LR 3.5 Plenum Swap to Rover SD1

[paulcnb]

Hi,
I have just fitted a rebuilt 3.9 Disco engine to my '85 SD1 VDP and have bought a 3.5 LR (flapper) plenum that I would like to fit instead of the original SD1 'federal' type plenum that is currently on the engine.

I'm OK with swapping the throttle hardware, TPS and other stuff from the SD1 to the LR plenum, but can't see where the SD1 over-run valve from the federal plenum will fit onto the LR 3.5 unit.

If anyone here has been-there-done-that, Id appreciate advice as to whether the SD1 over-run valve is needed with the LR flapper plenum and if so, how do I go about fitting it?
Regards,
Paul

[bee utey]

Not sure what the Federal setup looks like but the 3.5 flapper has an overrun vacuum switch mounted separately alongside cylinder #6 injector. In any case it runs perfectly without it, however you will use a small amount of fuel on overrun.

[paulcnb]

Thanks bee utey.
The SD1 federal plenum is a squarish two piece low profile unit that was manufactured for the US SD1 market and was consequently used on Oz SD1s. It doesn't have trumpets like the 3-piece LR unit and its ports are all rectangular and of the same length.
The UK SD1 forum guys told me that the single biggest thing I could do to realise a performance enhancement would be to fit a LR plenum. Thus my question re the over-run valve.
I'll try to source a LR valve to fit - but based on your advice, will run without if necessary.
Regards,
Paul

[loanrangie]

You'll need to fit the complete manifold as just the top section wont fit.

[paulcnb]

Yes - I have the complete LR plenum and manifold - minus the over-run valve from what I understand.