www.RX7fb.com

Hi all been awhile.
Just recently bought some 2001 Kia Sportage front diff open centre $330.
Its true they really do just bolt in the series 3 RX7 26 spline axle diff.
(somethings i learned, with the dohc kia sportage, u get 4.77;1 gears, with the sohc kia sportage more likely to come with 4.44;1 gears. u can always count the teeth)
You only need 1 bolt, original rx7 centre has 1 long bolt, which is not on the kia centre, u need another short bolt to match, use one of the originals to find a perfect match.
another area which affected me was the diff flange size was larger on the kia centre, with a 62mm x 62mm bolt pattern. so i had a suped up tailshaft made adding extra cost.
First impressions are great!
Its an old RX4 13b Nikki, 12a electronic dizzi,long tuned primary exhaust. maybe 100bhp not tested.
leaves the line much easier just cruising (original 3.91 were replaced)
got more zest at any rev range
does not feel like it is over revving, its more at its perfect set up.
i am an inner city daily driver and it now sits and behaves better on the local speed limits much better than with the 3.91 when trying to match them limits it would buck and bunnyhop.
This is a must have diff mod for any stock to mild port rotary owner who likes driving through the gears.

daily rotor wrote:Hi all been awhile.
Just recently bought some 2001 Kia Sportage front diff open centre $330.
This is a must have diff mod for any stock to mild port rotary owner who likes driving through the gears.

You can get a Kia Sportage limited slip differential I think ? So why you take the open front diff ?

unfortunately that was all that was on offer.
l.s.d and MX5 torsen options are on the expensive side even 2nd hand.

Anyone done this conversion before (3.91 to 4.77gears with series 2 box)?
What was speedo gear solution?
Its roughly 20% more on speedo than what it is doing.

have ordered a speedo correcter box with a 20% adjustment, from Marks4wd.com.
choose to go this way as i still have 3.9 diff centre in reserve and if i were to ever change back only have to unbolt the speedo correcter box. with all speedo drive gear and driven gear remaining original.
recieve it in 2 weeks time will let everyone know how it works out.
looks to be pretty simple install, and the fb has the space in that area for it.
these examples are bases on tyres being same diametre, and popular diff gear changes(mazda and kia)
there is -10% correction boxes suit someone who has gone from 3.91 to 4.3.
there is -12% correction boxes suit someone who has gone from 3.91 to 4.44.
there is -16.5% correction boxes suit someone who has gone from 3.91 to 4.62. (-18%)
there is -20% correction boxes suit someone who has gone from 3.91 to 4.78. (-22%)
they also do a custom box with percentage of your choice once diff gears and tyre diametre are known for a small amount more.
hopefully this works out simpler than trying to match drive and driven gear teeth sets, slight higher cost, easy reversibility.
http://www.marks4wd.com/speedo-correction.html

I love this stuff. Bits from other cars that fit, by chance, onto the 7's. Like the MR2 and old Mustang shocks that fit onto the 85.

What is it like on the motor way? Is it revving much higher at 60mph.

It revs somewhere between 550 to 650 rpm extra.
which in my underpowered rotor, gets the engine to a happier cruising speed where it will respond better to any pedal push even in 5th gear.
when changing from the 3.91 set up to 4.77 gears.
the 5th gear 0.825 turns into a 1.00 gear (it still is a .825 5th gear) from the 4.77 gears.
and feels like it to the driver.
just threw the old nissan silvia 16 x 7 rims back on, with new 195/45r16 up front and 215/40r16 out rear

here are some cruising speeds to common speed limits in my country.
with 4.778 diff gears and 22.8`` diametre wheels.
100km/h 5th gear 3,600rpm
80km/h 4th gear 3,550rpm
60km/h 3rd gear 3,700rpm
so in most driving situations the revs are sitting at a point for where it is easy for the car to accelerate away compared to being in same situation with 3.91 and 550 to 650 rpm less

just recieved speedo corrector
looks a pretty simple install (cant even put it in back to front)
fingers crossed for thread pattern
will take more time to lift it onto stands and off.


https://ibb.co/epJZov

smaller than what i was expecting which is great on the room side of things
weekend install planned and no more maths whilst driving

That looks a really neat solution