JT71
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| posted on 1/3/09 at 09:38 AM |
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HELP PLEASE!! Rear diff problem
Help please! I've recently put a 2007 ZX10 engine in my westy and although the acceleration is phenomenal, it tops out at 112mph (accurately
measured). On pretty much every track this is way too low, and I need to increase ideally to about 130mph which I think is a good compromise and
should suit most of the UK non GT tracks. Its really frustrating as I've just started the track day season so I need to get this sorted
quickly.
The only diff I could get my hands on at the time of the conversion was a sierra 3.38 (i was looking for a 3.14 but found it impossible to get one),
however even with a 3.14 I've calculated it would still only top out at 120mph. I've worked out that to hit 130mph I need a 2.9 diff,
which it seems I can get from a 1989 onwards mini or metro 998cc unleaded. Is my only option to use this entire diff and housing, make a new bracket
to support the diff housing and then weld the ends of the metro driveshafts onto my existing driveshafts? This all seems like a lot of hassle - surely
there are other people putting modern litre bike engines in without going through all this? Apparently the gearing on a new litre bike engine is very
different to the earlier blade / R1 engines most people historically had fitted onto their westies etc, hence the diff problems and the need to change
the existing diff ratio.
Thanks in advance!
JT71
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big_wasa
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| posted on 1/3/09 at 09:44 AM |
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2.8l capri has a live axle with 3.09 ratio 
I doubt you could get the metro diff to work.
[Edited on 1/3/09 by big_wasa]
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JoelP
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| posted on 1/3/09 at 09:48 AM |
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are you 100% sure you have a 3.38 diff in at the min? Sounds a crazy low top speed, i'd be double checking that first.
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Jason Fletcher
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| posted on 1/3/09 at 09:49 AM |
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I've have a 3.14 in mine and it's the best I could find without going the live axle route.
can you really put a FWD diff in a RWD Westie?
Jason
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Steve Hignett
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| posted on 1/3/09 at 09:50 AM |
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Surely for the potential hassle and cost that you are going to encounter doing what you suggest, it would be better to just give a Gear manufacturer a
call? Obviously Quaife being the first company that springs to mind.
I am sure that they would supply you with CWP to suit your Sierra (?) Housing to your required ratio.
Obviously it isn't going to be free, but sounds as if it could be similar (and a damn sight quicker) to what you suggest above.
ATB
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Jason Fletcher
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| posted on 1/3/09 at 09:54 AM |
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I doubt Quaife would make a CW&P. Even the ones in their new Sierra diff are out sourced to a company in Italy and I hear the qualitly is not a
patch on the real thing.
jason
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Jason Fletcher
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| posted on 1/3/09 at 09:59 AM |
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Would a bigger rolling radius in conjunction with a 3.14 diff be an option?
jason
[Edited on 1/3/09 by Jason Fletcher]
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jacko
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| posted on 1/3/09 at 10:03 AM |
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How about a freelander diff thats what quite a lot of people use with zx10 engines
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Jason Fletcher
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| posted on 1/3/09 at 10:18 AM |
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I think the lowest ratio in the Freelander is also 3.14.
Theres a Sierra one on Ebay at the moment and if the guy is correct on the ratio then you might pick up a bargain as he has listed it for collection
only and they never fetch what they would if he would post
it.Scabby Ebay
Jason
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Jubal
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| posted on 1/3/09 at 10:25 AM |
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quote:
Originally posted by Jason Fletcher
Would a bigger rolling radius in conjunction with a 3.14 diff be an option?
jason
[Edited on 1/3/09 by Jason Fletcher]
This has got to be an option if 3.14 isn't good enough. A 3.14 on a 13" wheel (185/60/13) gives a theoretical max of 124mph. I'm
using the following ratios:
1.611(Pr)
2.533(1st)
2.053(2nd)
1.737(3rd)
1.524(4th)
1.381(5th)
1.304(6th)
13000 (rev limit)
If you go to a 15 (195/50/15) then the max goes to 130mph.
All calculated using Chris Gamlin's spreadsheet. Plugging your (assumed) current setup in gives and answer of 116mph so it's pretty
accurate. http://www.gamlin.org.uk/Downloads/bike_ratios.xls
I found 124 mph to be easily enough for Cadwell, Oulton, airfields and the smaller circuits. But I can't comment on Snett or Silverstone as I
never went there. I think the poor aero on the Indy kicked in at those levels.
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JoelP
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| posted on 1/3/09 at 10:39 AM |
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quote:
Originally posted by Jason Fletcher
I think the lowest ratio in the Freelander is also 3.14.
all 3.21 open diffs.
I have one for sale if anyone wants!
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YQUSTA
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| posted on 1/3/09 at 10:46 AM |
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This company make different ratio cw & p.
I had a quote for a 3.14 and it aint cheap £623.88 ouch
Edit: they can make whatever ratio you want and I bet it will be alot mow than ^^^^
[Edited on 1/3/09 by YQUSTA]
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jimgiblett
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| posted on 1/3/09 at 11:05 AM |
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For a light weight car 205/60/13 will probably be a more compliant tyre and give a rolling radius similar to a 185/60/14 tyre combo.
- Jim
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bigrich
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| posted on 1/3/09 at 11:37 AM |
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I run a 3.21 freelander diff and 205/60/13 rear tyres, It will indicate over 130 on the clock (not sure how acurate this is but was close for SVA)
I would'nt go too high with the gearing, due to the very long 1st gear, it would make getting it of the line a bit tricky.
.JPG)
A pint for the gent and a white wine/fruit based drink for the lady. Those are the rules
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progers
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| posted on 1/3/09 at 11:38 AM |
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3.14 diff, 205/60R13 tyres, top speed 130mph. Job done
I wouldn't consider swapping for Freelander (its a weaker diff) as you already have the Sierra setup. The cost of conversion to alternative
diff would be no cheaper that the amount you will have cough up for the "rare" 3.14 diff. They come up reasonably often just need to be
patient.
- Paul
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Jason Fletcher
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| posted on 1/3/09 at 11:58 AM |
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quote:
Originally posted by JoelP
quote:
Originally posted by Jason Fletcher
I think the lowest ratio in the Freelander is also 3.14.
all 3.21 open diffs.
I have one for sale if anyone wants!
3.14 Freelander
CW&P
Not sure what the quality is like though.
jason
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Jubal
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| posted on 1/3/09 at 01:43 PM |
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quote:
Originally posted by progers
3.14 diff, 205/60R13 tyres, top speed 130mph. Job done
I wouldn't consider swapping for Freelander (its a weaker diff) as you already have the Sierra setup. The cost of conversion to alternative
diff would be no cheaper that the amount you will have cough up for the "rare" 3.14 diff. They come up reasonably often just need to be
patient.
- Paul
Wot he said:
Selected Primary 1.611
Selected Final 1
Selected Rev Limit 13000
Selected Ratio 1
Selected Differential 3.14
Ratio in 1st 12.81328182
Ratio in 2nd 10.38518262
Ratio in 3rd 8.78668398
Ratio in 4th 7.70921496
Ratio in 5th 6.98584374
Ratio in 6th 6.59633616
Total tyre diameter (mm) 576.2
Effective circumference (m) 1.774
Speed in 1st (mph) 67.1018573686769
Speed in 2nd (mph) 82.7905527105984
Speed in 3rd (mph) 97.8520464679669
Speed in 4th (mph) 111.528218316836
Speed in 5th (mph) 123.076759388022
Speed in 6th (mph) 130.344328769063
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prawnabie
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| posted on 1/3/09 at 02:12 PM |
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Forget the mini diff - half the housing is part of the gearbox!
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PAUL FISHER
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| posted on 1/3/09 at 05:06 PM |
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I had a 3.38 lsd fitted to my 2007 zx10r Indy,with 205 50 15 rear tyres it would do a true (rolling road) 124mph in top gear before hitting the rev
limiter at 13500 rpm,and as "bigrich" says a 3.14 might not be the best option on the 2006/07/08 zx10r's due to its very high 1st
gear,although it should pull out to max rev's in 6th,I would say accelleration above 110mph as with my car,would be very slow,so you would not
require it to be geared to much more than a true 120mph for a seven type car, in my opinion for most uk circuits.
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JT71
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| posted on 2/3/09 at 10:59 PM |
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does anyone know if all freelander rear diffa are 3.14? And would i need to change the drive shaft ends and the diff mountings?
JT71
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Jason Fletcher
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| posted on 2/3/09 at 11:18 PM |
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As stated a few posts up the Freelander diffs are 3.21 unless you get the after market 3.14 CW&P set. Not sure about the mounting though.
I think you need to bung 300 odd quid in to a Sierra 3.14 diff unless that one one Ebay comes at the right money.
Jason
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