Thread: 3.9 rebuild.....

Depends on your budget, but basically I would up the compression ratio a bit, reduce the deck clearance (quench) to about 45-50 thou (ie make sure the top of the piston is dead-level with the block at TDC if using composite head gaskets, or 25-30thou down if using tin), and replace the camshaft with a higher lift, short-duration one. The heads can take up to about 0.430" of valve lift without guide modification but no more. The trick is to have minimal overlap, low duration, but lots of lift and this will deliver strong torque in the lower and middle rev range, exactly where you need it. Make sure you bed the camshaft in correctly! Very, very important.

A few things you can guarantee with a Rover V8: 1. The quench will be 100thou or more which is completely useless. Target 45-50thou max so that you can run some compression without detonation and get a more efficient burn as a bonus. 2. The compression will be very low (a used LC engine will be well under 8:1). 3. The camshaft will be completely buggered.

You'll probably need to replace the full rocker gear too, as the aluminium rockers fill with swarf (from the dying camshaft) and then eat the rocker shafts.

If you run LPG most of the time and can deal with running 95RON (PULP) on the rare occasions you run on petrol I would bump up the compression to about 9.5:1. The LPG will cope with much higher as its rating is well over 100RON, but getting Avgas can be problematic... :P If the quench is optimised you can stretch this to about 10:1, but exceeding that could require 98RON. More squeeze = more torque and better economy, but requires better fuel.

Orger Engines in Bayswater are absolutely excellent for reco-ing any engine. Not cheap, but it will be done right by blokes that know their stuff. Not sure if they do the pull-out, re-install bit though as I've always taken bits to them for machining, balancing, etc and then done the rest myself. If you want to travel as far as Ballarat I can highly recommend Robinsons Racing in Wendouree. Ted runs/owns the place and does top work at great rates, but don't be in a huge hurry - or book well ahead - as he's in strong demand and always has multiple interesting jobs on the go.

Or have a brain-explosion like I'm doing and build a 4.9ltr stroker fully optimised with custom-ground camshaft, ported head and all. Ooooh - er, I need a lie-down now... and a bank transfusion.

I have a recently-reco P76 4.4 with Rover heads and adaptors, etc in the shed that I could part with for the right money... I also have a used 4.6 short motor surplus to requirements... I really must get around to listing them for sale.