I've been running a 12A box and locked S2 diff behind my 13BT (S5 hybrid on 12psi) for about half a year. I'm happy to say I've had no problems with either one and it's been driven hard pretty much every other day. So don't let a lack of funds for a drivetrain upgrade discourage you from turboing your 1st gen.

 

I'll certainly keep that in mind!

Does the locked diff give you any troubles in the twisties?

Jon

 

No. The only time you notice it is at very low speeds in carparks etc.

The handling is very neutral and predictable.

 

Ill vouch for the strength of the 1st gen rearend.
Ive got 5 1/2 years of daily driving on my stock SE rearend with pretty much the same setup (streetport S5,hybrid,14psi) and no failures of the catasthophic kind.I did change out the 3rd member while back,but that was for a worn pinion bearing that existed beforehand,and was getting worse. Never twisted an axle or shattered any gears.Seems if you give them good maintenence and dont clutch drop abusively,they hold up very well.Stock LSD works fine for me....having sticky 245-17's out back helps with traction,even if the LSD is tired.

Im not so trusting of the TypeM gearboxes.Ive yet to drive a 1st or 2nd gen N/A that didnt sound like a tin can full of marbles,even with stock power.The extra effort in installing a TII gearbox seemed worth it.....

 

Yeah, I've got no doubt it will let go eventually but so far it's held up very well.

 

Good to know, I'm going 13bt and plan on using my GSL rear at least until I have enough $$ for a KAAZ...

 

No garuantees about the older rears,although driving habits will dictate a lot.
The 79-83 rears had smaller diameter axles and bearings.....but,the 82 GSL rearend in my GLC did hold up to a torquey little, 150HP Chevy V-6 for many years with no problems.

 

If it's not an lsd lock it. The quickest way to pop the diff is by spinning one wheel.

 

I had been having this discussion with some guys out here and most have verified that the ring gear is only good to about 250HP after that with mild to heavy abuse you start to strip teeth of the ring gear. The smaller axles are hopeless with a locked diff and even mild abuse.

I was going to get some LSD side gears made to fit the standard Mazda Factory LSD so they would fit 28 spline 9' axles but most people put me off by saying that the ring gear wasn't much better than the axles.

Any thoughts or comments?


Duane

 

Heres my 100,000 mile old SE ring gear after 3 years of daily driven TII power (250 to 300HP) and a couple dozen 13.5 second passes down the track.The only reason I pulled it was for a noisy pinion bearing,the gears still look fine.....


Heres my stock SE axles that I run, to this day.After 5+ years of TII power,even with 245's out back and LSD, there are still no breaks,twists or stripped splines......

 

Steve,

It's great to see those components holding up so well. I'm running an S5 turbo in my SA with GSL-SE rear end. So far the LSD is working fine. Hopefully it'll have a long life similar to yours.

I initially tried to run n/a clutch and tranny with the turbo engine but that was a mistake. The stock n/a clutch in good shape wouldn't even hold 5-6 psi boost without slipping. That was swapped out in favour of an ACT setup, which held fine. A few tanks of gas later the SA tranny locked in 3rd gear. From disassembly inspection it looks like the failure was life-related rather than due to the increased loads of the turbo. In any case at that point I did what should have been done up front: TII clutch, tranny, and custom driveshaft. It's been trouble-free since.

BTW, I also followed your lead in modifying the fuel tank to accept an in-tank pump. It was a bit tricky on the SA tank due to reduced mounting area at the top of the tank, but with a bit of massaging it fit fine. That change has simplified the fuel system dramatically. In fact, performing that mod was less work than all the hassles related to the surge tank and second pump. Another lesson learned!

 

THANK YOU!!!

Thats exactly what I try to get across when it comes to the in tank mod!
Everyone is scared of chopping up or welding on the gas tank......but its really,really less work than dealing with the alternatives.Once the in tank work is done,its done for life and its super reliable.

My LSD is fried,has been for years.Ive not determined the exact cause but Im sure its age related.When you jack it up,either tire turns with ease.
But thats the beauty of the split-case,4 pinion, clutch LSD......all it takes is input torque to spread the thrust blocks apart and re-apply pressure to the plates.....pressure thats probably gone now due to flat cone springs and worn discs.So long as you have plenty of input torque(which turbo rotaries have) then even a worn LSD will work fine,when under load.
Even though my initial LSD preload is gone,I have no problem whipping the car around and spinning both tires under any conditions,once Im on the power.

 

I have a bunch of pics of the process I should post to a new thread at some point. I did no welding on my installation. I riveted the mounting flange to the top of the tank, sealed with metal-filled epoxy. The 'cup' was mounted to the bottom of the tank with two 3/16" rivets, sealed with the same epoxy. I used all FC n/a parts, but swapped in my Bosch pump in place of the stock unit.

 

renns: If you could post pics of that I'd really appreciate it, I'm going to be doing the same on my turbo swap in a few months, and even though I pretty much have in my head what I'll be doing it would be nice to see how you approached it. And damn steve those parts are in great shape, hope my rear end holds up that well....

 

Writeup is posted here:

https://www.rx7club.com/1st-generation-specific-1979-1985-18/efi-prepping-1st-gen-577867/