AE86 IRS Conversions

[PRIMRK]

I've been looking at the prices and crunching the numbers on this one and the option between installing a g series diff or an IRS setup from a dollar point of view is comparable (the IRS is cheeper but not by much).

Now as the car I'm building will be an all round grip/drift/drag car as I want to get the use out of it the rear end has stumped me for choice.

Now IRS will camber on squat this is bad for drift/drag but can be somewhat counteracted by dialing in some positive camber to make it as close to zero as possible while on the juice. IRS also offers much less unsprung weight and the options of diffs/LSDs is nice and wide. And if I use the S13 rear setup with R33 diff and hubs I'll have a strong diff internal drum hand brake and 2 pot rears where as the g series is tough but the brake options are lacking somewhat.

At the moment I'm torn between the 2 and am slightly leaning to the IRS from an S13 using R33 diff and hubs as it can be tuned to be used for each different event to a point, I also know that there will be somewhat of disadvantage in some events depending on the set up I choose. The thing that may tip me at the end is that the IRS looks better when slammed.

Well let me know what you think and back it up with some sort of reason so I can start some sort of pro and con list.

Cheers

[Skylar]

What do you mean IRS "looks better" slammed? geometry or stance/fitment?

[PRIMRK]

Stance really, negative camber on the rears.

[johl]

what will the car be used for? live axel will be fine for 99.9% of anything a normal driver can do to a car. unless your doing a build like magicman and will be competing with it then i say go for it.

for me it is too much of a hassle for what you get in the end. i see what your saying about all the adjustability, cheap lsd, brake upgrades but it will cost more to do. the amount of time and stress involved in measuring and building the irs into the car, is way more than just dropping in an f series, throwing some r32 discs and calipers on it and driving the next day.

my 2c, but if your just doing it because you can, then why not

[slydar]

i'd suggest you stick with the live axle.

1 question i'd start with is do you have much experience with that level of fabrication? irs conversion i mean. youre talking rotiserie etc with the irs. compare that to just swapping some mounts on a diff. its 1 days work v's possibly months..

a well exceuted live axle conversion would be a lot better than the.. "average" IRS conversion. converting your live axle set up to equal 4 link will also makes big gains and its pretty easy.

there is no real shortage of G series lsds. theyre a little more expenive/harder to buy 2nd hand but you only have to buy it once.

ive spoken to 1 or 2 guys that race IP. and in their oppinion, they didnt notice the differece converting to a heavier rear axle handling/lap time wise.

G series also has the advantage of readily available ratios for 3.7 to over 5.XX.


I've been looking at the prices and crunching the numbers on this one and the option between installing a g series diff or an IRS setup from a dollar point of view is comparable (the IRS is cheeper but not by much).

Now as the car I'm building will be an all round grip/drift/drag car as I want to get the use out of it the rear end has stumped me for choice.

Now IRS will camber on squat this is bad for drift/drag but can be somewhat counteracted by dialing in some positive camber to make it as close to zero as possible while on the juice. IRS also offers much less unsprung weight and the options of diffs/LSDs is nice and wide. And if I use the S13 rear setup with R33 diff and hubs I'll have a strong diff internal drum hand brake and 2 pot rears where as the g series is tough but the brake options are lacking somewhat.

At the moment I'm torn between the 2 and am slightly leaning to the IRS from an S13 using R33 diff and hubs as it can be tuned to be used for each different event to a point, I also know that there will be somewhat of disadvantage in some events depending on the set up I choose. The thing that may tip me at the end is that the IRS looks better when slammed.

Well let me know what you think and back it up with some sort of reason so I can start some sort of pro and con list.

Cheers

[hachi_dk]

have you thought about a live axle set up with bent axles for rear negative camber?

[PRIMRK]

Well the cost of fabrication to get it done right has been factored in to it, ill just generally brake down the costs quickly...
For G series
Diff $700
LSD $900
Diff Mounts $400-600
Brake mounts (using R33 callipers and disks) $400-600
Total $2600 ish

S13 Rear cradle (all adjustable) with R33 diff inc. LSD and struts and tower mounts $550 (Friend smashed their S13, so chop chop and away we go)
R33 hub assembly + cables $400
Fabrication $1000-1200
Total $2000 ish

The other good thing about the IRS rear end is that it has an mechanical internal drum hand brake so I wont have to use the twin calliper hydro handbrake set-up that will cost a bit more on top (looking at another $400 for a handbrake unit)

[johl]

can you do it or do you know someone that can do this type of work accurately?

[PRIMRK]

Oh and no i personally haven't got that level of fab skill but i do have a rotisserie so i can stitch weld the car later on and will be getting my local fab guys to do the work (they are currently putting an S15 rear end into an old fiat abarth) that way i know its done right, plus they are quick, looking less than a week turn around.

I do want to compete with the car at some point down the track (though i dunno what class a 4.3lt V8 AE86 with this level of moded suspension will fit into) and don't mind forking the money out early and doing it right the first time. Ill prob do time attacks or something...its a case that i want it to be able to be used any weekend no matter what event is on so i get the most out of the car.

[PRIMRK]

have you thought about a live axle set up with bent axles for rear negative camber?

I looked at this sort of set up (at least one that I believe your getting at here) and the cost was above and beyond any other options i had looked at (looking $8k for it done right)

[Stain]

if your going to go to this level. why not have a custom cradle made up instead of trying to adapt one from another car?
then you could choose _any_ irs centre/hub/brake and use adjustable rose jointed arms instead of stock bushed ones from a 20yo nissan.

[slydar]

i think your figures are a bit off with the G series conversion.

also, i also wouldnt trust a shop that turned that job around in a week and cost only $1200.

i would be throwing some "roll center" type questions at them. if they dont bombard you back with reassuring suspension tech jargon there is no way id do it.

in simple terms, you need to get the craddle as high if not higher in the 86 chassis as it is in the s13. to compensate for the shorter wheel base. shorter is going to affect the front/rear RC relationship in a (atleast slightly) negative way. also the front RC is fairly adjustable in a corolla... meaning youre able to get the front geometry closer, more easily. manipulating the height of the pan hard hard does the same thing at the rear. this is vetoed by changing to the s13 irs. which unless heavily modified isnt really adjustable independently of ride height.

these are just the problems i can foresee you/fabricator having just by thinking about it for 2 minutes. let alone taking any measurements..

[PRIMRK]

well yeh this is the sorta stuff i need to find out, what questions do i have to ask and what sort of answer am i hoping for.

the figures on the g series are all off the shelf ones cos i havent been able to find any friends that can help me with parts unlike with the S13 stuff

[KurtHS]

Seems like a bit of a waste of time and money to me, sorry dude. Can you see yourself winning the Australian Drift GP? Can you see yourself winning the Super Sedans series? Can you see yourself winning at drag events?

An estimated $4400+ on rear suspension to get a bit more grip and adjustment, seems like a waste to me especially in something that's always gonna be an 80's sports car.

[PRIMRK]

But it's not costing $4k it's cheeper than the live rear end, that's why I'm contemplating it.

[KurtHS]

Ahhhh I got confused and added them together. Still, I don't think it's worth it, it's that much longer till you can drive it, I have a feeling costs will blow out and then there's the chance the project may not get finished at all.

Anyway if you go for the live axle rear end setup to start with you can always change it down the track and you'll make your money back on the G series either as a whole or as parts. Live axle is proven to be reliable and to work well with a similiar setup to yours, ie Lloyd Smiths car.

[PRIMRK]

Hahaha...i was starting to think you may have done that

yes they have proven the live rear end but so has s13 IRS ie most of the MCN cars use it (i believe, ive found 3 diff builds from them using it so i may just give them a call)

and at the moment the car aint goin anywhere real fast cos of the wire up so it aint goin to blow it out all that much longer if anything...

What im realy after is infomation and opinions from a technical stand point.

[Skylar]

So, instead of asking a bunch of randoms on the net, wouldn't it be better to get technical information from credible sources like books? or you scour the whole internet and find enough information to prove what has been said by randoms is true or not? If you really want to make it YOUR car/build, you really aren't putting a lot of effort in from my point of view. Go buy how to make your handle by fred puhn or herb adams' book or something. Basic, but it'll get you moving in the right direction. Then go buy something more technical, but don't buy race car vehicles dynamics. I don't mean to say it's bad, it's just way over your head for what you want to do.

So, problems to deal with firstly:
1: what slydar said
2: where is cg of the car at the front and at the rear(doesn't really make sense but how high is the CoM above each of the axles. (gets you (a rough) mass centroid axis)
3: you talk about being slammed, roll centre moves around a lot more per ride height change in IRS than live axle but side view instant centre won't with IRS but will with live axle.
4: mount subframe high or whereever to make roll centre/camber gain/toe curves acceptable, then tilt for however much anti-squat then re-align diff angle to gearbox output (like adjusting pinion angle on live axles)
5: This is as much as I can be bothered to write. Go figure the rest out yourself. There's a lot more to it still.

Why not make your own bolt in subframe with adjustable whatever so you just change a few things to suit whatever you're going for.

and lastly. I wouldn't take the car to anywhere that charges to 1200 to do a subframe fit. For that much I'd only expect them to make the subframe fit in the most convenient position. I'd expect a decent job to cost 2500+, then again, I have no idea what a fabricator charges per hour. There's a lot of calculating for a job like that. Take it to a shop that builds and runs winning tube chassis race cars that know what they're doing with geometry, ride and roll rates and damping, not just a guy who thinks/says he knows what he's doing.

[PRIMRK]

The shop I go to specialises in chassis design and modification, i have also been talking to a few places that do a lot of suspension work for the V8's as well as other workshops round the world who have undergone the IRS job into 86's to try and find out if they have found a 'sweet spot' and how much modification is needed to get it there, those prices are prelim costing after showing them a few photos of how others have done it which doesn't take too much fabrication time.

At the moment its educated guesses and ill take all the help I can form professionals but I need to know what issues there may be so I can ask the right questions to get the right answers to then apply and see if it will work out, and not cost a bomb.

[kaibeecee]

its been said, but stick with live axle.

if you want to go to an IRS setup, only to set it back to 0* camber, whats the point? i think you're underestimating the value of a well setup live rear end.

And an IRS conversion is heavier than ANY live axle setup. my S13 rear end weighs a tonne. i couldn't lift it myself, as opposed to a fully-loaded F-series diff that i could move myself.

and just cause a shop deals with 'the V8's' doesn't necissarily mean that they're capable of adapting a nissan rear end into an old toyota.

[PRIMRK]

Different shops, the guys that deal with the V8's are just answering questions I have the fabrication will be done by the ones who make a lot of tube chassis.

[Rice86]

hm..wasn't there a AE86 in japan that had a r32 read end conversion done to it? dating back in 2008-2009
i remember seeing it posted up front page blog on HachiRoku forum..correct me if im wrong about it being a R32 IRS but im pretty sure it had the conversion done to it regardless

i would too rather just use "what it already has got" instead of converting to IRS simply cause it has been proven to work from 86rwkw - 250rwkw+ with just stronger live rear axle conversion parts..but there are benefits to gain from having IRS too if your gamed to tackle them and sounds like you are, hope this goes well for you and doesn't end up in the trash bin..

what is $500 when you playing with roughly $2000 in rear suspension already.. like im planing on spending $5k-$8k minimum on a set of coilovers ONLY if i ever get more serious about competing with my car, you getting what im saying?

[PRIMRK]

yeh the small difference in price is why im weighing it up