Diff's, Transfer Cases and Overdrives

[R704]

Hi All,
Iv'e been doing some research on the topic of getting the old gorls to go a bit quicker without blowing the engine.

I'd like to gauge opinion and thoughts  on the topic as well as the pros /cons and experiances had.

First option, Higher ratio Diff's,
To me this is the entry level and cheapest fix to get the engine happy whilst being to maintain a speed of 80-90kph

Second would be a higher ratio transfer case,   the one ive got info on claims a 31% overdrive with 1st un changed, 24% rpm drop per gear with 100 kph obtainable under 4000 rpm.
To me this sounds like a wonderful option, no mess no fuss and by rights should be fairly economical.

Third would be the bolt on overdrive units, My understanding of these is (limited i'll admit) that its basically like a splitter box Eg, you would have  1st, 1.5, 2nd, 2.5, 3rd, 3.5, 4th and 4.5  thus allowing an optionally higher ratio between each standard gear.
These to me sound useful but somewhat limited in application unless perhaps combined with the Diff option.
also having seen the price for second hand units, aswel as the new roamerdrive units mentioned a while ago make this seem like the least economical.  aswel as the downside of another knob to use, loss of the pto be it for winch or shaft.

Another that was mentioned to me was the old electric overdrives, as of yet i haven't looked into.

I for one if i had the cash, would be inclined to try the transfer case option, perhaps in conjunction with a diff ratio change to suit.

Your thoughts Gents?

[FFRMAN]

Hi,

I put a fairy over drive on my original ffr years ago, too mych trouble using it between gears so only used it on forth. Seemed to give not much more top speed maybe 5 km, but did drop revs but when it saw a hill had to drop it back out of overdrive.

Tried an overdrived gear box once ( not transfer case) took it back out after a week. The engine did not have the power to get it up to full speed and it really laboured and ended up going 5 km slower and slow getting up to speed in the gears.

Maybe tranfer case will be better way to do it.

An "old timer " told me drive the 6 cylinder motor under 2600 revs and the will go for ever, go over that and you burn exhaust valves, so about 80 km/hr

Will be keen to see what you work out.

[Diana Alan]

I think you have been misinformed about the transfer case option.  What it does is replace the transfer case high range ratio and therefore changes the final drive ratio across all four gears in High Range, IIRC all manufacturers of the high speed transfer boxes leave the Low Range ratio unchanged.  Take a look at the information on the Ashcroft kit http://www.ashcroft-transmissions.co.uk/the-series-vehicle/high-ratio-transfer-case-kit.html  There is also the alternative of a 5 speed transmission kit although there is additional work to make a LT77/R380 fit onto the Rover 6 cyl http://www.ashcroft-transmissions.co.uk/the-series-vehicle/series-5-speed-kits.html

Most of the overdrive/ratio change options suffer from the relative lack of power of the Rover engine the bolt on overdrive is the only one that leaves you with the standard ratios plus the overdrive.  So for the permanent change in ratio you would want to consider getting the Rover motor to perform somewhat better than it currently does.

[GGG]

I am only a newbie on this list but have been operating my own petrol Landrover for twenty years. I rather wonder why people want to make a vehicle into something that it is not. They were originally designed with off road performance in mind not for freeway use. Having said that mine has spent a fair bit of time up around 95 and I have yet to burn out a valve. I think that burnt out valves in sixes are more due to tappet adjustment or the lack of lead replacer than revs.

Geoff.

[Diana Alan]

I just thought I'd post up some ratio and speed tables if its any help.

• standard SIII gearbox on 32" tyres
• SIII gearbox with Toro/GKN overdrive on 32" tyres
• SIII gearbox HiSpeed TF on 32" tyres
• SIII gearbox on 3.54 diffs (Stage one/Perentie/Range Rover classic

[Diana Alan]

Another composite graph to show the relative gear splits between the standard box and the box with the Toro overdrive.

Note that 3rd O/D is close to but just under 4th standard so the O/D can't really be used to split gears

[R704]

Holy crap Diana, thats some serious data! 
I'll have to measure the rubbers she came on as they were a good 2" larger in Dia then my disco's wheels which are on it at the moment for the RWC and better "road use"

GGG,
As much as I love originality, just this once practicality wins out for me,  As she's going to be my new daily drive since the loss of my disco to a roo i need the ability to travel at freeway speed as i'm in a location that once its not within half hour its on the freeways,  including some potential interstate trips.  well speed V distance and some new plugs in the dash for modern fangled things but apart from that i'm trying to keep her original,  otherwise i'd have got one with a 186 or 202 in it.

FFR, 
Interesting you shuld mention the "uselessness" of the overdrives,

The one I was looking at turned out to be an import of the Ahscroft kit mentioned by Diana, but at twice the price I can get it direct. even loosing on the T box swap over.

As ive got the sacrificial carcas in the paddock i may go the transfer case option. using its box as the donor and go to town on it before swapping them over.

Heres hoping i can swindle the kit for my birthday,

[GGG]

R704, mate it is yours to do with as you wish but the idea of an interstate trip in a series Rover is to me a novel idea to say the least. We might agree to disagree regarding the practicality angle. I find my regular hour and twenty minute trip sufficient to curb my enthusiasm. Off road is different as I am too busy (or stupid) to realise that it hurts.
I was once given a Fairey O/D but was told by the gent who used to do gearbox work for me to use it for a door stop. Make of that what you will.

Geoff.

[Diana Alan]

From memory Disco RRclassic wheels are 29" while Series long wheelbase and Oz military short w/b tyres are a little over 31" which is why I did 32" but happy to be corrected on their dia.

Have never liked the Fairey (always made sure I have a standard gear, the cover plate and mainshaft nut/tab in the toolbox when running one) there were a couple of oil cycling mods that made them a little more reliable.  The Toro/GKN overdrives were more reliable and the Roverdrives/Roamerdrives far superior but a little expensive.  But would carry the standard parts with them also).  I would use one in my SIII FFR but given its a 6006B, I'd rather have the PTO winch.

One has to remember that Series Land Rovers regularly did outback Oz, just in recent years we are less tolerant of the lower series performance.  Most of us will remember the school textbook/reading list title "Journey among men" that journey was done in series 1 Land Rovers.

Diana

[THE BOOGER]

Would an engine swap to a holden engine do the job better? Diana how is your FFR with the holden engine I know it drives much better than my rover 6

[Diana Alan]

No a Holden engine won't do a better job (sort of).

The original Rover engine will rev higher than than a Holden engine.  Most Holden engines you can find suffer from lack of torque which you have to overcome with revs.

Yes I can drive my 202 all day at 90-100KPH but I find the Rover engines have better "manners".  The vehicle is more pleasant to drive with the Rover, and yes I fully plan to remove the Holden when some of the other projects are finished.

Both the Rover engine and Holden engine suffer from the ratio problems for long distance driving at highway speeds.

[fc101]

I cannot compare a Holden with the Rover 6 cylinder but the Rover 2.25 4 cylinder engine is better than the Holden.  Most people when they were replacing the LR engine were comparing a dead or poor LR engine with a newer Holden engine - also at the time it was far cheaper to put in a Holden engine - I even did it once noticed how well the new Holden motor went compared to the expired LR Motor.

Later I had a series 3 with a dead engine and had it fully rebuilt - when fully recoed it was far superior to the Holden.  As Diana said the Holden revs lower so ran out of puff at the top end and had higher fuel consumption.  The LR motor pulled stronger and the vehicle ran to a higher speed - it cruised at 100kph and top speed up around 110 but you would not want to drive at that speed for long.

Garry

[Diana Alan]

I must say that with a Rover 6 you were always having to work the gears, even down to 2nd on the hills at either end of the F6 where with the Holden it's top gear up hill and down dale, all day.

Last weekend I had a drive of Cookey's SIII with his new extractors and its performance seemed quite improved just on the short drive I had.  Stayed in top in places (like roundabouts) where you would usually change down and seemed to hold the revs quite well up reasonable hills.  Not something the Rover 6 is renown for.

Just waiting for the rest of the exhaust system to be done and for the porting he's planning so I can make my final decision to move on with the improvements.  The 202 will disappear very quickly after that.

[GGG]

Diana, My rover six has about twenty thousand on it and performs quite well torque wise. I don't normally use the F6, now known for some reason as the Prince's motorway, but as it is not far away I will do a run down there when time permits and see how it goes. With a clear run it will do Holsworthy Princes highway on Heathcote Rd. in either direction without a gear change.
I too am interested in Cookey's mods.
You do not notice a slow deterioration. My previous engine developed a blown head gasket (to atmosphere right at the back) so rather than fix that I had another engine reconditioned and the improvement was marked. The old one was obviously getting tired although it wasn't "drinking oil." I think that a lot of the oil consumption woes are leak related which is manageable but becomes more difficult as the engine ages and crankcase pressure increases.
Rover engines also do not reward owners who don't like changing the oil. I have seen a number of examples of that including a V8 which had so little left of the camshaft lobes we wondered how it had kept running. The performance was down a little!
Garry, l have no experience with Holdens in Rovers but what you and Diana say fits with what others have told me. I believe that they tend to wear out pretty quickly too.
Geoff.

[Diana Alan]

Gary and I often sit and chat over a cuppa on improvements to the Rover 6.

When you look at the engineering of the Rover engine and the Holden engine it's chalk and cheese.  There is a lot of work that can be done on the Land Rover engine to improve its highway performance, even if it's just to tune it to the settings of the Rover car engines.  Remember that a lot of the Land Rover specs is so that it will run on any grade of petrol around the world and operate in the full range of temperature extremes.  We don't have 3 months of sub-zero temperatures in Oz, co a lot of the cold weather elements can be discarded.  Particularly the air-flow restrictions associated with pre-warming the fuel/air mix desined for sub-arctic conditions.

I just love sitting back and seeing Gary's latest modification come into existance, whether it be re-profiling the shape of the valve heads, making a real set of extractors that not only allow the engine to breathe properly but will also allow us to still have a Bamford PTO winch on our military Landies.

The most important thing we can do on our landies is the spend the time to keep them in tune, particularly check and re-set the tappets at least every 12 months.