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Yet more questions. What's the normal route for upgrading front brakes on HCViva? Having dealt with slightly more common and not as good looking makes of cars inthe past where front brakes from a more powerful model are a straight swap I'm at a loss to what's the deal with Vauxhalls

I know on an OHC subframe you can swap the standard caliper (which I think is a P14) for the bigger P16 version, other than that I think there is fabrication involved. The HP Firenza had thicker discs along with the P16 calipers, but finding HPF discs is quite difficult, and I think you also need the corresponding upright, hub and lower suspension arm to match all the other slightly-different parts, and finding those makes finding the discs look easy.

What's the spec of the engine, that makes you want to upgrade the brakes? There are quite a few threads on here about upgrading brakes in general, one showing how to modify Renault vented discs to fit, which combined with a widened P16/M16 caliper might be enough.

Yep, as Mike says P16's can be fitted to OHC uprights without modification. They are ideally suited to the thicker HPF discs but I've successfully fitted them with standard Magnum discs. The OHV caliper mounting is different to the OHC so you need the OHC upright to fit OHC calipers. OHC disks can be fitted to OHV hubs as the hubs are the same but you'll need a caliper upgrade to suit the bigger diameter. I have a vague recollection that Metro calipers may be able to be adapted to fit OHV uprights but I've no experience of that route.

I believe some Renault vented disks can be easily modified to fit the hubs but are the same diameter as OHC discs so will not improve braking power but will improve heat dissipation in a race type high frequency or prolonged braking situation. I suppose that was the thinking behind the thicker HPF discs, improved heat dissipation.

So, if you have OHC uprights then P16 calipers are a very useful upgrade. Adding modified M16 pads to the P16's gives a further 15% improvement in braking pad swept area....more grabbing power.

Some people have fitted the later M16 caliper (metric) but the mounting holes in the caliper are metric and slightly bigger and you risk the caliper moving on the mounts and possibly shearing the bolts after prolonged use. I've read reports from competition car owners who have not had any problems with caliper movement with M16 on standard bolts after many miles.

Thanks for the replys. It's a standard Rover V8 with auto box.

What front and rear axles are you using?

The hub size and calliper mounting are the same - as far as I know - for OHV and OHC its just that the callipers are larger for the OHC with 9" discs and 8" discs for the OHV - with the larger calliper you cant fit the standard 13" steel wheel - has to be restyle, Avon Saftey or after market (minimise).
I think Ade used Austin Princes 4 pots on hid 5.7L firenza

Fred, the OHV and OHC uprights have different caliper mounts. The Snoot/Ventora uprights have OHC caliper mounts but thicker stub axle for bigger bearings and hubs.

I've achoice of either 1.8 or 2.3 rear axle to use.

The 2.3 has a higher ratio which would be better suited to the V8. There is no difference in strength....both are relatively weak! They will stand up to the power OK when moving it'e the wheel spinning torque that will chew the diff.

They that weak? It'll be a mild V8 and not have wide sticky rubber. More slow n low plodder. The odd over take but not planning on a track day ride