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3.9 conversion questions


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Hi, I'm thinking about putting a 3.9 manual in my 110

I'm converting from a 200tdi but I'm not sure about the engine mounts ect. Can I just pull one out of a disco and fit it in with minimal modification to the chassis?

The main question though, is it worth it? It's not a daily driver just a weekend toy. I Know there juicy but are they as gutless as Some people say? i want to to be fairly quick on the road and get away from the lights ok

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When i converted my td5 chassis i bolted gearbox (r380) to engine. Then connected the transmission to chassis mounts which then gave me position to weld the v8 engine mounts which i scribed onto chassis. Hope that makes sense?

Regarding whether it will be worth it? Yes. Yes it will. The RV8 will drink fuel but as long as its not a daily driver, it will be far more enjoyable than the diseasal.... ;)

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Yeah, I see the transfer case and gearbox being most crucial as I dont want to get different props or relocate the gear stick. Like I say I read that there is a specific defender bellhousing which can make life easer but I might have made that up in a sleep deprived stuper.

It's a fairly simple conversion then?

Obviously it would be rude not to try and get a few more ponys out of it, same old tricks with a N/A engine? Head porting, cam, exhaust

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If i remember correctly i bought a v8 bellhousing from a disco. Going by pics i found online, it put the engine more or less dead on where the factory v8 mounts would be.

Yes its an easy conversion.

Re tuning the rv8, search the forum. There is LOADS on the subject ;)

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The 4.6 does as you say have a longer stroke than the 3.9.

Are the blocks the same?

Depends on the age of the 3.9, IIRC 3.9 blocks from '95 onwards were cross bolted, earlier ones weren't, but yes you can use a manual gearbox with either (my 4.6 110 is a manual at the moment).

As for tuning any Rover V8, forum member Fridge Freezer has been known to say it's like "polishing a turd", might sound harsh but he is correct, the RV8 is a very old design, yes you can improve it but it will cost you lots for not much improvement unless you are prepared to pay serious money.

A 3.9 is putting out approx. 180 BHP, a 4.6 around 240 BHP, neither of which is great if you think about it.

By comparison the (Jag derived) SC 4.2 in my L322 RR is allegedly around 400 BHP.

Having said all that, don't discount fitting any RV8, they work very well in any Defender & always put a smile on my face :i-m_so_happy:

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I know that there a bit of a lazy engine. The 200tdi in the 110 at the moment is getting very tired and I don't want to keep throwing money at it for it to let me down elsewhere so I thought it Easyer to change engines. Just need something quick to do and cost effective which is why I'm not using my vortec

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Keep it efi, do as need4speed says as that's how I did mine... 300Tdi to 4.2 efi Rv8.

RR efi fuel pump will fit into the 110 but will need lengthening a tad.

Nice easy conversion, I drove 80 miles to my works workshop, installed it all in 3 days and drove home on the fourth no problems and I was an 18 year old apprentice... The only thing that spoilt it was, I was an apprentice and v8's love petrol and most of my wages went on feeding the beast which stopped 2 years ago when I put a bigger, more powerful and economic diesel in :)

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Ash, I read the article in lro about your 5.9 and you did a fantastic job there, to be honest that conversion was my first choice but I cannot find a 6bt for a decent price anywhere. I recall them on eBay for 500-700 with a gearbox a few months back now there 1500 with no box. i already bought the Salisbury front to put up with the torque but have just given up on finding the engine. Maybe that's just how much they are now.....

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dangerous doug, the biggest difference in driving the V8 is you no longer have the famous diesel "flat spot" under 1500rpm, which one tends to get used to whether one drives a 200, 300 or Td5 (never driven a TD4 so don't know the difference), and you have an extra 2000rpm to use, the diesels redline at around 4000 and the V8 around 6000, this gives your gears much longer legs and much better gear overlap, when I am empty I pull off in second, run it up to 60kmh and then change to 3rd, which takes me to 110kmh and it feels like you driving a sports car with big tyres on! no defender diesel I have driven can compare to this.

my land rover driving career started in the late 1990's, an ex military 101 that I used for safaris in botswana in the deepest sand and water that just about any land rover will ever see, loaded full with 12 clients + myself and pulling a 1+ tonne trailer that old, tired, low powered (not even 100hp i think), carb driven V8 was an awesome engine, then.... as the company grew I needed newer and more reliable (and less thirsty) vehicles and I progressed thru the 200, 300 and finally TD5, I have only ever driven these vehicles REALLY loaded, most of the lengthened to 150' fully loaded close to their 3,5t max weight and still pulling a 1+ tonne trailer and while the diesels did really well at pulling the heavy loads their only real advantage in my eyes was the slightly lower fuel consumption. but the low end torque of the V8 cannot be beaten....

which is why I bought myself an old 110 with a 3.5 V8 efi and I am loving every second of it, real grunt right from idle all the way up through the rev range till the valves bounce...... and that is from a tinkle little 3.5 with an archaic flapper injection system (before I get lectured about putting an MS in.... Nige's box of tricks is on the shelf waiting to get installed!!! just need to find the time and overcome my fear of eating elephants.)

for a work truck that other clowns drive, diesel is great but for a play truck that only you drive and don't mind the extra fuel bill the V8 is just SO much more fun.

PS I would also throw the extra cash at the 4.6 if I were doing a conversion.

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Ok I think I'll go v8 for the moment then.

I can't find a decent 4.6 so I'm trying to find a 3.9/4.0 and then buy a 4.6 crank. I can't look about for too long as I have 2 weeks off at the end of the month which is when I'll be doing the conversion so I need to accumulate parts fast. I've been stung before with someone selling me the wrong gearbox for the wrong engine and the only v8 manual box I can find is an lt77

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Good decision.

As Stuck said, seeing as you dont already have an engine, aim to make the biggest you can, which is 4.6. You can go bigger but it will cost £££££.

RV8's are difficult to tune on a budget so going for the biggest is the cheapest way to more horsepower/torque. EFI is essential for any kind of offroading, and if your budget will stretch Megasquirt is highly recommended. Give Nige (hybrid from hell) on here a shout.

If you need a step by step on building your engine, give me a shout. Happy to help.

Edit: There are always loads of R380's around ebay but bare in mind you will either need one from a defender, or you will have to change shaft in gearbox to suit..

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there is no replacement for displacement, is something my godfather used to say when we were building our 998 turbo mini. I guess he's right in this case

Yeah cheers. I have the money for mega squirt and it is a must. Is there anyway to ID a cross bolt block?

I've only built mini engines before, is there a lot more involved building the v8? Other than twice the amount of Pistons

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If you can build a mini engine, you can build an RV8. They really are pretty simple. Cleanliness and quality parts are key. Any machining work required will depend on the condition of the engine you buy.

One step at a time. Get your engine and we can go from there.

Regarding cross bolt block. Its a nice-to-have but really not essential. If i remember correctly all the 4.6 blocks were cross bolted, and some of the later 3.9's as well.

One thing to bare in mind is that the 4.6 was renowned for slipping cylinder liners, so you may want to budget for having top hat liners fitted to your block.

Like everything in life, its all about your available budget. Its worthwhile spending most of your budget on building a good engine though. Everything else is easily upgraded at a later date, but you dont want to be pulling your engine back out anytime soon.. ;)

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That sir is the whole reason for this conversion. Sort it now so I can forget about it!

There is a 3.9 down the road from me on eBay with just over 100k on it But it's from an auto car. There is a flywheel, and diaphragm spring on there aswell and a v8 lt77 so providing it all goes well I should have most of the bits fairly soon. Might also look for a disco transfer box so I can get slightly better mpg on the motorways but that's not essential

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doug you will also want to go R380 if you planning to put more than a 3.5V8 in, the higher powered V8's will pop the LT77 at some point.

I am no expert but what I have gleaned form the forums it doesn't make sense bodging a 3.9 into a 4.6 without the proper top hat liners etc, then you might as well start with an engine that is born 4.6..

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I know. I would much prefer to start with a 4.6 but I can't find any and the ones I can find are bare so I would have to buy the an anceleries so the cost would be escalating further.

As for the gearbox, again I can't find any. They are not cross comparable from diesel to petrol without a rebuild

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I am no expert but what I have gleaned form the forums it doesn't make sense bodging a 3.9 into a 4.6 without the proper top hat liners etc, then you might as well start with an engine that is born 4.6..

Sorry but thats incorrect. Nothing whatsoever wrong with building a 4.6 from a 3.9.

Also, the 4.6 is far more likely to have slipped a liner than 3.9. Mainly due to the fact that, by the time the 4.6 came along LR were having to run them so lean to comply with emissions regs that they were running very hot..

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I did my conversion on the cheap in terms of the gearbox, here's what I did....

300Tdi R380 defender box, R380 V8 bellhousing, Td5 clutch release setup as it is identilcle to the v8 gear just superceeded part numbers and a V8 slave cylinder.

Then had a v8 spigot bush bored out to 7/8" to suit the Tdi input shaft.

I drove it just over 20,000 miles like this absolutely no problem, the spigot bush ends up being about 1.5mm thick but I measured it for wear when I pulled the lot out to do the Cummins swap and it was absolutely spot on.

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