Strength of a RX7 IRS......
 

Hi guys, first time poster here. Known on other boards as natininwa. Anyway, I have this S-10 minitruck with a 420HP small block chevy in it. I was at the wreckers today picking up some Jeep Wagoneer door hinges to use as suicide hinges when I spotted a 86 RX7 near by. Always checking things out, I noticed it had IRS. So I measured and fell in love with the set up. i currently have the S-10 houseing, and with my new wheels I need a 1" spacer to make them fit. Not wanting to run a spacer, I need a wider rear.

First the RX7's rear is 1.5 inches to wide. Can the axles be narrowed, or something else be machined to make up the 3/4 inch differnce I need?

Second, it has a disc brake rear with a standard diff. Are LSD availabe, and typically what gear ratio comes in these?

And lastly, there was already a whole "k" member unbolted out of a car, looked the same, but had a 4 lug set up. Is there anydiffernce over the 5 lug. I noticed the 5 lug had a 4.5 bolt cirlce, I need a 4.75 bolt sircle, Can I just redrill the stubs and rotors?

I am a very skilled fabricator, so gettin dirty is not a problem, just unsure of the set up.

Thanks for any info, and have a merry christmas.

Ninwa

http://users.techline.com/natedogg/fullsides-10.jpg

IRS? Why are they after you?

Re: Strength of a RX7 IRS......
 

Sure.

Yes.&nbsp Most of them are 4.10:1.&nbsp There are a few 4.30:1 ones floating around, but these are very rare.

Redrill the hubs.


-Ted

i am havieng trouble paying my taxes. they want me dead!!!

Anyway, so the rear is up to the HP then huh?

And what do i shorten? The axles (or buy new?) or can some maching be done to some drive ends?.............I have dealt with VW CV's on my Sandrail. Is it possible to have the splines lengthened on the shaft?

And thanks on the redrill. Thats what I figured, but was not sure why this one was a 4 lugger, and the rest were 5.

Again, thanks for your help.


Ninwa

http://users.techline.com/natedogg/Composite_shot.jpg

The enter drivetrain of the Turbo II's are stronger. I'm guessing that was a N/A since it was 4 lug.
You could try to find that, but I don't know if the Turbo II rear end could take that kind of power (actually just the torque). There are some people with V8 swaps. I don't know how most of them handle this problem.
RETed (resident 2nd gen pimp) can hopefully answer the rest.

Also Viscous LSD's came on Series 4 (1986-1988) GXL's and all Turbo II's (only turbo model). I'm not sure on what other models had VLSD


Merry Christmas

Yep, welp, more so the torque.&nbsp If anything the "ears" on the diff case will break, but the diff itself should stay intact.

I thought you were the fab expert here. :)
You can either cut&weld the half-shafts or respline the ends with a broacher - I dunno how good you were with the machining. :)



-Ted

Resplining the rear axles is one thing, but what about the rear control arm and lateral link geometry??

PaulC

The rear geometry of the set up I am not worried about. I can almost bolt the whole thing up the way it is I think. I have do not have this set up yet. And only saw it for the 10 min I was measuring. I was more concerned about the width and shortening. Even with my VW set up, I was skeptical at cutting and welding the shafts. Not only keeping them true, but also worried about the weld joint itself, braking from the heat involved under power. (HAZ zone) And with this being my weekend cruiser, cant have a shaft break on me.

The whole reason for wanting to do this, is I have a possible cover shoot for a Magazine, if not that a feature (long stoyr) And just want to be different. IRS is the shit. I also thought about running the breaks inboard.

Just curios thoughts, wont see the unit again till next Saturday when I may pick it up. Without actually haveing the unit in front me to view, I am not sure if the axles (which I am sure is hardened) have enuf material to spline some more, or if I can machine some of the drive hubs.

Thanks again for all your help.

Ninwa

One more thing. I plan on ditching the coil over for an airbag set so i can lay the frame on ground..

Ninwa

OK, so I am full ideas today, all I have is time to think till this weekend. How much of a CV angle can the rear handle? I am sure I can move the brakes inboard, gaining a 1/4 per side. That means I only I need to make up a 1/2 inch. Since I dont have much travel, i thought I could move the center housing backward, could gain another 1/4 inch in angualrity that way, and I may be able to handle the extra width now. I need it to tuck my tires in my fnederwells.

Just brainstormy here.

Nathan

Yep, it's a matter of how much length you gotta worry when the rear is at full contraction (lowered) and full extension (wheels up in the air).&nbsp I don't know what kind of suspension travel you're looking for, so I can't answer this question for you.

I've seen drag Honda use rewelded half-shafts for hybrid swaps, and they don't seem to break.&nbsp Granted they are not pretty, but it does work. :)



-Ted

I need about 8" total lift from completly bottomed out. I can place the rear where ever I need to take advantage of the plunge in the CV. I need to get the frame on the ground, and lifted to about 6" to drive, and a bit higher to make entances.

I dont mind welding axles......can i have then rehardened?

Nathan

And is there a specific way I should set up the rear at drive hight?

Actually, 86-88 cars with LSD's had clutch-type units. 89-91's had viscous LSD's. ;)

Both 4-lug and 5-lug hubs have the same 4.5" bolt circle. You'd have to re-drill like Ted said.

Ren

interesting
Well more to know about the FC

Sure, the right shop should be able to do this for you no problem.

Ideally, you want the half shafts to be horizontal relative to the road surface.&nbsp This would give you the most suspension compression and extension from that position.&nbsp You might want to compromise on this depending on your application (sand rail?).




-Ted

How would you know if you have "LSD" and to maintane it in top shape...I have the 2/89 GXL model?

Thanks guys for all your help. I go to the yard today and got some better dimensions. That set up will almost fall right into place on my S-10. I remeasured the width, and I am only 1/2 inch per side I need to shorten. Wich I think is no problem. There is enuf plunge I can almost just move the trailing arm mounts inboard.

Glad to hear the bolt circles are the same.

the only differnce I saw, besides not being an LSD, the 4 lug has 10" brakes where the 5 lug has 11" brakes. Looks like it would take alot of work to get that 5 lugger out of there. So I will settle for the 4 lugger thats already on the ground.

I measured the 4 mounting points and various suspension points and the unit is square.

I just now need to find a driveshaft end for it.

I forgot to look today, but what kind of set up is the R+P? Is it like a Ford 9" that has a drop out center, or is it like my S-10 that has nondrop out?

I hate one legged burn outs, but will deal with it if I have too. I might be able to snag a LSD out of a 5 lugger if they do just bolt in.

Thanks again for all your help.


Niwna

what you are looking at is a non turbo rear end if it has 4 lugs. I dont' know if this will take 400hp... you would be much better off to find a 87-91 turbo rx7, the rear ends and haft shafts are stronger and will handle 400 no problem.

what have you done to your truck engine wise? my friend has a 90 or so S-10 with a 305 with heads, cam, headers, full exhaust, aftermarket intake manifold and intake / TB. injectors from a 350, and stand alone ecu. hasn't dynoed it but he's broken a couple camaro trannys :)

got any under hood shots?

I got me a 355 SBC. Trickflow alum heads, comp 280 cam, almost 11-1 compression, Holley 4150 750 CFM carb, home built headers, Edlebrock Performer manifold, MSD ignition.

I am running a T-5 out of a V-8 Camaro. Much stonger than a V-6 tranny. I have banged gears very hard dragging the truck, and still have the S-10 housing with LSD out of the same camaro.

The other 2 RX7 in the yarde are not Turbo models, just 5 luggers with a natural FI. Both modlels are 86's tho.

Not sure what these things sell for, but I am very good friends with them, and am trading them a intercooler out of a latemodel Superduty for it. i am in that 100$.

Plus I am building a Cover truck for a mag, so I want it to be nice when its done.

The pic I am posting is of its current state (almost, there about 3 weeks old) but you see what I am doing.

http://users.techline.com/natedogg/Firewall_11.jpg

Actually to drop the whole subframe is REALLY simple. (Right Paul?)

We did a swap on my convertible (removed NA stuff, put TII stuff in) last week. You'll need 1 big floor jack to drop it, but it takes 3 to put it back easily. You will want the car supported fairly high on jackstands or similar... Here's how you drop it:

1) Drop the exhaust.

2) Remove the driveshaft (4 bolts)

3) remove the brake calipers- 1 bolt each and they slip off. Hang them up out of the way. (You'll want to get them too... that takes a bit more work, but not much- just a line and a parking brake cable on each.)

4) remove the strut bolts (1 each side)

5) remove the camber link bolt (the rod that goes from center section area UP to the floor pan...) 1 bolt. Note that you WILL need a camber link like this if you decide to use the entire subframe.

6) Unbolt the swaybar- I usually unbolt it from the car and keep the bar attached to the rear suspension assembly. 2 bolts per side if done that way.

From this point foreward, you need to have the "pumpkin" supported with a floor jack or similar.

7) Remove the nuts on the studs that go through the mounts on the "ears" of the pumpkin. 1 per side.

8) Remove the nuts on the studs of the 2 subframe mounts. 1 per side.

9) Remove the nuts on the little studs that hold the brackets on the subframe mount studs (you will see what I mean!) 1 per side and slip the brackets off.

Now lower it with the jack and pull it out. That's all it takes.

For those of you doing the swap that I (with PaulC's help) did... first- is it a convertible? If not, the entire process is a pain... don't do it, it isn't worth it.

Just go buy a TII and get it over with.

that's pretty crazy, his whole front end is still 100% stock. he just removed the bumber and front section to get it in and made some custom mounts since all the kit ones put the engine into crappy places. now it just looks stock. he's using stock s10 rad with the stock clucth fan off the V8. so everything fits pretty good :)

he is using the t5 v8 tranny with custom driveshaft to fit. the case is fine but he rips the teeth off 3rd gear :)

Hell ya dropping the subframe is easy. 21mm socket, 18mm socket, 14mm socket, 14mm wrench, 12mm socket, 10mm socket, breaker bar, jack, 10mm flarenut wrench (if you care about the brake lines), pry bar and mallet.

Personally, I don't think a standard V8 Camaro T5 is going to live very long behind a 355 SBC. I'd find a T56 or the Tremec T5.

Have fun!

PaulC

why do you have 3 brake master cylinders?

Well the T-5 seems to be hikding up so far......a T-56 would be nice, but none are available in my area. The 3 cylinders are are Cluthc/Front brake/Rear brake to help preproportion the fluid for my 4 wheel disc set up.

Nathan

Always nice to have more smart guys on here ... even if they are smart piston guys :D

Sounds like a fun project!