The V8 Owners Forum -

I am changing my engine to a 4.6,is it worthwhile using the pistons from the 4.0 in the 4.6 to raise the compression or will pinking become a problem?would I notice a difference?

The 4.6 pistons have an offset gudgeon pin, where as the 4.0 pistons do not. Rover did this for a reason. You may well find out what that is if you try it. It is my understanding that it has to do with maintaining sufficient pressure between the piston and the outside arc of the bore.

Blocks designated by Rover for 4.0 litre construction were never used for the 4.6 as there is insufficient metal between the liners, even though both engines have the same bore and use essentially the same block casting.

Does your block have top hat liners fitted?

Ron.

"Rover did this for a reason"

Piston offset is normally used to improve cold start rattle. Not sure its true that 4.0 aren't the same as 4.6s in that respect.

The 4.0 pistons will fit straight into a 4.6 block and bottom end with no issues. It gives you about 3/4 comp ratio increase which is a 'free' benefit.

The max advance for power on a RV8 is normally mid 30s deg and it has about 10 deg of advance headroom (mid 40s) before det starts to be a big problem. You can use this headroom by increasing the CR.

The 4.0 piston swap only helps with no real downside.

Russ

Thanks Russ that is just what I wanted to hear,have you done this yourself?Ron the block is top hat linered.

According to my Land Rover Engine spec sheet the 4.0 and 4.6 pistons have the same offset and the pistons have the same dimensions, only the volume of the bowl is different.

Kevin.

Ooops My mistake. 4.0 and 4.6 pistons do indeed have the same offset.

Apologies to all for suggesting otherwise.

Ron.