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3.5 manual to 3.9 EFI Auto with megajolt !


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Currently I'm carrying out a little change for my 90, out with 3.5 carb with LT85 and in with 3.9 EFI, ZF4 auto and megajolt.

As it is the old engine and gearbox are out. I plan to re-use the LT230 with the auto box and change the ratios and hope the engine and gearbox are a straight swap. There seems to be some who say it is a straight swap and some who put it firmly in the "total nightmare" category. We'll see.

After the old engine was very obliging in coming out without any fuss the "new" engine promptly sheared 2 exhuast manifold bolts off in one of the heads, so if the head is coming off the whole engine is getting rebuilt. Got the injection manifold off today, but it leaves the question of what to get done while I'm taking the engine apart. Uprated cam ? Stage 1 heads ? Injectors cleaned ? Rumour has it the engine had 140,000 miles on it so a rebuild is probably a good thing.

I have an EDIS 8 from the US, coil packs and mejajolt all ready for that long distant time when the new gearbox and engine are in the 90 and I can take the ignition system to a whole new waterproof world. But my current task is take head off and work out how to remove broken studs and try to split engine and auto without flooding gargae in ATF fluid. I'll update this post with how I get on, in case it proves useful to anybody.

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I have not done thisConversion but know of 2 that have and whilst very worthwhile its not simple....

To save you sanity I would suggest you do this as 2 stages, gearbox and engine fit, and then MegaJolt it, get it running on stand everything 1st, you'll see a result quicker !

The things I think you have to possibly sort out.

1 Lengths ?....engine mounts and $ speed ZF may not have same lengths esp propshafts, in which case you'll need to make correct length props. Did you measure the fange to diff flange before removal of the old units ?....

2 Panel work. The 4 speed auto will need fabrication for the shifter mounts, or if you are feeling flush Nas 90 Auto or poss 50th anniversary auto maye provide parts to save fab time ?

3 Exhaust, may not fit as routing around box different, again 50th anniversary NAS90 may do it, or combo with RR 3.9 auto front pipes modded to suit ?

4 Oil cooler mounting / fitting

5 kick down assembly, unless you are lucky and the box and engine were bought as one

6 Pedal box, just removing the clutch is a bodge really, need to remake so spacing is correct for the pedals

Thats just from memory when I considered this route years ago with the Hybrid......

HTH

Keep us all posted

Nige

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I'm also preparing for a ZF4 conversion.

AFAIK:

1 Lengths ?....engine mounts and $ speed ZF may not have same lengths esp propshafts, in which case you'll need to make correct length props. Did you measure the fange to diff flange before removal of the old units ?....

I believe its ok if you have the right bellhousing.

since ashcroft's have given me a kit quote & no mount moving was mentioned.

3 Exhaust, may not fit as routing around box different, again 50th anniversary NAS90 may do it, or combo with RR 3.9 auto front pipes modded to suit ?

Again i believe its ok as standard. pipes clear current box by a mile. again no mention by ashcrofts.

6 Pedal box, just removing the clutch is a bodge really, need to remake so spacing is correct for the pedals

Kit comes with a blank for clutch & foot rest to fit in place, so no moving of brake (this would cause all sorts of probs with brake pipes if you did no?)

You do have to modify the seat box a bit i believe.

p.s. I have a built & tested, brand new MegaJolt for sale. Cost + postage.

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Gents,

I put a ZF onto the back of my V8 in the 90 last year. I'd recommend doing a search on this forum as there was some really good information put together.

To answer your current concerns:

Get the mounts for the ZF to chassis. The manual box ones are similar but slightly differnet fwd/aft offsets. The mounts will then line up to the existing holes in the gearbox.

The exhaust is fine. No problems in that Dept.

The front prop is also the same but the back one is different. Can't remember if it is longer or shorter but I got a custom one built.

For the pdeal box, I actually find it much easier with the old brake pedal "as is". I removed the clutch but the remaining setup is dead easy to use with both feet.

As HfH points out, you may need to hatchet the transmission tunnel and seat box slightly depending if you have viscous or manual difflock. Its not has bad as putting a V8 into a Series wagon so fabrication is straight forward to sort it all out. Its handy being able to place the shifter wherever you want it as it is on a cable.

Sort the wiring out for inhibit switches, reverse lights, difflocks out before you replace all of the floor panels because they are a swine to do later..

Splitting the ZF to V8 is straight forward, undo the four bolts on the flex plate (where the clutch normally sits.

Take heed about properly locating and measuring the torque convertor on the oil pump gear too or else you won't know you have a problem until way too late. It is confirmed by measuiring from the top of the flange on the converter to the face of the bellhousing...

Good luck and enjoy ! :D

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The front prop is also the same but the back one is different. Can't remember if it is longer or shorter but I got a custom one built.

uhh, hang on a mo. how can that be?

if the front prop is the same then the transfer box hasnt moved (much) so why is rear prop different???

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I removed an LT-77 box and transfer box then replaced with a ZF Auto and its transfer box. Flange to flange on the transfer box was longer but I never specifically chased down why. Trust me, it was though. ;)

Ok then.

But if pete (and me) are going to use our existing LT230's then nothing will change.

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In the process of this myself. From what I have gleened which seems to answer some of the questions is... if you are using the LT230 with your autobox (as per manual box install) then all 'should' be OK, but note the above comment on using the mount from the autobox. However if, as many do, get their autoboxes from a Rangie then, as standard, you have the different BW Xfer box which, if you are going to keep it requires the front propshaft to be used from a RR. There is a difference in the front output flange distances on the two Xfer boxes (can't remember if longer or shorter).

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  • 2 months later...
The exhaust is fine. No problems in that Dept.

[Thread hijack] 3.9 headers etc are obviously different to 3.5, what did you use exhaust wise for the 3.9 install. I'm currently going through the process of trying to install a 3.9 exhaust system, but want to make as few mods to the exhaust as possible. (Part numbers would be a help too guys). [/Thread hijack]

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3.9EFi exhaust manifolds are almost identical to 3.5EFi, just slightly bigger bore. 3.5 carb versions may well differ though.

I must currently have a 3.5 carb system. The headers on a 3.9 are different with two ports as opposed to one larger port on the 3.5 set up. Also the connection to the Y pipe differs somewhat. Anyone got the pn's for a defender 90 3.5/9 exhaust set up (particularily interested in a Nas/ 50th set up as my vehicle has an auto box)?

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Did you have to lop the tunnel about? What was the car originally? I'm trying to work out if a 4HP22 with an LT230 will sit on standard LT77/LT230 mounts under an LT77 transmission tunnel.

John,

Unfortunatley I'm not sure as i didn't put the car together. Adrian Turner built the car. Hopefully he'll be along here shortly, if not give him a PM

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It will fit under an LT85 tunnel with not a lot of space to spare, and as thats much bigger than an LT77 tunnel I would guess it won't fit.

As for mounts, my experience with a V8 conversion is that the ZF replaced the LT85 without having to move any mounts, you just use the gearbox mounts that come from the donor with the gearbox. The gearbox mounting holes in the chassis are in the same place on 90/110/RRC and I guess DiscoI too.

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I must currently have a 3.5 carb system. The headers on a 3.9 are different with two ports as opposed to one larger port on the 3.5 set up. Also the connection to the Y pipe differs somewhat. Anyone got the pn's for a defender 90 3.5/9 exhaust set up (particularily interested in a Nas/ 50th set up as my vehicle has an auto box)?

Anyone? (I thought Ralph might have been along by now ;) )

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I think early Range Rover/Disco non cat auto downpipes should fit, that's what I'm using on my V8 50th instead of having the shockingly badly designed and restrictive cat jobbies. I think you can often get them on ebay from people who have gone for a tubular set up.

Hope this helps.

Charlie

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I think early Range Rover/Disco non cat auto downpipes should fit, that's what I'm using on my V8 50th instead of having the shockingly badly designed and restrictive cat jobbies. I think you can often get them on ebay from people who have gone for a tubular set up.

Hope this helps.

Charlie

Charlie,

Is your rear section a standard section for the 50th?

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It was, I have a rather loud Overfinch stainless system but I think the non-cat down pipes and catalysed ones are interchangeable as I fitted the stainless system to the standard down pipes but was a bit disappointed with the increase in noise (not enough!) so after speaking to Overfinch they said to get rid of the cats which resulted in an increase in performance as well as a fair bit more noise.

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