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hey guys, i have a chance to grab a 6speed diff for an OK price. the questions is whether its worth swapping it over. The car is a turbo'd 1990 NA6 with approximately 150hp. The guy said it was a direct swap with nothing else needed, is this correct?

Depends what it comes with as to whether its a straight swap, it will be taller geared so you will go faster in each gear.

Benefit is that it will never ever break.
Ever.

Dann

To put a late model diff in a NA6 you need the diff in the late model housing (as they are a different size to the smaller NA6), the tailshaft and both drive shafts as all are different sizes. If you have all of this then it bolts in place of the NA6 diff, tailshaft and driveshafts.

Wait... 6-speed diff??

Combined with a 6 speed box it would be a 36 speed.

"6 speed diff" = 7" with a 3.63

Your speedo will be out unless you get a different sender. (ref solomiata for the right one). 4.1 in a NA6 seems to get the speedo dead on, they were naturally optimistic with the 4.3.
eg when your speedo reads 100 with a 3.63, you'll actually be doing ~110-115.

3.6 is very tall gearing for a 1.6, it would make a good cruiser, but you would notice a difference in the acceleration dept.

Hope you don't mind if I post in here, just didn't want to start a new topic.

I'll be importing a 6-speed box soon and need to decide on what diff ratio to go with it. Can just do a 4.3 which is easier to obtain or build a 4.6/4.7 using Kia Sportage ring/pinion gears. Bear in mind that my new head/cams will make power later in the rev range.

Engine is a 1.6L, extensively ported head, 280deg 10.5mm lift camshafts, oversized valves.

Unless you have a need to rev the hell out of it I'd go for a 3.9

Compare the actual gear ratios - as I recall the first 5 gears of a 6 speed, with a 3.6, are equivalent to the five speed with a 4.1

So a six speed with a 4.something would render first almost completely useless

A 6 speed diff is a weird way to describe a diff. I use a 4.1 diff with a 6 speed, but if I had the chance would go with a 4.3. For road use a 4.1 is a good choice.

i dont know what ratios the diff came with, was just told its from a 6speed car.

if it is an ADM car then 3.6 and 3.9 if it off a JDM car.