"rovieman" <
[email protected]> wrote in message
news:
[email protected]...
>I need all the torque that I can have and will go for an overbore.
> Are the outside diameter of the 3.5 and 3.9 liners different ? If the
> original liners are thick enough to be overbored to accept the 3.9
> pistons, why replace them ? There are some really good machine shops
> overhere.
They are not thick enough to bore, you need the new liners. If you want
ultimate strength, get some "top-hat" style liners for better gasket
sealing.
> Can the bigger crankshaft of the 4.0 replace the original(for strenght
> reasons)?
Yes, if you line-bore the block with caps torqued down, but then you weaken
the caps, even if they have ARP studs holding them.
The std 3.5 / 3.9 crank isn't noted for being failure-prone, I'd leave it
alone other than balancing, and fit with ARP stud kit for reliability and
clamping strength.
Why not look at a big-capacity kit, such as 4.3 or 4.8 from real steel? As
for fuelling it, if sticking with EFI then I think you'd need to look at a
re-mapped version of the hot-wire setup from a 4.6 if going any bigger than
4.0.
If sticking to 3.9 with the modded flapper type efi system as per my earlier
suggestion, then fit a genuine 3.5 efi rangerover cam for max low rpm
torque. Do not let anyone fool you into a carb cam or a "this one fits all,
sir" camshaft. They ARE different. Get the compression up a bit would help,
but remember the bolt alignment for the inlets. i'd start with 10 bolt heads
and composite gaskets as a minimum spec, don't hog out the ports too much
either, smaller ports have a higher gas velocity at a given valve
lift/vacuum and so are better akin to producing low rpm torque, enhanced by
the gas velocity's scavenge effect. Relatively small-bore tubular headers
are a good help also, not big-bore as these reduce the gas velocity at lower
rpm's.
Badger.
