I've been ploughing through all the information on the search but I just wanted to check with someone. Also I've decided that Hellfires guide is the new 'book' (great mate) Am looking at getting a ZX9R engine and am I right in thinking that the lower the second number for the diff the better? Just wondered. Apologies in advance for asking a common question - commence the flaming.

you are indeed correct and all the better for asking you will also find that as well as being better they are more sought after and generally command a higher price than the higher ratio diffs

No icon for bashful so thank you kindly will have to do...

Steve

iirc (not that i know much about bec's!) the zx9 gearbox is slightly worse than the blades and is suited to a lower number dif. a 3.62 will probably top out at quite a low speed (jasper had a 3.89 escort axle iirc and that topped out at 98mph!) so you'd probably want a 3.38 or 3.14, 3.14 are like gold dust and expensive when they do come up, 3.38's are more plentiful (though not mega common) and normally found in diesels more than any other models.

Ned.

ps there is a quaife gear calc about and a spreaesheet calculator thingy that can calculate the speed's/ratio's when you input the gearbox ratio's and tyre/wheel size combo's.

[Edited on 21/8/06 by ned]

3.62 diffs are fine for ZX9's especially if you use 15" wheels, although you might hit the rev limiter in top gear at some tracks, i never found it to be a problem.

I'm running a 3.62 diff and 16" Caterham HPC wheels (205/45 tyres) which tops out at 118mph.
It's scary enough, don't want it to go faster

Have a look in the BEC section (bike engined cars) for any post by Chris Gamlin. He has a link to an excell spreadsheet which allows you to see the effects of different bike engines/diffs/wheel/tyre sizes.

HTH

Mike

Thanks to all. Its really well appreciated.

The 3.38 is your best bet. the 3.14 is a ittle too much for a zx9; you'll need a hayabuse or similar to use a 3.18 without doing in the acceleration.

Not according to my drag day times its not




the 3.14 is a ittle too much for a zx9; you'll need a hayabuse or similar to use a 3.18 without doing in the acceleration.

Alright, for some people it's fine, but all the other people I've spoken to have said 3.38.

another thing to remember is if you want limited slip diff then you really have two options as a bolt in 3.62 or 3.9 from the 2.0 litre and v6 4x4 sierras . you can combine the lower ratio diffs with the lsd unit and its been covered on here before but off the shelf lsd come in the two lowest ratios

They were probably too tight to go for a 3.14

no seriously, the only difference iv'e found between 3.63 and 3.14 is the engine holds in the gears longer, acceleration is much the same, especially as you get less wheelspin.
dragstrip times have improved since the swap and cruising is more relaxed. Car sets off on a whiff of throttle with no clutch slip when in traffic etc. I must add i now run 13" wheels, rather than the 15" which is a contributing factor, although the rolling radius isn't much different due to the higher profile tyres.

Originally posted by DIY Si
Alright, for some people it's fine, but all the other people I've spoken to have said 3.38.

Whats that about the LSD sorry? Are you saying they only come in 3.62 and 3.9 or are you saying that only the 62 and 9 will combine with a LSD unit? Sorry to mither, would like to get hunting the scrap yards though. Thanks again.

lsd only comes as standard with the 3.62 and 3.92 diffs. It can be fitted to others diffs but isnt entirely straight forward.

My car is zx9 powered, i *think* my diff is 3.54 at best (live axle), ive never got anywhere near flat out, on roads, motorways or trackdays.

Bearing mind that the LSD diffs weight 10kgs more than open diffs, which equates to 2% or more extra weight on an average car. Thats a significant difference.

My personal opinion would be to do without until you have driven with an open diff and decided that you want or need an LSD, rather than the other way round. Saves weight and money and allegedly makes the car less likely to bite. All IMHO though.

Ah Froggy meant 3.92 then. Yeah I see where you're coming from, weight over LSD. Think I'll just have a wander to the scrappies tomorrow then and just have a see what he's got in and hope he don't realise that the different ratios are worth more. The diff ratio's on a tag on the side (amongst other things) if I remember from an earlier search. I'll let you know.

the tags can be very grubby, easier is the vin plate under the bonnet, twixt headlights. The letter code is in the box entitled 'axle pt ar'

by all means wander round the scrappies ,but you should jump in the tardis and go back to 1994 first as i cant remember seeing a diesel sierra in a scrappie since then

it all starts getting a bit silly now .both lsd diffs 3.6 and 3.9 have bolt on drive shafts called lobro joints and the two lower ratios 3.38 and 3.14 are push in type .from a weight point of view the cheapest option would be to find a drum braked sierra at a yard and use the lot . i picked up a complete rear end with drums recently for £60 but if you want lsd then try and get a complete 4x4 rear end which will have lobro type shafts and discs.
you can buy 3.14 and 3.38 gearsets brand new as well . i had two built with me supplying a 7"3.62 diff and getting a 3.15 back as new but it costs £700each plus the £180 i paid for the diffs in the first place

Diffs are not only on diesels though are they and I thought that the Ford ones were interchangeable so's I could look at the escorts and Granadas too. Tis a pretty good scrappy I have in mind but theres loads aroung here. Otherwise I'll have to get one off fleabay. Won't be paying £700 though!

Well you're right, not to many Sierras left in scrappied now and they've all tidied up their acts, guess thats with all the new regulations. Found 3 in one yard though. A 3.92, 3.64 with the LSD on a Cossie and 3.62. Might wait out a bit longer for a better ratio maybe? By the way I have the different ratios according to the letters on the VIN plates if anyone thinks it might be handy?

escorts never had a stand alone rwd diff as such. They went from rear axle to fwd. Granadas have a heavier diff, 7.5" wide.

the better ratios are nearly all in diesels too, and usually just 3.38. I broke several sierras in the past and never found a 3.14. A 2.0 auto i broke had a 3,92 diff, not the 3.38 i was expecting.

[Edited on 22/8/06 by JoelP]