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3.5 to 3.9 Transplant Woes


Shackleton
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<_< as a time capsule for anyone in the future transplanting a real early RaRo with a 3.9 from a late car...

Do not attempt this conversion without sourcing a complete late donor car. There are simly too many ancillary bits you'll need. Heres the latest;

Everything will be going reasonably swimmingly until you offer up the exhaust down pipes / Y piece to the manifolds. They come up a good 5" short.

WHY?

The early cars have a big f-off box section cross member under the gearbox where the late cars have a dainty shaped tubular steel version which upsweeps at each side allowing the exhaust to rise and meet the manifolds.

They seem interchangable, bar some minor hole boring. There is however the possibility that the late member will foul the front drive shaft - it comes damn close to the one coming out of the late ZF box, but the jury's still out cause I haven't had the chance to drop the early cross member. I say drop, these things won't just drop out, as per the other cross member post you are suppposed to brace the chassis to get a little give so you can pull them out. After much effort with blocks of wood, steel bars and hydraulic jacks my ensuing rage found me tying a rope to the cross member and towing it out with Mummys car... :D job done.

The "BONK tinkle tinkle tinkle" of the submissive cross member popping out made the green fade from my skin and I returned to normal size.

Anyhoo - as I said - just for anyone thinking of doing this conversion. (Don't)

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Thanks man, that is actually quite heartening.

I'm crapping myself that once/if I can get this baby cranked up that she'll need head gaskets or something. In hindsight it was foolish not to do them while I had the lump half stripped. Instead all I did was make sure the heads were well torqued :unsure:

I've had to do way too many mods and figure so much stuff out that there's no way I'm gonna let myself forget all the hurdles. Gotta write up some kind of guide to capture all the info. Most of it isn't online and what is there is surprisingly hard come by...

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I'm crapping myself that once/if I can get this baby cranked up that she'll need head gaskets or something. In hindsight it was foolish not to do them while I had the lump half stripped. Instead all I did was make sure the heads were well torqued :unsure:

Been there :( Just had to do the head gaskets on the engine I put in over the new year. Just to add insult to injury I went from a 3.9 to a 3.5 (but much easier than yours, as they were both hotwire EFI engines).

I've had to do way too many mods and figure so much stuff out that there's no way I'm gonna let myself forget all the hurdles. Gotta write up some kind of guide to capture all the info. Most of it isn't online and what is there is surprisingly hard come by...

Good man - reckon you could write it up for the tech archive? :)

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Well firstly I didn't know you could do that. Now that I do I wonder what it does in terms of economy/power?

I went this way for a few reasons that add up to the decision rather then one main reason.

* My original 3.5 unit was a cacophony of tappets and bottom end noise - so that had to come out.

* Not that its a mantra or anything but if you're gonna change might as well upgrade

* I've done some sums and the difference in weight should see the 3.9 produce (I didn't write it down) but between 1.5 and 2.25mpg in the earlier car. Thats based on weight alone so maybe a fraction more.

* I wanted rid of the need to adjust carbs

* Rover V8's aren't ten a penny here in any guise but I was always much more likely to find a late donor

* The ideal engine to my mind is the TD5 - and I don't have €10k to go spashing out on trying to get one of those in there.... The way I look at it is by the time I need to be rebuilding this V8 (and given the arrival of the new Defender lumps) the TD5 hopefully will be more accessable.

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In terms of economy/power:

3.5 carb: 132bhp @ 5000rpm / 186lb ft @ 2500rpm

3.5 EFi: 165bhp @ 4750rpm / 206lb ft @ 3200rpm

3.9 Disco (Carbed?): 164bhp @ 4750rpm / 212lb ft @ 2600rpm

3.9 Range Rover (EFi): 185bhp @ 4750rpm / 235lb ft @ 2600rpm

From here

I still love the fact that the switch from carbs to EFi yields 33bhp / 20lb ft on the 3.5 :blink:

Your choice to go faster or get better MPG really ;)

If the EFi system has Lambda sensors (closed loop) the economy *should* be better than one without (open-loop).

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* Rover V8's aren't ten a penny here in any guise but I was always much more likely to find a late donor

So whereabouts are you? your profile dosn't say so I had assumed UK....

Keep at it though, and please do do the write up :)

Cheers

Mark

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Heh - that clue would lead you on a very round about journey.

I'm Irish/Greek (and in Ireland) but my other half is Kenyan. I bought the RR from one of the better known UK specialists last April and brought it back here. (I'd been on the lookout for about 2 years)

Yeah the 50hp jump super nice (not forgetting the 50lbft jump too...) but the few more mpg is just as important to me...

It's a pity that site doesn't give the MPG figures but it should be 15 for the 3.5 carbs and depending on what you read it's either 15 or 18 for the 3.9.

I based my calculations on 15 for the 3.9 so if it is indeed 18 then thats just a bonus and with the O/D maybe I'll see over 20mpg.

RE the build. I've very little left to do. Next Saturday is thee day - it's really only fit the alternator some few other ancillaries - rebuild the interior and run a host of checks before offering her some cranking amps. The late cross member was duely painted yellow and dit went in without any fuss. It'll have to come back out at a later date to have an extra bit of flange welded in on both sides as it tapers in towards the bolt holes on both sides at the bottom where as the early one is bolted squarely at each corner. So mine is now held in by 3 bolts rather then four. (thats hard to grasp I know but it's too small a thing to explain properly in this thread :lol: )

But I gotta say I feel dirty - I had to bore two holes in my front chassis cross for the rad. Thats just wrong. Then when I offered it up it fouled the original mount bracknets. :( So rather then cutting those out I bent them out of the way with a mallet. But then there are two brackets on the chassis right under the rad - they hold on support bracketry for the bumper. There's no cutting those off so I used extra bottom rubbers as risers for the bottom rad mounts.

But now the rad is sitting about 1.5" higher then intended - not a massive problem there's plenty of bonnet clearance and it shouldn't affect the cooling to any great degree (pardon the pun) but I'm guessing with my luck the fan will foul the cowl (there's a mouthful) and thats why I'll be scratching my head this week for a solution by Saturday.

I know it sounds like a strange and obvious statement but the '70 car just wasn't meant to have the late running gear in it.

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  • 2 weeks later...
3.9 disco would be hotwire EFI - it was an upgrade from the 3.5 EFI round about '93/'94. I've got a '92 disco engine in my rangie, which is 3.5 hotwire EFI. Pretty sure the early 3.5 discos were carbed though.

It's surprisingly down on power compared to the 3.9 RR lump then, is this just done for marketing purposes or what? :huh:

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