Z31 IRS into an S12?

what the differences between the S12 and Z31 IRS?
im thinking of using a Z31 IRS setup in my gazelle coupe
i just need to know who hard it will be to bolt in

The A arms from a Z31 will bolt straight up to an s12. Not sure whether the crossmember mounting points are any wider, but it certainly bolts up exactly the same way, (I've checked).
Couple of little secrets to here folks. Ages ago I did a write up on how I used R31 GTS-T struts to do my 4 spot brake conversion, well guess what the front struts of an 87 to 88 Z31 turbo have the same floating rotor setup as a JDM R31 GTS-T. So the Z32 4 spots bolt straight up to them and the Z32 rotors go straight on to them also, and they are 5 stud. Actually if you can get the hubs only they will go onto any Z31 strut, and the 4 spot calipers will bolt up to any Z31 strut.Actually these hubs would also go onto an s12 strut, but the calipers won't bolt on to our mounting points, you would need to make up a custom caliper mounting bracket.(I mention all this because in some places s13 coil overs and suspension are illegal for road use, on an s12). The hubs must be from this exact spec vehicle though: All non turbo Z31's of any year use the older style behind the hub rotor, and all turbos before 87 also used the older style setup.
The rear setup off these vehicles has a ventilated rear rotor and will bolt straight up to an s12 crossmember, (you need the whole a arm complete with discs, calipers and rotors). Even if you can't get this A ARM, any model of Z31 has a better rear brake setup than an s12, the caliper is the basicly same,(they use the same pads as an s12) but the rotor is 290mm in diameter which is a vast improvement. Brakes work on a lever principle, so the large diameter rotor you have, the more braking force you get.

I was at a wreakers today after i got my new coupe and seen a Z31 with 4stud hubs, it had no diff or axles, and also the rotors and calipers were gone. i will call them up and ask what they want for the setup that they have left, i will go back and measure the width aswell so i can let everyone know for sure, it looks the same as the gazelle setup.

are the 4 stud rotors 290mm?

Sorry I forgot to mention that 84 -85 model Z31's, non turbo only I think use a 4 stud setup.I don't know if I'd bother if it didn't have the calipers or rotors. What I would do is go there with a caliper off your IRS car, and see if it bolts up to the A ARMs. This is to check whether the a arm has longer mounting ears on it and uses the exact caliper as an s12, or if the caliper itself on a Z31 actually has elongated mounts on it to cope with the larger diameter rotor. If your calipers do bolt up, then I would get them, if you don't mind buying new rotors that is. Don't give them to much for them though, as they are only bare a arms.
I'm very interested in whether the s12 caliper will bolt up to these a arms. Let me know on this.

I will go back in a few weeks and check. could i use S13 rear rotors on the Z31 hubs or are the Z31 rotors 290mm? basicly the irs setup only has the A arms and craddle/crossmember. i will offer under $100 and see what they say.

I would'nt give them anymore than that, actually I would'nt give them much more than $50 a side with rotors and calipers!, (but that's me I'm a cagey bastard, hell I only paid $150 for my pair of R31 GTS-T struts and hubs with King springs and I've seen them go for $800 if you can find them). No point using the s13 rotor as its the same as an s12 one, (I have both of them here). Actually s13 rear brakes are the same shit as on an s12, only difference is the style of mechanism that operates the handbrake, and the cables are different.

Sorry forgot to say also that the s13/s12 rotors are much smaller in diameter than the Z31 ones, so they would fit but the caliper would probably mount to far out, so would'nt be in contact with the full 'face' of the smaller rotor. Also there would be no point you may as well keep your s12 A ARMs as the only improvement is the larger 290mm Z31 rotor, (bigger diameter rotor, more brake clamping pressure!)

the reason im looking at the Z31 IRS is for my solid axle coupe, i will leave the std IRS in my other coupe.

Okay, sorry I'm concentrating on brakes as I'm going to put the Z31 brake setup on the rear of my car as the s12 rotors are pissy. Best bet is to get under your IRS car with a tape measure and acurately measure the width of between the foward mounting pins, (the pins coming from the body that slot through the crossmenber bushes to secure it to the floor of the car, you know what I mean, if not check with Neb. he will certainly understand exactly) where your suspension crossmember bolts up to the body. Then go to the Z31 and do the same, if the measurement is the same then your in business baby, she will be exactly the same crossmember for both s12 and Z31. If that's the case there are going to be a lot of happy Aust solid 4 link rear axle diff setup folks. As they can use the asses out of Z31's to convert their cars to IRS!

i understand what you mean, i will do that very soon. if it works out i will let everyone know. then look out Z31's of OZ 8-)