Robert Thornton R.Thornton at adelaidecitycouncil.com
Fri Jul 30 00:13:12 BST 2004

<Would you go P76 4.4 or Rover 3.9?

What sort of power can a 3.9 put out? What about 3.5?>


Personally I'd opt for a 3.9 - because of the bore/stroke combination
it's the smoothest of the Rover V8s. You also get a good increase in
power - up from around 155 to 182 bhp (though this depends on the spec
of your engine) and, more importantly, a hefty increase in torque. The
3.9 cam is a good one, designed for the LR 4x4s - ie to move a heavy
vehicle off the line - and would go well in the relatively heavy P6. 

However all that glitters is not gold. The Aussie spec Discos were low
comp 8:1 cr engines enabling them to run on low grade fuel and meet
local emissions laws without the use of cats and lambda sensors, so if
you want to retain your 9.35:1 cr (which I think is what the 3500 P6s
imported into Oz had) then you have a number of options: 

1. try to find a used high comp 3.9 engine as fitted to the UK spec
Discos/RR - easier said than done; 
2. fit smaller combustion chamber 4.6 heads (this will increase your
costs however); 
3. fit hc pistons to the 3.9 (again expensive); 
4. machine the block/heads faces to raise the cr and fit steel shim head
gaskets (you will have to shave the faces of your inlet manifold by a
corresponding amount to get them to refit); 
5. weld up the combustion chambers on your 3.5 heads to reduce their cc
from the existing 36/37cc to around 28/29 cc and hence raise the cr; 
6. buy a new high comp block/short engine - by far the easiest option
but by no means cheap.

Alternatively you could just install a low comp 3.9 and live with that -
perfectly ok but about 10bhp less. Your 3.5 heads will fit this ok but
post '76 SD1/RR heads with the larger valves will work better with the
bigger bore of the 3.9.

The 4.4 P76 is alright but the long stroke makes them a bit harsh and
nowhere near as smooth as the 3.9. They do produce good torque which is
why so many have been installed into older RRs. Finding a good 4.4 may
take a bit of work as they were last produced in 1974, but they do
occasionally appear for sale. A number have found their way into P6s and
the owners seem pretty pleased with the outcome. Try to get a sedan
engine rather than the Leyland Terrier truck version.  The P76 heads are
basically the same as the older 3.5 ones so there's no probs there,
although because the P76 block is slightly higher and therefore wider at
the top than the Rover engine you will need to fit spacers to the inlet
manifold/head faces - available from some of the specialist Rover tuners
(TR Spares, John Davis, Vitesse Developments, etc).

A rebuilt 3.5 with high comp pistons will also be a good bet - but avoid
the low comp Aussie SD1 engines unless you have access to a supply of
9.35 or 10.5 pistons.

One last option is to try to find a used 4.6 from a wrecked P38 RR, or
buy a new short hc one for around 4k. You can fit your 3.5 heads using
steel shim gaskets and it will really make your P6 fly.


-----Original Message-----
From: rovernet-bounces at lyris.ccdata.com
[mailto:rovernet-bounces at lyris.ccdata.com] On Behalf Of Herbert Greer
Sent: Wednesday, 28 July 2004 9:11 AM
To: rovernet at lyris.ccdata.com
Subject: RE: [ROVERNET - UK] 3500S



Would you go P76 4.4 or Rover 3.9?

What sort of power can a 3.9 put out? What about 3.5?

Herbert & Roger


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