V8 110 county gearing?

[V8Johnno]

Hi Guys,
ItsTime to overhaul the ol girl , and do some engine and gearbox swapping etc.......

The car is a 3.5 V8 county on dual fuel, but mostly gas, use built for touring with roofracks and 270 litres of fuel etc... theres a 350 holley, torquey cam extractors and a 2.5 inch system.
running 275/70/16's

I have a santana and an R380 , I could use, both with pretty similar(ish) 5th gear ratio's.

the donor car is a 1996 V8 3.9 disco auto.
all disco's have a transfer ratio of 2.2222 ? is this correct?

the reason i ask , is that , considering the four speed auto has almost the same top gear ratio as both the 5 speeds,,,,,
bear with me on this..............
if I put in the 3.9 , with my holley and extractors , one of the 5 speeds and the transfer box out of the disco , into the county , then I will end up with the same top speed cruising ratio the disco had , ie 2250rpm@ 110kph....

As ive got the roofrax and the extra fuel weight, I usually prefer to travel around 100kph for ecomony purposes ( cackles to himself at the impossibility of getting economy whilst touring in a V8 as aerodynamic as a wardrobe ) will this be too tall, when fully loaded up with camping gear as i dont want to change down at the first whiff of a hill ....

and my next query is thi s.....

As the car is more of a tourer and spends most of its time at the lower rpm end of the scale then would it be best to use the auto cam that is in it , innit , or put another low rpm torquey cam in it , innit?

cheers in advance for any suggestions / advice...

ps if u run a 110 V8 , ?is it a 4 or 5 speed what tyre size do u run?? and what rpm is it doing @ 110kph?

Im just tryin to get a picture of what ratios are most suitable for my touring heavywieght purposes..

thanks again, in advance, for the flood of advice

V8 Johnno

[justinc]

Johhno,

I would stick with the 3.5 (As long as it is a high comp engine, 9.35:1 which was factory fit) if you have to rebuild it DO NOT fit low comp pistons!! and a R380, with 1.410 standard 110 gearing. The Santana is exxy to repair, the 1.222:1 disco case is too high ratio, and the 3.9V8 is too low compression to effectively use LPG efficiently. Use a factory EFI cam and EFI exhaust manifolds/ engine pipes too.

Plus, the 3.5 is a legendary little motor


JC

[V8Johnno]

Hi Justin,
I have just digested your reply, and I have a couple of other questions/puzzlers

Is the 3.9 is too low comp to run lpg efficiently?? Ive driven a 3.9i disco on lpg and I thought it went quite well. Would you need to raise the compression when you lpg a V8 disco?

Will the R380 go in without any floor pan mods?

At the moment it has a 1: 1.125 transfer out of an early 5 speed rangie, which i put in to see how it went, and which is , in my opinion, slightly too tall. So i thought the 1.22 was half way between that and the 1.4 which I took out, and would have a slightly lower cruising speed than I have now.

Also, the original 3.5 was a bit of a slug of a low compression motor with a book output of 113bhp and went well on lpg. , so even with a nice set of rangie heads which I fitted, the standard 3.9 disco motor must have a higher power output than a County 3.5. Plus Ive stripped a plughole in the 3.5 and dont trust helicoil inserts in a long range tourer, so I need to do something.
Would, in your opinion, skimming something off the disco heads raise the compression ? or would that mess things up with low comp pistons?

Cheers for your input

V8Johnno

[clive22]

In terms of gearing you really need to decide on the tyre size you will be running for touring, as gearing decisions will all revolve around this.

FWIW

I have an '85 County originally with a 3.5L,LT85(5 speed), but now with a 4.2RR LSE motor - twin carb & LPG fed. I use 33" & 36" inch tyres, and found the response from the from the much stronger motor about right with the stock 3.54 diff ratios and 1.4 transfer and 33" tyres, i.e. pulls 5th well, down change only for steep hills, no problems with headwinds, etc.

With the 1.22 ratio box, and 33" tyres, or 15% higher again my experience is that it would be too high and advantages of higher gearing in terms of fuel economy would be theoretical only with too many switches back to 4th: minor uphills, 20-30 km/h headwinds etc. This is roughly equivalent to when I run my 36" tyres which I believe is over geared, especially loaded up as you are when touring.



Clive

[V8Johnno]

Thanks Clive,

Justin was right about the 3.5 being a 9.35 and the disco being a 8.13 low compression motor. I went and checked because the motor, in its original state of tune was as i said, a bit of a slug. heaps of torque but nontheless a slug.
I have been reading peoples posts on lrocwa and they all seem happy with 3.9 discos on gas. would a head skim be advisable? what compression is the 4.2?

I am thinking the 3.9 (maybe head skimmed) with either the santana or the R380 (will it fit without major floor mods?) and the original 1.4 to one gearing as I am running 275/70/16's which are quite tall.

Everyone who has told me to put a 1:1222 in has said it'll give me a decent cruising speed....as the car is overgeared at the mo and has a hideous top speed , I now know I want to cruise in 5th below 100kph fully loaded, so ill flip ( makes it sound so easy) the original transfer case back in.


Just puzzled as to whether i need to skim the heads or not?


cheers
V8Johnno

[isuzurover]

At the moment it has a 1: 1.125 transfer out of an early 5 speed rangie,

No such beast. Early RRCs had a 1.192 t-case - which is close enough to the disco ratio. Incidentally, late model D1s had a 1,21:1 t-case.

The R380 is as strong as an LT85/Santana according to Ashcroft.

Not sure I agree with Justin on the 3.5. A good 3.9 will outperform a good 3.5 by a decent margin. However - you also need to fit the EFI to make the best use of it.

The ratio calculator on the ashcroft site may be useful for you.