oibren85

Guys,

got a Kit car based on a sierra and the Diff which i've been told it is limiting my top speed to 110mph, which it is fine around Cadwell but it started to run out of steam. Whats the best diff ratio or diff to use to increase the speed up to around 150. The engine is ZX12r motorbike engine. Its going to the ring next year so want it to be good at the high speed stuff as it is at the low speed stuff.

Cheers

Brendan

RWD_cossie_wil

iTrader: (9)

What gearbox are you using, and do you have any idea of the current diff ratio?

oibren85

Seems to be the bike engine box as its sequential. Not a clue on the ratio, its all been built prior to me owning it.

tabetha

I sold a diff to a guy who has the same engine as you in a kit car, as he was running out of speed as well, a lot of the bike dudes use a 3.38:1, which is what I sold.
tabetha

oibren85

Tabetha, do you know what the diff was off and what speed that got him up to?

Mark V8

iTrader: (2)

Some info here

http://www.cobraclub.com/forum/pilgr...grim-sumo.html

S1-Tiz

iTrader: (1)

2.3 diesel sierras have a 3.14 diff.

Red16

I'm not sure on the gear ratio for your ZX12, but I'm using a Landrover Freelander rear diff (3.21:1) with my ZX10R engined Mac#1 Work kit car, this gives me a top speed of 137mph on the limiter in 6th.

From what I can gather the 3.14:1 Sierra diffs are rather hard to come by, and they tend to command a bit of a premium when compared to the more common ratios.

Have a look over on www.locostbuilders.co.uk you'll probably fiond your answer there.

Porkie

iTrader: (1)

You won't get 150mph out of it without a serious power increase dude. Seven type cars struggle massively over 100mph as they have rubbish aero.

Be good to change the diff though for the Ring though you are right

Still not had mine out there. Will deffo do it later this summer.

Red16

Sorry t stray off topic but do you have any idea how much your Westy weighs Lee?

tabetha

Mine was off my old sierra, a mk1 2L GL, automatic, carburettor pinto engine, he hasn't finished the kit so don't know about speed yet.
There is a website that I've put on here loads, a gear/speed site, just put in tyre/box ratio and diff it works out the mph/1000rpm.
We use a 3.14:1 on the xr4i, this came from a 2.3d mk1 estate sierra.
tabetha

oibren85

150mph would be a little scary in the indy! But would like to get a good set diff as in the future i will turbo the lump to get the extra power needed.

Had it at Cadwell this weekend and was spot on just that top speed was annoying, and i know it will be crap round the ring for that! 137mph would do me nicely. i'll have a look at the freelander diffs!

RWD_cossie_wil

iTrader: (9)

Hi mate, have a look on the diff, there should be an ident tag on the rear cover that tells you the ratio. If it does not have one, take the rear cover off, and count the teeth on the crownwheel, and on the pinion. You can then easily work out the ratio by dividing the crownwheel teeth by the pinion teeth

I've had a look for the ZX12 gear ratios, and have come up with this:

6 speed constant mesh
Wet multi-plate hydraulic clutch
Drive chain ???
Gear ratios :
************ 1 - 2.429
************ 2 - 1.824
************ 3 - 1.440
************ 4 - 1.250
************ 5 - 1.130
************ 6 - 1.033

What size wheels/tyres are you running? What does the engine rev to?

oibren85

Cheers for the info, I'm running 205/45/15 and the engine revs up to 12k. I'll have a look tonight regarding the diff and see what i come up with.

RWD_cossie_wil

iTrader: (9)

Was the 110mph on the limiter in 6th?

oibren85

Pretty much, not a lot more to go if any....

Jim Galbally

what about BMW diffs? sure they cant be hard to find and fit?

those use ratios in the 2.somethings!

RWD_cossie_wil

iTrader: (9)

Somthing isn't right, as I am getting speeds of over 200Mph using:

11500 Rpm Shift point
205/45/15 wheels
1.033 6th gear
3.9 Final drive (common ford kit car diff ratio from the xr 4x4)

Red16

Try the speed calculator in this link, it has a zx12 listed

http://www.locostbuilders.co.uk/foru...php?tid=121319

Fudgey

iTrader: (4)

ive got a mk1 sierra 1.6gl diff for sale, i cant remember the ratio but i will find out.

it was off a 4 speed type 9 box.

irrc stavros calculated that if i had run it on the 3dr with a T5 box and hit 7krpm in 5th it would do something like 204 mph

polly_x

iTrader: (2)

Both mine and Lee's weigh just over 700 kgs wet. So with all fluids and 40 litres of fuel.

oibren85

Have you still got this Fudg? would be interested if you could fined out the diff ratio and the price was right.

Fudgey

iTrader: (4)

yes mate i have, ill dig it out at the weekend and get back to you, ill whip the cover off and check the drive ratio

oibren85

Cheers fella, PM me when you get a chance.

foreigneRS

bigger wheels not an option?

oibren85

Had bigger wheels on it but it upset the handling too much. Made it a bit more skitty in the corners.

Fudgey

iTrader: (4)

curiosity got the better of me, just dragged it down off the garage roof, they are heavy fookers diffs nearly fell off the ladder lol

anyway, i cleaned the tab off an it says 3.62 on it.

let me know if thats what you are after mate. it came off my 65k mile 3dr

NEEDFORSPEED

just go with a 3.3 if you can get one. i started with 3.6 them moved onto 3.1 but had nowhere near enough power to pull it so am back on the 3.6 now and shopping for a 3.2. if by any chance your running a 7.5 inch diff rather than 7 i have a new fully reconditioned 3.3 with lsd! a guy i know who works for mk runs a 260hp busa lump in his race car and only runs a 3.3 so just goes to show how much power you need for them!

Mark V8

iTrader: (2)

3.14 diff on Ebay cheap at the moment

http://www.ebay.co.uk/itm/Sierra-7-D...item2eb78e7665

Red16

Good call

NEEDFORSPEED

you really dont want a 3.14 youd need a load of power to pull it a guy i know in blackpool with a zx10 turbo runs 328hp and stil runs a 3.3 just goes to show.

Red16

I've been out in a number of ZX10R powered cars running a 3.21:1 diff and they don't struggle at all, personally i think a 3.3:1 diff would be a bit short on a ZX10R, especially a turbo ZX10R.

NEEDFORSPEED

hes compared and timed both as has danny keenan who races the busa (different gear ratios i know) have a read on locost builders and see what they have to say

Red16

I'm already a member of locostbuilders. I know they don't suit all bike engine cars due to differing ratios etc, but the longer diff ratio really does suit the ZX10R engine, especially a turbo one, which is what I currently own.

To go back onto topic, the OP really needs to find out what diff he currently has in the car now before going any further, otherwise he could end up buying a diff which is no use to him at all.