The V8 Owners Forum -

Hi all, I am looking for some information concerning the rebuild of my Rover V8, I have read somewhere that using 4.0 pistons with 4.6 rods and crank is a good set up, can anyone give me any further information on this

Having, this morning, just stripped down my (new to me) 4.0 and compared the piston to a 4.6 one, I can see that the dish in the 4.0 is shallower than the 4.6, so I presume the piston change would up the compression rate, is that the reason for this swap.

I am fairly new to all this but I do understand that I will have to do a lot of measuring and dry building to make sure that valve and pistons don't collide and to get the VTG right depending on cam choice as well

Kind regards, Lester

If you have 4.6 rods and crank in a block and fit the 4.0 pistons this puts up the compression ratio.

One of the reasons for choosing this combo would be using the earlier 14 bolt heads and composite gaskets without dropping the compression ratio.

I bought a short engine from V8 Developments and was given the option of 4.0 or 4.6 pistons. As the stage 3 heads I wanted to use were 14 bolt ( bigger combustion chambers than 10 bolt) using the 4.0 pistons saved me the cost of getting the 14 bolt heads skimmed to 28cc combustion chamber size - same as the 10 bolt.

Thanks very much, I thought that would be the case, nice to have the confirmation and the other info you posted, cheers

Kind regards, Lester

The other reason for doing it is if you run on LPG. The rise in compression ratio is worth having.

If you run the older heads on composite gaskets, you might have bother getting the tappet preload right, and the inlet manifold might be a bit marginal on fixing hole alignment.

Chris.

ChrisJC wrote:The other reason for doing it is if you run on LPG. The rise in compression ratio is worth having.

If you run the older heads on composite gaskets, you might have bother getting the tappet preload right, and the inlet manifold might be a bit marginal on fixing hole alignment.

Chris.

I've used older style heads, comp gaskets and a stock inlet manifold, it all bolted together OK and the preload was within limits.
Best regards
Mike