Hey, I hope someone here can clear something up for me.

I've got a 2006 6AT model RX-8, and I'm trying to find a limited slip diff to replace the open diff I've got now. (Side question: I've got a very steep and oddly curved driveway such that one rear wheel gets less traction at a certain point and always spins when I'm driving up, so I'm hoping the LSD would improve that. Seem logical?)

I've seen some advertised online that say they're compatible with both the manual and the automatic transmission, and a guy I spoke to at Mazda New Zealand (where I am) told me that as far as he knows there's only one type of LSD for all models, but the guy at the 'Mazda Parts Centre' said that the LSD for the automatic and manual had different part numbers but didn't know if they were interchangeable, and also that it would cost me $3000 (about US$2500).

So, does anyone know if the 6AT can take the same LSD as the 6MT?

Thanks in advance.

 

You sure about this statement? Do some more reading.

Upgrading the diff so you don't get wheel slip going up the driveway, well I have never heard that one before.

You can swap it out, but the change in everyday drivability will make you regret it and at a cost of 2-2.5K depending on what you get is not worth it for daily driving IMO that coupled with the extra maintenance and the increase cost for speciality diff fluid that must be changed once a year nor do I see the point doing this to an auto.

 

Carbon, I don't think the MT 8s suffer for daily driving with an LSD, so I have trouble agreeing with you on that point.

I suspect that they are interchangeable, but I'm not positive on that point. I generally agree that the cost is likely not going to be worth it... unless he can take one off a wrecked 8.

Kinbote,
Generally, the LSD will prevent the wheel from spinning, but not from slipping. Especially when it's wet, you will still hear it slipping against the pavement, although at a lower speed/rate than it probably does currently.

 

Thanks guys.

I realise that it can only send a multiple of torque to one wheel or the other, so it won't eliminate slipping entirely.

I would have thought an LSD would improve daily driving; more torque where you want it, etc. What's meant to be the disadvantage?

There are used 6MT LSDs here for $350, so price isn't a big issue.

Another (related?) question: the gearing seems a little odd to me. I have to get up to about 60 kmh / 38 mph before I'm redlining in 1st. Is that normal? Seems like performance could be increased a lot by putting the gears closer together / lower down. Would changing the final gear ratio have that effect?

 

The primary disadvantage of an LSD is that you will slip one wheel far more frequently, leading to more tire wear. It's helps the car put power down coming out of the corner, but at the cost of overall maximum grip. In low grip situations, this reduction in maximum grip does increase the likely hood of losing traction on both rear tires, though it's not suddenly dangerous like a welded diff would be.

Gearing is rather subjective, and Mazda has their own preferences for gear choices. I personally like the gearing of the Series1 8, though to address the point that you have, they did increase the rear gear to a 4.77 for Series2 to bring them closer together. I had to go the opposite direction for my Mazdaspeed Miata, as it was at 4.1 gears, 6,500rpm redline, and twice the power of a standard Miata which has a 7,200rpm redline. I could hit the 6th gear rev limit rather hard, basically all 6 of my gears were in the same speed range of just 1st through 4th in the 8, although I had 20 more horsepower and 500lbs less weight. I literally could start in 2nd without issue, and shift directly to 6th and it was still viable. A full throttle run had me constantly changing gears, 1st gear would disappear faster than the time it took me to shift to 2nd once boost hit. I ended up paying a total of about $1,500ish to change to a 3.63 rear gear to give me a usable 1st and a greatly extended top end.

So if you want to change the gearing, this is the time to do it. The 4.77 gearing from a Series 1 is the easy option, though 5.12 gears exist as well and are what the race RX-8s use.

 

Okay that's interesting, I'll have to think a bit more deeply about the LSD then.

If I change the final gear ratio am I also going to have to recalibrate the odometer and/or speedometer? and is that a big task?

That Miata sounds nuts, dude. What modifications did it have? Is there a thread about it?

 

There was a speedometer drive gear on my MSM that had to be swapped at the same time, but I don't see any reference to one for the RX-8 in the service manual. I think the RX-8's speedometer uses the ABS wheel speed sensors, and so wouldn't be affected. I don't recall any 4.44 to 4.77 swap discussions mentioning a need to change or recalibrate anything relating to the speedometer. I believe the odometer uses the same sensors for it's calculation.

The thread on my MSM: https://www.rx8club.com/general-auto...-build-244600/