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Boss Engine Diff Ratios? What are they and whats recommended 

 

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 Post subject: Boss Engine Diff Ratios? What are they and whats recommended
Posted: Fri Dec 31, 2010 10:35 am 
Getting Side Ways
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Ride: AU XR8 220 Manual

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!
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 Post subject: Re: Boss Engine Diff Ratios? What are they and whats recommended
Posted: Fri Dec 31, 2010 4:27 pm 
Oompa Loompa
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Ride: el futura

Location: tumut
NSW, Australia

my rents bf mk2 xr8 6sp manual is 3.46 lsd
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 Post subject: Re: Boss Engine Diff Ratios? What are they and whats recommended
Posted: Fri Dec 31, 2010 8:04 pm 
ACT Cruise Moderator
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Age: 36

Posts: 6275

Joined: 24th Nov 2004

Ride: '06 BF GT-P

Power: 293 rwkw

Location: Canberra
ACT, Australia

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.

 

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1998 DL LTD in Sparkling Burgundy, daily, 302W, stereo, slow - 97.5rwkw
2006 BF GT-P in Ego, mods. 293rwkw - 12.427@109 - 0-1000m 24.838@221

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 Post subject: Re: Boss Engine Diff Ratios? What are they and whats recommended
Posted: Sat Jan 01, 2011 11:27 am 
Oompa Loompa
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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 :)
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 Post subject: Re: Boss Engine Diff Ratios? What are they and whats recommended
Posted: Sat Jan 01, 2011 12:51 pm 
ACT Cruise Moderator
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Ride: '06 BF GT-P

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Location: Canberra
ACT, Australia

rooseEL wrote:
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.

 

_________________

1998 DL LTD in Sparkling Burgundy, daily, 302W, stereo, slow - 97.5rwkw
2006 BF GT-P in Ego, mods. 293rwkw - 12.427@109 - 0-1000m 24.838@221

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 Post subject: Re: Boss Engine Diff Ratios? What are they and whats recommended
Posted: Sun Jan 02, 2011 5:42 pm 
Getting Side Ways
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Joined: 20th Nov 2005

Ride: AU XR8 220 Manual

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
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 Post subject: Re: Boss Engine Diff Ratios? What are they and whats recommended
Posted: Sun Jan 02, 2011 7:17 pm 
ACT Cruise Moderator
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TUF250 wrote:
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).

 

_________________

1998 DL LTD in Sparkling Burgundy, daily, 302W, stereo, slow - 97.5rwkw
2006 BF GT-P in Ego, mods. 293rwkw - 12.427@109 - 0-1000m 24.838@221

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