TDI Gearbox conversion

[smitty12]

Hi all,

Its been a while since i've been on here but I could do with some advice (If someone has been mad enough)

The gearbox on my R32 blew up yesterday and I'm now thinking of re-building it but using TDI ratio's. I've done the maths on top speeds and it flat out in 6th it could hit over 200mph (if the engine had the power) however my engine is just standard 241bhp.

Has anyone on here done a diesel box conversion on the 1.8T? I know theres a lot of guys on here pushing above and beyond 200bhp but would be great if I could find someone with experience of a diesel box conversion so I could compare it to what could happen with my R32.

I'm not worried about 0-62 speed, I am worried about motorway cruising, 6th gear could be totally pointless as 5th will push over 170mph and I'm not sure what rev range 6th will be at at around 70-100mph (on autobahns obviously!) and whether it will struggle and need sticking back into 5th? :S

Very confusing but hopefully someone could help!! Thanks in advance

[scarr89]

Are the R32s 6 gears? O2M gear box? Bolt straight on maybe? Or is it the ratios that you are worried about 

[smitty12]

The R32 is a 6 speed so I'd need a 6 speed diesel box, its not a straight bolt off/bolt on job, you can swap the internals though.

My main concern is the ratio's them selves with having a diesel box on a petrol engine I'm not sure of the characteristics of acceleration/top speed. I've done the maths (with some minor error) but at 7000rpm from the 3.2 V6 the max speeds of the standard box against the diesel box would be...

Standard R32 Gearbox
 1st - 31mph
 2nd - 51mph
 3rd - 72mph
 4th - 96mph
 5th - 123mph
 6th - 147mph

EFF (Most commonly used) Gearbox
 1st - 35mph
 2nd - 64mph
 3rd - 100mph
 4th - 138mph
 5th - 170mph
 6th - 204mph

Obviously the standard power of the R32 wouldnt be able to pull anywhere near 200mph but my main concern is how the car will feel on acceleration & cruising at motorway speeds, will the car feel limp in 6th at around 70-100mph (Autobahn obviously) and will the acceleration be compromized with the longer ratios from 3rd? 1st and 2nd are pretty similar so i dont see an issue there but 3rd seems quite long as does 4th, 5th and 6th so would 6th be rendered useless? 

Not sure how it would compare but does anyone have a gttdi (Preferably 130 standard) now running around 240bhp? or as close as? If so how does the gear box feel when pulling through the revs?

[tshirt2k]

It's not the power you should be concerned about. It's the torque. TDi's have lots of low down torque that enabled them to pull these ratios.

You haven't said what size wheels and tyres and is it still 4wd? Not sure housings will be the same.

Seems the 1st 3 gears would be ok but the rest would be too long and you will be forever changing down to do any overtaking on motorways etc.

Find yourself a gear ratio calculator and put ratios in. It will give you the rpms and you can compare with what you already have.

Unless you have increases power I wouldn't go any more than 500rpm drop between gears. But that is dependant on your torque characteristics.

[smitty12]

Your right with the torque figures, again the car is standard and runs around 240lb/ft which should be adequate as its higher than the standard GTTDI and I'll have the extra 2000rpm

The wheels & tyres are 225/40 18" and the boxes cant simply be swapped the internals need changing, and yes the car is still running 4WD

I did find a calculator last night and it seemed to drop it around 500rpm, looked quite good but I know there will be some error there

[Rhyso]

Would it not be more cost effective to have your gearbox rebuilt with stronger internals rather than faffing about with a TDI box and worrying about the ratios 

150TDI  more torque as standard FYI 

[smitty12]

Would it not be more cost effective to have your gearbox rebuilt with stronger internals rather than faffing about with a TDI box and worrying about the ratios 

150TDI  more torque as standard FYI 

Ahh sorry your right 320lb/ft!

I could just re-build it but I just think the standard ratios feel to short, your up the gearbox so quickly round the doors and in 6th on the motorway at 70-80 the engine sits at over 3000rpm which is just burning fuel for no reason?

The only concern is the acceleration and the power when putting my foot down on motorways at the lower rpm of the longer ratios

[tshirt2k]

If the box is being rebuilt why not change FD on 5th and 6th

http://forums.thecarlounge.com/showthread.php?5016422-The-02M-4Motion-transmission-upgrade-thread.

[Prawny]

Standard R32 Gearbox
 1st - 31mph
 2nd - 51mph
 3rd - 72mph
 4th - 96mph
 5th - 123mph
 6th - 147mph

EFF (Most commonly used) Gearbox
 1st - 35mph
 2nd - 64mph
 3rd - 100mph
 4th - 138mph
 5th - 170mph
 6th - 204mph

Hmmmmmmmmmmmmmmm,

as a comparison, my 5 speed 1.8T will do 75 in second, 115 in 3rd, and 145 in 4th, all on a 7.4k limit

When you put it that way, I don't think the tdi box would be that bad, it'll just be like driving a 5 speed (which is better!), and 6th will be like an ultra low over drive gear to save fuel

[smitty12]

Standard R32 Gearbox
 1st - 31mph
 2nd - 51mph
 3rd - 72mph
 4th - 96mph
 5th - 123mph
 6th - 147mph

EFF (Most commonly used) Gearbox
 1st - 35mph
 2nd - 64mph
 3rd - 100mph
 4th - 138mph
 5th - 170mph
 6th - 204mph

Hmmmmmmmmmmmmmmm,

as a comparison, my 5 speed 1.8T will do 75 in second, 115 in 3rd, and 145 in 4th, all on a 7.4k limit

When you put it that way, I don't think the tdi box would be that bad, it'll just be like driving a 5 speed (which is better!), and 6th will be like an ultra low over drive gear to save fuel

Thats what i'd like but I dont want 6th to be dogish as i dont have the torque of a diesel. My figures were based on 7000rpm so there would be a tad more and there is some error there! 

I'm liking the idea of just replacing the final drive ratio!