henry-john Posted July 6, 2010 Share Posted July 6, 2010 Hi, I bought a cracked rover 4.6 EFI serpentine engine (was in a P38) now, I've got a 3,9 multibelt engine. A friend of mine had heard that I could make the 3,9 into a 4.6 but wich are the modifications i would need to do to the 3,9? I'd like to keep the distributor for the moment, aswell as the V-belts... convert it to multibelt would be when i convert it to MS... All info is welcome!! kind regards Henry Quote Link to comment Share on other sites More sharing options...
elbekko Posted July 6, 2010 Share Posted July 6, 2010 Bore should be the same, just a different stroke, so you take the 4.6's cam and crank, put those in the 3.9, and that should be it. The only possible problem would be the ECU, as I doubt the 3.9's ECU can do 4.6, but you can always put in the GEMS from the P38, although I'm not too sure how well that'd work without all the other P38 electronics hooked up to it. Quote Link to comment Share on other sites More sharing options...
p76rangie Posted July 6, 2010 Share Posted July 6, 2010 Hi, I bought a cracked rover 4.6 EFI serpentine engine (was in a P38) now, I've got a 3,9 multibelt engine. A friend of mine had heard that I could make the 3,9 into a 4.6 but wich are the modifications i would need to do to the 3,9? I'd like to keep the distributor for the moment, aswell as the V-belts... convert it to multibelt would be when i convert it to MS... All info is welcome!! kind regards Henry You can make a 4.0 into a 4.6, but not easily a 3.9 into a 4.6. The main problem is that all the bearings for the crank are different sizes to the 3.9. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 6, 2010 Share Posted July 6, 2010 The 3.9 shares the same bore diameter, but that is about it TBH. Off the top of my head, this is one way to go about it (though i am sure there are others): Rebore to +020 as the stroke in a 4.6 is much longer. Regrind the 4.6 crank down to fit the smaller and much inferior 3.9 main bearings, other fettling may (will) be required. I don't think it is good practice to line bore the block to take the larger bearings... the bottom end isn't that strong on the 3.9s anyways, due to the lack of cross-bolting. Use the 4.6 rods Use new +020 pistons and rings, get them pressed onto the above rods Use the 3.9 camshaft, front cover, horrible chain and sprockets Use the 4.6 heads, with composite gaskets Use the 4.6 rockers and pushrods Fit a crank spacer for the pulley. Probably the thick end of £1500 for parts and machine shop work. Or something along those lines anyways..... HOWEVER, top hat linering the 4.6 block can be done for £1000 with enough change for a gasket set and a new cam/followers -this would be my preferred route TBH, you end up with a stronger bottom end (cross bolted) and no mucking about with trying to force parts together which were never designed to be! My thoughts anyways Quote Link to comment Share on other sites More sharing options...
iomlt Posted July 6, 2010 Share Posted July 6, 2010 Easy. just put the 3.9 electics onto the 4.6 and buy a 3.9 ecu fueled for a 4.6 (RPI tornado chipped) that i have for sale simples* Quote Link to comment Share on other sites More sharing options...
henry-john Posted July 6, 2010 Author Share Posted July 6, 2010 Easy. just put the 3.9 electics onto the 4.6 and buy a 3.9 ecu fueled for a 4.6 (RPI tornado chipped) that i have for sale simples* that's what i was thining.... but no possible way to fix the cracked 4,6 block.... still looking for possibilities.... Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 6, 2010 Share Posted July 6, 2010 that's what i was thining.... but no possible way to fix the cracked 4,6 block.... Why not? Just how bad is the crack? Quote Link to comment Share on other sites More sharing options...
henry-john Posted July 6, 2010 Author Share Posted July 6, 2010 Why not? Just how bad is the crack? it's an early 4.6 P38 engine..... probably nothing very useable... but to be sure I should get the block here, and get it opened up Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 6, 2010 Share Posted July 6, 2010 If it is just leaking coolant/pressurising, get it top hatted and job done surely? Unless of course by cracked, Â you mean a bloody great hole in the side where the con rod exited Quote Link to comment Share on other sites More sharing options...
henry-john Posted July 6, 2010 Author Share Posted July 6, 2010 If it is just leaking coolant/pressurising, get it top hatted and job done surely? Unless of course by cracked, Â you mean a bloody great hole in the side where the con rod exited cracked as in, coolant still leaking in the block after new head gaskets Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 6, 2010 Share Posted July 6, 2010 Top hat liners will sort that then.... Quote Link to comment Share on other sites More sharing options...
elbekko Posted July 6, 2010 Share Posted July 6, 2010 Looks like there are a lot more differences between the 3.9 and 4.0 than I thought My bad, sorry for the bad info. Quote Link to comment Share on other sites More sharing options...
p76rangie Posted July 7, 2010 Share Posted July 7, 2010 Looks like there are a lot more differences between the 3.9 and 4.0 than I thought My bad, sorry for the bad info. Even though most don't realise it, it was one of the most significant changes in the history of the Rover V8. Everything in the bottom end changed from the block to the pistons. Basically nothing from the 3.9 block can be used in the 4.0. Basically the heads, and cams are the same. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 7, 2010 Share Posted July 7, 2010 In fact, the cams are different too! The 3.9's have the facility for the distributor drive gear whereas the 4.0/4.6 doesn't! Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted July 7, 2010 Share Posted July 7, 2010 ...and the heads are different, they deleted the outer row of head bolts & skimmed the heads to account for the thicker composite head gaskets. I have to say I think you're on a quite expensive hiding to nothing with this block, if you're going to throw £1k at your engine I'd give the 3.9 some love (eg a cam kit & overhaul) & go Megasquirt & EDIS. Quote Link to comment Share on other sites More sharing options...
p76rangie Posted July 7, 2010 Share Posted July 7, 2010 ...and the heads are different, they deleted the outer row of head bolts & skimmed the heads to account for the thicker composite head gaskets. That happened in 94 while the 3.9 was still being produced. But 14 bolt heads can readily be used on 10 bolt blocks without any issues. Quote Link to comment Share on other sites More sharing options...
henry-john Posted July 23, 2010 Author Share Posted July 23, 2010 what would i need, i mean, CAN i join a viper V10 (old version or new version) with a rover auto box? would the engine fit the engine bay? thx Quote Link to comment Share on other sites More sharing options...
vougese39 Posted August 8, 2010 Share Posted August 8, 2010 That happened in 94 while the 3.9 was still being produced. But 14 bolt heads can readily be used on 10 bolt blocks without any issues. yes but the heads are 30" bigger thus a very low compression engine not a high comp as the newer one is but if you skim 30" off the old heads then you have the same spec as new heads simple! me personaly top hat linner the block new cam swap the front cover off the old engine and away you go i would stick with 14 cux Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted August 9, 2010 Share Posted August 9, 2010 The 28 thou skim really doesn't affect things noticably. Quote Link to comment Share on other sites More sharing options...
p76rangie Posted August 10, 2010 Share Posted August 10, 2010 The 28 thou skim really doesn't affect things noticably. Obviously you have never driven a low comp motor with Composite gasket head gaskets then. It makes about a 15% difference on your compression ratio. So if you have a high comp motor it will bring it down to just below a low comp one. But if you have a low comp, it doesn't drive well. The heads are actually 40 thou thinner, not 28. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted August 10, 2010 Share Posted August 10, 2010 Oh jeebus, let's not go round this again... Whatever they are, I'm running them, and it works fine. (3.9 heads on 4.6 block with comp gaskets) Quote Link to comment Share on other sites More sharing options...
p76rangie Posted August 11, 2010 Share Posted August 11, 2010 Oh jeebus, let's not go round this again... Whatever they are, I'm running them, and it works fine. (3.9 heads on 4.6 block with comp gaskets) I am not sure why you keep on bringing it up then. What are 3.9 heads anyway, they are possibly the same as 4.6 heads. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted August 11, 2010 Share Posted August 11, 2010 I am not sure why you keep on bringing it up then. What are 3.9 heads anyway, they are possibly the same as 4.6 heads. If you don't know I'm not telling you, you'll only argue Quote Link to comment Share on other sites More sharing options...
p76rangie Posted August 11, 2010 Share Posted August 11, 2010 If you don't know I'm not telling you, you'll only argue Obviously you don't know. The 3.9 came with both 14 bolt heads (Tin gaskets) in its early years and 10 bolt heads (Composite gaskets) in its later years. The 10 bolt heads are the same as you will find on the 4.0 and the 4.6 Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted August 11, 2010 Share Posted August 11, 2010 I take it all back, you'll argue anyway. Quote Link to comment Share on other sites More sharing options...
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