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Old February 24th, 2011, 07:19 AM
Rufus's Avatar
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1994 NAS D90 ST #1118
Join Date: Apr 2010
Location: South Shore, MASS
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4.6 in a D90 - questions

I know there are threads that talk about 4.6 engines... but I wanted to get some feedback from you guys that are already running them. Did you get them used or new? Is the mileage different? maybe (being hopeful) it is even better? One thing that scares me, is I have a buddy that had a 4.6 in a Disco and slipped a sleeve.....nightmare situation.....I have heard this was not that uncommon with some of the 4.0s & 4.6 engines... and then it got fixed. Do you know what years they are susceptible to this? and when they fixed it?

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Old February 24th, 2011, 09:36 AM
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Bill Adams
66 109 sw 94 lwb
Join Date: Jul 2009
Location: kensington md
Posts: 6,094
If you think there is any chance of getting more miles per gallon with a 4.6 over a 3.9 forget it. What do you want from a larger engine?Low end oomph? high end speed? broader mid range? You can't have all three! Just want an improvement in seat of the pants feel? Without replacing the engine in your truck, much can be done with the existing lump to get more out of it, to the point that replacing it with a 4.6 would be moot. It all costs money, and serious money at that.
The first thing to do is replace the exhaust manifolds with headers and deleting the catalytic converters. This will help the breathing for any other improvements you make in the future. There are several available for the Rover engine.
The second thing to do is install a cam with higher lift. This will allow the engine to breathe better, but installing a bigger cam may mean installing injectors that can deliver more fuel. The third and probably the most hp per dollar spent increase is a supercharger. The easiest to install is a roots type which goes on top of the intake manifold and is driven by a pulley. It is downstream from the Mass air sensor so tweaking the computer usually isn't necessary. Turbocharging is probably a better way to go but with the plumbing, aftercooler, custom exhaust, etc, you are into some big money. However it would not be out of the question to expect a minimum of 350 hp (probably much more) with a twin turbo installation. This gives increased hp in all rpm ranges. Adding nitrous boost gives about a doubling of hp, but only for short periods. A rev limiter is essential for nitrous.
Over and above that you start talking about minor things like deleting engine driven accessories and improving internal engine components. The addition of a Buick 300 crank will allow a longer stroke, but that means pretty much all new internals so it's a major thing.
All these things may kill your truck's emissions, so you may have to re register it as a street rod.

Bill Adams

1966 109 5 door wagon 300Tdi "spermaceti fueled"
1994 RRC LeWiB "ruining the air behind me"

All my troubles are Rover
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Old February 24th, 2011, 12:12 PM
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Lucas Forgue
1988 RRC
Join Date: May 2009
Location: NB, MA
Posts: 124
rufus where in MA are you?

ive got a 4.6 in my RRC and love the seat of the pants...but i did go all out on it
smoothed out the intake and heads
new rings and bearings
tweaked the mafs
8mm wires

havent got a chip yet but its still nice compared to some d1's and d90's ive been in

the slipped liner issue has a bunch of gray area...i feel if you can find a GEMS 4.6 block or a 4.0 block and find a 4.6 rotating assembly and assemble it that way....you'd be better off but if you can stay away from any 03 bosch blocks lots of problems there in my experience

good luck
88 Rangie 4.6 toy conversion
59 SII....on the back burner!
05 LR3 168k!
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Old February 24th, 2011, 12:16 PM
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Beluga '97 90
Join Date: Sep 2008
Location: Los Angeles
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One of my 4.6s had a slipped liner that was discovered at only 50K miles. Dealer replaced the engine. Read this:

Originally Posted by rijosho
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Old February 24th, 2011, 02:05 PM
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Andrew J. Hutton
1993 Defender 110 200TDI
Join Date: Oct 2007
Location: Ottawa, Ontario, Canada
Posts: 735
All Rover V8 can slip a liner if overheated, the 4.6 issue was bad front-covers on the D2 and it was a fairly narrow production timeframe. If you're starting from a bare block get it bored out to accept top-hat sleeves and you're good.

If I was converting to a V8 I'd go with the 4.6 and matched exhaust as mentioned above and Megasquirt so that I could get fine-grained control over fueling, this step means you can tune more correctly and with a dyno and exhaust sniffer get it running as cleanly as it can while still producing good power.
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Old February 24th, 2011, 02:36 PM
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John B.
1991 Defender 90, 200TDI
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Originally Posted by o2batsea View Post
It all costs money, and serious money at that.
Except getting a 4.6 is cheap and easy....

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