IRS swap options

I'm restoring/restomodding a 1967 triumph GT6. I had planned on swapping the miata IRS and front knuckles to the gt6. The miata's track width is wider so I planned to narrow it. I want to keep the stock control arms for easy/cheap replacements. My problem is finding miata parts. The bone yards want to piece out he IRS.They quoted me $850. I've been seaching the coparts yards for wrecked ones. I was thinking I could take the parts I need and part out the rest of the car to get my money back. The problem there is there are no miata's in my local coparts yard. The nearest ones are 6-9 hours away. It would just add up to too much to go and get one that far away. There are none on any local craigslist.

This got me to thinking there are a few cars at my local coparts yard that I think I could score cheap enough with IRS. Cars like subaru outbacks, legacys gt's, foresters, a 2000 lincoln ls. I've tried to research some of these cars for IRS swaps and havn't come up with to much. I wantted to see what you guys thought?....

You might try these guys. http://www.panicmotorsports.com/

He usually has a couple of junk Miatas floating around for parts. Shipping might be painful though.

How much too wide is the track? HOw does the WB measure out compared to the Miata? Weight of finished car?

There is a TON of geometry engineering that went into the final dimensions of the Miata suspension. We mess with that at our own peril. So, if you keep the A-arms and narrow the mounting points, you have changed the roll centers to somewhere the Miata designers did not intend. The good news is that you CAN figure it out and decide if you like it or can live wit it.

Where it gets trickier is in figuring out what the mods have done to the transient dynamic behavior: Say you are going deep into a corner, hard on the brakes and start to turn, how is the car gong to handle it?

Easy, buy blown up miata, and part/scrap the not needed parts.

Toyman01 wrote: Shipping might be painful though.

Shipping would be be killer that far away

Just keep your eyes peeled for a rusted out/blown up NA. They come up every once in a while and cam be had for under 1k if you look around. Then you can part it out and make back most if not all of your investment.

spit project

You might just pick this up and save a lot of time.

Spitsix wrote: spit project You might just pick this up and save a lot of time.

Is that yours? I might be interested if it wasn't on the other side of the country.

In reply to MKI_GT6:

I recommend the Toyota Supra rear but that's even wider. If you narrow the suspension some odd side effects: bump steer and wild camber gain are possible. The Mustang heads do this to T-bird rears and it's not what they hoped for. I'm trying to think of a modern car with a... hey! How about a 323GTX rear? That's probably too wide too. This is tougher than it sounded.

spkorb wrote: In reply to MKI_GT6: I recommend the Toyota Supra rear but that's even wider. If you narrow the suspension some odd side effects: bump steer and wild camber gain are possible. The Mustang heads do this to T-bird rears and it's not what they hoped for. I'm trying to think of a modern car with a... hey! How about a 323GTX rear? That's probably too wide too. This is tougher than it sounded.

Well my thoughts were to shorten the rear subframe, keeping the control arms and mounting locations the same. Then just shorten the axles. This shouldn't have very much affect on the geomotry...? (all the comments make me doubt the motion)

In reply to MKI_GT6:

Not mine but it is in the $2013 Classified section

After some more research, it looks like most subarus use a trailing arm for a lower control arm. Not a easy system for a swap. The lincoln IRS looks as though it may have potential. It would be plenty strong enough.

It's a 67 GT6, so AFAIK it will have swing axles rather than rotoflex.
You can swap in a Subaru R160 (or Nissan R180) diff (using easily fabbed adaptors), without any frame or body surgery.

Could install stock GT6+ roto components (but not the rotoflex axles!), which basically bolt right up, by welding the lower wishbone brackets (available new in the aftermarket) to the frame.

Still need to fangle CV axles, and perhaps alternate 4x100 hubs or even uprights to match the Miata front.

That allows you to keep the existing GT6 frame, suspension pickup points, tire/wheel clearance, etc..

Some criticise the GT6+ suspension geometry, but in fact, it's not that bad (former National SCCA champions), and you can tweak things.

This is a well established upgrade, lot's of examples and details out there
that you can reference for ideas and gotchas.

MKI_GT6 wrote:

spkorb wrote: In reply to MKI_GT6: I recommend the Toyota Supra rear but that's even wider. If you narrow the suspension some odd side effects: bump steer and wild camber gain are possible. The Mustang heads do this to T-bird rears and it's not what they hoped for. I'm trying to think of a modern car with a... hey! How about a 323GTX rear? That's probably too wide too. This is tougher than it sounded.

Well my thoughts were to shorten the rear subframe, keeping the control arms and mounting locations the same. Then just shorten the axles. This shouldn't have very much affect on the geomotry...? (all the comments make me doubt the motion)

Miata is 56" track. Spitfire is 48" rear track. That means you pull an 8" section out of the middle of the subframe.

In my world, that is going to change your geometry significantly. If the goal is to have the car pivot around an axis running down the middle of the car, you might now be trying to pivot around some point either side of the middle. You might be OK if your front is trying to do the same thing? I don't have enough experience to forecast results.

On the subject of shortening axles; do you know for a fact that there is a supplier who will do the custom axles for you? The Miata and Cobra guys have suppliers who do this stuff, but I would not assume that they want to do one-off work or that they will do it at a reasonable cost.

On the other hand, it really would take an effort to come up with a worse suspension than the Triumph engineers did originally, so you probably don't have much to lose!

http://grassrootsmotorsports.com/forum/build-projects-and-project-cars/gt6-project/57420/page1/

Maybe this will help.

93EXCivic wrote: http://grassrootsmotorsports.com/forum/build-projects-and-project-cars/gt6-project/57420/page1/ Maybe this will help.

I've been following this thread too. It comes down to parts avialablility and price again.

If you want to build a lower budget version of my setup, I will be selling the Rotoflex stuff, as in the arms etc. Fab brackets to bolt the lower control arms in place, then fab up a bracket that will go on top of the GT6 diff and some short upper CA's (70% of the length of the LCA's should be about right) then mount some coilover shocks and you'd have 80% of the Rotoflex weirdness out of the way. Since you'd be using the stock GT6 diff, big HP would mean a very light right foot.

As far as shortening CV shafts, Dutchman Motorsports and Moser Axles both can do it.

Miata is 56" track. Spitfire is 48" rear track. That means you pull an 8" section out of the middle of the subframe.

I'm sure its been posted, but I say widen the body http://www.britishv8.org/triumph/geraldkannenberg.htm

NOHOME wrote:

MKI_GT6 wrote:

spkorb wrote: In reply to MKI_GT6: I recommend the Toyota Supra rear but that's even wider. If you narrow the suspension some odd side effects: bump steer and wild camber gain are possible. The Mustang heads do this to T-bird rears and it's not what they hoped for. I'm trying to think of a modern car with a... hey! How about a 323GTX rear? That's probably too wide too. This is tougher than it sounded.

Well my thoughts were to shorten the rear subframe, keeping the control arms and mounting locations the same. Then just shorten the axles. This shouldn't have very much affect on the geomotry...? (all the comments make me doubt the motion)

Miata is 56" track. Spitfire is 48" rear track. That means you pull an 8" section out of the middle of the subframe. In my world, that is going to change your geometry significantly. If the goal is to have the car pivot around an axis running down the middle of the car, you might now be trying to pivot around some point either side of the middle. You might be OK if your front is trying to do the same thing? I don't have enough experience to forecast results. On the subject of shortening axles; do you know for a fact that there is a supplier who will do the custom axles for you? The Miata and Cobra guys have suppliers who do this stuff, but I would not assume that they want to do one-off work or that they will do it at a reasonable cost. On the other hand, it really would take an effort to come up with a worse suspension than the Triumph engineers did originally, so you probably don't have much to lose!

Good points. I know of a couple shops around the country that will shorten and respline axles. I don't know how much though. A crazy amount I'm sure. maybe I'll hold out for a miata

Curmudgeon wrote: If you want to build a lower budget version of my setup, I will be selling the Rotoflex stuff, as in the arms etc. Fab brackets to bolt the lower control arms in place, then fab up a bracket that will go on top of the GT6 diff and some short upper CA's (70% of the length of the LCA's should be about right) then mount some coilover shocks and you'd have 80% of the Rotoflex weirdness out of the way. Since you'd be using the stock GT6 diff, big HP would mean a very light right foot. As far as shortening CV shafts, Dutchman Motorsports and Moser Axles both can do it.

I can't use a triumph diif for 2 reasons. 1. mine is blown up 2. at some point I plan to really push the potential of this motor (350hp range)

I suppose i'm getting ahead of myself. Looking back at the pics you posted, I just need a couple up-rights, a diff and both the upper and lower control arms look easy enough to build the way I want. That seems to be the way of the least compromisses.

Fact is, there's a lot of commonality in CV components.
The shafts can be altered without a lot of drama..

Raxles is a GRM advertiser, and worth a look.

But lot's of shops around that cater to the Offroad and 4x4 market.