wotagr8bigchief

iTrader: (1)

Does anyone have first hand experience comparing these two boxes? I know the gear ratios 1st thru 4th are exactly the same but the JDM has a different drop gear, does this make it faster off the mark?
Also are the rear diffs the same ratio? Believe mines got the R180 but not really sure how to tell.

BlueBugEye

iTrader: (12)

JDMs are lower all the way through the gears, a lot depends on the engine it's matched to. I have a JDM box on a 2.5 and the gears are in all honesty too short for the torque curve, may well be better on a 2.0 or 2.1 which needs more revs.

Infected by sti

iTrader: (6)

I would say my jdm blob box is quicker trough all the gears than what my uk blob was, not a lot obviously but lookin at the speedo to the rev counter I would say the jdm is roughly 500 rpm higher at 70mph than the uk car. If you have a uk car then the rear diff ratio is 4.444 with the uk 6 speed and the jdm has a rear ratio of 3.9 with the shorter geared jdm 6 speed box

Hope that helps

banny sti

iTrader: (68)

Both gearboxes are the same from 1st-4th, only 5th and 6th are shorter on the JDM. The drop gear on a JDM is 1:1 and rear diff ratio off 3.9 and the UK is drop gear ratio of 1:1:1 with a rear diff ratio of 3.545

Infected by sti

iTrader: (6)

Now I'm proper confused

I was told that my old uk Sti blob has a 4.44 rear diff banny, and if the drop gear is different on the jdm boxes to the uk wouldn't that make the ratios incompatible? ( Genuine question ) I always thought the gearing would be different on a jdm box with the 1:1 drop gear through all gears or is it the case the drop gear only equates to the final drive gearing?

What I'm trying to get at is could you run a 3.54 rear diff then or a 4.44 with a jdm box then if you only used 1st - 4th if the gearing is the same up until that point?

dazdavies

iTrader: (22)

You UK blob has a 3.545 rear diff

If you wanted to put a jap box on your UK blob you'd need the matching rear diff which is a 3.9

Having had both I actually prefer the JDM box as stated 1-4th are identical to the UK but the jap box has the 5th and 6th closer together so no massive jump from 4th to 5th.

ScoobyDoo69

iTrader: (17)

Never been a big fan of the jump from 4th to 5th on my box either. Really have to keep 4th revving high if you want to make progress in 5th.

Infected by sti

iTrader: (6)

So how does the ratios work on the rear diff? I take it they only make a difference then in 5th and 6th gears which is what the drop gear does on the final drive to give a matching ratio? So is it the case you could use the 3.54 rear diff on a jdm box if only using 1st to 4th? This is where I'm confused as if the boxes have the same gearing until 4th then could you run any of the diffs up until 4th gear with no problems?

Never had much to do with gearing tbh so just interested on how it all works

wotagr8bigchief

iTrader: (1)

Cheers guys, I have the jdm setup from an 03 sti. Its fitted in my 93 wrx that will be running 380-400 bhp on a forged 2.0 with v3 sti heads when mapped in january. I like the idea of it being a bit faster thru the gears as I rarely go very fast on the motorway, was just worried gears would be a little too short.

ScoobyDoo69

iTrader: (17)

380-400bhp on a 93 WRX with short JDM ratios will be awesome

banny sti

iTrader: (68)

JDM has 3.9 front diff 1:1 drop gear so needs 3.9 rear diff
UK has 3.9 front diff 1:1:1 drop gear so needs 3.545 rear diff to maintain the ratio

So not possible to do what you're suggesting

wotagr8bigchief

iTrader: (1)

Cheers buddy, yeah I am hoping so. Been a long time coming this car.