3.5 to 3.9 INLET SWAP

[UK CRAIG]

Hello guys,

I've got a 3.5 EFI RRC, I've just bought some tubular exhaust manifolds for it, what I am now wondering is if I change the inlet manifold/plenum chamber/airflow metre to a 3.9 will this increase the airflow into the engine or not, and therefore an increase in power?

If so is the airflow metre wiring compatible or will I have to change the whole loom and ECU etc?

Any help will be greatfully accepted.

[300TDi Disco]

I have got the tubular manifolds on mine. I was thinking the same idea of changing the cam to the 3.9. I was also thinking of changing the exhaust from the manifolds to side exit's.

[hairyasswelder]

Need to change airflow, ecu, injection/ecu loom for non cat 3.9 items unless fitting lamda sensors :-k :-k

How about the cam  :D :D I been told that good for a few horses  :twisted: :twisted:

been toying with the idea  :dance: :dance:

[bogie]

From what i recall,put a 3.5 injection system on a 3.9 and you will blow it up,as with a 3.9 on a 3.5 a dought it will do it any good,incorrect fueling?

[hairyasswelder]

From what i recall,put a 3.5 injection system on a 3.9 and you will blow it up,as with a 3.9 on a 3.5 a dought it will do it any good,incorrect fueling?

????? never heard of that,,, the flapper has a manual mixture screw...

I know people that run 3.5's with 3.9 systems on, 4.6 with carbs and a 3.9 with SU carbs straight off a 3.5 and thrash the ..........ks off them  :? :?

I think it is the best combo, 3.5 has the best block and the 3.9 has the best efi system and the cam has a higher lift,

If in doubt on the fuelling use the later system with lamda sensors and it will correct itself through the emissions??

[Range Rover Blues]

The 14CU  EFi system was introduced on the 1988 RRC (along with concealed hinges) for the US market.  It was ANALOGUE and did not include lambda sensors but had the same plug and pinout as the 14CUX introduced on the 3.9 just over a year later.  Imprtantly, the 14CUx also existed on Disco 3.5 up untill about '95 IIRC.

Chipped properly the 14CUx works well on either engine, on the 4.2 and on the 4.6 (hell, I run it on a 5.0).

But it has to be chipped properly.  IN "standard" form it can re-tune to cope with perhaps a K&N filter and possibly a set of headers, no more.  THe EFi headers were far better than the carb exhaust and the 3.9 system better than the 3.5 (well bigger anyhow).

The 3.9 also had a better camshaft and this, rather than the capacity gave it the extra 15BHP.

The EFi needs rechipping to allow for the fuel map to cover the whole operating range of the engine, at above 80% tyhrottle the fuelling is different and the chip needs to know the engine is full-throttle and almost flat-out.  Sticking a 4.2 ECu into a 3.9 for example would lead to excessive fuel consumption and rich running at med throttle, wherreas running a 4.2 on a 3.9 ECU would cause limited power and lean-running at higher engine speeds.

So, exhaust-wise the 3.9 is best of the standard (it's the same pipe in the 4.2 but longer) unless you fit tubular headers, these are usually the same for both 3.5 and 3.9 engines so biggers gains can be had fitting them the 3.5s.  Note however that the late visible-hinge cars had a different gearbox crossmember and exhaust routing because of it, plus different hangers!

Inlet wise, you cannot just change the inlet. the injectors, sensors and plenum are all different, plus there are subtle changes in the cooling system.  If you retro fitted the whole hot-wire EFi, the 14CUX then you would get better engine control and possibly economy.

Fitting a better cam, or the 3.9 cam is worthwhile, as is replacing the timing chain on an otherwise standard engine.  Cam wear is often first symptomised by high fuel consumption, the retarding effect of cam wear being the culprit, stands to reason that a worn timing chain will have the same effect.

IN standard frorm the inlets are very similar, if you want to tune the inlet then better to replace the trumpets within the plenum with shorter, wider-brimmed parts and spend time on smoothing out the throttle and pipework outside the plenum.

So the exhaust is an easy upgrade, the rest of it I'd leave alone unless you want to run the hot-wire EFi rather than the flapper.  Hot wire will run in open loop (non-tuning) mode without lambdas and closed loop (self-tuning) with lambdas.  You change a resistor in the wiring loom to tell the ECU what to do.

Wiring a 14CUX Hot-Wire system into a 3.5 car is possible but it will be missing the road speed signal and gearbox signal on the auto that it needs to work properly in closed loop mode.  Without them you will get slightly higher fuel consumption, though mine runs smoothly enough.

[bogie]

well that answered his question!

[squaddie_fox]

I'm currently running a two door range rover with a 3.9 block and injection sytem, 14CUX ECU, 3.5 front end and tubular manifolds with no Cats. the rear silencer on the exhaust is looking likely to be taken out and turned into a side exit, leaving just the middle pipe for the back pressure. Once i have worked out the fuel consumption after fixing a major leak while going around left hand bends :roll: :oops: i will be changing the trumpets with slightly shortened ones and a K&N (not a cone type) filter, as i will be fitting a snorkel, but facing it backwards.


if you want to change the injection system from a 3.9 onto a 3.5 its not that difficult, but wont make much difference without also swapping over the later type air flow meter and ECU Etc.

i would just stick a cam from a 3.9 in and change the timing chain and go from there.

[craig_midz]

me personally id put ya tubular manifolds on and a 3.9 cam u can use the 3.9 injectors but the increase aint worth the hassle but changin the cam u will defo notice the difference

[UK CRAIG]

WOW...................................

Seems like a lot of info for my liitle brain to take in!!

With regard to the 3.9 cam, is it best to use a standard or a slightly modified one from Crower/Comp Cams etc?

Thanks to all for the posts.

[Range Rover Blues]

The 3.9 cam will probably give you a smooth idle with plenty of grunt and decent power.  The ECU might need chipping though.

A performance cam will be designed to develop more power by allowiing the engine to rev, frequently that may come at the cost of low down grunbt, so choose the performance cam wisely.  You will need an ECU remap.

Also, the 3.9 cam will cost you significantly less than a "hot" cam.

[dod51e]

So the exhaust is an easy upgrade, the rest of it I'd leave alone unless you want to run the hot-wire EFi rather than the flapper.  Hot wire will run in open loop (non-tuning) mode without lambdas and closed loop (self-tuning) with lambdas.  You change a resistor in the wiring loom to tell the ECU what to do.

Sorry, thread hi-jacked here a bit.  The resistor you talk about.  Where would it be hiding and what does it look like exactly.  I ask as I have a 3.9 with Cats and Lambda Engine in a non cat/Lambda loom!!!!!  Engine swap you see.  Should it be running a 14CUX ECU or the older 14CU ECU.  The car/loom is a 92 and the engine a late 93.

Cheers

[Range Rover Blues]

The 14 CU was earlier than that, it's also much bigger and not watertight, so easy to identify.
The tune select resistor is in the loom under the seat andf close to the ECU, it may be taped back.  It is sealed into a clear plastic sleeve.

The lambdas will give you the self-tuning but you don't need to keep the cats.  The timing is slightly retarded for a cat car too, though I think it may be to ciope with regular unleaded rather than 4-star, not sure.

Your best bet would be to swap the TSR, it unplugs, but also to get rid of the lambdas if you don't need them.  The engine is internally the same thing.

You will also find the ECU was re-released virtually every year with very minor tweaks, but any 14CUX will run with or without lambdas/TSR.  Some wiring looms however did not have the lambdas connections fitted as a cost-saving.


The ealry analogue 14CU wiring loom also uses a different colour code, though it uses the same pinout.  The 2 are interchangeable.