Narrowed C4 rear mods

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Garys 68

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I've been trying to find an appropriate forum for this and with the wealth of suspension knowledge here, this is probably the best place.
Anyway, I've been looking at doing another LS conversion since I finished my 6.0 LSx vette. I've wanted to do an aluminum 5.3 L33 in a Triumph Spitfire ( I know, not a vette). Obviously the weak spitfire rear wont hold up so I've been looking at C4 rears.
The spitfire rear is IRS with axles articulated at the diff but not the wheel, axle and wheel hub are solid. Single trailing arm, and transverse leaf springs, even the wing style body mount. Some similarities to both C3 and C4 rears. I like the C4 because of price and availability. Not sure if it's lighter than a C3, but looks to have a lot of aluminum parts.
So this will be strictly a street car. Would narrowing the halfshafts, lower control arm, and toe adjustment rod all by the same percentage be adequate? I was thinking about trying to duplicate the geometry of camber change of the spitfire, but may be overthinking the issue.
For the single to twin trailing arm arrangement, I would probably have to shorten those too, but would make them adjustable in length and frame mount location.
 
I would caution you to look out for "unintended consequences". For example, shortening the parallel forward links makes the wheel travel forward with droop and/or compression (depending on the links' relationship to ground "level"). This movement can then induce roll steer. The forward links are already too short in a C-4. With the C-4 IRS, you can run a suspension program (like Performance Trends) using the IFS module that will help you relocate the instant centers (lateral and forward) to keep the roll center and anti-dive/anti-squat under control. As long as you don't have excessive wheel travel, you can get by with narrowing a C-4 suspension quite a bit. My $.02 worth.

Click on "my Photos" in the upper right hand corner of this post and you will see a couple of photos of a C6 suspension "narrowed to the max" (same principles as narrowing a C-4) and a photo of one of my C-4 based suspensions - widened with lengthened forward links.

Pappy
 
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I'll have to take a look at the capabilities within a small car like a spitfire. One reason I'm looking to start now is that there's a frame I can get cheap to start planning the suspension. A solid axle might be easier, but I kind of like keeping the IRS and C4s are pretty easy to find.
 
Does a Spitfire have a wishbone frame? I had a TR6 with a wishbone frame and it super twisty. If you jacked up a corner, you couldn't get the doors open.
 
Yep, another reason I'm looking at picking up just a frame now. To stiffen it up.
Btw, this has been done before with a C3 rear suspension.
http://www.ye-beast.com/

BBShark said:
Does a Spitfire have a wishbone frame? I had a TR6 with a wishbone frame and it super twisty. If you jacked up a corner, you couldn't get the doors open.
Click to expand...
 
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I've found an 84 C4 complete rear and 78 triumph frame locally. Guessing I can get both for about $500 total. I think I'll pick them up.
I noticed in the link above the guy used the stock C3 trailing arm, so I'm guessing the stock length of the C4 dual trailing arms wont be an issue.
Next issue is figuring out a chevy 5 lug wheel/tire combo that will clear the bodywork and C4 rear calipers. Then determine how much to narrow.
 
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