Best Diff Ratio

[jamie]

Hi all,

 

What do people think is the best "all round" diff ratio for use with a Zetec and type 9 gearbox?

 

Tyre size is 245/45/13...

 

Thanks!

[SmokeEm]

3.9:1 for me but its all down to personal taste.

 

i.e. Acceleration v Top End

[over_head_cam]

Like Dave says, the 3.89:1 is a good all round diff. As you're running a type 9 you could go to a 4.1:1 for some quick acceleration, but you may suffer a little on top end. If you've got plenty of torque and want a lot of top speed you could go right up to a 3.54:1

[jamie]

Cheers !

[rallyesport04]

3.89 cheap plentifull an good starting point

[LUKE261]

3.89 good all 3.54 for ultimate street pleasure

[LUKE261]

That should have said 3.89 good all rounder

[mk2 mike]

On a similar note, how can you tell what diff you have? Is the ratio stamped anywhere?

[over_head_cam]

Without taking the diff out the way I would do it Mike is to jack one wheel up at the back and take it off. Put a mark with tip-ex at the top of the drum and then put a similar mark on the diff flange. Then you can turn the prop and count how many turns it takes to make the drum turn 1 revolution.

3 1/2 turns - 3.54

just under 4 - 3.89

just over 4 - 4.1

nearly 4 1/2 - 4.4

I may be wrong of course, I often am

[Tall paul]

On a similar note, how can you tell what diff you have? Is the ratio stamped anywhere?

 

I think some of them had a metal tag on the diff housing but most have rotted away by now other than that you will have to count the cwp.

[SmokeEm]

Without taking the diff out the way I would do it Mike is to jack one wheel up at the back and take it off. Put a mark with tip-ex at the top of the drum and then put a similar mark on the diff flange. Then you can turn the prop and count how many turns it takes to make the drum turn 1 revolution.

3 1/2 turns - 3.54

just under 4 - 3.89

just over 4 - 4.1

nearly 4 1/2 - 4.4

I may be wrong of course, I often am

 

If the tag was missing, thats how we used to do it

[over_head_cam]

99% of the tags are rotted away anyway

[mk2 mike]

Cheers Phil, very useful! Sorry for the hijack Jamie.

[jamie]

No probs at all mate....

 

Useful info - thanks again!

[shaun1.6ghia]

Duffs mean nothing without a wheel and tyre size. I run Zetec with type9 on 13x7 with 175x50x13 tyres. Cus tyres stretched makes the radius so small a 3.5 is perfect for me.

Couldn't run any higher on the road everyday as would do my head in. An it's fast enough off the lights only been beaten once lol

[over_head_cam]

You're right Shaun. The op's tyres will have a larger radius (22.75mm) compared to a 175/50 so running a 3.89 would probably work quite well. On the other hand, with a 3.54 it would certainly be a motorway muncher lol

[puddy]

Excellent gear ratio calculator on a westfield site here.........

 

http://www.google.co.uk/url?sa=t&rct=j& ... crMOQ8Eg5A

 

I just put in 1.1 for 4th gear ratio as I only have a 4 speed box.

 

You can compare tyre sizes, diff ratio's etc,cool!

 

puddy

[shaun1.6ghia]

@puddy great idea, a calculator for it is perfect

Mine int a real motorway cruiser to be honest. (So noisy with twin 40s) seems perfect for everyday driving. Final drive ratio would totally depend on what you want to use the car for, just for shows, everyday, pod, occasional traffic light race lol

[Posse]

I put a 3.89 in my old escort which had 175/50’s and I thought they worked well together

[LUKE261]

Great info phil on how to check ratio this saves stripping it and counting the teeth of the crownwheel and dividing by the anount of teeth on the pinion like i normally do

[Escort Mk1 4 Door]

using that mine must be a 3.77 diff as i get about 115-118 at 6700-6800 in 4th

[radjay mk1]

if you have the diff out dont you count how many crownwheel teeth you have and the the planet gear teeth then divide them together?

or something like that,its been a very long time since i last done it

[over_head_cam]

Close Radjay, but not quite

 

You have to divide the crown wheel by the pinion gear