Matt2000
Member
- Posts
- 36
- Location
- Leics/Northants border
Time to do something about my bobtail D1, its gearing and/or engine.
1990 bobtailed D1 with a 200Tdi that seems to be a little worn out, no intercooler and a heavy external roll cage. I fitted an intercooler last year to see how it ran but it just caused it to burn oil with little improvement in power.
Originally the truck had a very worn LT77 when I bought it in 2017, I swapped that for the R380 out of the 300tdi Disco I was scrapping at the time. I didn't realise it at the time but the previous owner had probably swapped the transfer box for a Defender one to compensate for the 33" Insa Turbos, muggins here just swapped in the R380 with 28D LT230 and ditched the old 'box.
Out on the road it struggles with hills, I've ignored it for a long time but it's becoming an issue. The engine may be getting weaker or I'm just not able to ignore the problem any more. I know the gearbox and transfer box ratios but I didn't know the diff ratios for sure, I watched the revs yesterday (I believe the rev counter and speedo are vaguely trustworthy) in different gears/at different speeds and they equal 3.54 according to the The Ashcroft chart below, I do also have pictures of a 46 tooth crown wheels that back this up.
The chart also shows that 4th is OK-ish at 2645 @ 60mph but 5th drops the revs down way too low to 2037, peak Tdi torque being at around 2700rpm. Anyway my point is I'd like to upgrade to 35" tyres next time I buy some and obviously this would be a disaster with the current gearing.
Using data from the Ashcroft calculator I made a little chart to lay out my options against the current gearing.
Looking at this, it looks like I'd be better off switching the diffs to 4.37 gears. Acceptable engine speeds with 33" tyres (I rarely take it motorways) and perfect with 35s. The only snag is that the rear has a KAM electric locker (remember those?) and while I can change a transfer box I don't have the skills to change a crown wheel and pinion myself, especially with the locker.
4.37 gears are probably the right choice (£200 per HD crown and pinion set from Ashcroft), but I'm not sure about my future plans for the Disco. If this 200Tdi bites the dust, I really want to put a V8 in it. Ideally a 3.5 on carbs because I want to keep it all mechanical.
I can't find torque curves that I trust for a V8 like that, does anyone know how this compares to a 200Tdi and if this new gearing would work as well? The last thing I want to do is spend this cash just to find out it's completely wrong for a V8. Would a 3.5 be happier with my current gearing? Again I have no intention of doing lots of motorway miles so a slightly higher rpm that ideal while doing 70 is OK.
I'm going to speak to Xcess 4x4 next week as they have experience with the KAM diffs and also V8s through Megasquirt, in the meantime it would be great to get some input. They do say on their site that 35s are pushing the limits of the axles, which is unfortunate! Both diffs are 4-pin and are pegged (photos show me this).
Cheers.
Matt
1990 bobtailed D1 with a 200Tdi that seems to be a little worn out, no intercooler and a heavy external roll cage. I fitted an intercooler last year to see how it ran but it just caused it to burn oil with little improvement in power.
Originally the truck had a very worn LT77 when I bought it in 2017, I swapped that for the R380 out of the 300tdi Disco I was scrapping at the time. I didn't realise it at the time but the previous owner had probably swapped the transfer box for a Defender one to compensate for the 33" Insa Turbos, muggins here just swapped in the R380 with 28D LT230 and ditched the old 'box.
Out on the road it struggles with hills, I've ignored it for a long time but it's becoming an issue. The engine may be getting weaker or I'm just not able to ignore the problem any more. I know the gearbox and transfer box ratios but I didn't know the diff ratios for sure, I watched the revs yesterday (I believe the rev counter and speedo are vaguely trustworthy) in different gears/at different speeds and they equal 3.54 according to the The Ashcroft chart below, I do also have pictures of a 46 tooth crown wheels that back this up.
The chart also shows that 4th is OK-ish at 2645 @ 60mph but 5th drops the revs down way too low to 2037, peak Tdi torque being at around 2700rpm. Anyway my point is I'd like to upgrade to 35" tyres next time I buy some and obviously this would be a disaster with the current gearing.
Using data from the Ashcroft calculator I made a little chart to lay out my options against the current gearing.
Looking at this, it looks like I'd be better off switching the diffs to 4.37 gears. Acceptable engine speeds with 33" tyres (I rarely take it motorways) and perfect with 35s. The only snag is that the rear has a KAM electric locker (remember those?) and while I can change a transfer box I don't have the skills to change a crown wheel and pinion myself, especially with the locker.
4.37 gears are probably the right choice (£200 per HD crown and pinion set from Ashcroft), but I'm not sure about my future plans for the Disco. If this 200Tdi bites the dust, I really want to put a V8 in it. Ideally a 3.5 on carbs because I want to keep it all mechanical.
I can't find torque curves that I trust for a V8 like that, does anyone know how this compares to a 200Tdi and if this new gearing would work as well? The last thing I want to do is spend this cash just to find out it's completely wrong for a V8. Would a 3.5 be happier with my current gearing? Again I have no intention of doing lots of motorway miles so a slightly higher rpm that ideal while doing 70 is OK.
I'm going to speak to Xcess 4x4 next week as they have experience with the KAM diffs and also V8s through Megasquirt, in the meantime it would be great to get some input. They do say on their site that 35s are pushing the limits of the axles, which is unfortunate! Both diffs are 4-pin and are pegged (photos show me this).
Cheers.
Matt
