Can I improve my Top Speed?

Post by **Swampy** » 30 Oct 2006, 19:50

Any advice would be appreciated on this..

I have a 1/2 decent Type25 Carthago Camper from Holland. It's a 1985 1.6TD (Left-hand drive) with 4-speed gearbox. An unknown history, but the Van seems straight enough for it's age.

The engine seems to be a sound & reliable runner. After throwing a bottle of Diesel Magic down the Fuel filler I'm getting around 45mpg, doing a steady 95kph (Around 60-ish).

Having said that, when I get to the 100 kph mark, the engine feels like it wants me to shift into a higher gear. My wife's Renault has a 1.6 Petrol engine with 5-speed gearbox & that manages 80mph without ragging the engine too much.

My Van will do 120kph if I put my foot down & 140kph if I floor it, but I'm not too happy about ragging the engine like that.

I know the Van's twice the age of our Renault, but is there any way to get a higher top speed out of the Van without revving the engine too much?

I've seen the subject of larger wheels discussed to get more speed for your revs, which I may toy with when the tread wears out on the old tyres.

If I replace the gearbox for a 5-speed version would that make any difference? I've been told that the VW gearboxes had the same final drive ratio, so there seems little point in putting a 5-speed gearbox in.

All ideas welcome!

Post by **oldiguana** » 30 Oct 2006, 20:58

eyup duck,i dropped a 1.9 diesel in marladys 1.6 diesel this year,the top speed without thrash was an unbelieveable 45-48.poopoo!,so i bobbed a 1.9 petrol gearbox in it,virtually a straight swap except for the input shaft and bell housing which takes about 30 mins to do,and now she cruises nicely at about 58-62 mph without any real thrash...........the other way if you dont want the hassle is with larger radius wheels and tyres,i bought a set of alleys to fit on ours but havent got round to it as top speed is ok,loads on the dreaded flee-bay nice and cheap.................

Post by **Swampy** » 30 Oct 2006, 22:49

Aha! So swapping out the gearbox would make a difference! That's it, I'll save up & find a compatible 5-speed gearbox. Thanks for that.

I'd rather get a new gearbox for the existing 1.6TD engine as it really does still have some poke left in it. I'm not that into acceleration (Christ, I drive a diesel) but getting up to a motorway capable top speed without being cruel to the engine is the thing for me.

If a petrol gearbox offers an improvement I'll see what my Father-In-Law can find from his local scrapper. I'm sure he said there were a couple of wrecked T25s near him.

I totally agree with the bigger tyres approach. Problem is I've such good tread on the existing tyres I'd rather keep them until they're bald. I'll certainly be fitting bigger wheels/tyres on when the time comes, though.

Thanks again. That's boosted me, that has.

Post by **HarryMann** » 30 Oct 2006, 23:09

If I replace the gearbox for a 5-speed version would that make any difference?

Its not the 5 speeder that makes a diff, its a box with a higher diff, so watch what you buy... or don't.

You should have a rev-counter in a TD diesel, is it getting up to 4200~4500 in top?

Overgear it and you'll regret it as soon as the slightest slope is met on motorway or a headwind... Iguana above is not quoting from which box to which box, there are quite a few ratios across VW T25 transaxles - a warning.

Post by **Swampy** » 31 Oct 2006, 00:00

Right, so it's the diff that's important. I see.

I'm afraid my Van doesn't have a rev counter on it (hmm... Did all TD vans have rev counters?). I just go by the sound of the engine.

It sounds OK up to 90-95kph (60mph). Once I hit the 100kph mark the engine sounds like it wants to go into 5th gear (if I had one). If I do 120kph (75mph) then the van really sounds like it's working hard. Plus the fuel consumption goes down to that of a petrol car if do 120kph for any length of time. I was hoping lower revs would aid the old fuel economy too.

I might have to be a bit more careful than I thought. Thanks for the advice.

Post by **camper** » 31 Oct 2006, 07:24

I had a 1.6n camper and now have a 1.6td.I never did like the gearbox on them for my use.I replaced the 1.6n box for a 1.9 petrol and had no problems with speed drop due to the higher gear.I am now running my 1.6td with a DK box that came from a 2ltr Aircooled.If your van is a light conversion as was my 1.6n a long up hill incline road which some times dosnt appear obvious on a motor way it will take slow pace.Even with the standard gear box fitted on the 1.6 it struggled .When it had the 1.9 gearbox i just changed down.Overall i found it makes a more relaxed drive with the higher gearing.If your vehicle is fitted with a later linkage its not a straight change for a DK box you need the early linkage and to slightly lengthen it .You also need to modify the DK box gearbox mount to fit.Its best to change it to a petrol 1.9 box as the linkage is the same as is the mounting.

Post by **Mocki** » 31 Oct 2006, 07:33

BUT the input shaft isnt the same..... so change them over.

Post by **oldiguana** » 31 Oct 2006, 07:40

yes harryman youre totally right as i didnt explain myself too well(its the ale you know)my original gearbox for the 1.6 n/a diesel had a final drive ratio somewhere close to a ride on lawn mower,swampy what you will have to do is get the gearbox code from your van and compare it on brickyard gearbox page.(extremely usefull!)and that will tell you which box(if any)will be of use. http://www.brick-yard.co.uk/VehicleSpec ... gbx.htm,is the page and i went from a acp code box with a 5.83 ratio to something with a 4.83 ratio,if you use this chart you can in theory work out the new top speed roughly with any gearbox,but remember if you overgear it means playing with tyre size to compensate for slugishness,my apologies for my somewhat poopy post earlier...............................

Post by **"WEAZLECHIN"** » 31 Oct 2006, 08:16

put some 225/75 tyres on the rear.

Post by **camper** » 31 Oct 2006, 10:09

Mocki wrote:BUT the input shaft isnt the same..... so change them over.

And diesel bell housing.

Post by **Swampy** » 01 Nov 2006, 00:17

I think I've got a better picture of what's required now:

For a reasonably straightforward swap, find a 1.9 petrol gearbox - change over the imput shaft & bell housing.

Otherwise, that chart was also a help as well. I'll use that to see if I can find any other compatible boxes. My Father-In-Law said he knows of a couple of old vans that are rotting in a scrapper near his home in Belgium. I'll see if I can get the gearbox codes out of him & if the boxes are still in good nick.

Fantastic! Thanks again for the guidance.