T25 engine conversion but revs are too high.. please help

[Chrisoh]

I have a Mk3 Golf engine 1.9 TDI (engine code 1Z) in my 1988 T25 Multivan.
It runs well but at 80 kph revolutions are up to 3000 rpm.
Revs are quite high throughout the gear range.

I am trying to find out how I can sort this out, at 80 kph revs should be just under 2000 rpm. How can I achieve this?

Do I need to uprate the gearbox? If so how can this be done?

Can I use any other gearbox? If so which one can I use?

please help me with this...

[Zebedee]

Either fit bigger diameter rear tyres to bring the revs down or upgrade the gearbox with different ring and pinion and highter 5th gear (£500-£1000 sort of price).
What code gearbox in in your multivan already?

2.1 petrol 'box will go some way to sorting your probs but you still might need to fit a different 5th gear ratio to it.

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[Chrisoh]

Thanks for your replies... I've been waiting to see if others said anything else...

Yes it was a 1.6td

The tyres sounds like a good idea, I was thinking of changing them as they are 15'' and far too small... can you go upto 18'' never would have thought that...

thanks...

[sven]

Yeah, the TD-boxes revs out the engine pretty fast. I'm changing to a new AAP-gearbox in my pickup and a I have tyres just a few percent bigger than standard. That is with the same engine, 1Z.
If you have a 4-speed box, the gear shaft doesn't fit right away if you get a 5-speed box (I'm making a wire based stick anyway). The 5-speed boxes are a little bit longer, the gear switching mechanism is therefore closer to the front with 5-10 cm. It's not a big deal to cut the switch shaft and make it fit, so a replacement box is not very difficult to put in.

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