dvollebregt Posted March 20, 2014 Share Posted March 20, 2014 Hi all,I just bought my first series III. The car has quite some modifications.It has overdrive, range rover classic diff, 200 diesel engine and larger tires but I feel like it lacks power in 4th(overdrive gear) my current top is around 55mph with the right wind.How can i calculate my top and what is better to fit the old or range rover diff(impact)? Should i try to find the turbo for the 200 diesel aswell? What is the expected impact? I found this site : Engine RPM CalculatorBut I cannot find out how it works.ThanksDuco Quote Link to comment Share on other sites More sharing options...
Gremlin Posted March 21, 2014 Share Posted March 21, 2014 You just found out what over geared means! the simplest would be to go back to 4.7 diffs, then fit the turbo back in. Or remove the overdrive Mine used to max out at around 85mph, with the series box 4.7 diffs and overdrive, and 31" tyres, but the noise was horrendous! G Quote Link to comment Share on other sites More sharing options...
ToyRoverlander Posted March 21, 2014 Share Posted March 21, 2014 This calculator is quite fantastic, and is easy to use http://www.grimmjeeper.com/gears.html Quote Link to comment Share on other sites More sharing options...
Snagger Posted March 21, 2014 Share Posted March 21, 2014 A SIII transmission and 3.54 diffs is just slightly lower in 4th than a Defender in 5th. Having the additional 28% gearing from the overdrive is too much, even with the turbo. I broke the third gear in my gear box by using overdrive in conjunction with 3.54 diffs - there's too much strain from the high gearing and the gear box is the weak link. Go for the high diffs or the overdrive only, or limit use of the overdrive to 4th gear. Quote Link to comment Share on other sites More sharing options...
Snagger Posted March 21, 2014 Share Posted March 21, 2014 You just found out what over geared means! the simplest would be to go back to 4.7 diffs, then fit the turbo back in. Or remove the overdrive Mine used to max out at around 85mph, with the series box 4.7 diffs and overdrive, and 31" tyres, but the noise was horrendous! G Likewise, and the 3.54 diffs give a lower top speed with overdrive because of the torque drop-off. Slightly less engine noise at 60 mph, but more gear noise, gives slightly more relaxed cruising, but if you have a roof rack or other accessories, the engine is working too hard to have significant fuel savings. The diffs are better than the overdrive for saving fuel as they don't increase the number of gears or bearings in the system and don't sap power like an overdrive. But they do screw up low range and the speedo calibration. A high ratio transfer case is better. Quote Link to comment Share on other sites More sharing options...
Jon White Posted March 21, 2014 Share Posted March 21, 2014 Fit the turbo back on. I've never understood why people take the damn things off! It will make an enormous difference.......mine with a bit of fiddling is just as quick as it ever was with a v8 fitted. When the turbo hose blew off on the way up the dual carriageway one time it was truly dreadful and wouldn't go over about 50mph. Jon Quote Link to comment Share on other sites More sharing options...
samc88 Posted March 22, 2014 Share Posted March 22, 2014 Fit the turbo back on. I've never understood why people take the damn things off! Jon Horrific insurance costs for any owners who are still quite young. Partly why I kept the 2.5 N/A in mine when I rebuilt it Quote Link to comment Share on other sites More sharing options...
discomikey Posted April 7, 2014 Share Posted April 7, 2014 A SIII transmission and 3.54 diffs is just slightly lower in 4th than a Defender in 5th. Having the additional 28% gearing from the overdrive is too much, even with the turbo. I broke the third gear in my gear box by using overdrive in conjunction with 3.54 diffs - there's too much strain from the high gearing and the gear box is the weak link. Go for the high diffs or the overdrive only, or limit use of the overdrive to 4th gear. i highly disagree remember the overdrive is an extremely useful "optional" gearing increase and on motorways at ahem.. 70mph.. it drops the revs right down whilst still providing the neccessary torque required to efficiently cruise and it can be used as a "third and a half" which is always useful. Ashcrofts gearing ratio calculator is extremely good at showing you what you have Quote Link to comment Share on other sites More sharing options...
Snagger Posted April 11, 2014 Share Posted April 11, 2014 Mikey, reread my post - I said to use one or the other, OR to only use the overdrive in 4th if you use both. If you use the overdrive in lower gears with those diffs and that engine, sooner or later you will break the gear box. It took me six months, and could take you less or more, but eventually it'll break because the box can't take that much strain. Quote Link to comment Share on other sites More sharing options...
discomikey Posted April 14, 2014 Share Posted April 14, 2014 Mikey, reread my post - I said to use one or the other, OR to only use the overdrive in 4th if you use both. If you use the overdrive in lower gears with those diffs and that engine, sooner or later you will break the gear box. It took me six months, and could take you less or more, but eventually it'll break because the box can't take that much strain. Ahh i see now, i also broke third gear in my box, although not through overdive use. well actually i didnt break it at all. i let a friend drive and he decided that he wanted to make it drift by kicking the clutch on a gravel track in third... lost a couple of teeth on the layshaft ive been using the O/D with third for 3-4 years though no issues, thats with 3.54 diffs and 235/85R16 tyres but then again i have always considered my box to be a "strong" example Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted April 15, 2014 Share Posted April 15, 2014 http://forums.lr4x4.com/index.php?showtopic=86617&hl=%2Bgearing+%2Bcalculator Quote Link to comment Share on other sites More sharing options...
ejparrott Posted April 22, 2014 Share Posted April 22, 2014 Throw away the lead boots first, then put the turbo back on, and then you'll have what I've got, and no problems. I have 200TDi disco engine, SIII transmission, with OD, and 3.54 diffs, running 235/85 tyres. I've not yet found the top speed, I keep running out of road, but I certainly don't lack performance, especially with the wife driving. I have not broken any tranmission parts, although the wife did break a half shaft with the 19J that was in before. 1 Quote Link to comment Share on other sites More sharing options...
discomikey Posted April 23, 2014 Share Posted April 23, 2014 103 isnt its top limit i cant tell you that! although must be close Quote Link to comment Share on other sites More sharing options...
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