A while back I thoroughly molested a Triumph Spitfire, stuffed a rotary in it and reworked the stock suspension to the point that the body shell was really the only thing Triumph left from the poor thing and is why it got named the Abomination.
I have to thank the GRM gang for steering me in that direction, the RoSpit is what gave me the impetus to build mine. They built the first atom bomb, so to speak; I followed in their footsteps. My good fortune was that when I built my car the Miata had been out long enough for them to land in the junkyards, making my swap much simpler.
Surprisingly I get a fair number of Emails asking for clarification of what was done. Since I really didn't document it very well, I have no real way to pass on what I did.
Recently a good friend bought a 1970 GT6+ which was in pieces, it's a restoration that had been started but got stalled. Rather than put it back stock, my bud has asked me to do that Triumph molestation thing again. This time I plan to document the suspension mods better; maybe this will spark a few more cars! This car is not being built to any specific rule set, but in SCCA Solo 2 it's going to land smack in Modified. It could conceiveably run XP, except the firewall will be cut and that moves it to Modified.
Keep something in mind: all Spitfires and GT6's 1962-1980 have the same front track width etc. On the rear, the early cars (1962-1970) are narrower and that's what we are working with here. 1971-1980 are wider.
Here's pics of the rolling chassis in stock form. The first picture shows a Triumph anomaly which is really irritating when pretending to be a race car driver. Notice that the right tire is turning sharper than the left? That's backwards. Ackerman effect is where the inside turns more than the outside. It's due to the tie rod angle, in the pic you can see how they point toward the rear of the car. With fat grippy tires this will yank the steering wheel out of your hands! The fix is to move the steering rack rearwards. But as with anything, it sounds easy but the reality...
Next up, check out the rear suspension. This is a Rotoflex car, that's what those big goofy rubber rings are and it was Triumph's version of IRS. It was a pretty good start, but what is wrong with this picture? Check out the camber; it's positive. That's because Triumph used the transverse spring as the upper control arm. For proper camber gain, the upper arm should be shorter than the lower and since the spring flexes near the differential the upper arm is a helluva lot longer than the lower. The toe link at the bottom of the pic shows how they decided to control the toe, problem is that since the end of that link describes an arc as it moves it changes the rear toe as the body rolls in a turn. So here's a double whammy: positive camber combined with not very well thought out dynamic rear toe.
Spitfires and swing axle GT6's have a camber curve which adds negative camber as the suspension compresses, but they still have dynamic toe change and the 'jacking' effect that caused Ralph Nader to go ballistic on swing axle VW's and Corvairs and countless sporty car types to soil their undies.
The stock diff is also only good to about 100 HP, any more than that means driving very gingerly and that simply will not do. 
Next up: the front suspension. Again we have positive camber. The upper control arm is shorter than the lower meaning the wheel gains negative camber as it rises, but not enough. Then there's the bump steer issue. Notice how much shorter the tie rods are than the lower control arm? That causes the wheels to toe in as the suspension extends and compresses, more of that dynamic toe thing. The fix is to have the tie rod as close to the length of the lower control arm as possible and to have it parallel. (It's actually a bit more complicated than that.) So this means that along with the rack moving rearwards, it has to be narrowed and must be raised to level out the tie rods. This is nearly impossible with the Spit motor in the stock position, since it already is between the oil pan and the front pulley.
The idea here is to straighten out the front suspension and steering's awful geometry then make the new powerplant fit the chassis.
The Spit uses a 3 3/4" bolt circle, there's not a huge wheel selection for that pattern. Since part of this project is a big power upgrade 
more rubber is essential. We'll be using 15x7 wheels with 205-50-15 tires, they are almost exactly the same OD as the stock 155SR13 tires. These wheels will be a 4x100 bolt circle and used on Miata hubs. Those hubs will be on Miata uprights all the way around. This also opens the door for a whole bunch of nice inexpensive brake upgrades.
More as I dig into this further.
If we could subscribe to threads, I'd be subscribed.
In case you're interested, I did a kind of "build thread" on my GT6 a few years back, though admittedly my goals were not track-oriented and really just to make it a fun weekend driver. Far more modest than your goals for sure! It's still a bit of a work in progress, but I did take a lot of pics and who knows, you may get some ideas from me or from the other GT6 pros that posted in the thread here and there.
This was my first real in-depth take-apart-and-put-back-together of a car (I previously had just done a lot of suspension/brake stuff on my autocross cars and daily driver)....so I made some mistakes but came up with some ideas as well I think...
Here's a link: http://club.triumph.org.uk/cgi-bin/forum10/Blah.pl?m-1206842587/
Anyhow, good luck with the build. Will be watching it with interest.
Josh
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This is one of those threads that I shouldn't follow, looking forward to it!
Glad to have you on board! The suspension on this car was pretty well rebuilt and was well underway with a restoration (I think the PO's Mrs got in the way 
) so there's a lot of noice odds and ends to sell, such as a full set of SPAX 14 way adjustable shocks which have never seen road use. The engine will be for sale, as will the 4 speed tranny (no O/D, sorry) the stock rear suspension and axles etc.
I'll be watching this one too.
I suppose it's a given that the Miata diff will be used.
But if you are also considering the Subie diff, I have some research material that may help.
Carter
In reply to chandlerGTi:
well, ya learn something new every day :)
Curmudgeon wrote: Glad to have you on board! The suspension on this car was pretty well rebuilt and was well underway with a restoration (I think the PO's Mrs got in the way
erg....stop tempting me. I already have about 3 cars worth of GT6 random parts sitting around here, and I haven't even worked on the car in over a year (been busy with my e30 rallycross project). What I really need is some good body panels and someone who is good at paint :)
Since you're going all Miata drivetrain, I probably don't have much stuff that would interest you though (like the nice spun-polished SU carb velocity stacks that I'll never use)....
don't suppose by some freak of nature that someone put a Quaife LSD into that diff, eh? 
At this point, the 1.8 Miata diff is in the works. An easy upgrade for that is a 1st or 2nd gen RX7 clutch type limited slip, it's a drop in swap in the Miata housing. The Miata diff has a shorter nose then the Subie or 2nd gen RX7 diffs, making for a longer driveshaft with less angularity.
While we are on the subject of Miata stuff, we are using 89-93 1.6 suspension/brake stuff. The reason for that is 13" wheels will fit over those brakes and that means we can run 13x8's or similar and still stay under the stock fenders (with the proper offset, of course). 94-up have larger brakes making 14's or larger a must. That may or may not be a concern to anyone else planning their own build but it's good to know. 1.6 CV axles will fit 1.8 hubs, too.
Sorry, the diff currently in this car has no limited slip. 
Cool project.
I only have spare upper mounts for a Spitfire. If you want to sell the rear brakes off the GT6, let me know. I need GT6 rear brakes.
Dibs on the front brakes to convert a Spit (uprights, rotors, calipers, and even the front chassic hard lines if possible)?
Pretty please? 
While I already have a spare engine and trans, a 2nd spare is tempting... granted... SC is a long ways from PA.
I need to de-stall my project. This will be good motivation. I'm at the front suspension stage myself.
93 and Ian, not a problem. I have to yank them off and that might be a week or two. The hard lines and calipers are at my buddy's down in Charleston.
93, when you say 'upper mounts', I'm not sure what you are referring to?
In reply to Curmudgeon:
The metal that comes up from the frame and the upper control arm and shock/spring connects to.
Okay, I know what you mean now. I call those frame horns. The ones on my project are in good shape, but thanks. Tell you what: I could use another steering U joint and steering column lower shaft if you have them.
FYI: the frame horns (or suspension towers?) are different for a GT6 than they are for a Spitfire. They look really close, but the holes for the engine mounts are in a different spot.
Thanks! I'm in no rush. The car they would go on has a hurt engine so it's not going anywhere anytime soon.
Are the front Spax the adjustable perch types or just adjustable damping?
Adjustable damping only. It looks like a set of eBay coilover sleeves and hats could be used on them, though. And I just happen to have a set of those too.
Ian F wrote: FYI: the frame horns (or suspension towers?) are different for a GT6 than they are for a Spitfire. They look really close, but the holes for the engine mounts are in a different spot.
Didn't know that... Then I have a set of GT6 frame horns that are useless to me.
What, you don't have a drill? The mount plates on a GT6 are further forward than a Spitfire. It's not difficult to move them back, just takes a spot o' welding.
Everything in life needs more brap!
Curmudgeon wrote: What, you don't have a drill?
But why drill when I already I have set that came predrilled for Spitfire from the factory. Then again I am talking about Triumph not guarantee they are in the right place to begin with...
my shock towers in the front have shims on top of shims attempting to make them straight, lol....
fidelity101 wrote: Everything in life needs more brap!
I heart teh brap in teh Spitfire. My buddy wants boingers. Oh, well; it's his money.
93EXCivic wrote:Ian F wrote: FYI: the frame horns (or suspension towers?) are different for a GT6 than they are for a Spitfire. They look really close, but the holes for the engine mounts are in a different spot.Didn't know that... Then I have a set of GT6 frame horns that are useless to me.
Triumph called them 'Turrets'.
(anyone here suffering from 'Turrets' syndrome?)
Hokay. Front suspension real work commences. The idea all along is to keep the wearable parts easily sourced 'off the shelf' and easily replaced, as much as possible. This will keep the car from being off the road while fabricating some weird one off part, if something breaks. So there's some adaptation involved.
The GT6 upper ball joint won't fit the Miata upright, the shaft's too big. It's also tapered. Can't just drill the damn thing out.
Tapered reamer to the rescue!
Now it fits.
The Miata lower ball joint comes nowhere near fitting the GT6 control arm. Some fabrication is in order.
Closeup of the tip of the control arm:
The bolt hole for the ball joint is in the same place as the GT6 trunnion bolt. But the control arm is actually longer. How is this, you ask? The Miata ball joint pivots 1" from the bolt hole, the Triumph pivots at the bolt hole. So the modified arm is actually longer even though the hole's in the same place. This is very important, because it affects scrub radius and the motion ratio which affects the wheel spring rate and also the wheel travel.
Triumph upright in place:
Miata upright in place:
The lower shock mount has been sorta 'roughed' in, it still needs to be boxed in to prevent bending. The final work on that will come after the shocks have been sourced and the fit is 100% verified correct.
There's still some positive camber which has to be fixed. This will mean moving the upper ball joint closer to the car's centerline, which will have some other effects. More on that as it happens. The next step after that is shortening the steering rack.
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