Specifications (SVW Review Issue 20, 2011)
Standard VA TPBG engine
Horse Power 11.98HP
Power 54 bhp
Police Specification VA TPDG engine
Horse Power 13.22HP
Power 67.7 bhp (est)
You need either WA Pistons or the MGA 1600cc "Flat-Top" Pistons for the increased 1708cc cylinder bore. The MGA Pistons are usually easier to find, but will need the gudgeon pin hole reaming out slightly to take the original connecting-rod little-end pins. (This hole must be reamed to be a sliding fit).
SVW Parts also stocks a slightly larger Wolseley Engine head gasket which is more suitable for the larger 1708cc bore.
Is it 1708cc or 1709cc?
My maths says pi*bore/2*stroke*4/1000 = litres and I get 1707.638cc or 1708cc when rounded.
Wow, this post resulted in some really good information from the SVW egroup on Yahoo as well as the SVW Register, thanks for all the feedback. I summarise below:
Robin Page - Australia
I asked my engine man to do this to my VA1880S. He carried out an ultrasound and did not consider there was enough meat in the block. So he bored to 72mm. Pistons and conrods were made to order to achieve a compression ratio of 8.55:1. Capacity is now 1657cc. Standard MGB camshaft grind. Engine was balanced. It is a very strong and torquey engine and feels more like a 6 than a 4.
For what it is worth.
Bas de Voogd - Holland
I think there is quite a difference in casting thicknes’s possible. Personally I am not in favour of this operation. Remember MG’s only experimented with it. There is no proof of larger VA engines other then 5 experimental ones and the typed Policecar Sales leaflet. Quite well possible that even these five TPDG experimentals were a thicker casting too. There are however a number of succesfull enlarged bores running around without hassle so far.
The attached photos (courtesy John Bannister) show a blown up engine but this might have been caused by a loosened up small end pinch bolt and neglecting the rattle. I know more then one VA loosing their engine this way.[Contact me re photos]
A thought might be to grossly overbore, then press in a thick, engineered sleeve designed to seat on a machined ledge at the bottom.Then bore to specs.Core shift was a real problem on most early engines, world wide. It made thin wall, light engine blocks something for the future.