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[cem_devecioglu]

searching for the threads on differential ratios

pre 1998 2.5
auto 3.9:1
manual 3.7:1

so if I keep the auto differential during conversion my acceleration will be better but maximum speed will drop compared to manual differential .. is that correct ?  :-/ 

[Jimbob]

Thats my understanding...

along with sitting at higher revs and therefore also consumption at any given speed

[cem_devecioglu]

Thats my understanding...

along with sitting at higher revs and therefore also consumption at any given speed

 :-/  yep.. consumption is a critical decision factor..  but anyway I wont use it everyday.. and I already port polished the heads so I'm after performance and decision fixed.. Thanks Jimbob

[2woody]

maximum speed will drop compared to manual differential .. is that correct ?  :-/ 

not necessarily.

[Matchless]

I wouldnt worry about the top speed...its still fast enough to run out of talent very quickly.

The 3.9 is fine for a 2.5 manual, and was used on later 2.5s. When I first wrote the auto - manual guide I kept the 4.22 diff from the auto, acceleration was very good but I made too much use of the performance and paid the price at the fuel pumps.
If you use a 3.7 you will find it a little bit high geared in 4th and 5th.
Remember that the speedo is driven from the wheel sensors so you dont have to worry about that reading incorrectly.

Have you broken another auto box?

[cem_devecioglu]

I wouldnt worry about the top speed...its still fast enough to run out of talent very quickly.

The 3.9 is fine for a 2.5 manual, and was used on later 2.5s. When I first wrote the auto - manual guide I kept the 4.22 diff from the auto, acceleration was very good but I made too much use of the performance and paid the price at the fuel pumps.
If you use a 3.7 you will find it a little bit high geared in 4th and 5th.
Remember that the speedo is driven from the wheel sensors so you dont have to worry about that reading incorrectly.

Have you broken another auto box?

nope.. I bought a manual box (from 2.5) (and some other bits, today breakers prepared them, will buy tomorrow) (keeping my auto aside for future) and equipment.. also trying to to avoid differential expense..

will follow your guidelines