Gearbox / Engine matchups

[Stesaw]

This is a bit of a question for the more savvy than myself about such things.
Been doing a fair bit of work under the van recently thanks to the nice weather we are having. As I've been picking through things I've cleaned down the gearbox a bit and found out it has a DX code.
Now a quick search shows that's a gearbox that's generally fitted to a 1.6D and not a 1.9DG.
Just to say there is nothing wrong with the box mechanically as far as I know, smooth changes and no clunks. The only issue it has is a oil leak from between the bellhousing and the case, but with regular checks and topping up when needed I don't think would be an issue.( Idealy I want to sort it but I'd imagine that's an engine out jobbie and I am limited on space where I currently am.)

My question is, as far as my knowledge goes the DX box has a higher final drive than most petrol boxes so It's gonna make the engine work more at speed. Is it something I should think about swapping out for a petrol box for a better motorway / cruising experience for better for MPG, or would it be worth re-gearing 4th and 5th maybe?

What I'd like to eventually do is either swap to a 2.1 WBX or something a bit more involved and go for a EJ20 (or EJ22 if I can find one.) Would you guys reckon the DX gearbox would be suited to those engines?

[Aidan]

As you have found DX is a 5.43 final drive 5 speed box, but it has the 0.765 5th gear so top gear is 4.15 overall
ABN 1.9 petrol box has a 4.83 final drive and a 0.82 fifth gear so 3.96 final gear overall so that's only a dadge more than 4% quicker for the same revs
ASM 1.9 petrol box has a 4.57 final drive and a 0.85 fifth gear so 3.88 final gear overall and that's only 6% quicker for same revs

what you'll find is that you can miss 1st gear a lot of the time if rolling, or even pulling away on the flat or downhill, you get through the first 4 gears and accelerate briskly but once in top gear there's very little in it and cruising along at 60mph the engine is in it's happy place and fuel economy is pretty much as good as any 1.9 wbx; it's not a modern engine and likes too be pulling 3k rpm plus and it's not a modern vehicle that you can lug around at speed at 2500rpm and the advantage of the lower final drive you have is that small to moderate hills you don't have to change down because you have enough revs to be in the power band

my advice to any engine change is do the conversion and be happy with it, then decide if you need to regear, most scooby vans run perfectly happy with stock box, they are just a more modern wbx

[Stesaw]

Thanks for the info Aidan,

I've done a fair bit of looking through the gearbox codes to see the differences, There isn't a lot in them but I thought I'd put the question out there out of curiousity to see if the van had a bodge done in the past. I know the last owner had this box fitted but I wanted to be sure it wasn't going to cause any issues. I do tend to miss 1st a fair bit as you've described as it's just unnecessary going down hills from pulling away.

As I my cluster doesn't have a tach I'd be interested to see what RPM's the engine is doing on the motorways and faster roads, sometimes on some of the quicker roads the engine seems to be going a bit mad which sometimes bothers me as I don't want to be overrevving it for a long period of time or any kinda time really. Maybe I should invest in a proper tach and replacement gauges to fit it. I find having just a temp and iffy fuelgauge there a waste of space .

But going back to the topic, I will keep it as is.. unless anything bad happens in the mean time.

Thanks for the insight though.

Oh just out of curiousity, what would you say is the "best" code box? and would you say a 4 or 5 speed box? perhaps a 5 speed with a LSD?

[Aidan]

a manifold vacuum gauge can show when you are driving economically, revs doesn't automatically equate to fuel consumption; quiet air intake and exhaust systems help the vehicle to sound economic and VW went to a lot of trouble to limit engine noise (and road and wind noise) incursion into the vehicle particularly on higher end models, bog standard panel vans have less sound deadening as standard and so campers built on that platform will generally be noisier than a Westy and the engine seem busier

there is no best box, VW geared the vehicles according to the engine, body type and planned usage. and 85 model year on geared a bit more conservatively as they had to pass emissions at speed whereas before that they could over fuel them at revs as long as they passed the very limited emissions test at idle, hence they stopped using the 0.765 fifth gear as 'clean' the engines couldn't pull it cleanly or reliably

[Stesaw]

Cheers for the info Aidan.