Thread: 3.9 Plenum top cover spacer ?

Been looking in the files for this, but finding plenty of hot air...

Is there any 'seat of the pants' improvement to be had by adding a spacer under the plenum cover ? I'm thinking maybe 1 cm which would give more clearance at the trumpet tops... which is marginal according to what I've heard. - Correct me if I'm rrong...

The other thing seems to be adding a heat-insulator spacer under the lower plenum mounting, between it and the inlet manifold.

Either way, anyone done the deed, and if so, how high can I venture before fouling the bonnet?

I've got the plenum top off at the moment, to give clearance and working space as I muck around a few hose jobs in the area... going Gen III injectors and by-passing the heated manifold - floor thingy... it's totally blocked.

I noticed that some recommend the THOR inlet manifold as being the best way 'up'... Interestingly, the plenum cover has part numbers for my 3.9 AND the 4.2 moulded into the inside surface.

- Are they worth it / How much - roughly ?

The Lady Sarah, 1995 3.9 Vogue SE with working air suspension...
- don't mention the B.W(AR)

SQ,
I have a Bakelite insulator in my 4.5 V8 D1. I did not do a "before and after" dyno but I think it has made a difference (the people in the UK say an insulator adds 10 hp). On the dyno that I use the car has 110kw at the wheels. I'm told a standard 4.6 Rangie puts out around 90kw at the wheels on the same dyno, but I'll take this with a grain of salt!
My insulator came from a plastics mob in Bayswater in Melbourne, and cost $90. They cut them using a CAD file supplied by Stirlsilver of ute fame in Tutorials. Perfect fit. If you PM me I'll send you the contact details. They also have Stirling's file for a plenum cover gasket that will give you another 10mm. I have not done this as I'm in the process of popping the trumpets out and shortening them by 20mm. This is what the Ginetta and TVR guys do in the UK, it apparently give a good power increase without impacting the torque curve too much.