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Hi there i'am running a 300tdi with standard defender gearing and GKN overdrive and i find i am running out of puff at higher speed's i used to run discovery gearing and could go faster and seemed to get better to the gallon can you run disco gearing and the over drive or is this just total overkill? or am i better off just going back to disco gearing and flog the gkn?? :huh:

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what size tyres are you running? if 7.50 or equivalent it should be OK i would have thought.

Ralph is running a 200tdi with def gearing and GKN on 255/85s (about 10% bigger then 7.50s) and i dont think he has too many problems with umph!

If your running out of puff with def gearing and o/d then forget a disco t box and the GKN, you will certainly not have enough puff.

when you say higher speeds it depends how high you mean. at 70mph or thereabouts i would have thought a tdi in std tune and good health on 7.50 would hold 5th + O/D no problem and give about 33mpg to add.

not that its that helpful but my td5 (122bhp) held 70 with 5th and overdrive no problem.

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what size tyres are you running? if 7.50 or equivalent it should be OK i would have thought.

Ralph is running a 200tdi with def gearing and GKN on 255/85s (about 10% bigger then 7.50s) and i dont think he has too many problems with umph!

If your running out of puff with def gearing and o/d then forget a disco t box and the GKN, you will certainly not have enough puff.

when you say higher speeds it depends how high you mean. at 70mph or thereabouts i would have thought a tdi in std tune and good health on 7.50 would hold 5th + O/D no problem and give about 33mpg to add.

not that its that helpful but my td5 (122bhp) held 70 with 5th and overdrive no problem.

I am running 265/75r16 and it's runnig out of puff at higher speeds than 70 i know it's not perticular legal but if i floor it out of overdrive it does 80/85 and then drop the overdrive in and it won't go any more it just sits there??? yet with the disco gearing she'd do 90+..

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I use mine aa a splitter & OD in 4th & 5th, can pull 75 with my trailer on the back & 400kgs in 110, my 200Tdi is totally standard driving through a R380 & standard transfer box, haven't worked out mpg, so can't tell you what I'm getting. 110 is much happier at 60/65 though with or without the trailer & better for me

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what's the top speed for a 300tdi with standard ratio's

Standard 110 300TDi with EGR

My SatNav has a trip function and I've had 90 recorded on it but the engine sits best at 60, it will do 70 all day long, will run at 80ish but tends to be quite noisey and let you know its nots a brilliant idea. 90 with a bit of a run up and a good following wind and only as short burst.

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i reckon yours is about right then, perhaps the OD and 5th is slightly taller than 5th with 1.2 T box hence why the engine has no puff.

If it will do 90 then i reckon there nothing wrong with it, thats 8mph more than the 07 MY def will do!

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i reckon yours is about right then, perhaps the OD and 5th is slightly taller than 5th with 1.2 T box hence why the engine has no puff.

If it will do 90 then i reckon there nothing wrong with it, thats 8mph more than the 07 MY def will do!

IIRC the overdrive is taller gearing than a 1.2 ratio transfer. On my 300Tdi 90, 235/85 tyres and 1.2 transfer, mild tweak to pump will do 90 flat out, 70 up the steepest hills on the mway all day. If you can get to 85 without o/d but then can't accelerate/go faster with o/d - it would back up it being a higher ratio ( than a 1.2 transfer). Don't forget drag goes up with the square of the speed, at around 85+, drag will be about equal to engine power - a higher ratio gearing means the engine is further back down the power curve ( as revs are lower) so it won't go as fast....

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