Hi all,

I was wondering if anyone could tell me what the diff ratios for the various boss motors with manual gearboxes are? The only one I know for sure is the original BA XR8 5 Speed which was 3.23. Maybe someone could fill this in?

(looking at manuals only at this stage)

BA XR8 - 3.23
BA XR8 Mk II -
BF XR8 -
FG XR8 -

BA GT -
BF GT -
FG GT (5.4) -


Now I know these motors are criticised for lack of low torque (I havnt driven one yet so I wouldnt know?) but would a shorter set of diff gears help eliminate this? What is recommended behind the manual gearboxes for a weekend car? would 4.11 be too short? any thoughts are welcome

Cheers!

my rents bf mk2 xr8 6sp manual is 3.46 lsd

diff ratio was based off of the transmission type not engine/model.

4spd auto got 3.45
5spd manual got 3.23
6spd manual got 3.45 (BA2+)
6spd auto got 2.72 (BF+)

4.11's behind a 6 speed manual (or 4 speed auto) is a common upgrade. It'd be far to short behind a 6 speed auto (upgrade them to a 3.45 like I have).

As for "lack of torque" the 260's are soft, but the 290/302/315 are a very different drive.

data_mine check your gt but our xr8 is definitly 3.46 and not 3.45 however there is a bees forskin difference so it doesnt really matter

Yeah you're right, should read 3.46, and 2.73 for the 6spd auto.

I originally upgraded using a 2nd hand diff from a manual GT (so the 3.46 ratio), when that decided it didn't want to play any more, I got after market gears (and truetrac centre etc.) so not sure what exact ratio I got (I asked for the same as what came out), but it's close enough I can't tell the difference.

excellent info. thanks.

Well done on your gt. very impressive 1/4 time and power figure. true testimony to how good those boss motors are.

So you feel the 290 motor is that much better in base form? dosnt suffer from the apparent low down torque? what did you do to yours to upgrade the performance to well?

cheers

The higher static compression ratio, makes it better all over the rev range, and the bigger cams picks up the top end. There's a more noticeable surge of torque at about 3800 in a 290 as the cams come on song. But that's not to say it's lacking down low, there's just lots more to come.

As for mine, all the bolt ons, and a good tune (i.e. took a lot of time over several iterations).