I have a Silver top Zetec on Twin 40's connected to a Type9 box, when I built the car I fitted a 3.89:1 diff into the English axle, it goes really well through the box but your into 4rd before you know it and crusing at 70 is 3500 RPM in 5th which is OK on a short trip but not so good on a long one.
Having done a bit of math with excel I was looking at changing to a RS 3.54:1 diff which should make the gears longer and mean that 3000 RPM will be the legal limit in 5th.
What ratios is everyone else running ? - Road use NOT track
I'm running 185x60x15's (I think), I know the rolling radius is 1.8m as I had to measure it to calibrate the Speedo, so when I did my calculations I took that into account to give approx roadspeed per 1000 rpm in each gear.
And your comments about first gear are valid, however the ratio in the box is sooo low that changing the diff from 3.89 to 3.54 only adds 3 MPH at 7000 RPM....
Looks like i'll be looking for a 3.54 dif at a sensible price !
I have a 2.0 zetec and built it with a 3.54 which was good.....
but when I changed to a 3.89 the difference in apparant power was up there with cam change / remap etc.
I think you will find a 3.54 too tall and will be dissapointed as the car will definitely lose some performance.
In fact - I.m even now contemplating a 4.44.....
Sold my 3.54 diff for £100 too - they definitely go for a premium, still if you find you don't like it, you'll sell it ok and not lose owt on it.
SSC Sylus 2.0 Dunnell Black Top Zetec weber alpha / DTA + cams, 236@fly. (aka NORMA)
there is a gear calculator also on the quaife website which is excellent. you can select tyre size, all the gear ratios and the final drive (diff) ratio. put all that in and it'll give you the top speed in each gear for the rpm of the engine and also give you the rev drop between gears which is also very helpful.
i have got a 4.44 ratio in my stylus which would be great if i had a longer 1st gear. the 1st on a standard sierra box is pretty pointless in a car this light. you gotta change gear before you've even moved anywhere. as for 5th gear, yes my engine does rev a little higher at 70 than most but i don't really see this as a problem.
for a car for the road i think a 3.89 or a 4.1 is good. i think any lower than those like 3.45, you'd find each gear not as useable and the car wouldn't be as much fun.
maybe rob will agree! 4.4 for track? 3.89 for road?
One of my concrens was loosing the acceleration, I wondered if a 3.77 mex diff (rare and even more ££££) might be a good compromise as the ratio between what I have now and the RS diff. Decisions, decisons !
Some years ago I had a Robin hood with a 1600 GT pinto (Ok a 1600 with a 2L carb & cam), I built that with a 3.54 and 5th gear was useless accelaration poor I changed to a 3.89 and as you say it was like gaining 50% more BHP, but that was in a heavier lower powered car. I have a 3.54 diff in TD project Im working on (but not on the road yet), for the sake of a couple of hours work and a diff gasket I may chuck it in and try it if I don't like it I'll rebuild the tired 3.89.....
Hearbear - According to haynes 5th gear in a standrd type 9 is 0.82:1, for the Diesel box I read its 0.75:1 but can't confirm this.
It appears that my first forum reply worked OK, so here goes again!
B@man & Hearbear quoted that they would use 3.54 ratio in their diffs, mainly for good cruising mileage.
When I settled on the Nissan S13 -- CA18DET upgraded engine for my Stylus I also decided on a 3.54 ratio. Bill at Adelaide Turbo Service said to me after I had him hi-flow the turbo, Hi-temp ceramic coat the exhaust manifold, Turbine housing & the 3" rounded dump pipe, then quote what I was getting for the Intercooler system, "Hell, if you do not get at least 250HP on the wheels, it is not tuned correctly" !!!
Do not know the torque figure, but 250hp calculates to nearly 400 BHP per Ton. As Rolls-Royce once said, "It will be adequate"!
On gearbox ratios. ---- Tyre sizes & road speeds.
The forum quoted tyres are not available in Australia so the following is calculated on Simex SM 9300 road tyres, not specifically sport types.
195/50 R15 --- load rating of 475Kg per tyre & a rolling diameter (at Stylus weight) of 560 mm.
This calculates to 914 revs per mile & 18.5 MPH/1000 RPM
or 130mph (210Km/hr) in 4th. direct gear at the red line of 7000 rpm.
Can go to the rev limiter of 7500, but 7000 will be enough!
1st gear is 3.321 giving only 39mph at 7000rpm and will "get there, very quickly" !!!
2nd gear is 1.902 for 68mph (109Km/hr) which is 1 Km under our legal speed limit in open country/highways.
3rd. gear is 1.308 for 99.4 mph (159 km/hr)
4th. is direct for 130
5th. overdrive is 0.838 giving 155mph or just under 250km/hr.
68mph (109km/hr) in overdrive calculates to 3077rpm, less than half red line revs, so should return rather good cruising mpg.
We are currently paying $138 or more per litre for 98 ron petrol & going up week by week. Would be much more if our dollar had not risen from about US65cents to over 91 cents per A$1 the last few months.
A great days run in the Stylus could easily cover upwards of 300Kms.
Adelaide & back for parts or whatever is 465 Km without any extra running around!! Easily another 100Km. Long Day !!
With the tall 3.54 ratio and 3.321 in first, giving an overall ratio of 11.756, hopefully the axles will not twist off. If I went to a 4.11 diff, (giving 14.55 overall) probably they will twist!!
Then it would be a Quaife & hi-tensile axles OR Mazda have some interesting LSD units ????
