craig1410
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| posted on 14/5/09 at 10:33 PM |
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Sierra Lobro 7" 3.14/3.36/3.38 open diff wanted. 3.92 swap?
Hi,
I currently have a 3.92 7" open diff with lobro shafts in my Locost but the gearing is not ideal for my Rover V8 engine. I would like as low a
ratio as possible but appreciate the 3.14 diffs are rare so maybe a 3.36 or 3.38 might be more accessible. If anyone has a good diff for sale or would
like to swap me for my 3.92 diff then let me know. My diff appears to be in good condition although I've only driven it for 70 miles so far. No
nasty noises, not much backlash and no obvious oil leaks is about all I can tell you about it.
Location in central scotland (Kilmarnock) but willing to drive up to 100 miles or so to avoid postage charges.
Many thanks,
Craig.
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wilkingj
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| posted on 15/5/09 at 08:11 AM |
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You want a 3.62 (get LSD option) or a 3.38 (never made as a LSD)
I have a RV8, and a standard Rover LT77 box with a 3.62 LSD diff. (17" wheels with 235/40 rear tyres)
It has 190 Bhp and does 0-60 in 5 secs (dead), 135mph top speed and 2800 rpm for 70Mph.
Its plenty fast enough, and excellent acceleration.
Also I get 26Mpg cruising at 70 the motorway. This is probably the only area where a 3.38 will give benefit over a 3.62.
I think unless you have well in excess of 200 Bhp you will find a 3.38 a tad less acceleration. (3.14 even more so) You dont need the top speed of a
3.38, as the 3.62 will do 150Mph at 6000 rpm (in theory, as it wont pull that much due to the aerodynamics / power available, I get 135 max - which is
plenty for the track and more than enough for the UK roads, ie 70 Max)
A 3.62 was fitted to the 4x4 and would have a LSD. Not all 3.62's are LSD so check then tag numbers on the Diff before buying.
3.38 was fitted to the 2.3 Diesels.
You are unlikely to find a 3.14, as they were fitted to the early diesels, and are like Hens teeth, with a price to match. Even a 3.38 will fetch a
very good price.
3.62 LSD about £70 - £100
3.38 about £100-150
3.14 Well...Crazy money for a Sierra Diff!!
Search on here for Sierra Diff numbers as its all listed in a thread somewhere
Hope this helps
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
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craig1410
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| posted on 15/5/09 at 12:30 PM |
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Hi Geoff, thanks for the info.
I'm not sure if I want an LSD and would appreciate your thoughts on the matter. I have been told that if your suspension is set up correctly (eg
corner weighted) then an LSD is not necessary and actually not having one makes the car more progressive and less likely to throw you backwards
through a hedge. Have you tried your car without an LSD as well as wife or has it always had the LSD?
As for the ratios, yes I agree that top speed is not a priority but I was hoping to use 5th gear as a cruising gear which is what it was intended for
on the SD1 which was geared for 180MPH at 6k RPM IIRC. I'm not looking for quite as high as that but with my current 3.92 diff I can only manage
117MPH at 5500RPM (6k is not recommended on a stock RV8 for anything but a quick buzz really and max power is at 5250). This means that 60MPH is
around 2800 RPM which is a bit buzzy for cruising and won't be very efficient. I'd like to get this below 2500RPM for sure and ideally in
the low 2k's. My tyres are 195/55R15 by the way.
A 3.62 diff would mean 60MPH would be 2600 RPM and a 3.38 would yield 2400 RPM which would be fine. I think if I find a 3.16 at a price I'm
willing to pay then the most likely course of action would be to sell it for a profit and then buy a 3.38... 
On a related subject, my fuel consumption so far is just under 16MPG which is definitely NOT good enough. To be fair, much of this has been with the
engine running and the car not moving and the rest has been short journeys to test it out. I've not done any proper "cruising" in it
yet to establish what the steady state MPG might be.
Anyway, thanks for your help, I look forward to hearing your thoughts on LSD's in an RV8 engined Locost!
Craig.
[Edited on 15/5/2009 by craig1410]
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