3.5 > 3.9

[jjsaul]

If i want to change a 3.5EFi to a 3.9EFi...what do i need to change?

I know i need to change the front part of the exhaust, and the gbox crossmember...what else needs modifying?
I will be fitting LPG as well.

Cheers

James

[Guardian.]

the engine? :roll:

[datalas]

your signature too :D

[hairyasswelder]

If i want to change a 3.5EFi to a 3.9EFi...what do i need to change?

I know i need to change the front part of the exhaust, and the gbox crossmember...what else needs modifying?
I will be fitting LPG as well.

Cheers

James

ECU, wiring, rad, expansion tank,

WHY????? The 3.5 is a better motor, rarely slips a liner and approx 8% power gain is not really noticable

Steve

[jjsaul]

cheers steve

i think im going 3.5 now anyway due to cheap engine coming my way...was just exploring all options!  :)

see my thread 'ooops i killed it' and you will see why i need an engine!

[hairyasswelder]

cheers steve

see my thread 'ooops i killed it' and you will see why i need an engine!

Saw the thread  :shock: bit of a mess  8)  and the offer of the low milage engine  :D sounds a good deal

Steve

[Range Rover Blues]

The big gains (I'm not sure about the 8%, that's about 5 BHP) comes not from the capacity as much as from the camshaft and exhaust.

The 3.9 is simply a bigger bore, with the same EFi headers, but as you will have noticed it is routed differently around the gearbox crossmember (which is different).

I have gone back to a 3.5 sports pipe (same bore as the factory 3.9 pipe) and 3.5 crossmember to protect it a little more anyway.  The chassis hangers are differetn on the 2 exhausts :roll:

The big difference in UK market is the hot wire EFi as opposed to the flapper.

Hot wire would work on the 3.5 just as well, if not better.  The late 3.5 were hot wirem but it's an early version and I've only ever seen 1.

Oh, oil cooler as standard on the 3.9, so new radiator, and the Borg-Warner T-Box has a slightly different ratio.

[hairyasswelder]

(I'm not sure about the 8%, that's about 5 BHP)

5bhp???? that would make it around 65 bhp total :oops:

3.5 V8 (88.9x71.1)165 bhp @ 4000rpm
3.9 V8 (94.0x74.1)181 bhp @ 4750rpm

Maybe 10% then  :roll:  but the gain would be less if not using the hotwire system,
If using the hotwire system the wiring and ECU (14CUX) need to be changed, not an afternoon job  :(

The early Disco's used 3.5 with hotwire but dont know output on this set up (still need 14CUX ECU)

The issue I would have is the wiring, must be 30+ wires.
You would need to buy a complete RR 3.9 very cheap (good engines fetch GOOD money) and transfer a hell of a lot of stuff.

Take the low milage motor, drop it in and go.

my opinion is to Forget the 3.9, too much money, trouble and too little gain.

For the money, use a 3.5, upgrade the cam and heads if you really need the extra horses then you

Just dont put a diesel engine in it  :lol:  :lol:  :lol:  :lol:

Steve

[jjsaul]

For the money, use a 3.5, upgrade the cam and heads if you really need the extra horses then you

Just dont put a diesel engine in it  :lol:  :lol:  :lol:  :lol:

Steve

will probably do that in the future...just gonna fit a carbed 3.5 for the time being as a cheap fix.

as for diesels  :? eurgh no thanks  :twisted:

[Range Rover Blues]

Even with the carbs it's worth fitting an EFi engine, or at least the heads/exhaust.  The EFi only really adds reliability.

The hot -wire system is easy to fit if you get the wiring loom with it, without it I wouldn't bother.

[hairyasswelder]

Even with the carbs it's worth fitting an EFi engine, or at least the heads/exhaust.  The EFi only really adds reliability.

The hot -wire system is easy to fit if you get the wiring loom with it, without it I wouldn't bother.

The EFI cam will give it a little help too I think  :D

As for reliability, is there that much of a gain against early flapper system with LPG or is it just 6 of one 1/2 dozen of other??  I know the hotwire is better but with all the mods etc. (old ground)

Steve

[Range Rover Blues]

Even with the carbs it's worth fitting an EFi engine, or at least the heads/exhaust.  The EFi only really adds reliability.

The hot -wire system is easy to fit if you get the wiring loom with it, without it I wouldn't bother.

The EFI cam will give it a little help too I think  :D

As for reliability, is there that much of a gain against early flapper system with LPG or is it just 6 of one 1/2 dozen of other??  I know the hotwire is better but with all the mods etc. (old ground)

Steve

 #-o  Yes, the EFi heads, cam and manifold/downpipe make the difference, rather than the EFi itself.  Personally I wouldn't touch the flapper system to retro fit, parts are too hard to come by and they do let you down.  The Hot-Wire is much better and safer to gas up, unless you go multi point and that's a whole new topic.

[hairyasswelder]

MMMMmmm multipoint LPG.....  :roll:  second ECU drilled manifolds, lamda sensors, laptop and software to set up and major financial strain  :roll:

Bloody goood system if set up right though   need to put some miles on it to repay the outlay, not sure if that good or bad  :?

Steve

[Range Rover Blues]

Well it's a whole new can of worms isn't it? for driveability you can't beat a multi point but it's not as economical (or doesn't appear to be).  It's more tuneable, more reliable and doesn't restrict your pwtrol power the way that cheap single point systems do.

But mine cost £1250 with a spare-wheel tank.  When Blue goes 4.6 it'l need another LPG system, I'd like to go multi point but for th emiles I drive it now, I might stay petrol.

[hairyasswelder]

mate of mine had a 4.6 HSE on single point, that I used to drive when we went pub, The reason I bought RR.  It was 'ok' but when you wanted power you needed to switch to petrol for the full power.
We upgraded it to multipoint after blowback damaging airflow and airbox.
Cost him around £650 but it went like it should  :lol: and was still worthwhile for savings
The tank, pipes etc were already there so not replaced  
Vertical toriadoral tanks are around the £300 mark.
Cant remember if we changed the vaporisor  :oops: but dont think we did
This was a few years ago now so it might still be worth a look on just 'upgrading' the system??

Steve

[Range Rover Blues]

TBH when the new engine goes in the LPG will get binned, it's running badly at the oment.  Whether I bother fitting another sytem or not depends on how much I use the car.

[jjsaul]

TBH when the new engine goes in the LPG will get binned, it's running badly at the oment.  Whether I bother fitting another sytem or not depends on how much I use the car.

is it a multipoint systemyou will be getting rid of?

[Range Rover Blues]

There's optimism, no JJ it's the old draw-through that's on Blue.  Whether I can justify the £1250 for the multipoint like on the LSE depends on the mileage I do, though I'd like to put LPG on it certainly.