I'm currently undergoing a VVC upgrade on my Spyder.
The VVC engine i bought came with a gearbox which is labelled as the C4BP which is the right version for a 1.8VVC so all good.
I've also got another box that hasn't got a label (came as part of the spares with the car as the previous owner kept the R65 when he upgraded from 1.4 to 1.6). I believe this box came from a mems 3 1.6 MGF so it most likely a C6BP.

As far as I can tell from the net the only difference is the final drive ratio as all the gear ratios are the same in the box itself. C4BP has 4.200 and C6BP has 3.938 final drive.

Anyone have an opinion as to which would suit a Spyder with a 1.8VVC better?

Some forums I've read suggest the C6 needs a different flywheel and clutch but that seems like a red herring as the gearbox input shaft and bellhousing looks the same on both?

I would definitely go with the 4.2 as it suites the engine well.

As far as I am aware all the PG1 boxes will fit.

Thanks Roger. I was tending to think that myself. Acceleration is more important than top speed and the lower final drive will effectively make the ratios closer. I was surprised and had to double check as it seems odd at first that the 1.8 VVC would have lower gearing than the less powerful 1.6 but it seems the higher revving VVC works better with lower gearing and as it redlines higher the change up road speeds are similar through the box based on what I've read. If it made it to the red line in 5th it would be 145mph so unlikely to be a problem. If I saw 125 before Avon Rise at Combe I'd be more than happy! The 1.6 only just gets past 100, maybe 105 there.

The only other difference between the 2 boxes is the gear change fitting. On the later box it goes forwards but on the earlier box it goes backwards. Looks like they should be swappable (with all the brackets too) if the cables prove too short. I've already extended them by about 75mm.

Different engine different car but...

My car on smaller wheels/tyres than yours has a 4.2 diff

Neil

You can just knock the roll pin out and change the mech on the shaft for the gearchange.

If a 4.2 is good enough for you then its good enough for me, the way you came past me at Combe in June when you opened your can of VTEC and squashed my Spyder!