I cannot find any indication in Ron,s book of ground clearance i.e. from bottom chassis rail to road. 120mm appears to be what I'm going to end up with, is this about right?

depends how much your engine hangs down, and how safe you want it to be. Its a compromise. The lowest you can really go would be 3 inches under the sump, but thats pushing it what with speed bumps etc. I have about 4" under mine.

I used data from a Westfield build manual for my car - they suggest the following:

Front = 5.75", +1" to -2" from chassis to floor

Back = 6.25", +1" to -2"

Not forgetting 4" clear under the lowest point of the sump - usually the bottom of the bell-housing is the limiting factor.

David

For info the max (legal) height of a speed bomp is 4", I have a min ground clearance of 5" under my car, it only very occaisionally grounds - it does have a much longer wheelbase than a 7 which exagerates any ground clearance problems