Comparing brakes between two completely different cars is difficult to simply attribute to the calipers. Many factors are involved:
*tyres and tyre pressures
*weight of car
*disc diameter (and thickness), and thus leverage/torque effect
*master cylinder size
You might be lucky and have a good improvement if you changed to Porsche calipers (presuming they are easy enough to fit). But you may simply benefit from fresh brake fluid and higher quality pads, say Ferodo DS2500 (properly bedded-in).
Some clever person may be able to model the effects of the caliper change, keeping everything else the same (ie: just by changing the calipers and matching pads) according to piston diameter and number and pad surface area...
What's the design of the Porsche calipers, and what's the surface area of the pads compared with the 75?
Thanks for the replies, I'm not that technical so I don't know the specs of the 944 calipers, only that they work so much better then my 75 ones!
Yes of course there are lots of factors and the 944 is much lighter than my 3.0L 75 but the braking difference is night and day!
I am fitting some new front discs (black dimond grooved) and new pads (green stuff) so hopefully they will improve. The rear discs I'm getting a specialist to look at as they are more complicated to set up correctly.