Landowner Posted October 25, 2013 Share Posted October 25, 2013 My mate has a 1974 petrol series and he is converting it to a 2.5n/a diesel I wondered if the petrol gearbox would take the extra torque from the diesel engine? thanks Quote Link to comment Share on other sites More sharing options...
discomikey Posted October 25, 2013 Share Posted October 25, 2013 in a word, yes, poeple may say no, but i have no problem running a tweaked TDi at 20psi boost through a series 3 gearbox. it could be brok with a 2.5 N/A. then again it could be broke with a 2.25p. The 2.5 NA is similar to the 2.25 in hp figures with a pinch more torque it should be fine taking it unless he sets iff everywhere at 350rpm and sidestepping the clutch. Quote Link to comment Share on other sites More sharing options...
Pollywog Posted October 25, 2013 Share Posted October 25, 2013 They're ok with TDi's and V8's so I don't see why a 2.5n/a would be a problem. So long as he has some mechanical sympathy that is. Quote Link to comment Share on other sites More sharing options...
Landowner Posted October 25, 2013 Author Share Posted October 25, 2013 That's good news, are the gear ratios and overall gearing the same because with less revs available he may be slower that the 45mph it's capable of at the moment Quote Link to comment Share on other sites More sharing options...
discomikey Posted October 25, 2013 Share Posted October 25, 2013 with the extra torque i would look into "coiler" diffs or an overdrive. i have both currently and can run motorway speeds at low revs as it has taller tyres. but you have to be careful of the torque. ashcrofts website has a gear ratio/speed/rpm calculator so he could have a look at that to see what speeds he will be looking at obviously in top gear you might not necisarily have the torque to reach full RPM etc but you can get a good idea. Quote Link to comment Share on other sites More sharing options...
Phil Hancock Posted October 26, 2013 Share Posted October 26, 2013 If it will only do 45mph at the moment there is either a serious problem or it has a 1 ton box fitted which has lower transfer gears. Series boxes are the same for 4 pot petrol and diesel, the 6 pot had a different bellhousing unique to that model. Quote Link to comment Share on other sites More sharing options...
Landowner Posted October 26, 2013 Author Share Posted October 26, 2013 If it will only do 45mph at the moment there is either a serious problem or it has a 1 ton box fitted which has lower transfer gears. Series boxes are the same for 4 pot petrol and diesel, the 6 pot had a different bellhousing unique to that model. My 2.5 n/a 90 struggles to get over 45 at times, its on bigger 110 tyres and a bit over geared, have run it at 65 with a Disco on a trailer behind me on the motorway but had a following wind. Motorway its ok at 50 / 55 but hills kill it and I imagine the petrol would be the same with defender diffs. I think it will be ok with series diffs because I spend more time in 4th allowing the engine to run on a light throttle without too much load, it will be more economical despite being higher revving...., not enough power for high gearing. Quote Link to comment Share on other sites More sharing options...
BSF Posted October 30, 2013 Share Posted October 30, 2013 That's good news, are the gear ratios and overall gearing the same because with less revs available he may be slower that the 45mph it's capable of at the moment It really should do more than 45. My 109 did 55 to 60 with a fairly knackered 2.25 petrol. It now has a 200 Di (TDi minus turbo) and it easily does 65. I don't feel like going any faster with the series 3 steering. I used a normal Series 3 gearbox, but rebuilt it first. It also now has an overdrive more for noise reasons than speed. With any of these bigger, torquer engines you need a level of mechanical sympathy to avoid trouble with a series 3 'box, but I am intending to use a standard box with a 200 TDi and an overdrive in my Series 2b and I don't anticipate trouble. Any increase in torque will lead to faster wear, but without a turbo you shouldn't need to worry much. Gearboxes are easy to rebuild anyway! Quote Link to comment Share on other sites More sharing options...
Landowner Posted October 30, 2013 Author Share Posted October 30, 2013 It really should do more than 45. My 109 did 55 to 60 with a fairly knackered 2.25 petrol. It now has a 200 Di (TDi minus turbo) and it easily does 65. I don't feel like going any faster with the series 3 steering. I used a normal Series 3 gearbox, but rebuilt it first. It also now has an overdrive more for noise reasons than speed. With any of these bigger, torquer engines you need a level of mechanical sympathy to avoid trouble with a series 3 'box, but I am intending to use a standard box with a 200 TDi and an overdrive in my Series 2b and I don't anticipate trouble. Any increase in torque will lead to faster wear, but without a turbo you shouldn't need to worry much. Gearboxes are easy to rebuild anyway! That's good news then, he's probably exaggerating about the lack of speed. He did say he's only getting 20ish to the gallon though. Seems hell bent on having the 2.5 out of my 90 so I'm looking after it for him till in comes out to leave space for the 200tdi Quote Link to comment Share on other sites More sharing options...
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