MK Charlie
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| posted on 23/11/07 at 10:47 AM |
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Changing diff ratio
Hi all. At the moment my diff is a 3.62LSD from a sierra cossie (I think) This is good fro cruising, but not acceleration, and thats what i want. I
think that a 4.4 would be a good ratio for what i want as a 4.7 is just a bit too short for me. I want to keep the LSD so what is the best way to do
this....change the whole diff, or just buy the crown wheel and pinion from a 4.4?
Also if i do the latter, which diff do i need to get the bits from?
All help greatly appreciated.
Charlie
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tks
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| posted on 23/11/07 at 10:58 AM |
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are you sure???
a change from 3.3 to 3.6 changes allot!!
we talk over an reduction from rearwheel rpm of 30% and an increase of torque with the same amount.
are ya sure??? my topspeed changed from 200km/h to 177km/h
i think you need to do the maths again...
Tks
The above comments are always meant to be from the above persons perspective.
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wilkingj
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| posted on 23/11/07 at 11:09 AM |
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I think you will find that the lowest ratio you can get from a std Ford sierra is 3.92 this will give you more acceleration and less top speed.
I believe you just need a Crown wheel and pinion to change the ratio.
Mind you if i was stripping it that far, I would fit new bearings seals etc etc.
A std diff from a scrappy should cost you £20-40. Lok at the Tab on the back of the diff as it will give you the ratio installed.
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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mookaloid
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| posted on 23/11/07 at 11:38 AM |
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I think Quaife sell ratios like 4.44:1 for the 7" Sierra diff but hugely expensive.
If you have a 7.5" diff then there were some standard ratios fitted to granadas which are nearer to to what you are looking for - they are
quite a bit heavier though.
You are correct that this would give you improved acceleration - I would have thought it would be ideal for a 4age engined car.
Cheers
Mark
"That thing you're thinking - it wont be that."
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tks
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| posted on 23/11/07 at 11:52 AM |
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wich topspeed do you get to now?
to change from 3.6 to 4.4 its a bloody huge step!!
do the maths...
tks
The above comments are always meant to be from the above persons perspective.
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D Beddows
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| posted on 23/11/07 at 12:08 PM |
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I'd have a little check of your maths too if I were you TKS......unless you are in fact running on 6 inch rather than 15 inch wheels 
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MK Charlie
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| posted on 23/11/07 at 12:22 PM |
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Well with my current set up in 5th i'm doing 70mph at bang on 3000rpm, and i can hit 125mph and still hav loads of revs left. This is why i want
a shorter diff, because i run out of aerodynamics before i run out of revs. Raw engineering sell the 4AGE's with a type 9 gearbox on a 4.7 diff,
so i must be fine to run a 4.4, i dont think there should be any problem. Which diff could i use that is 4.4 LSD (or similar ratio) ???
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2b_pablo
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| posted on 23/11/07 at 12:48 PM |
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im in a similar boat, on my local track Im hitting about 90mph on the straight at the top of 3rd so 4th and 5th are almost a waste of time. its not
worth the while changing into 4th.
would also like to change the ratio in my sierra LSD so interested to know whats involved.
if its a case of using the parts from another non LSD diff then my mech breaks all sorts of sierra etc so finding a donor shouldnt be a problem.
I suspect a ratio of 3.9/4 would be good for me. Its nice to be able to sit on the motorway at 80 without revving the nuts off the car.
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NS Dev
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| posted on 23/11/07 at 12:51 PM |
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yep 4.4 will do the trick, though cruising will be a bit frantic, but then these cars are hardly civilised anyway!!
As others have said though, if you can find a 4.4 on the cheap, let me know where!! 
I'm going for 3.92 over the winter once I've found a diff builder locally who will do the swap and mesh it up properly for me.
I have 3.62 currently with 200hp vauxhall xe 2.0 16v and its bloody quick but having now driven a similarly powered caterham with closer ratios I
think the 3.92 will do more good than harm.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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MK Charlie
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| posted on 23/11/07 at 12:55 PM |
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hmmmmm....best be off to see my mate who owns A1 gearboxes then and see what he can do for me. I dont want any bigger than a 4.4 cos that will destroy
all cruising abilities, is there such ratio for a sierra diff as a 4.1? My opinion is if I'm going to do this, I may aswell do it properly and
get a diff that will make a large improvement. I dont think a 3.92 will make HUGE improvements, but i may be wrong.
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NS Dev
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| posted on 23/11/07 at 01:05 PM |
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some time ago steve broughton at SBD in surbiton was selling 4.1 7" cwp's for sierra diffs. No idea if he still does though!
Alternatively, work on the engine for more torque!
I certainly don't feel that the 3.62 holds my VX back (it still does 0-60 in under 4 secs) its just that it would be a touch quicker with the
3.92, though it would then need 3rd to get to 60 probably, whereas it does around 75 in 2nd at the mo.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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NS Dev
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| posted on 23/11/07 at 01:10 PM |
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give these a try, they make em, but obviously minimum orders apply but they may have some on the shelf..................
KAM Differentials Ltd. Clock Barn House. Hambledon Road, Godalming. Surrey. GU8 4AY. United Kingdom.
Phone: (+44) 01483 419779, Fax: (+44) 01483 416009
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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mookaloid
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| posted on 23/11/07 at 01:21 PM |
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quote:
Originally posted by NS Dev
give these a try, they make em, but obviously minimum orders apply but they may have some on the shelf..................
KAM Differentials Ltd. Clock Barn House. Hambledon Road, Godalming. Surrey. GU8 4AY. United Kingdom.
Phone: (+44) 01483 419779, Fax: (+44) 01483 416009
That's where I've seen them not Quaife 
http://www.kamdiffs.com/sierra.htm
£518 + VAT you won't regret it
Cheers
Mark
"That thing you're thinking - it wont be that."
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tks
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| posted on 23/11/07 at 01:42 PM |
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quote:
Originally posted by D Beddows
I'd have a little check of your maths too if I were you TKS......unless you are in fact running on 6 inch rather than 15 inch wheels
i'm bec and have the revs....
Tks
The above comments are always meant to be from the above persons perspective.
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timex
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| posted on 23/11/07 at 01:46 PM |
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Check this out, it may be of some use????
http://westfield-world.com/gtc.html
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2b_pablo
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| posted on 23/11/07 at 03:17 PM |
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type-9 box ratios for anyone who needs them for the calculator:
1st: 3.65 2nd: 1.97 3rd: 1.37 4th: 1.00 5th: 0.82
more here:
http://www.westfield-world.com/gearboxspecs.html
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2b_pablo
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| posted on 23/11/07 at 03:20 PM |
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on my wheels (185/55/13):
4.4 ratio:
7000 Rpm
1st: 27mph
2nd: 50mph
3rd: 72mph
4th: 100mph
5th: 121mph
3.6 ratio:
1st: 33mph
2nd: 62mph
3rd: 88mph (back to the future )
4th: 121mph
5th: 148mph
given Ive no real desire to top 110ish I think the likes of a 4.4 would be perfect.
[Edited on 23/11/07 by 2b_pablo]
[Edited on 23/11/07 by 2b_pablo]
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mcerd1
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| posted on 23/11/07 at 03:40 PM |
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Raceline still list 4.1 & 4.44 crown wheel and pinions for £646 a set
http://www.raceline.co.uk/gearboxanddifferentialframes.htm
I'm building mine with a 3.92 LSD just now but was thinking about a 4.1 later when I tune the engine a bit more (depending on how it drives) and
what rev limit I decide on (8000 to 9000ish)
but I'm also going to get a BGH gearbox
1st = 2.98 / 5th = 0.87 (2nd, 3rd & 4th are std. type 9 ratios)
http://www.bghgeartech.co.uk/html/5_speed.html
oh and I've got 16" rears with 245/45's
ps - here is another gearcalc - it has all the common Ford, BGH, Quaife and other ratios built into it
[Edited on 23/11/07 by mcerd1]
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MK Charlie
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| posted on 23/11/07 at 03:44 PM |
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On my wheels (205/50/15 at the rear) the speeds with a 4.4 seem quite sensible as 2nd gear would still produce just a tad over 60 at 8,000rpm. Only
thing is I dont know if this smile factor would be worth all the extra money compared to the cheaper option of getting a 3.92.
What do others think they would do in my situation???
I think with the current mods i'm running about 150bhp and would rather adjust the diff than start tuning the engine. I'm only 20 and
have a restricted budget, but I always promised myself I would get my Indy to be as much fun as possible by spending sensible amounts of cash on it.
I'd love to tune it up to around 200bhp but my wallet just says no at the moment.
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worX
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| posted on 23/11/07 at 05:17 PM |
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I think that with the availability and price of 3.92 diff's I would try one of those first! It's not a massive job swapping over and you
might just save yourself a bundle of money!
Thats if you can put your hands on one easily - most BEC owners that strip a donor leave the 3.92 in it! (well I did)
Steve
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bracey
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| posted on 6/1/08 at 09:24 AM |
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so which way round doesit go with ratio oppossed to acceleration top speed etc thanks
richard
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MK Charlie
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| posted on 6/1/08 at 05:13 PM |
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If i understand your question right.... a diff with a lower ratio will be slower on acceleration, but a higher top end. A higher ration will be faster
acceleration but lower top end.
Just to fill you all in...a friend of a friend used to do a lot of grass track racing and he had an old diff with 4.4 CWP. £20 later and it is now
mine.  I will be taking it with my current diff to get it all changed. Now i need to invest in a fairly decent clutch ready for some fairly quick
launches.
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