Hi all.  Longtime lurker.  Occasional poster. 

I'm kicking around designs for a muscle car IRS retrofit. Not any specific existing IRS being transplanted (Jag, T-bird, Cobra, etc.)  More of a clean-slate job, probably using Ford 8.8/Cobra drivetrain parts.

Right now I'm struggling with ground clearance & wheel travel.  As best I can figure, this issue is a crappy compromise with pretty much any IRS compared to a solid axle.  


A (real street) vehicle gets designed by the factory to remain safe all the time.  An OEM suspension can be compressed VERY hard without the undercarriage hitting the ground.  Suspension arms hitting the bumpstops, tire sidewalls mashed flat, etc.  But this is only easy with modern wheels (rims).  

With old muscle car wheel dimensions, this becomes a problem.  The short (diameter) rims allow the chassis to fall very low when it's bottomed out & tires compressed.  That calls for the differential to be mounted higher up in the chassis for clearance.  But the wide offset (low backspace) of old wheels makes the half-shafts shorter, which calls for a lower diff location.  

Therefore, when it comes to using muscle car wheel sizes with an IRS  .  .  .  . 

--  good wheel travel
--  mild CV angles  
--  the differential cannot whack the pavement

Pick any 2 of the 3.  


The only fix I can think of is using CV half-shafts capable of larger angles.  The standard ones must be kept less than 10-12* ride height and maybe 20* in brief extreme swings.  The inner "tripod" plunging end is always the hangup.

But after a couple days of internet surfing I have not found any hint of a solution here.  The half-shaft customizing activity all falls into two groups: #1 stronger versions of the stock shafts, and #2 higher-angle shafts that eliminate the telescoping feature (with the whole suspension being redesigned for that).

Do I have an accurate picture of the situation here?  Any feedback?  

Thanks.  

  

Last edited by thedude (9/17/2015 9:13 am)