Changing Gear Box Ratios

[Guest fredster]

HI

 

Does anyone know if its possible to open up a gearbox and put a new ratio cog on for fifth gear? At 70mph my 8v 1.9 is doing 3k plus rpm. Would like to get a taller 5th gear in there so it cruises nearer to 2k rpm at this speed, what with the car having plenty of low down torque and petrol costing what it does.

 

 

Possible?

 

cheers

fred

[Ben 0]

Think yourself lucky mate, my 1.6 is doing 4.5K rpm at 70mph!

[boombang 2]

You can change gears, but tbh it'd be easier and probably cheaper to change gearbox.

 

IIRC a 306 S16 box would have a suitably long 5th without leaving gaps in the ratios.

 

Alternatively you could fit a diesel box which again IIRC is a bit longer even, however the low down torque you mention isn't actually that low or torquey, which would certainly slow the car down a lot.

 

I've always found a 1.9 box to be pretty long myself!

[gti-si 0]

It is possible to do this yes. I think asking for 2k at 70 is going to be asking abit much though. Your probably better changing to a 5th from a diesel box. This won't give you ideal spacing between 4th and 5th though. The 5th gear is the same in the 205 GRD and Mi16 at 0.757. That would take you to about 2.8k at 70. If you really wanna change it, get the 5th from a 405 1.9 GR , thats .658 and will be good for 2.4k (all with 195/55/15) but good luck with that . TBH, I don't think it's worth it on a standard 8v, im not sure if it actually has enough torque for such ratios, and with such a change, the spacing between 4th and 5th would be rediculous. Perhaps a slighty longer 5th and change the CWP would be better than going for a really long 5th? Failing that change the box?

Edited January 5, 2008 by gti-si

[welshpug 1,666]

I dont think it'd be a good idea to be asking the 8v to pull 70mph at 2k, 50mph at 2k yes but not 70, too much load for the engine IMO.

 

if it was a turbo 8v it'd be a totally different story though.

[Guest fredster]

Cheers for that guys - maybe its a better idea to convert car to lpg to save on the pennies. My other vehicle is a VW camper so I'm getting hammered on fuel costs at mo on both vehicles.

 

fred

[pug_ham 245 3 Cars]

Changing fith gear is actually quite easy if you have access to an air gun because you only need to remove the end cover which is in the nearside wheel arch (& possibly drain th gearbox oil) but finding a suitable ratio to replace it with is a different matter.

 

If you have a healthy 1.9 that pulls well then the 0.757 from the diesel or S16 gearbox is about the best you'll find & not to much of a drop from fourth to fifth. At best this will only drop your rpm at 70 to just over 3k (4k = 90mph).

 

Other than that a diesel gearbox should see 70mph at about 3k, my STDT with the correct box in does 2750 rpm @ 70 but the box I removed a few weeks ago was nearer 2.9k even though they both have the 3.47fd.

 

Graham.