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TDI top end performance


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Is there anything that can be done to improve the top end grunt on a 200TDI defender. Mine struggles past 65-70, especially in a strong head wind/uphill.

I know it's slightly over geared with a 1.2 transfer box and 235/85 tyres, currently running 1.2 bar of boost and the pump diaphragm turned about 60 degrees.

Ideally I don't want to change the gearing as this is perfect the rest of the time.

At 65mph on a long run it'll get 29mpg, but as soon as I push past this (an it's a real effort) the mpg drops to around 24.

Any suggestions or am I just dreaming ?

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I'm not that wise to tuning, but I've had a play with my 200's and without going mental and fitting performance heads, performance exhaust and really "blue printing" an engine your top end power is not an easy thing to improve as this is a little more fundamental to the engines design, low and stuff is a lot easy to play with.

In my 90 I've got an old 200 Disco lump which I have not real history on, although I suspect it is close to around 200k miles. After the boost diagram mechanism seized I started looking at its performance, I gave it a little more overall fueling, didn’t touch the in boost fueling, but I happened to have an Ali sport intercooler lying around so that went in, I then fitted a set of refurbished injectors, and finally took the viscous fan off and fitted an electric unit on a manual switch.

Now I didn’t do all those things at once but in stages over a few months.

I remember first driving it around I wasn't that convinced that anything had changed until I was on my daily commute I needed to do some overtaking and before I realized what I'd done I was cruising past folk much more easily than I ever had, then I realized that when driving around previously the foot was always pretty much to the floor at 60mph, now I've got reserve power to easily get me up to 80 but I very rarely do as I'm dubious of the drivetrains ability to deal with it for long periods!

Having said that, any kind of headwind uses that extra power easily its like driving through treacle sometimes.

So to summarise, unless you be having lots of money to buy new variable turbo's and stage 3 tuning with performance heads etc, I'd go back to the basics and look at your fuel injectors, and maybe your air intake system...

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If you're satisfied that everything is working as it should, I'd be thinking of tweaking the governor settings, to increase the high rpm / high load fuelling capability. (Have a read of the Bosch VE pump manuals)

But it sounds to me like your setup is down on power already, so best not to fiddle with any settings until you know all is in good order.

When I had a standard 300tdi in the Ibex, it could fairly easily pull 80mph with the overdrive in on the flat, and I reckon my 200tdi 90 wouldn't be much different.

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My disco is the same gearing etc and will pull 80 (on closed roads obviously) without to much effort however add a hill or strong head wind it will drop to 70 ish. The disco has slightly better aerodynamics but I feel it is over geared and my 110 with a 1.41:1 t-box with 33" tyres was better. So I'd say your a little down on power but your gearing is making it much more noticeable. Not really answering your question but hopefully helping with the why.

Mike

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I think its the gearing that is the issue. My 110 300tdi is std apart from a Van Aaken pump tweak and a K+n filter, with std t/box. It will return 33+mpg on a run yet will pull up to an indicated 90 on the flat, ...ok its revving to its max. The point is the engine can't pull with the power it has without being able to rev., but being overgeared it can't rev freely enough, I bet if you put a std t/box back in, it will be quicker. I think the 1.2 has to considered as the old fashioned overdrive, not a5th driven gear, ok for economy but not for speed. Even the economy is a bit of a misnomer. The most eco speed is around 56-60mph, which with a 1.4 is about right. But up the gearing to a 1.2 and then the eco speed 'aerodynamically' is still 56-60, but the engine would be labouring a bit, so you go a bit faster so the engine works less, but you are now pushing more air.

Next time you find yourself struggling up hill into a head wind at 65, try dropping to 4th, wouldnt surprise me if you go quicker.

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The most eco speed is around 56-60mph, which with a 1.4 is about right.

This is what I've found too. Seems the most efficient as you say.

Doing more than 60 with a Tdi is not worth it in my experience, you just get a lot of noise and fuel economy drops like a stone. Fair enough I'll take it to 65 for the odd overtake but there's no sense cruising at that speed. Better to have 10mph in reserve anyway, and not be at max power so that when you hit a hill it doesn't drop off. And it's faster than the lorries by enough that you can get by without issues.

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Hmmm something wrong me thinks. My 110 (300 tdi) has had mild pump tweak (no smoke), large intercooler, disco transfer box, 265/75 BFG MTs.... will cruise all day at 80 and if you get a bit of a run or a slight downhill can see the wrong side of 90 (on the GPS speedo). I did fit a brand new turbo when I rebuilt the truck so not sure how much that helps. On 3000 mile trip round Europe we averaged between 28-32 mpg per tank. Around here now with short trips on country roads and lots of towing and a heavy right foot I am seeing between 22 & 25 mpg.

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This is what I've found too. Seems the most efficient as you say.

Yes it hits a sweet spot and feels right. I don't bother overtaking lorries, just sit with them, 2 reasons really, firstly you get sucked along, and secondly, and most importantly , it regulates your speed, . Every time you overtake , it costs you money, but you don't necessarrily gain in time.

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Your avatar shows a roof tent. That will sap 15-20mph off your top speed for a start.

I would start by giving the engine a good service - filters, good oil, belts, tappets and timing check. I'd also put a good quality injector cleaner through, like Wynns or Forte. After that, I'd look at the engine's breathing, checking the condition of the air hoses and, as long as you don't go into very dusty conditions much, a performance filter like K&N. If that's not enough, a high flow intercooler and sports exhaust may free things up a bit. I don't like the idea of fiddling with boost pressures and fuel metering - it will cause the engine to be under considerably more stress and will cause wear or damage in the long run.

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currently running 1.2 bar of boost and the pump diaphragm turned about 60 degrees.

Any suggestions or am I just dreaming ?

First suggestion is to turn the diaphram properly, you cant turn them properly with out removing them, wind the "star" wheel down a couple of turns at the same time and safely stash the plastic collar under the diaphram on the floor or in a hedge.

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Your avatar shows a roof tent. That will sap 15-20mph off your top speed for a start.

I would start by giving the engine a good service - filters, good oil, belts, tappets and timing check. I'd also put a good quality injector cleaner through, like Wynns or Forte. After that, I'd look at the engine's breathing, checking the condition of the air hoses and, as long as you don't go into very dusty conditions much, a performance filter like K&N. If that's not enough, a high flow intercooler and sports exhaust may free things up a bit. I don't like the idea of fiddling with boost pressures and fuel metering - it will cause the engine to be under considerably more stress and will cause wear or damage in the long run.

Roof tent lives in the garage so just the roof bars to add drag. No viscous fan, no front silencer and road based tyres should all be helping me, but it looks like my unknown millage 1992 engine is definitely down on power.

It's due a major service once the weather improves, so will also do a tappet and timing check and injector clean.

If no improvement then a bit more tweaking may be the only answer?

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David, a few thoughts,

Have you checked the timing is correct? are the tappets set properly?

Please don't put a k&n filter in, truely awful advice :-(

Do you have a brake dragging? One thing i always do when I come back from a long run is to check the wheel temperatures (just with the back of your hand) probably worth checking the trans brake on a landy as well

Where are you measuring the 1.2 bar?

And as Vulcan hinted at above just turning the pump diaphragm is just a shot in the dark, remove the pin and align the steepest side with the pin.

When you are trying to push over 65, what is you boost pressure? And if you carefully watch your mirror (in the dark with headlights behind you helps) can you see any kind of hase from your exhaust?

My old rangy 300/r380 1.2 255/85r16 would pull past 90 with ease and I could easily return high 30's

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David, a few thoughts,

Have you checked the timing is correct? are the tappets set properly?

Please don't put a k&n filter in, truely awful advice :-(

Do you have a brake dragging? One thing i always do when I come back from a long run is to check the wheel temperatures (just with the back of your hand) probably worth checking the trans brake on a landy as well

Where are you measuring the 1.2 bar?

And as Vulcan hinted at above just turning the pump diaphragm is just a shot in the dark, remove the pin and align the steepest side with the pin.

When you are trying to push over 65, what is you boost pressure? And if you carefully watch your mirror (in the dark with headlights behind you helps) can you see any kind of hase from your exhaust?

My old rangy 300/r380 1.2 255/85r16 would pull past 90 with ease and I could easily return high 30's

Will check timing, tappets etc when it gets a service. brake and hand brake all good, no binding.

Boost gauge measuring from the turbo to pump line, at the turbo end.

It will boost up to 1.3 when flooring it but I lift off a bit as it doesn't seem to give any extra oomph.

Yes, haze from the exhaust visible in headlights.

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David,

What is it like on the flat otherwise? On a hill or in a headwind I wouldnt expect much more to be honest.

If its not any better I would have thought that it sounds like she could be down on compression and maybe needing some new rings and pistons....

A 1992 engine is now 22 years old so could easily have 300,000 miles or more so maybe due a freshen up.

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If you check this post there is a diagram of the FIP and the boost compensator, I would reccomend to check Item labelled No.4 - it should be pretty much free floating in its housing, its a quick check. - just makes sure you're getting the correct compensated fueling.

http://forums.lr4x4.com/index.php?showtopic=85023&hl=

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Dave, and its taken you this long to notice it :P

Take a sliver of material off the white coller, it will allow the piston to move further down to bore and give you a bit more fuel, I have heard of it being removed totally but not 100% if this is a good idea or not

Def need a EGT gauge to try that IMHO

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Take a sliver of material off the white coller, it will allow the piston to move further down to bore and give you a bit more fuel, I have heard of it being removed totally but not 100% if this is a good idea or not

I took the collar off of mine about four years ago, upped the boost a tad to 1 bar, diaphragm is on max fuel delivery, pump pressure is increased by half a turn, starwheel turned clockwise about two turns ( - not sure if this part really made any difference TBH)

Need to check the engine is in good state of service prior to doing any of this though as you may just be masking a problem otherwise.

(i have a brunel intercooler fitted as well)

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Iv got the same problem with mine. 1.2 box on an old 200tdi engine with 161k on the clock. Its just so gutless, really am thinking about going back to 1.4 box. I have to use low ratio sometimes when towing. Im gonna try some injector cleaner. Hopefully that will help abit. Done the timing belt shes well serviced aswell. Have also been considering smaller tyres. Would be quicker to walk up most of the hills.

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No point touching the diaphragm if you look for top end performance, that will not change. You will only change acceleration. If you see black exhaust fumes already, I would not touch the fuel pump full stop personally, especially if you care about MPG. So, I'd say go back to basics, timing, compression, and if you state a turbo pressure, is this at the inlet manifold? I've had a tiny split in an inter cooler pipe once, and it took me a long time to find. I did find it by pressurising the inlet tract with my lungs and listen if you hear any sissing.

Daan

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