttle, and I know for sure that if I programmed a 964RS Motec system with the same characteristics no customer would accept it if it drove like this all the time. So, not a DBW problem as such, just a Motronic programming problem that could be resolved (in my opinion) .....

TB993tt

Thanks for this..... It is what Colin said I guess, never getting it 100% right. Also what Geoffrey said about splicing and causing voltage drops sounds a recipe for niggling problems.....
Also I still can't visualise what is happening when the wheelspin initiates at 4000rpm under WOT, the injector pulse is cut on one or more cylinders, the ECU is still signalling the wastegates to allow more air mass (boost) and there is less energy going into the turbos (less burnt fuel) - so what the hell is the ECU thinking then ? it all sounds way less than ideal for an engine which is running close to the edge and finely set up.

Felix

Could the TC be used to fool the ECU into reducing power by faking a knock input and/or high IAT's? This would at least appear to allow the ECU to see coherent inputs and engine behaviour. But assuming this worked it still might not be a big enough torque reduction?

Geoffrey

Hey Colin, that is an interesting observation on DBW. Not having driven a DBW car in the rain, you now have me curious. Certainly with the MoTeC multimap capability, you would have a "rain" map anyway which can change the linearity of the throttle and make it much easier to drive in the wet. The implementation with the MoTeC didn't seem to have any issue in the dry. I don't have a linear relationship between throttle pedal and throttle blade, but it is also a turbo engine with large turbos (laggy in relative terms if you will) and it helped the car to feel more responsive. The difficulty may be in the fact that there are so many different ways to control all of the actuators on the car and for the OEMs to have one (or two with a sport button) settings that will please everyone is a difficult task. However, I don't have any insight into how the Motronics was programmed in a factory car as a reference point.

When I was setting up the DBW, I was surprised at how fast the motor moves the throttle blade. I can't say whether it is faster or slower than a cable without measuring it but I can say that it moves very quickly and you can lose a finger if you aren't careful. The 996DBW works on 14 volts at a frequency of 8000hz. In the process of setting up the throttle blade I cut the supply voltage in 1/2 to 7 volts in case the parameters were outside the range of motion for the throttle blade so as not to run the blade hard into the end of the mechanical travel. Even at 7 volts, it did not strike me as moving much slower than with a cable. I think there is much more to learn about DBW and its application.