Shorter Ratio Gearbox

[boggs]

I have tried doing some searching on this topic but all I can find is information about longer ratio gearboxes for 306 hdis. Has anyone thought about or carried out a swap for a shorter ratio gearbox for a 306 hdi? A XUD one or a straight diesel box? Would there be much benefits in this and is it a straight fit? Whats all needed?

Thanks

[Midnightclub]

An XUD box is 'shorter ratio' but it's only the final drive that's shorter IIRC. You could swap it to a GTi6 gearbox as that's a much shorter ratio but you'll have a top speed of about 90/100 mph and your RPM at 70mph is going to be pretty damn high..

[mr_fish]

http://306oc.co.uk/forum/showthread.php?...058&page=8

I did it with a NAD box, I was led to believe it that the FD was 19:77, opposed to 19:75 for a DT. So a little shorter across the range.

70mph was just over 3k.

[Piggy]

Generally...diesels strength is in its torquey mid range punch...so a very short ratio box won't exploit the diesel torque so much.
Plus the noise at 70mph be deafening

[boggs]

Is a XUD box much shorter than the hdi one? Final drive wise of course as the gear ratios are the same. I would like a shorter box but 3k at 70mph is not ideal

[Piggy]

XUD is about 500rpm per gear more at same speed than hdi box

[Poodle]

At the risk of being a pedant; at what speed or point in the revs is that, Piggy? Because it will change considerably depending on those two variables, if it gains 500rpm at the point of 2000rpm then it will gain 1000 at 4000rpm, if that makes sense..?

[silverzx]

BE1 off a 1.8 N/A be even shorter again.

[mr_fish]

A moderately tuned XUD or HDi, with a long ratio box, will see you north of the national speed limits fairly quickly...

...and (annoyingly) you still have 2 gears to go.

[boggs]

Would a xud gearbox be a good upgrade on a stage 1/2 306 hdi? Acceleration wise? Or would it be a disadvantage?

[Midnightclub]

Put it this way, people generally put HDi boxes onto their XUD's. If you want acceleration there's much better ways to do it than swapping the box.

[Dum-Dum]

You want a longer box, the standard 19:70 FD is too short as it is in a tuned car for acceleration as you spend too much time changing gear.

With a decent stage 2 first gear is so short your faster to 60 if you start in 2nd rather than 1st. If you are doing 1/4 mile from a standing start in a santa pod / motorway slip road senario you'll be wanting to change into 5th before the end of the quarter mile meaning 4 gearchanges at half a second each.

The only final drive longer is the 19:63 in the hdi eco and its not a straight fit, infact to my knowledge nobody has ever managed to fit it to a 306.