V8 modification

Hi ! Is modifying/converting a V8 3.5 EFI engine into a 3.9 a matter of overboring and changing pistons ? What about the electronics(Air Mass Meter, ECU, throttle pot and plenum etc.,etc.)which are different ? I kow it's cheaper to buy a complete V8 3.9 EFI engine, but shipping it to Indonesia is next to impossible ! Thanks !

Hertriono Kartowisastro

Reply to
rovieman
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Bore out original liners, insert new liners and finish bore/hone to size. Needs a good engineering shop to do the work accurately enough to prevent future problems. Fit 3.9 pistons. If it's a flapper type efi system, fit an adjustable pressure regulator and set the fuel pressure to 45 psi, remove airflow meter cover and adjust flapper spring tension until correct co can be obtained with mixture screw roughly 3/4 turn out from fully in. If it's a hotwire, I *think* it's just an ecu swap, and the correct tune resistor in the harness, see rangerover factory book for resistor values etc. Badger.

Reply to
Badger

My thinking is more conservative (although I run a Discovery that started a

4.0 and now claims to be 4.6 and a 250 kW Defender) The 3.5 block is weakened by the boring and also, bigger more does more for power than torque.

I would rebuilt with 10.6 compressions Rover SD1 pistons, 3.9 cam from LR, gasflow heads, profile valves, free flow exhaust and either turn up fuel pressure or rechip. This setup will make more ponies than a 3.9 and will be reliable.

Reply to
Aubrey

Hmmm... general rule of thumb is that more cubes = more torque, you need to make considerable breathing improvements to get the power that the capacity increase is theoretically capable of producing. That is why the 4.6 produces good torque but low power for its size, compared to the 3.5, it is restricted by breathing.

Turning up fuel pressure without recalibrating the rest of the system will not give more power. See thread elsewhere about cam timings, do not be fooled about 3.9 cams, it is a 3.5 SD1 cam advanced by 2 degrees!! You may end up with slightly more power, but you will have a lot less torque at lower rpm's - where a 4x4 needs it most! BTW, what pistons would you use to achieve 10.6cr?? Highest cr SD1 piston was 9.75, P6 was available with 10.5 but a weaker piston that doesn't lend itself to higher power outputs, it also has thicker rings that cannot accept higher revs reliably, higher revs being what your suggested mods would give more power at. Badger.

Reply to
Badger

I need all the torque that I can have and will go for an overbore. Are the outside diameter of the 3.5 and 3.9 liners different ? If the original liners are thick enough to be overbored to accept the 3.9 pistons, why replace them ? There are some really good machine shops overhere. Can the bigger crankshaft of the 4.0 replace the original(for strenght reasons)? Your thoughts Badger and thanks,

Hertri> > Hi ! Is modifying/converting a V8 3.5 EFI engine into a 3.9 a

matter of

shipping it

resistor in

Reply to
rovieman

Reply to
Badger

They are not thick enough to bore, you need the new liners. If you want ultimate strength, get some "top-hat" style liners for better gasket sealing.

Yes, if you line-bore the block with caps torqued down, but then you weaken the caps, even if they have ARP studs holding them. The std 3.5 / 3.9 crank isn't noted for being failure-prone, I'd leave it alone other than balancing, and fit with ARP stud kit for reliability and clamping strength. Why not look at a big-capacity kit, such as 4.3 or 4.8 from real steel? As for fuelling it, if sticking with EFI then I think you'd need to look at a re-mapped version of the hot-wire setup from a 4.6 if going any bigger than

4.0. If sticking to 3.9 with the modded flapper type efi system as per my earlier suggestion, then fit a genuine 3.5 efi rangerover cam for max low rpm torque. Do not let anyone fool you into a carb cam or a "this one fits all, sir" camshaft. They ARE different. Get the compression up a bit would help, but remember the bolt alignment for the inlets. i'd start with 10 bolt heads and composite gaskets as a minimum spec, don't hog out the ports too much either, smaller ports have a higher gas velocity at a given valve lift/vacuum and so are better akin to producing low rpm torque, enhanced by the gas velocity's scavenge effect. Relatively small-bore tubular headers are a good help also, not big-bore as these reduce the gas velocity at lower rpm's. Badger.
Reply to
Badger

Thanks Badger ! I'll look at all your suggestions, but who makes those 'big-capacity kit' ? When you said 'remapping', do you mean to the standard 3.9 ECU or the GEM or even the THOR ? Or are they all the same ?

Hertriono

Reply to
rovieman

Thanks Badger ! I'll look at all your suggestions, but who makes those 'big-capacity kit' ? When you said 'remapping', do you mean to the standard 3.9 ECU or the GEM or even the THOR ? Or are they all the same ?

Hertriono

Reply to
rovieman

Thanks Badger ! I'll look at all your suggestions, but who makes those 'big-capacity kit' ? When you said 'remapping', do you mean to the standard 3.9 ECU or the GEM or even the THOR ? Or are they all the same ?

Hertriono

Reply to
rovieman

They are available from Real Steel who do 2 kits, 3.5 to 4.3, or 3.9 to 4.8.

01895 440505 is their telephone number, they are the supplier that I use through personal preference. Rpi no doubt do them, J.E.Motors, Oblic engineering (anyone know if oblic are still around??), V8 Developments and no doubt many others, all in the UK. When I referred to remapping, I meant the std 3.9/4.0 but the best man to talk to re. that side of things would be Mark Adams, Pharmhouse marketing, last email address I had for him was snipped-for-privacy@bjds.com , I think! Badger.
Reply to
Badger

On or around Thu, 3 Feb 2005 13:53:04 +0000 (UTC), "Badger" enlightened us thusly:

ooh, tempting. Mind, I'd need a better gearbox. I doubt this one would handle the extra go.

3.9 engine and box from a wrecker would be the best option, probably. Can the 3.5 hotwire be adjusted to run a 3.9, or does it need a full remap?
Reply to
Austin Shackles

Why not just fit the 3.9 ecu???

Reply to
Badger

On or around Thu, 3 Feb 2005 17:15:49 +0000 (UTC), "Badger" enlightened us thusly:

might not be available. Though of course would be the easy option if it was.

Reply to
Austin Shackles

You could always go for a cheap aftermarket ECU... like this one:

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more details at:
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That way you can adjust the fuelling map as often as you like and, if you wanted to go the whole hog, the ignition timing too. It's also a good way of getting rid of the air flow meter. Total cost of mine so far, including buying two new LR ignition coil packs is 230 UKP. Fuelling only would cost you around 120 quid. To my mind, having an ecu that you can map yourself with free software that allows you to change fuel and ignition in real time is the only way to go.

cheers

Dave W.

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Reply to
Dave White

On or around 03 Feb 2005 22:54:07 GMT, Dave White enlightened us thusly:

would be neat, especially if you can map the ignition timing, as would be good for the LPG. However, I'd be more likely to spend that sort of money on equivalent box for the LPG side. Don't use the petrol all that often.

Reply to
Austin Shackles

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