1988 Engine rebuild question...

[astateofmike]

Are these figures correct?

Capacity 3528cc
Bore 88.9mm
Stroke 71.12mm
Max. Power 165bhp @ 4750rpm
Max. Torque 206lb ft @ 3200rpm
Applications 19xx-xx: Range Rover

Capacity 3948cc
Bore 88.9mm
Stroke 71.12mm
Max. Power 178bhp @ 4750rpm or 185bhp @ 4750rpm
Max. Torque 220lb ft @ 3250rpm or 235lb ft @ 2600rpm
Applications 19xx-xx: Range Rover

So what is the difference in the 3.5 and the 3.9? Heads? Can I put 3.9 heads on the 3.5 block when I rebuild? Thoughts?

[Paul Grant]

As far as I know you could put 4.0L heads on your 3.5L block. The changes that occurred to the heads over the NAS years wouldn't precluded you from using any one of them. If the heads you choose to use are the later style with ten bolts you must use the composite head gaskets and new torque bolts (or studs as some have stated in other threads). You can use the composites on 14 bolt heads and leave the bottom row of bolts off if you want to. Just remember that the composite gasket it a little bit thicker and can reduce compression (however marginally). It's not a major issue, especially on 9.35:1 engines but the lower compression engines you might want to skim the heads a bit more to make up for the loss.

[Paul Grant]

I was looking over the specs on the 3.5L and I think the HP figure you quoted was for ROW not NAS. Our Range Rover put out a meager 150 HP when dressed in full EPA trappings.

My carburetted 3.5L, fresh from the factory in 1985 put out a barn storming 128HP!

All that to move a 4600 lb. barge!

[p76rangie]

Changing the heads is not going to make a 3.5 a 3.9. The difference in power is to do with the larger capacity and the different EFI system.

[Elemental]

I have Cranks,Pistons and rods fro both the High and Low compression 3.9.
Used, but good parts.

Free for the taking.Its in St Louis.


The heads are the same. The difference between a 3.5 and a 3.9 is the engine bore.

If you use these cranks and pistions you will have, in esance a 3.9.

To convert the block to accept them, you will have to take it to a machine shop to have the proper sleeves installed.

[Elemental]

Originally Posted by Elemental

I have Cranks,Pistons and rods fro both the High and Low compression 3.9.
Used, but good parts.

Free for the taking.Its in St Louis.


The heads are the same. The difference between a 3.5 and a 3.9 is the engine bore.

If you use these cranks and pistions you will have, in esance a 3.9.

To convert the block to accept them, you will have to take it to a machine shop to have the proper sleeves installed.

- Range Rover pistons are graded L, M or H (Low, Medium and High) and are marked on the crown with the appropriate letter grade.

- Range Rover engine blocks are also graded L, M or H with the letter indicating each bore grade stamped on the water jacket on the outside of the Vee.

- Since tolerance exists within each grade, the attached table should be used when measuring pistons and bores.


Please note that the specifications are to be tolerance of .0001" (English) or .001 mm (Metric). Since most shop micrometers read to the nearest 0.001" or 0.01 mm, you may have to round the last digit up or down.

Examples: 88.844 mm rounds down to 88.84 mm
3.4978" rounds up to 3.498
0.0007" rounds up to .001"
0.041 mm rounds down to .04 mm


NOTES ON MEASURING

- All parts and measuring tools must be at room temperature and oil free.

- Measure pistons at right angles to the piston pin at bottom of skirt. See Workshop Manual, Sec. 12, page 17.

- Measure bores at right angles to the piston pin 40 to 50 mm (1 1/2" - 2") from the top. See workshop Manual, Sec. 12, page 17.

- Bore taper and/or out of the round must not exceed 0.0015 in. (0.04 mm)

[p76rangie]

Originally Posted by Elemental

The heads are the same. The difference between a 3.5 and a 3.9 is the engine bore.

If you use these cranks and pistions you will have, in esance a 3.9.

To convert the block to accept them, you will have to take it to a machine shop to have the proper sleeves installed.

It would not be worth the expense of having new sleeves fitted. You can just go and get a second hand 3.9 block. But if you are going to do that, you should seriously look at getting a 4.6 block for a little extra.

[Elemental]

It could be. If your having sleeves installed, you can go with a top hat style and forgo the pesky slipped sleeve thing.

[astateofmike]

My engine is running, luckily, but just "underpowered" on the highway. Luckily have not had an issue that the 1st gear and CDL couldn't help with.

So, it seems that if I need a total rebuild, then maybe worth changing things, but then I might as well try and find the 4.6L

Pardon my lack of knowledge, but will a 4.6 bolt right in? I would need to find one with everything, including EFI and ECU, correct?

I have determined that I am ok being slow on the freeway hills, as I cruise nicely at 70 along the flats. Looking for the torque to pull a trailer uphill for camping or for getting up the mountian.

Any suggestions?

[Elemental]

A 4.6 will bolt right in with slight modification. You do not need to change the ECU, or wiring to accomodate it.

[astateofmike]

Originally Posted by Elemental

A 4.6 will bolt right in with slight modification. You do not need to change the ECU, or wiring to accomodate it.

Slight mods? Like new suspension, new transmission etc....(This is what the wife will hear)

What are slight mods, engine mounts or hoses/wiring mods?

And Thanks for the information everyone!

[Elemental]

Originally Posted by astateofmike

Slight mods? Like new suspension, new transmission etc....(This is what the wife will hear)

What are slight mods, engine mounts or hoses/wiring mods?

And Thanks for the information everyone!

No, to the engine. Take a look at www.discoweb.org for more info. Quite few fellas have put 4.6s in Classics.

[roverandom]

If your engine is running fine but it feels underpowered on the hwy the best plan $$$ wise is to change the gear ratio in the diff's. This is alot less complex than a engine swap and the best way to compensate for larger tires, extra weight of trail equipment and towing.

[astateofmike]

Originally Posted by roverandom

If your engine is running fine but it feels underpowered on the hwy the best plan $$$ wise is to change the gear ratio in the diff's. This is alot less complex than a engine swap and the best way to compensate for larger tires, extra weight of trail equipment and towing.

Its a hard choice. Yes, she accelerates slow, but fully loaded on cruise control she will run 70 all day on the flats, but slows up hill. Friends suggested a diff switch, but then I'll climb hills better, but slower on the flats....Since I have to do both, its a one or the other thing...

Thats what prompted the engine questions.....

[roverandom]

A diff switch may not impact top/crusing speed as much as you think. Don't know what size your tires are or if you have compensated the speedo etc but lowering the ratio will return the Rovers performance to normal, or closer to normal anyway (ie. before the big tires) Remember, one revolution of your larger tire is going to cover more distance than a stock size tire. That is why if not adjusted your speedo shows you going slower than you realy are ( your speedo reading indicates speed calculated on revolutions of the output shaft adjusted for known ratio's of diff's and tires, any time you change these ratio's you take your Rover out of its engineered powerband) You can always "hop up" the engine to make more power without going to all the hassel of a engine swap if that is what you want. If ya don't got power (rover engine) then ya goin need gears, if ya don't got gears then ya goin need a s**t load of power !