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V8 discussion 3.9 to 4.6

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Not technically a land rover, but I am intending to buy a range rover classic for the 3.9 V8 engine for my AC Cobra, the problem I am faced with is it must be pre 1992, to avoid emissions. So that means I am stuck with the 3.9 block...however there are no regulations on what I can do to the engine, so long as the block remains the correct age.

So, begs the question, what can you do to a 3.9 V8 to make it perform much much better, any ideas welcome :) Thinking being the same bore a 4.6 crank and pistons might fit

Discuss :D


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hmm going by those figures perhaps I should be looking at going down the yank route...hmmm

Perhaps if not I could convert a older 3.9 to the newer 3.9 serp set-up with the better oil pump

I seem to remember that's been discussed before, and it is a big costly change due to things like different crank lengths.

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Am I right thinking that the difference between a 3.9 block and a 4 litre block are cross bolting of the block itself?

And the difference between a 4 and a 4.6 is the crank, and therefore the stroke length?


Couldnt you, Cross bolt your block, and therefore get the appropriate internal machining done, to allow clearence for a 4.6 crank??

Then, you would have a 4.6 in the original 3.9 block.

(im only speculating btw, i dont think I 'actually' know what im talking about!! :lol: )

You could even...

Beg/borrow/steal/BUY(hint hint) a 3.5 off a friend, and get it machined out to 4 litre, with new liners and cross bolted, and then fit a new crank... :D

However, none of its cheap... :(

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Thats why i went with my Audi motor.

Plus, unlike most cheap yank motors, it has nice modern multivalve cylinder head and bosch EFI etc making it pretty efficient and as economical as a big V8 can be!

Why the requirement for an old engine? Is it an IVA requirement?

Personally, i'd rather have a modern engine and have to equip it with a pair of cats, than a clagged out old heaper just so i could avoid it.

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Plenty of folk building Locosts manage to fit cats in while retaining sidepipes... Although it might also be quite common for the cat to fall off afterwards ;)

Also IVA regulations say engines from 1st Aug 1995 require cats, engines prior to this do not.

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Yes but meeting the emissions requirement without a cat is near on impossible with a V8, regardless of regulation. Also I don't see twin cats being cheap either :s

Have now decided to go back to the rover idea haha!

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Not worth doing much as you have said, I'd look at throwing a more roady cam at it and obviously MegaSquirt'n'EDIS which makes lots of things nicer and should pass emissions should it be needed. The old style oil pump worked fine for the first million or so, hardly seems worth the hassle.

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