MWMburton

so i have an 85 gsl. in the summer i'll be swappin a jdm s5 tII motor in and i got a buncha stuff to make it work in the car. my biggest concern as of now it the rear end. im wondering how much power will the stock rear will hold up to and for how long. im hoping to be a lil higher than stock power and id be nice to be have around 220 so let me hear what u think. please dont give me the run around n tell me to go do my research, i remember a thread on here with ppl that put v8's in n they said the rear end held up but i just want to make sure its not a bunch of hubub

85rotarypower

As long as you don't run drag radials and launch hard too much with 220hp it should last a little while. No way to really tell though. I know their usually fine with NA engines up to that power, but no idea about a high torque turbo motor.

twinkletoes

iTrader: (17)

I'm confused^^? The GSL model never had a 13B engine in it from the factory. The GSL-SE did. Back to the question. I don't know if it will hold up because mine is stock so I don't know. If it doesn't though, grannies speed shop has a ford 8.8 rearend that is bolt on.

fluffysheap

Rear ends are usually tougher on NA RX-7s than the transmissions are. But if you are gentle either will handle 220HP... stuff will start to break if you start getting fancy. The T2 transmission and the Ford rear end are probably your best bet although there are lots of other rear ends you can use.

Tsi_Xtreme

I don't know about GSL but my SE has 245hp at the wheels and my buddies had 330... however he dragged it with drag tires and ended up braking two diffs. I'm getting ready to put on a new turbo soon and it should put me at the 330-360 range. i think it should hold up for street driving.

vipernicus42

iTrader: (4)

If you drop a stock S5 TII into your GSL, you'll be okay with the stock rear.

As TSI_Xtreme said, as you approach 300hp you'll be looking to replace the rear end, but until then it should hold fine.

The stock S5 TII puts out 200hp. Concentrate on getting that installed, and running. Once you have it installed and running okay, then take a step back and plan the next stage of your project, ie: upgrading ECU/Turbo/etc.. and figuring out if you'll reach towards that 300hp mark and need the new rear end.

The other thing you want to consider is whether or not you *need* that much power. 200hp in an FB is fully double what the 12a FBs had stock, so you're really going to feel it. As part of the swap, you may even put an aftermarket ECU in to make the swap easier, so you might end up a little above that...

So you should be okay with the rear for now. If you start making serious power later, look for alternatives such as the Ford rear end swap. I don't really like recommending Grannysspeedshop because they do a lot of piston-related work, but their work is quality from what I've heard and they are pretty much one of the only places that makes a swap-in kit for Ford rear rear ends (either 8.8 or 9", I can't remember).

If you're sticking near the 200-250hp level and just want better transfer of power to the ground, search up for some info on swapping a Miata Torsen diff into your housing, that should help you hook up and still be okay for that power range.

Jon

MattG

iTrader: (2)

I will be running a S5 TII in my SE, and I plan on using the stock rear.

MWMburton

yah i know but that doesnt mean u cant swap a 13b t into it.



would swapping the ecu really make it an easier swap to do cause if so i'll probably end up saving a lil bit more cash n go standalone. and i've heard of the miata torsen into the fb housing but i'll do a lil more research on it and ask around.

thanx for all ur guy's imput and once i get this swap done i'll post up the results

steve84GS TII

Basic rule of thumb that Ive discovered, and pretty much proven over the last 6 years with my TII swaps.....

If you stay within the stock TII ECU abilities,then the stock 1st gen rearend will hold up fine.Thats usually about 275hp with the S4 or about 300hp with a S5,which is where Im at now.If you go with a standalone,then your HP potential will go way up,and you better start looking at something else for an axle.
The stock rearend is tough,provided you treat the car with the respect it deserves........constant clutch drops,drag racing all the time,and slicks can break a rearend in no time,even with only 100hp.

MWMburton

hmmmm. . .sounds good to me. i dont really have the time or money to go standalone cause i have expensive tastes but yah stock TII is going to be more than enough for me, i'll probably scare the **** out of myself just driving down the street. thanx for all ur guy's help

mar3

iTrader: (8)

With the stock rear, open, and on 225/50's, NOT drag radial, I've managed to kill the rear end with the stock motor in 1 years time of hard driving. This is the '84 that I don't plan on keeping. If you plan on getting any stick with big rear tires, that stock rear end cannot handle 3000+ rpm drop launches for long...if you add in more torque, the life has to be just has to be shortened more, if you push it hard like I did for that year. The rear ends are not all that difficult to replace, though.

I'd invest in a set of custom M-W or Strange Engineering custom axles, though. That's a bear to constantly replace.

steve84GS TII

Like I said,it depends on how you drive it.

I dont drag race,hence I dont "launch".....not really neccesary with so much power in such a light car.If I wanna go fast from a stop I just slip her out a little,then floor it.My 245-17's and LSD take care of the rest.Its proven to be a reliable way for me to extend my rearends life indefinately.

Here are my stock axles after almost 50K miles of daily driving,and heres the stock gears after about 25K.I did change the 3rd member a few years ago,but only for a noisy pinion bearing.....

MWMburton

yah i probably wont be running the **** out of it cause im sick of messing up my car. i took a very clean gsl n turned it into a semi clean in some areas old car. so im probably only gonna be doing a lil winding road driving and maybe a lil drifting of n on but thats pretty much it, i dont have the money to replace things like some people. n i probably wont run anywhere near a 245, my suspension isnt that stiff and with 195's in the frnt i still rub all over. so im goin widebody up front to fix that but 245's are huge

kenn_chan

any kinda of drifting is going to kill the diff fast, the constant "kicking" of the clutch to keep the rear end tipping over the traction/slipp line will quickly destroy it. so if you want to make it last, and not spend a lot of money then don't drift.

remember
cheap, fast, reliable..... you can only get two of them at a time its either cheap and fast..not reliable, or cheap and reliable (IE: its not a mazda product ) or fast and not cheap think anything with a rotary

kenn

XLR8

iTrader: (52)

Overall, the stock diff is relatively strong considering the power output it was designed to handle. I believe the rear-end can handle upwards of 300HP. It's all about how you drive and how you launch.

dbragg

iTrader: (7)

driftlanta have cars built solely for the purpose of drifting, nothing else. im pretty sure i read in one of their posts that one of them has been on the same 3rd member for over 5 years. this is in a car that is only used for drifting.

what you need:

kaaz LSD
moser axles

you can buy moser axles from respeed. hes selling them with 5x114 and he has posted he can get them in 4x114. im sure billy could get them for you in a range of offsets. so you have many options. you could even run his brake upgrade kit, running T2 4 piston calipers and T2 rear calipers. with that set up youll be 5x114 though. just some options.

steve84GS TII

Moser axles and a stronger LSD will definately adress some of the issues,like twisting splines and "gription". Although,Ive had very good luck with the stock,input torque sensing clutch LSD.But in a drifting situation,having the best LSD you can get,is an advantage.For street and drag,I really like the stocker.

The weak link at that point becomes the actual gearsets themselves.Not that Ive seen a lot of failed ring/pinions,but it does happen and shock loading will be the typical cause.The other is lack of fluid maintenence,so keep it clean,cool and full of the good stuff,like Redline.I run their shockproof gear syrup in mine,its so thick Id hardly call it oil.

85rotarypower

What is the most common failure point on the stock axle? Seems to me the axle shafts would be the strongest point actually, even stock ones. The weak link IMO is the gearset and casing flex, most likely the spider gears.

mar3

iTrader: (8)

It was the pilot bearing that went South on the '84....which makes sense when I think of it...

vipernicus42

iTrader: (4)

The only differential listed from Kaaz for the Rx7 is for an FC. Will that fit?

What about Torsen diffs, like the miata ones? Are those weak or strong? Are there aftermarket diffs for miatas that we might swap in, since the stock miata diff from a '99 (IIRC) swaps into our housing.

I'm really looking for the best hookup when *not* beating on my diff. I "launch" nice and easy like Steve does, and I'll be re-doing my whole rear end in a year's time. I want to do axels, diff, bushings, brakes, the works. I figure if Billy can get me Moser axels in stock bolt pattern, I just have to choose a diff. I had been thinking about the miata Torsen, but if there's a stronger one with the same torque-distribution ability I'll jump on it!

Hell, anything is better than the open diff my '84GS has.

Jon

85rotarypower

The diff carrier for the NA 2nd gens is the same as the 1st gens I think, so yet that Kaaz diff will work. The major difference is in the length of the pinion and the style of the casing, otherwise I believe they are the same.

REVHED

IMHO, this is the only way to go when running a stock diff.

vxturboxv

iTrader: (2)

If you don't "power shift" or drop the clutch you can run drag radials just fine. I've been in 2 different v8 swapped FB's and they were both running the gsl-se rear ends with nitto drag radials. No problems at all...

I wouldn't suggest running a standard radial. The car will kick out on you to easily at power IMO. Just let up between shifts and roll into it off the line. You'll be fine. A factory TII is no torque monster.

Just for the record. I've been running factory original GXL rear end and 3.90 gears in my FC with over 400 ft lb or torque for over 3 years without any problems yet. And these are the little axles not the beefy TII ones. Netting 1.6x 60' times all say long

. It's also an automatic... shocking the drive line by dropping the clutch with stick tires is what breaks parts.

Richard Miller

Remeber also that the 84 and 85 years had a beefier axle than previous years, for both the SE and it's 12A powered siblings. I don't have any real life experence in high HP applications, but from the many rotary shops I have talked to over the past ten years 300 hp under non abusive conditions seems to be the agreement.

mar3

iTrader: (8)

Welded spider gears equals = no fun going around street corners and God help you in the rain...