At 100kph, what would be the difference between a 3.88:1 and 4.12:1 r@p and what revs would you be pulling on both ratios?......cheers Vaughn

Hmm, depends pretty heavily on the tyre and rim combo not to mention your 4th gear ratio.

Someone like Dangerous seems to be able to answer these these sorts of things off the top of his head, while I use a little spreadsheet thingy that BajaWes has on his site www.offroadvw.net/bajawes.

According to that, a standard IRS tranny with 0.93 4th gear, a 3.875 r&p fitted with 630mm OD tyres (about what a bog-standard 15" tyre and rim combo is) would see about 3059rpm. The same setup but with a 4.125 and you'd get 3240rpm. But hey - who runs around with standard rims and tyres !!!



If you fit something like 205/50/15's things change a fair bit cos your tyre OD drops by almost 50mm, and you end up with 3263rpm and 3473rpm respectively.

the wheels will be 17s with 45 profile tyres

Dave is correct,
but also remember that most gearboxes that have the 4.125 use a taller 0.889 or 0.883 fourth ratio.

Based on Dave's calc with 3059,
the earlier box will have around 3080 rpm....hardly worth it.

The 1st through 3rd ratios will be taller, and 3rd and 4th will be much closer ratio to each other however,
so this may suit you.

If you are having the gearbox totally re done,
and don't mind spending some extra on different gea ratios, you can combine the best of
both boxes.

An example is to add a lower ratio 40hp third gear to the "L" box.

Or better still, a taller, closer ratio 1st, 2nd, and 3rd, to a box with the 4.125 diff.
It all depends on your application,
and of course your budget.

The gearbox is a super pro street from pacific customs in the states,it has a close ratio 3rd @ 4th and able to handle 350 to 400 hp.I will be running a ej20 turbo with 17s and 45 profile tyres and the box will be about $1800 delivered to brisbane.....cheers vaughn

I doubt it will handle the quoted HP.

What diff does it have ?

As long as it can handle around 250hp,i will be happy 4.12:1 RING AND PINION
SUPER DIFF
HEAVY DUTY SIDE COVER
WELDED SYNCRO HUBS
CHROMOLY PINION RETAINER
HARDENED KEYWAYS
LATE STYLE THROW OUT BEARING
CLOSE RATIO 3RD AND 4TH GEARS
thats all the info i have about them at the moment...cheers vaughn

The life of a type one gearbox with 250hp will be disapointing.
But if you drive carefully you may be happy with it.

PM one of the other fellows on this forum about what has failed in their tranny with boosted subaru and get those upgrades as well.

You will want the stronger 3.875 diff and an aftermarket 1st and 2nd mainshaft set.
The axles, if swing axle will need to be better(Sway-A-Way) or Kombi CVs if it is IRS.
If IRS, the output splines are too small, but the quaife diff has larger bus splines.

If you want nice Highway cruising, you will be best to use stock ratio 3rd and 4th.

PM westi and ask him what he thought of his 'pro street' tranny from the USA.

Ahh diplomatic Dave.