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Which V8 is better......


spcollins
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for long term realibility - 3.5 EFi or 3.9EFI? I aready have a 3.5 and it's running fine but just about to do an auto conversion in the 90 (autobox from a 3.9 which I belive will mate straight to the 3.5) and the 3.9 engine is going cheap, If I want it.

Would it be worth the hassle of changing the 3.5 out for the 3.9 for the extra power (is here much of a difference in power between the 2?)? I heard that after 120,000 miles the 3.9 is prone to block cracks.

All help / suggestions / pi$s taking appreciated ;)

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I would say there is a massive improvement in power but i have not sufferd any block problems with a V8 in the 10-12 I have had just always wanted more power and abuse has killed a few

Ask V8freak he has just swapped 3.5 out for a 3.9 in his 110.

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IMHO

3.9 does have more power

3.9 does have a better EFI SYstem (although some 3.5 Hot wires were made they are quite rare)

3.5 Flapper system is deemed to be simpler, but can be a Pig (Don't ask me how I know :P)

3.5 have no issues on liners or blocks, some 3.9s do but its more a 4.6 thing, and often IMHO grossly over talked about

Is NOT the amount of miles on a V8 that kills it - its lack of service and oil changes etc

HTH

Nige

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Power in standard RRC trim with Inj, goes from 165 to 189bhp in 3.9.(varies on CATS i think).

Opinion will vary, it always does, but other persons i know with V8's, not landies, have the feeling that the bigger the capacity, the weaker the block. However the guy's i am talking to are running TVR's that are tuned aswell. Some have had issues, others swear by big capacity. I think the 3.5 is stronger as it is the 'original' capacity and least stressed.

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Yep

Get a 3.9 and ensure you get the full harness ECU AFM and other bits.

Then remove the 3.5EFI and you will find that the EFI LOOM is a completely seperate unit, ie unplug from the LR and remove with the engine. Its a Fab bonus that the loom for the engines are completely sepetae to the main loom for the 4x4 !

Shove new one in, you'll have a few connection tweaks, but prob no more than 6 wires different - mainly oplug to plug is the issue

Nige

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Minor point HFH, depending on the year of the RRC with the 3.9, depends if the engine harness can be seperated. This was discovered with my donor RR for the hybrid. Its registered as a Jan 1990, a previous RRC 3.9, was a Autumn 89 registration. That was seperate harness, think its called rationalisation!!

Just a point to watch. Could always bang the 3.9 on carbs, kill the fuel but who cares(eeek).

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3.9 does have more power

What do you use your truck for? Off road, in a standard truck, it makes bugger all difference (in theory the 3.5 might actually be better - peak torque is at lower revs), but on the road the 3.5 feels gutless after the 3.9, especially at the top end.

3.9 does have a better EFI SYstem (although some 3.5 Hot wires were made they are quite rare)

V8 Discoverys were 3.5 hotwire up to about '93. Range rovers had already been on 3.9 for a few years by then, so I guess early discos are the best source of them.

Is NOT the amount of miles on a V8 that kills it - its lack of service and oil changes etc

Although judging by the one I stripped down recently, by about 150k they need a rebuild if you want them to last (bearings and cam starting to wear). I'd guess if you didn't mind doing permanent damage it would run happily enough for quite a while after that, though?

mmmmm - Thanks for the replies. Maybe a 3.9 is on the way so!! :D

Does anyone know if it an easy change? I haven't looked at it in too much detail yet.

Pretty straightforward if you don't do anything stupid... Given a decent workshop to work in, I'd allow three days not including the wiring work - pushing on late to get it done in a weekend was what got us in trouble :(

Mine has been swopped in the other direction - 3.5 Hotwire replacing a 3.9 that had some minor timing gear issues, and apart from our slight stuff up that meant a second weekends work, it was pretty straightforward - I did have two friends helping though, one of whom was Robhybrid, who actually knew what he was doing (unlike me) and the use of Rob's workshop. Externally the differences between the two hotwire engines were pretty much limited to the number on the plenum - I would imagine differences with the flapper are limited to the intake manifold upwards.

If your current engine is a flapper one you could always fit the flapper intake on the 3.9 then it will just plug into your existing loom. I'm not sure whether the flapper will fuel a 3.9 adequately without modifications, though.

I've heard that most of the difference in performance between the 3.5 and 3.9 is down to cam profile rather than the additional capacity - don't know how true this is, but changing to a 3.9 (or even better aftermarket high torque) cam in your current engine would be another possibility.

The forums wonderful search function will not allow you to search for words containing less than three letters

Unfortunately there's nothing we can do about that. For the techies among you, it's a limitation of the underlying full text search system. We could switch back to the basic search system which did allow a lower limit, but it was already getting horribly slow a year ago. With the volume of posts we have now if it worked at all it would be virtually unusable.

It's a pain though - we have plenty of two and three letter acronyms it would very useful to search on.

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Converted my 3.5 carb Disco to 3.9 EFi last year,drove into the workshop on Friday night at 6 O'clock, roadtested at 4 pm on Sunday with the new engine :) .

Had some help to lift old engine out and lift new one in, otherwise single handed for the rest of it.

Wiring is fairly straightforward but I found out you will need a vehicle speed transducer in the speedo cable or the idle goes all over the place after about 5 miles of driving.

Shaun

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