Rover 4.0 pistons

rscob · Post by **rscob** » Fri Jul 22, 2011 5:10 pm

Hi guys,is it worth my while sticking 4.0 rv8 pistons in my 4.6 that i'm rebuilding to raise the compression if so how much extra bhp will it give me and are there any negatives about doing this piston swap.

Cheers rob

Muscle-Manta · Post by **Muscle-Manta** » Fri Jul 22, 2011 5:34 pm

I have done this mod to my 4.6 engine as I am using 14 bolt heads which lower the compression ratio due to the larger combustion chambers.

The 4ltr pistons brought the compression back up to around 10:1

rscob · Post by **rscob** » Fri Jul 22, 2011 5:40 pm

Have you noticed any running vibrations on the engine with it not being balanced with the original pistons.

Rob

Muscle-Manta · Post by **Muscle-Manta** » Fri Jul 22, 2011 8:04 pm

I had the complete rotating assembly balanced by Bassetdown Balancing Swindon.

CastleMGBV8 · Post by **CastleMGBV8** » Fri Jul 22, 2011 9:14 pm

Rob,

Swapping to 4.0 pistons will increase comppression to around 10.75/1 subject to exact measurement of deck height chamber size ect, which is a little high for a road engine, and would require at least Shell optimax fuel although if your engine has a knock sensor, that might give a bit more protection from detonation.

Kevin

sidecar · Post by **sidecar** » Fri Jul 22, 2011 10:20 pm

Hi Kevin,

We Buretted Mr Muscles pistons and chambers when the 4.0 pistons were fitted, the CR was around 10:1 but like you say it should be measured, not guessed at! (With 28cc chambers the CR would go through the roof!)

V8 Developements sell 2 thicknesses of comp head gaskets, one is 1.0mm and the other is 1.3mm thick so there is some adjustment to be had there.