R32 GTR Full-time 4WD

[slow13dude]

Can it be done?

[Sydneykid]

Easily, but they understeer like cops when you do.

PS; By "4wd" I assume you mean 50/50 power distribution.

[slow13dude]

ATTESSA can distribute from 0-50% of power to the front wheels, so could the distribution be set to 30/70?

[Scooby]

Easily, but they understeer like cops when you do.

PS; By "4wd" I assume you mean 50/50 power distribution.

How about a permanent but less pigish understeering ratio like the Coupe 4?

I've never fully understood the whole 4wd intention with the GTR - the mechanics are easy but the implementation seems quirky.

Am I right in assuming that while it might be great for the track it's not great for the road? I've read the famous Autospeed article on their torque splitter etc but then an ex-GMS guy (was it you SK?) Julian E spoke to who said that the idea was to reduce front wheel drive when lateral g forces were experienced??? which took him by surprise also as he thought, understandably, that it'd be the reverse.

Does the fact that R33s and 34s have progressively earlier fwd actuation suggests that Nissan has made its later ATTESSA setups more road oriented? Or is it just that technology has allowed them to do what they'd have done with the R32 if they could. I understand some people tighten up the clutch packs in the R32 transfer case to provide more fwd but that's only half the equation; the other is the speed at which it actuates. If we could only convert our R32s to later ATTESSA systems...

SK can you shed any light on this please?

Cheers

[RBN1]

get a torque splitter then you can have 2WD, Normal and 4WD mode.

[Beer Baron]

ATTESSA can distribute from 0-50% of power to the front wheels, so could the distribution be set to 30/70?

with a torque spilit controller, yes it can.

[Warpspeed]

Well.... The thing is controlled by software, so in theory you can write a program to make it work any way you want. The difficulty is deciding what is the best way for all situations.

No doubt Nissan have put a lot of work into it to suit what they consider the average driver. The average driver is not a drag racer, or a rally driver. It must also work in wet slippery conditions or in the dry, and be fairly predictable. A pretty tall order.

People I have talked to that have modified the standard system say things like, yeah it's fantastic when xxx, but when yyy it really sucks. That is the problem as I see it, there is no single best all around solution, but many have tried.

[Col-GTSX]

I have driven a 50/50 GTR..... Not a comfortable experience at all....

I had to fight it threw a corner at 50kph under 12psi.... In a GTS-T you might get a little arse tweak in this condition... But 50/50 is a bitch.... Trust me....

Power steering???? Where...... Fight, fight, fight.... smile if you get it right..... On the news if you dont.... LOL

[PHATR32]

does anyone know why the 33,34 kicks in quicker than the 32? is it hardware?

steve

[Tommyk]

The later models had a better attessa computer which monitored traction across all 4 wheels at a much higher rate

eg my 33 vspec monitors @ 1000 times per second

[slow13dude]

Ok this is good info.

Where do I get a torque splitter and how much?

[Tommyk]

I do believe www.nengun.com sell it

Its only a couple of hundred bucks

[gmc]

I don't think the aftermarket torque splitter is that good because it sets the torque at that level and doesn't let the ATTESSA ECU vary the torque to the front wheels according to the conditions experienced...

[Warpspeed]

Some of the Japanese torque control units modify the three G sensor outputs, so the ATTESSA still works normally, it is just being fooled about what the car is actually doing.

I agree a permanent 50/50 full lockup of the FWD clutch is a horrible idea.

[Sydneykid]

How about a permanent but less pigish understeering ratio like the Coupe 4?

I've never fully understood the whole 4wd intention with the GTR - the mechanics are easy but the implementation seems quirky.

Am I right in assuming that while it might be great for the track it's not great for the road? I've read the famous Autospeed article on their torque splitter etc but then an ex-GMS guy (was it you SK?) Julian E spoke to who said that the idea was to reduce front wheel drive when lateral g forces were experienced??? which took him by surprise also as he thought, understandably, that it'd be the reverse.  

Does the fact that R33s and 34s have progressively earlier fwd actuation  suggests that Nissan has made its later ATTESSA setups more road oriented?   Or is it just that technology has allowed them to do what they'd have done with the R32 if they could. I understand some people tighten up the clutch packs in the R32  transfer case to provide more fwd but that's only half the equation; the other is the speed at which it actuates. If we could only convert our R32s to later ATTESSA systems...  

SK can you shed any light on this please?

Cheers

Well, Julian and I have "spoken" a few times, I simply don't agree with his opinion on R32 GTR's. He thinks they fail in their design because the "Wallys" can get into trouble. I believe that they are excellent in their design as they enable good lap times, maintained over long periods when driven by "Drivers". Each to his own.

The later GTR's have faster and more powerful ATESSA ECU's. Some "Drivers" say they take the enjoyment out of driving, but they are more benign for the "Wallys"

More clutches in the ATESSA also speed up the transfer of torque as well as making it happen. In a high power GTR with plenty of grip, the standard clutch packs slip too much so you can get slower activation and, as well, it might not be physically able to get to the desired level.

We have ATESSA controllers in both race GTR's (one elctronic one and one purely hydraulic), the drivers use different settings for different conditions. You can adjust both the amount of front drive and the rate of transfer. More front drive in the wet for example. If the rear tyres start to go off, they move a bit more drive to the front. They start the race with zero front and then add about 30% as soon as the car moves off.

By the time you add adj stabiliser bars, adj ride height, adj roll centres, quad adjustable shocks, different spring rates to the 4wd controller functions, my brain hurts trying to set them up for different circuits on different days.

Hope that helps:cheers:

[Scooby]

Thanks SK.

Can I clarify some issues then please?;

the WRX and GTR are both acknowledged as quick 4wd cars but have significantly different 4wd operations. what do you see as the rationale behind each system and their pros and cons?

is the GTR system designed for the track more so than the street?

is 4wd worth retaining in a GTR if it's a fast street car that doesn't see the track?

why is it the GTR system cuts front wd when lateral g forces are experienced (unless JE got it wrong). i'd have thought that on a road car the opposite would be desirable, or at least partial permanent 4wd as in the Holden Coupe 4.

Cheers

[PHATR32]

so is it possible to use the attesa ecu and snesors on a r32 box, and get an improvment?

im come from a 4wd background (laser tx3 4wd, 200hp @ all 4) and i totally love 4wd, especially around corners. So having 4wd grip, especially when cornering is important to me.

steve

[Sydneykid]

Thanks SK.  

Can I clarify some issues then please?;  

the WRX and GTR are both acknowledged as quick 4wd cars but have significantly different 4wd operations. what do you see as the rationale behind each system and their pros and cons?

is the GTR system designed for the track more so than the street?  

is 4wd worth retaining in a GTR if it's a fast street car that doesn't see the track?

why is it the GTR system cuts front wd when lateral g forces are experienced (unless JE got it wrong). i'd have thought that on a road car the opposite would be desirable, or at least partial permanent 4wd as in the Holden Coupe 4.  

Cheers

The WRX is basically a front wheel drive car that can aportion some drive to the rear. They took a front wheel drive chassis designed for low power and simply added a tailshaft and a diff at the rear. The "centre diff" was mechanically based, no electronics, it simply looked at the realtive front and rear diff rpms and tried to match them. Consequently they always the display the fundamental chassis characterisitics of a front wheel drive car. The later generations are slightly better, with improved roll centres and more integrated rear drive systems. Evo's are much the same, although Mitsubishi spent a but more time (money) properly integrating the 4wd much earlier in their model life. With this front wheel drive dynamic they make the basis of a pretty good rally car, but any comparison between a WRC car and a road car is a complete waste of time.

In comparison the R32 GTR was always going to be a 4wd, but coming from a rear drive chassis. It was designed for one thing and that was to win Group A Circuit Races. It had to have the handling characteristics and therefore chassis dynamics that suited circuit racing, hence the rapid turn in and throttle control from a rear drive bias. The front drive was there to prolong the tyre life, take the power transfer loadings off the rear tyres. Hence the ATTESSA system was designed to kick in when the rear tyres were displaying slip in comparison to the front. Such as that encountered in straight lines or cornering, this required computational electronics and hydraulic activation.

Very early in the design process Nissan found that it simply wasn't necessary to have the front wheels driving all the time. It soaked up power, used more fuel and gave out more emmisions for no benefit, so it was eliminated from the programming wherever possible. This also resulted in longer ATTESSA clutch life. So whenever possible they run rear drive, this doesn't mean that all the time when you are driving in a straight line. The ATTESSA has certain parameters before it makes that decision.

That said, I never saw a circuit racing Group A GTR that used the standard ATTESSA ECU, the ones I have seen used a manual (driver selected) operation. Having been involved in setting up a few GTR chassis, the 4wd adjustability adds a heap of variables to the possible set up. Add that to adj stabiliser bars, adj ride height, adj roll centres, adj camber, adj caster, adj toe, quad adj shock absorbers and many possible spring rate combinations. As I have said previously, it makes my brain ache.

The Wallys of the world found this rear drive bias (holy crap, oversteer is possible) to be not to their liking. Since this includes most (not all) of the people with money enough to buy a new GTR in Japan, Nissan added a bit more front drive in later generation GTR's. This lowers the rear drive bias and makes the Wallys feel more comfortable when pushing their (small) envelope. Plus computational power increased and they were able to add more parameters and faster responses (think of what a PC was in 1989 and what is was in 2003).

So anyone who buys an R32 GTR and expects it to handle like a front wheel drive car is going be dissappointed.

[Scooby]

Hence the ATTESSA system was designed to kick in when the rear tyres were displaying slip in comparison to the front.   Such as that encountered in straight lines or cornering, this required computational electronics and hydraulic activation.

Thanks SK, that was great. Julian E wrote that the system was designed to reduce front drive when lateral/cornering force was felt by the g sensors, whereas you've said that the ATTESSA kicks in when the rears displaying slip in comparison to the front...such as that encountered when cornering. I'd have thought that in a power oversteer situation while cornering you'd want more not less front wd (but not enough to understeer of course). Mine certainly feels like it pulls from the front when it gets taily. Did he get that wrong?

Do you think that the 4wd system on the GTR is a bit of a waste of time for the street?

Cheers

[Scooby]

Hence the ATTESSA system was designed to kick in when the rear tyres were displaying slip in comparison to the front.   Such as that encountered in straight lines or cornering, this required computational electronics and hydraulic activation.

Thanks SK, that was great. Julian E wrote that the system was designed to reduce front drive when lateral/cornering force was felt by the g sensors, whereas you've said that the ATTESSA kicks in when the rears display slip in comparison to the front...such as that encountered when cornering. I'd have thought that in a power oversteer situation while cornering you'd want more not less front wd (but not enough to understeer of course). Mine certainly feels like it pulls from the front when it gets taily. Did he get it wrong?

Do you think that the 4wd system on the GTR is a bit of a waste of time for the street?

Cheers