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!

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]

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.

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

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

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

Would a bigger rolling radius in conjunction with a 3.14 diff be an option?

jason

[Edited on 1/3/09 by Jason Fletcher]

How about a freelander diff thats what quite a lot of people use with zx10 engines

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

quote:

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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]

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quote:

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Originally posted by Jason Fletcher
I think the lowest ratio in the Freelander is also 3.14.

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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]

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

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.

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

quote:

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Originally posted by JoelP

quote:

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Originally posted by Jason Fletcher
I think the lowest ratio in the Freelander is also 3.14.

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all 3.21 open diffs.

I have one for sale if anyone wants!

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quote:

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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

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Forget the mini diff - half the housing is part of the gearbox!

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.

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?

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