3.9L/4.6L Differences - Defender Source
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  #1  
Old February 20th, 2007, 01:00 PM
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Question 3.9L/4.6L Differences

This may be a real stupid questiion to ask but, what are the main differences between a stock 3.9L and a Land Rover 4.6L? I realize that the 4.6 has more power...is it larger crank throw?, larger bore?, longer stroke? I read up on ERC projects and thay seem to install several 4.6L (and 300Tdi's) in 90's and 110's.

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  #2  
Old February 20th, 2007, 01:07 PM
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4.6 is a different block with cross bolted mains and bigger bearings. The bore is the same but there is a longer stroke. The 4.6 has a longer crank snout. To install a SHORT BLOCK 4.6 in a 95 you need a crank spacer but everything else will fit off the old block. It would be silly not to replace the cam and lifters at the least when doing this.

Ron
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  #3  
Old February 20th, 2007, 05:36 PM
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So other than the spacer its a bolt in? Why would anyone rebuild a 3.9l then? Or are there other considerations such ECU etc.?
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Old February 20th, 2007, 08:19 PM
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Quote:
Originally Posted by ScottYates
So other than the spacer its a bolt in? Why would anyone rebuild a 3.9l then? Or are there other considerations such ECU etc.?
Per ERC'c project documentations (well done and informative!), the 4.6L engine requires a chip specific to that engine . So the 3.9L heads, intake/exhuast manifolds, water pump, alt, power steering pump, and A/C fit directly onto the 4.6L? I am just trying to figure out why/how the 4.6L (@275HP) has ~93HP more than the 3.9L (@182HP)

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Old February 20th, 2007, 08:25 PM
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Quote:
Originally Posted by evilfij
4.6 is a different block with cross bolted mains and bigger bearings. The bore is the same but there is a longer stroke. The 4.6 has a longer crank snout. To install a SHORT BLOCK 4.6 in a 95 you need a crank spacer but everything else will fit off the old block. It would be silly not to replace the cam and lifters at the least when doing this.

Ron
I was just gonna shave the teeth off an old timing gear as the spacer, cut off the pin on the rear crank and put a rubber plug in the hole where the crank position sensor should be.


Neil
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Old February 21st, 2007, 12:40 AM
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The 4.0 (same displacement as the 3.9) and the 4.6 share the same block. You can build any 4.0 into a 4.6 (including reusing the heads and fuel injection) since both blocks share the cross bolted main (which really is the only difference, and technically, you could do your 3.9 this way just without the cross bolt). You will need to use the 4.6 crank/rods/pistons for this to stay in the 9 ish compression range. If you try and use the 4.6 crank with the 4.0 rods/pistons, I think my math came up with it in the 11's compression wise. As for the chip, the chip in the 3.9 will work, but it won't unleash all the potential. For $40 or so, go to a dealer and get the 4.2 chip--that is all you will need and it only takes a minute to do the swap in the 14CUX ECU.
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Old February 21st, 2007, 04:30 PM
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So the 3.9 heads and assorted parts fit. Won't be doing this now of course, but when the time comes.......
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Old February 21st, 2007, 04:53 PM
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Quote:
Originally Posted by ScottYates
So the 3.9 heads and assorted parts fit. Won't be doing this now of course, but when the time comes.......

All the rover heads from 3.5 on up will fit, except if you get AIR tube type heads you have to plug up the holes with brass plugs if you want to use it in a D90. Also with later heads, you might have to tap in a hole or two depending on what type of belt set up you require. But the trick is to get the heads to someone who knows how to machine rover heads so you don't have to shim the rocker pedestels (They grind away material from the top of the valve stem so you don't have to use shims)

Neil
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