3.9 diffs
#7
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Rainbird runs 3.9's from memory. Best mod my mate ever did to his 3 door.
TiB off here still managed 178mph at Brunters running a 3.9.
I wouldn't say they are too bad on the road, just the cruising speed needs to be more like 70 not the 80+ that your maybe used too.
TiB off here still managed 178mph at Brunters running a 3.9.
I wouldn't say they are too bad on the road, just the cruising speed needs to be more like 70 not the 80+ that your maybe used too.
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#10
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the standard one is 3.62:1 so the "upgrade" to the 3.92:1 is only 1 less tooth on the pinion drive with 14 instead of 15 or something along those lines
it's "easier" to put the power down with less gears to turn and, in essence, makes your car "feel" more powerful without actually adding any more power to it
it's "easier" to put the power down with less gears to turn and, in essence, makes your car "feel" more powerful without actually adding any more power to it
#12
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No
You can still do over 180mph at brunters. My Sierra did it...
The speed limit on road is 70mph. The fastest you will go on any racetrack is what 150mph?
so what more you need?
You can still do over 180mph at brunters. My Sierra did it...
The speed limit on road is 70mph. The fastest you will go on any racetrack is what 150mph?
so what more you need?
Last edited by Porkie; 09-11-2011 at 06:25 PM.
#13
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#16
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Love this subject but as always things are not what you think.
The Sierra left Ford with 205/50/15 tyres giving = 23.7mph/1000rpm
Every Tom, Dick & his Harry then fit :
225/40/17 = 24.75mph/1000rpm or 225/40/18 = 25.77mph/1000rpm if you change the Diff to 3.9 on the 225/40/18 = 23.92mph/1000rpm so you need the 3.9 to get it back to standard gearing.
The correct gearing is the shortest gearing that will give you grip no point fitting a 3.9 on mine it would spin its wheels at alltimes everywhere .
The shortest i can go is 3.54 diff with 235/40/18 = 25.72mph/1000rpm.
You can indeed reach 180mph at Brunters with a 3.9 provided the Tyres selected allow you to reach 180mph at roundabout max power.
The Sierra left Ford with 205/50/15 tyres giving = 23.7mph/1000rpm
Every Tom, Dick & his Harry then fit :
225/40/17 = 24.75mph/1000rpm or 225/40/18 = 25.77mph/1000rpm if you change the Diff to 3.9 on the 225/40/18 = 23.92mph/1000rpm so you need the 3.9 to get it back to standard gearing.
The correct gearing is the shortest gearing that will give you grip no point fitting a 3.9 on mine it would spin its wheels at alltimes everywhere .
The shortest i can go is 3.54 diff with 235/40/18 = 25.72mph/1000rpm.
You can indeed reach 180mph at Brunters with a 3.9 provided the Tyres selected allow you to reach 180mph at roundabout max power.
#24
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if you can find a dohc 4x4 sierra then the diffs are a direct swap, buy the car, swap the diffs, sell the car
you only need to do the gearbox mod if you change the front OR rear diff as it's the step down gearing to keep the centre diff spinning at the correct speed
you only need to do the gearbox mod if you change the front OR rear diff as it's the step down gearing to keep the centre diff spinning at the correct speed
#26
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ebay throws up a few for around the Ł500 mark occasionally
http://www.ebay.co.uk/itm/ford-sierr...item3cbe2448ff
this one though is a bit much
http://www.ebay.co.uk/itm/ford-sierr...item3cbe2448ff
this one though is a bit much
#28
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I've fitted a 3.9 to mine (2wd) It deffo makes pottering about and pulling away with an evil clutch nicer than before, the whole car just seems more driver friendly.
Can't comment on performance as haven't had my car on boost much since running it
Hi Rod,
Makes a lot of sense
How would my actual car speed compare to my indicated speed then? I'm runnning a 3.9 diff (2wd) with 235/40/17.
I guess not *too* far out at legal speeds?
Can't comment on performance as haven't had my car on boost much since running it
Love this subject but as always things are not what you think.
The Sierra left Ford with 205/50/15 tyres giving = 23.7mph/1000rpm
Every Tom, Dick & his Harry then fit :
225/40/17 = 24.75mph/1000rpm or 225/40/18 = 25.77mph/1000rpm if you change the Diff to 3.9 on the 225/40/18 = 23.92mph/1000rpm so you need the 3.9 to get it back to standard gearing.
The correct gearing is the shortest gearing that will give you grip no point fitting a 3.9 on mine it would spin its wheels at alltimes everywhere .
The shortest i can go is 3.54 diff with 235/40/18 = 25.72mph/1000rpm.
You can indeed reach 180mph at Brunters with a 3.9 provided the Tyres selected allow you to reach 180mph at roundabout max power.
The Sierra left Ford with 205/50/15 tyres giving = 23.7mph/1000rpm
Every Tom, Dick & his Harry then fit :
225/40/17 = 24.75mph/1000rpm or 225/40/18 = 25.77mph/1000rpm if you change the Diff to 3.9 on the 225/40/18 = 23.92mph/1000rpm so you need the 3.9 to get it back to standard gearing.
The correct gearing is the shortest gearing that will give you grip no point fitting a 3.9 on mine it would spin its wheels at alltimes everywhere .
The shortest i can go is 3.54 diff with 235/40/18 = 25.72mph/1000rpm.
You can indeed reach 180mph at Brunters with a 3.9 provided the Tyres selected allow you to reach 180mph at roundabout max power.
Makes a lot of sense
How would my actual car speed compare to my indicated speed then? I'm runnning a 3.9 diff (2wd) with 235/40/17.
I guess not *too* far out at legal speeds?
#33
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No as the cosworth 4x4 mt75 has a thicker main shaft i am told so will be slightly stronger,
Also if you change the front and rear diff to 3.9 ratio then nothing has to be done to the standard cosworth gearbox, you only need the drop gears if you leave the front diff as a 3.6 and change the rear to a 3.9 to make up the difference in rotational speeds
Thanks
Marc
Also if you change the front and rear diff to 3.9 ratio then nothing has to be done to the standard cosworth gearbox, you only need the drop gears if you leave the front diff as a 3.6 and change the rear to a 3.9 to make up the difference in rotational speeds
Thanks
Marc
#37
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I'm good though thanks, gave in with the escort in the end. Doh
The pug runs a pinto with 8 injectors and a t4 making about 450hp
Last edited by JonnyBravo; 24-11-2011 at 07:40 AM.
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