3.9ltr, 1992 Range Rover block into P6 V8, How easy?

DamianZ28

Active Member
Hi Guys, was wondering how much is involved in swapping my standard 3.5 blk with a 92 Range Rover 3.9 EFI unti?

I've seen one on Ebay but not too sure if enging mounts, auto boxes etc are compatable. I Would keep my carb set up & use my Mallory disty, I'd need to change the drive gear on the shaft.

Anyone done this conversion ?

Cheers Damian
 
All the block mounts are there to enable it to drop straight in, you'll just need to change the ancillaries, the timing cover, and the spigot bush.
 
In addition to what Harvey has already covered, you'll also need to use your P6B sump, windage tray along with the dip tube and the dip stick.

Ron.
 
Is it correct that all engines newer than 3.9 are a big improvement? Just thinking if you're doing an engine change it may be worth holding out for one of the bigger ones?

Rich
 
Hi Rich,

The only engines newer than the 3.9 are the 4.0 and 4.6. The 4.2 litre came out prior to 1993 whilst the 4.0 and 4.6 first appeared in late 1994.

Certainly in terms of capacity and thus torque delivery, the 4.6 is on a different page altogether.

Ron.
 
Just had a look around and wikipedia says (so it must be right :D ) that 4.0 and up engines have crossbolted main bearings and improved ribbing on the block. So assuming the wikipedia page is correct there are some differences apart from displacement....

Rich
 
Yes the 4.0 and 4.6 both feature large journal crankshafts held in place by cross bolted main bearing caps. The crankshafts, rods and pistons for these engines cannot be fitted in 3.5, 3.9 or 4.2 litre blocks. The blocks for these engines were different to all Rover V8 engines before them.

Ron.
 
rockdemon said:
Just had a look around and wikipedia says (so it must be right :D ) that 4.0 and up engines have crossbolted main bearings and improved ribbing on the block. So assuming the wikipedia page is correct there are some differences apart from displacement....

Rich

Sparky has the 4L unit. It is the same displacement as the 3.9 but has, as you say, the crossbolted mains. The main bearing journals are also bigger.

They called it a 4L to differentiate between the two. Some company in Somerset area is now casting the blocks, and the casting is a lot better than the old stuff.

Crossbolting for those who are interested, means that the main bearing caps are machined to fit the block, so they cannot wiggle about under load, and then bolted up in the normal way. They are then bolted in from the side as well to form a more rigid bottom end.

Richard
 
Apparently all the blocks are the same as far as the external holes/mountings are concerned. Differences are all internal and in the ancillaries.
 
Small journal blocks, ie 3.5, 3.9 and 4.2 suffer from fretting of the main bearing caps at very high mileage. The 4.0 and 4.6 blocks don't suffer like this, BUT they DO suffer from liner movement / leakage. The only completely bullet proof blocks are the modern "Coscast" blocks, which are essentially 4.0 amd 4.6 blocks cast to the correct quality control standards that the originals should have had but didn't! If you do suffer from liner leakage in your 4.0 or 4.6 then top hat liners are available which cure the problem.

Chris
 
chrisyork said:
BUT they DO suffer from liner movement / leakage. The only completely bullet proof blocks are the modern "Coscast" blocks, which are essentially 4.0 amd 4.6 blocks cast to the correct quality control standards that the originals should have had but didn't!

From what I've heard the jury's still out with those.

Not that this means anything one way or the other, but one well known company reckons they're the best thing since sliced bread.....when they have them in stock, and a pile of cr*p when they haven't, and so would rather take your money and sell you something else....)

chrisyork said:
If you do suffer from liner leakage in your 4.0 or 4.6 then top hat liners are available which cure the problem.Chris

IIRC the last time someone I knew enquired the machining and liner costs alone were about £1200, and although that was a highly reputable company they wouldn't offer any guarantees.
 
The large bore blocks,...3.9, 4.0 and 4.6 all in OEM form suffered from dropped liners to one degree or another. The 4.0 suffered the most, the 4.6 the least. From all that I have read and from all that I have spoken with, the cause appears to fall into the domain of a combination of lean fuel mixtures and excessive running temperatures (for the Rover V8). As an example, the P38 Range Rover which housed the 4.0 and 4.6 were fitted with 96 degree thermostats, so the normal coolant temperature was 100 degrees C or more. To keep a lid on things so to speak the radiator cap was rated at 18.5 psi. Using an OEM block without top hat liners in say a P6B where an 82 degree C themostat would feature,...likely no problem. Still, top hat liners do provide a feeling of security.

Ron.
 
Using factory blocks and heads and the p6b twin su intake, what's the best streetable combination (barring the 4.6 - has no dizzy takeoff and I don't want to go to the effort that ron did)

Just that there are some very cheap 3.5 litre motors out there from range rovers and later 3.9s/4.0's also seem to pop up occassionally for a low price
 
Hi Geoff,

For an increase in power and especially torque (the latter is all important where an auto is concerned) while working to a budget, I'd opt for a 3.9 short motor, fit your P6B timing cover and oil pump, windage tray, oil pickup and sump. Cylinder heads,..14 bolt will be up until 1993, 10 bolt from 1994 onwards. The latter are better, fit composite gaskets, 3.9 camshaft and a Rover steel timing set. You'll need to fit the engine breather pipe into the valley in the same style as on your 3.5. New rocker assemblies, lifters and pushrods. Refit your rocker covers and inlet manifold. Chose BAF needles for the carburettors, fit Lumenition into the distributor and refit.

Ron.
 
Keep the 3.9 Heads? No other head from the same engine family is a better choice? (ie SD1 Vitesse?)

Is there a particular year that's better or one to avoid etc?
 
The Rover Vitesse was never officially imported into Australia, and any that did appear (I have never seen one) would be as rare as hen's teeth, so finding a pair of heads would be next to impossible. However, from late 1989, all Rover V8 cylinder heads featured Vitesse waisted stem inlet valves. With the introduction in 1994 of the 4.0 and 4.6 litre engines, a new cylinder head appeared, typically referred to as 4.6 heads. These had improved porting and also featured the Vitesse waisted stem inlet valves. For all intensive purposes, these are essentially as good as the Vitesse heads. So either find 14 bolt heads manufactured from say 1990 onwards or 10 bolt heads from 1994 onwards.

Ron.
 
If you're going to the effort of removing the engine from the Range Rover then why not keep the fuel injection system too?
 
ewokracing said:
Keep the 3.9 Heads? No other head from the same engine family is a better choice? (ie SD1 Vitesse?)

Is there a particular year that's better or one to avoid etc?

Hi Geoff,
I have recently gone back to the LR 3.9 after my 3.5 rebuild fiasco. I chose fitting composite head gaskets with the Vitesse heads from my 3.5. As the compression ratio is lower I decided to fit a Hurricane performance camshaft which works really well with the 3.9 as you don't lose out on bottom end torque(even with an automatic), and have a nice smooth delivery with a punch at higher revs.

When I had the 3.9 fitted previously, I had fitted the standard LR 3.9 heads with the LR 3.9 cam. This set-up is for higher torque delivery at lower revs(obviously suited to a heavy 4X4 vehicles), and in my SD1 it had a relentless surge of torque on any road from around 2000revs onwards. Very impressive. But I find the engine is much more refined, smoother and more balanced with the performance cam fitted to the bigger engine in a relatively light car.
 
testrider said:
If you're going to the effort of removing the engine from the Range Rover then why not keep the fuel injection system too?

Just spent an eye watering amount having the twin SU's rebuilt a few months ago.
 
Can anybody advise if the tall plenum chamber of the 3.9 from a Disco will clear a P6B bonnet please? Have access to such a 3.9 with injection and loom, and maybe a P6B soon. Also somewhere I have read that inlet manifolds from after 76 wont fit pre 76 heads and vice versa - true or false?
thanks
jp
 
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