Rover V8 Capacities

[corazon]

There's so much information bandied around the internet and in fact generally concerning the different capacity variants of the Rover V8.
I thought it would be very useful to hear from people who have 1st hand real world experience of the positives and negatives of each block.
You can read people's regurgitated, overheard opinions endlessly and come full circle, not knowing whether to ever stray from the standard 3.5 litre.
I know that there are a few key forum members who'll contribute to this, but I'd also like to hear from anyone who has actually run/worked on 3.9,4.0,4.2,4.6 capacity engines, and/or bored/stroked versions of any blocks.
For example I could easily say 4.6 engines all get slipped liner problems, but I know I've not seen that happen personally and I would just be repeating information.
Let the conversation commence!

Jim

 

[rockdemon]

The other thing that isnt normally answered by these discussions is at what mileage does a slipped liner occur... At 6000 miles a year that might mean you'd wait 20 years on average to experience a slipped liner or it might happen at 2 or 3 years which makes it a different proposition? Also dont the later engines get run much hotter, and therefore under more stress than we'd exert on it in a p6? P6 is meant to be 88 degrees. Isnt it 96 degrees on a range rover installation of the 4.6?

 

[1396midget]

interesting topic

Can I join in? I must be one of the few with an overbored 3.5 (+20) - most would go with a 3.9 I guess from a tired 3.5. Thank RPI and the previous owner for that It seems to be fine, been going for about 6 or 7 K in my ownership and hasn't exhibited any overbore related hiccups. Harvey mentioned he wouldn't do it as the liners get a bit thin, and I think I would have gone for a bigger engine myself if the 3.5 was toast. And I will, if it does.

 

[SydneyRoverP6B]

Just a quick intro for the moment as I have a fairly busy morning ahead, so I'll post up a lot more detail later in the day.

The 4.0 and 4.6 litre engines did indeed run far hotter than any preceeding Rover V8 engines, as Rich mentioned, the thermostat was set to open at 96 degrees C. However unlike all the other capacities where the stat is located within the inlet manifold just prior to the coolant entering the top radiator hose, the 4.0 and 4.6 litre engines have their thermostats located within a plastic housing, fitted within the bottom radiator hose. The normal running temperature for both engines was not less than 100 degrees C.

More to come,

Ron.

 

[chrisyork]

OK then. There are two distinct families of Rover V8 - old style block and cross-bolted block. Plus if you're feeling very flush, Cosco block engines, where the design is as per the cross bolted engines, but the execution (importantly the casting) is by Cosworth rather than BL/ARG/BMW. In most varieties there are a variety of compression ratios available - usually by varying the pistons.

From SD1 onwards, there's not a lot to choose between heads - they all get the same valve sizes, but the chamber volume decreases with the adoption of composite gaskets. This was achieved simply by machining a bit more off the block face of the casting. And (I think) roughly contemporary with the introduction of the P38 Range Rover, all heads lose the outer row of small head-bolts (from '96). So yes - a 4.6 is breathing through the same valve sizes etc as a 3.5 SD1......

Rich is right about the vagaries of the P38. In an attempt to up the efficiency of an old design, LR/BMW increased it's operating temperature as far as they dared. Fine on a new vehicle, not fine on an elderly or ill maintained one. So P38 onwards engines are prone to being cooked, and this may well be one underlying cause of slipped liners on later engines. But only one cause, there appears also to be a casting quality issue with the blocks on later engines - hence the popularity of the Cosco blocks.

The early family of engines all suffer to varying degrees with main bearing cap bother. The cap loosens with age and starts to fret against the block. This is a certain block killer when too advanced. The cross - bolted engines eliminate this altogether and have larger crank journal diameters.

As far as capacities go, there are essentially only two bore sizes and three crank throws. So:

3.5 ltr => 89 mm bore X 71 mm stroke
3.9 ltr => 94 mm bore X 71 mm stroke
4.2 ltr => 94 mm bore X 77 mm stroke

4.0 ltr => 94 mm bore X 71 mm stroke and X Bolted
4.6 ltr => 94 mm bore X 82 mm stroke and X Bolted

Note that all engines apart from the 4.6 are heavily "oversquare", ie much bigger bore than stroke. As a rule, the longer the stroke relative to the bore, the torquier an engine becomes. In this case the reverse is true. The 3.5 is the revviest of the engines, getting progressively softer as the capacity increases. There must have been some heroic work on cams to achieve this unusual effect.

So what would I build? Easy. 89mm bore from the 3.5 with the crank stroke from the 4.2 to give a rather squarer engine proportion and without upping the capacity too far beyond the capacity of the heads to feed - which arguably the 4.6 is. So that gives me around a 3.7. And can I have it cross bolted please? Of course you can't actually build that spec, because you can't get a cross bolted block in that bore size or a big journal 77mm crank. So I'm just going to have to accept an early block 3.7! Balanced and with careful attention to the main caps and bolts that should be able to rev a bit beyond the rather pathetic 5200 of the standard engine and still be pretty torquey with the right cam. And it doesn't ask too much of the heads in terms of gas flow.

Chris

 

[SydneyRoverP6B]

chrisyork wrote,...

So yes - a 4.6 is breathing through the same valve sizes etc as a 3.5 SD1......

Just a quick correction Chris, the valves have waisted stems, ie Rover Vitesse, not standard 3.5 SD1 :wink:

Ron.

 

[SydneyRoverP6B]

Ok, so as to address Jim's original question....

I thought it would be very useful to hear from people who have 1st hand real world experience of the positives and negatives of each block.

I drove my Rover with the original factory engine until 2007 covering just over 203,000 Miles (327,000km). The only mechanical parts within the engine that had been changed since 1974 were the rocker shafts and head gaskets in 1997. The original rockers I transferred to the new shafts, something that I would not do now, having learnt considerably more since then.

Apart from the main bearing caps coming loose in the late 1980's, no top or bottom end problems ever surfaced. Of all the parts within the Rover, the engine was easily the most reliable. I never had any problems with the block, no leaking welch plugs or dropped liners.

I have driven a number of P6B Rovers over the years, and by that I mean Rovers that belonged to other people. Some were very pedestrian in their performance, others performed in much the same way as my own.

In 2007 the time had arrived for the engine to either be overhauled or replaced. Power and torque had dropped from what they once had been, the original camshaft, lifters and timing set with over 203,000 Miles on them were all very tired indeed. After a wide ranging consultation, I elected to go with a 4.6 litre, the block would be fitted with top hat liners prior to building.

In the 6 years since installation, the new engine has covered some 88,000 Miles (142,000km). Impressions,...the engine is very much smoother compared to any 3.5 litre engine that I have driven. I am not saying that the 3.5 litre engines are less than smooth, rather I am speaking relatively. The block has given no problems (now typing very quietly just in case it is listening) at all thus far. The difference is power and torque is astounding, like night and day.

If you have any questions Jim, please ask away

Ron.

 

[corazon]

Thanks for the replies everyone, keep them coming!
Quattro if you're around, what are your experiences with the different engines you've had in your P6's? Especially Sparky's current?
Harvey, I guess you're keeping quiet because you don't know where to begin, but what's your ideal block/do you have it in your car? :wink:

Ron, what compression ratio is your 4.6? And you still use the P6 V8 diff right?
I'm very interested in doing something similar to you with a few differences.
The SD1 heads I'm swirl porting and tidying up would replace the 4.6 heads, I'd most likely retain the SU carb set up as you have done (very successfully I might add). I'd use the stainless headers yet to be fitted to my 3.5. Since the torque with the 4.6 is as good as taken care of, I think minor breathing improvements could only be a good thing for the other end of the rev range? Then perhaps fit 4.0 pistons and skim the heads to achieve some more compression just to put the icing on the cake..

My project has taken a little detour now with the zfhp22/24 hybrid box so I'm going to keep the engine as is to get the car on the road again with the new gearbox. I've just been thinking I shouldn't really put any money into the 3.5 if it will be replaced in the near future.
Once gearbox is in and working well I think I'll get hold of the best 4.0 or 4.6's I can find for reasonable money and run it as is ( either with or without all the mods I've listed to begin with). Then address any problems if and when they arrive, liners etc..

Over the last month I've removed/refitted a few different V8's, P6 3.5's, an SD1 Vitesse 3.5 efi, and most recently DIscovery 3.9 hotwire, so have been noting all the differences and feel confident in removing them regularly. Running 4.0/4.6 can be bought for similar money to that which I'd spend on my 3.5 top end rebuild so I'm trying to weigh up the pros/cons

Jim

 

[stina]

Hi Jim .
I can see the sense in what your saying , and weighing up . Not including normal servicing costs In my nearly 3 year owner ship i must if spent around the grand on the engine .
SD1 heads
water pump
Oil pump upgrade
steel timing set / duplex chain
Cam (3.9)
lifters
Manifolds
Edit . push rods , rockers , shafts , seal conversion . ( keep remembering bits ! )
Add in nuts , bolts , gaskets and your getting close . Then a fan and controller upgrade , and your getting close :shock:
I can see where your coming from .
Ps glad the old man can't use the computer

 

[1396midget]

My PO bills put the rebuild of the 3.5 that's in mine at 3.5K, in 1999. That's £1000 per litre. :shock:

 

[SydneyRoverP6B]

corazon wrote,...

Ron, what compression ratio is your 4.6? And you still use the P6 V8 diff right?
I'm very interested in doing something similar to you with a few differences.
The SD1 heads I'm swirl porting and tidying up would replace the 4.6 heads, I'd most likely retain the SU carb set up as you have done (very successfully I might add). I'd use the stainless headers yet to be fitted to my 3.5. Since the torque with the 4.6 is as good as taken care of, I think minor breathing improvements could only be a good thing for the other end of the rev range? Then perhaps fit 4.0 pistons and skim the heads to achieve some more compression just to put the icing on the cake..

Hi Jim,

My 4.6 has an 8.37 : 1 CR, and there is a very good reason for going down that path. The gent who built my engine has over 30 years experience with building and dyno testing Rover V8 engines and vehicles. From that experience, for a vehicle with an automatic transmission, a low compression engine has an advantage over a high compression engine. That advantage stems from the way in which the engines build power, the low comp engines delivering at a greater rate per unit revs. The final maximum power is slightly down on the high comp engines, but in terms of useable power, the low comp engines have the advantage.

Yes indeed, the diff is the original, no changes. Mind you, I could easily break it if I chose too, hard accelerating from low speeds not to mention breaking traction would soon see it ruined. I tend to drive very concervatively in the main, especially when pulling away from a standing start.

Ron.

 

[chrisyork]

Ron is right up to a point on the characteristics of the lower compression engines.

The reason Rover went for high compression engines - 10:1 on the TC and 10.5:1 on the V8 - was to reduce fuel consumption. Thermodynamics theory and in particular Boyles Law dictate that the higher the compression ratio of an engine the more efficient the liberation of energy from the products of the fuel combustion. So this applies to all engines, not just Rovers. In a way, it's a cheats way out, because today we can achieve combustion chamber design which gives us much better efficiency than Rover ever achieved whilst still using relatively low compressions. Carried to extreme, high compressions are a problem, both because they impose shock mechanical loads on the engine and because it becomes increasingly difficult to avoid pre-ignition or pinking. You reach a point when what you actually have is a diesel and you can throw away the ignition system. Which of course is why diesels have inherently better fuel consumption. Mitsubishi and a couple of other manufacturers have tackled this problem by switching to diesel like direct injection into the combustion chamber, so they only need the spark plug at very low revs.

But back to Rovers. Ron is right that for a given camshaft lowering the compression will produce a softer engine power curve, but the real answer is to match the camshaft to the engine you've built. So with everything else the same, a higher compression engine needs a softer cam for the same power output characteristic.

An aside to this is that softer cams also produce better fuel economy as a rule. "Hot" cams invariably have a high overlap, ie the inlet valve opens before the exhaust valve closes. This is great for ensuring that the cylinder has the maximum amount of fuel in it before the spark plug starts the combustion. The exiting exhaust gases are allowed to "entrian" ie suck in, the static gas in the inlet port and get it moving. Excellent, but, inevitably, some unburnt fuel air mixture is carried over into the exhaust. So low overlap equals efficient combustion, high owerlap equals some wasted fuel but a much bigger bang!

So ideally you use the highest compression ratio you can get the engine to run without pinking on, allied to the softest cam that produces you an acceptable amount of top end power.

Again this drives you to make the most effective and unrestricted inlet and exhaust tracts from air intake to exhaust tailpipe that you can.

Chris

 

[quattro]

Keeping it more simple, :-

My first V8 was a manual 3500S, and was stock. It was fairly quick and very smooth. I didn't have it that long and is stayed as stock throughout its life with me.

I had a white V8 auto for a while and to be honest, it wasn't very good at all. I remember testing my cars for outright power by blasting at top speed up a long hill near where I lived at the time. The manual was around 85mph, and the auto only ever managed 77mph, even though I tried several times. I do think it may have been more down to the engine tune than the box.

Then Thunderdog came along and he got to 88mph on the first test, he was quick, and felt lively. After a few mods, (SD1 Heads, AAA needles, Mike the pipe 4:2:1 headers, 30% lightened flywheel, SD1 dizzy, and a 5 speed box) he managed 97mph . I actually managed an indicated 140mph once along a very long (private ) road in Somerset. great fun to drive and I kept the car for many years.

All of the above were 3528cc

Then Sparky came along.

The spec for this car was reported to be - New 4 litre cross bolted V8. Pair of stage 1 unleaded RPI engineering cylinder heads. Piper RP4 high torque cam and followers. New rocker shafts. Steel rockers. Cloyes duplex timing chain and sprockets. New oil pump. New water pump. Lightened (35%) and balanced flywheel. New 3 piece clutch. New clutch master and slave cylinders(didn't last long). High torque gear reduction starter motor. Mallory dual point distributor (changed for an SD1 electronic Dizzy). RPI engineering A&P electronic ignition power amp. Correct ignition coil and ballast resistor(12V coil no ballast ?). Magnecor 8mm plug leads. Offenhauser dual port inlet manifold. Weber 500 carburettor. K&N air filter. Facet red top fuel pump. Malpassi fuel pressure regulator. J&P stainless exhaust manifolds with 1 3/4" primaries. Custom 2 into 1 front section of exhaust. JR Wadhams high capacity 3 row radiator (only has two rows ?) Kenlowe electric radiator fan (changed for a 14" fan controlled by a revotec sensor). Stripped and rebuilt LT77 5 speed gearbox (yeah right :shock: ).

Ooerr :shock:

Problem was, when I got him, was that the engine was badly installed and ran like a bag of nails. Most of it was down to the electrical system which seemed to be based on little blue scotch clips and hope. That is how Sparky got his name :shock:

I did rewire it, and then replaced the dizzy as the huge amount of under bonnet heat had damaged it. He then went a fair bit better.

I spent so much time on other things that I never really got the best out of the engine, but I did replace the melted engine mounts, have a complete stainless exhaust made up for him, wrapped the manifolds in a vain attempt to remove the heat problem, then had them ceramic coated inside and out, changed the Dizzy for the SD1 unit, rebuilt the gearbox, and cleaned and painted some bits.

I now do have a calibration kit now, and have read up on the carb. I have rebuilt it with new gaskets and jets, etc and was getting some good results with the power coming on strong from around 1,500 rpm and revving cleanly up the 5,200. It does move very well and I would recommend the upgrade. I actually bought Sparky with all that kit listed above, but I don't know if I would have paid out for it all. I have bills for £6,500 for the engine and gearbox :shock: :? .

I don't have access to Sparky at the moment for reasons I won't be going into, but will be updating the progress as and when

Richard

 

[TokyoP6B]

Thermostat temperatures were raised on later model vehicles as it was the only way to meet enhanced emissions standards
Running a later V8 engine with an earlier thermostat on a P5B or P6B the block won't be subject to the "late model" temperature swings and likely won't suffer slipped liner or block-cracking-behind-the-liner issues either
Coscast blocks are subject to ultrasonic checks to establish core thickness prior to engine assembly and aren't as prone to failure

GW

 

[corazon]

That's interesting Graham. So running 4.0/4.6 for example in a P6 could in fact be saving it's life :wink:
Jim

 

[ghce]

Running a later V8 engine with an earlier thermostat on a P5B or P6B the block won't be subject to the "late model" temperature swings and likely won't suffer slipped liner or block-cracking-behind-the-liner issues either

GW

Surely running the block at lower temperatures would cause more problems as the running tolerances would be very sloppy, the pistons and bores sizing would be incorrect at the lower temps and the liners would possibly be more likely to slip as they wont be fully expanded into the block?


Graeme

 

[TokyoP6B]

That's interesting Graham. So running 4.0/4.6 for example in a P6 could in fact be saving it's life

Part of the emissions test for EU, Japan and USA is the "cold start" test where a vehicles emissions are checked after 10 minutes running; the only way to get the engine hot enough, fast enough, is to use a heftier thermostat

Our P5Bs, P6Bs and SD1s and the Buick 215, never had to meet those standards, ran cooler and dont seem as a result to have suffered the same slipped liner issues of the later V8s

Granted, I could be wrong... but thats my thinking. The requirement to run the engine at a hotter temperature serves no other purpose than meeting emissions standards and has pushed the design limits of the expansion rates between the aluminium block and steel liners

Graham Ware

 

[SydneyRoverP6B]

The running clearances on all the engines from the 3.5 through to 4.6 according to the Land Rover engine overhaul manual of 1997, are the same. The original P6B clearances in some cases are also the same, others offer slightly more tolerance.

The thermostat opening temps on all Rover V8 engines fitted with fuel injection as standard run between 88 degrees C to 96 degrees C. As Graham (TokyoP6B) rightly said, its purely for emission purposes.

I run an 82 degree stat in my Rover's 4.6 litre engine, and there is no indication thus far of any problems at all. In terms of dropped liners, all 3.9, 4.0, 4.2 and 4.6 litre engines are predisposed to this phenomena, with the 4.0 litre engines suffering the most, followed by the 3.9, 4.2 and finally the 4.6, which has the lowest failure rate of the big bore engines.

You could run any of the big bore engines with stats at no more than 82 degrees C, and probably not have a problem with a dropped liner. Personally though, if given a choice, I would always opt for top hats being fitted, as not only do they prevent that problem from ever occuring, they also allow an improved seal between the cylinder head and gasket.

Ron.

 

[TokyoP6B]

For those not familiar with the "slipped liner" problem and "top hat" solution for the later V-8s;

Here an engineer is pointing to a crack in a V8 block that has appeared between the water jacket and the steel cylinder liner; the liner has been removed and the crack highlighted. This is the typical failure, with water going into the sump and/or cylinder and the liner then typically slipping a few mm down the block. While this doesnt look that serious it is cheaper to replace the block than attempt a repair

The solution when building a replacement motor is to fit "Top Hat" liners where a step is machined in the top of the block prior to the new liners being pressed in, the liner now cannot physically slip down the block and as Ron has pointed out, these make for a better cylinder head seal as well

Heres a view from the top

These USA-made Top Hat liners include an O-Ring near the bottom of the liner, so if a water jacket cracks behind a liner, water cant get into the cylinder or the sump This is as good a solution as exists...

Best!

Graham Ware