HI,
Why does no one use the MX5 rear subframe complete? I know it weighs a little more but would speed up the build no end

They do, look at the MEV vehicles - Exocet and Replicar - but they use the whole mx5 "chassis" including the front subframe and connecting framework.



But in a Seven type car they add a lot of weight for little return when you can do the same with a lot less 1" tube to replicate the mounting points plus you do not get the benefits of double wishbone suspension and would have to revert to the McPherson strut type suspension.

Like the concept of the space frame Bauer Catfish is using:
http://nebula.wsimg.com/fed772661e14e1c94fbcf62e678ec306?AccessKeyId=F9677BCFCAD27219EACC&disposition=0&alloworigin=1

That's nice