3.9 - 4.6

[Pilley]

Hi,

I am about to put a 4.6 low compression engine in my classic range and will be using the existing ancillaries and hotwire ignition.

I would be grateful for any advice regarding mods and checks etc, I am also running lpg (romano multi point)

Will i need to change fuel regulator and chip ECU?

What do you guys think of Rpi's A and R ignition module.

Any help and advice would be appreciated

Thanks Stu

[Coastcard]

Fuel reg should be OK. Air side of things should be OK. Fuel is likely to be an issue. Not likely to sort it properly with a chip in the Hotwire system.

Never thought I would say this, but... Megasquirt is your friend really for a 4.6 install. Use it for the sparks as well and will save you the RPi ignition module.

A proper chip and ignition will be £300 - a sizeable chunk towards MS. Plus, you know it will work well.

[CR88]

Fuel reg should be OK. Air side of things should be OK. Fuel is likely to be an issue. Not likely to sort it properly with a chip in the Hotwire system.

Never thought I would say this, but... Megasquirt is your friend really for a 4.6 install. Use it for the sparks as well and will save you the RPi ignition module.

A proper chip and ignition will be £300 - a sizeable chunk towards MS. Plus, you know it will work well.

The engine mounts and the gearbox are the same in 4.6 as in the 3.9.

It is possible to make a direct swap???

[Pilley]

Cheers coastguard,

I will be looking into the full cost of the megasquirt system and reading up on it,

Is this the best option for a mappable ecu and is it very difficult to set up ?

I will keep you posted on the progress and may well have a few more questions

before im done

[Ally V8]

Before getting all excited about changing everything I'd simply try it.Esp if you can scope the oxygen sensors,most systems have more capacity that are given credit for,so when running closed loop the ecu should be able to widen the pulse width of the injectors to cope with the extra swept volume.Outside of closed loop ,(ie large loads/wide throttle openings)the only way you are going to know whats going on is to add a UEGO, (wideband oxygen sensor) in each bank.Have a look at Graham Goode Racing's website for their LM1 kit - this will drive a 52mm gauge to indicate air / fuel as live data.You could use an adjustable fuel pressure reg to up petrol fuelling to get 12.5/1,(max power) and then adjust the LPG ecu to give 13/1 for propane.

The beauty of the UEGO's is that they can run all the time - no need for dyno runs,plus it will allow you to keep an eye on the gas system going out of tune.

Just an idea...........

[FridgeFreezer]

Scoping the normal lambda sensors would work for checking what's happening at high load/RPM/throttle, you want to see it going rich and staying rich. If it goes lean you're asking for trouble. Granted you won't know how rich or lean it's going, but that's a secondary concern.

The Hotwire system should run a very close approximation of what's right, being mass-airflow. However, that doesn't mean it would be actually right for the 4.6. A built MS ECU, an EDIS-8 module, and all the ignition hardware will set you back similar money to a chip with a generic fuel map on. Installation isn't tricky since you already have 95% of the loom and hardware attached to your car already. You also gain switchable ignition maps for petrol/LPG running.

You don't really need a wideband sensor per bank unless you really want to tune per bank, plus it would get expensive. The Innovate LM-1 or TechEdge are good buys and can talk directly to the MS ECU, saves buying a gauge and means you can datalog readings and auto-tune to a given air/fuel ratio map.

Mind you, with MSTweak you can get 90% of the results of a UEGO with a normal narrow-band lamda sensor.

Adjusting the fuel pressure reg to correct for the wrong fuel map? - Sorry, no.

No offence... but no.

[Ally V8]

I'll shut up then cos I know very little about efi - all I did was offer a low cost system that allows constant monitoring in real time to ensure correct fuelling under all conditions with 2 fuels wether you are after absolute power or economy.Whats wrong with adjusting the fuel pressure at the rail ? Have you ever watched a Gems equipped RR adjust its fuel trims when the reg vac pipe gets blown off after a backfire from a carp LPG tune?

I'm fed up with giving bad news to V8 owners because they are unaware of the poor fuelling,(Often on one bank) that their engine is suffering.Kill the engine on a P38 - esp an early one and you have a difficult descision,the replacement engine is more than the value of the car,with a RRC its even worse.

[Pilley]

Thanks for the info Fridge,

Will i have to change from the distributor as i already have the cam with dizzy drive fitted? Does this mean i cannot run the switchable ignition on this system.

I am using all the ancillaries off the old 1992 3.9 engine and was planning to use the old cam chain cover and replace oil and water pump

Can megasquirt still advance and retard the ignition as the ignition module from rpi does.

I will aslo have to add the lamba sensor as mine currently runs without but that is not a problem.

I am not overly concerned with performance I just want a comfortable reliable daily drive, once this is finished i will be putting the old 3.9 into something else.

Feels like like this project is still a way off, last year i replaced most of the bodywork and repainted it, the year before was head gaskets and before that the lpg conversion, the joy of owning a range rover !!!!!!

[FridgeFreezer]

Ally - As I said, no offence, but tweaking up the fuel pressure to compensate for the wrong ECU/map is not exactly optimal is it?

Pilley - You can leave the dizzy in place - it just won't do anything other than drive your oil pump. Rog very kindly modified mine for me:

You bolt the trigger wheel to the back of the crank pulley and the MS uses that to measure crank position. I too am using a 3.5/3.9 setup on a 4.6 block so we know it works

MS is fully mappable and you have two separate ignition maps, one for petrol, one for LPG so it's smarter than RPi's box which just adds a certain amount to whatever the dizzy is doing - I daresay Ian (BBC) would know more about how to tune the ignition map to take full advantage of LPG.

[Ally V8]

I agree that adjusting the fuel pressure is not ideal,but at least you can adjust it,with chipping you are stuck with its settings.When running closed loop the standard ECU will easily cope with the different capacity/raised pressure to allow proper switching of the sensors.Out of closed loop I cant see any other way but by using UEGO's of seeing whats going on,the standard oxy sensors will just flatline rich,(under wide throttle openings)but not tell you how much.For running on propane its just a simple matter of adjusting the software to give a 13/1 air /fuel ratio.The MS route is really nice and gives lots of oppertunties to improve fuelling and ignition curves - but I cant see the point unless you can prove that its set up correctly.UEGO's stay with you all the time and unlike dyno runs you can check any time you like.

[FridgeFreezer]

If you read up on how MegaTune works with narrowband O2 sensors it's:

a) Very cunning

b) Pretty reliable

c) Super handy

Long story short with narrowband O2 I can still prove that my fuel map is within a gnat's whisker of being perfect. True for the last few % a UEGO is required but since it already runs so much better than a stock or chipped ECU I'm not really bothered about finding the last couple of %.

MegaLogViewer can also do virtual dyno runs with a few bits of data plugged into it working on acceleration in a given gear, it's not as accurate as a dyno for car-to-car comparisons but for tuning one car & comparing before & after with the same constants it's pretty nifty.

[CR88]

Hi again,

I know that my doubt maybe is stupid, and I should concern this questions and issues with more detail, but I have a possible project to swap a 3.9 efi for a 4.6 efi and the mechanical suit is more important to me.

It possible to swap, in terms of mechanic fit, directly??? This in RR 3.9 efi...

[FridgeFreezer]

It possible to swap, in terms of mechanic fit, directly??? This in RR 3.9 efi...

Are you using all of the parts of the 4.6 or are you using 3.9 timing cover, pulleys, inlet manifold, heads...?

Both will fit, you need a spacer for the crank pulley if you put an earlier front cover and pulleys on and blank off the hole on the opposite side to the starter motor that holds the crank sensor.

[landmannnn]

I am not overly concerned with performance I just want a comfortable reliable daily drive, once this is finished i will be putting the old 3.9 into something else.

If you are not concerned about performance I suggest you sell the 4.6 on fleabay and get hold of a decent used 3.9 (not from fleabay though). That will put at least £500 in your pocket, and it will save the hassle.

[Pilley]

Hi Landmannnn,

The reason im using this 4.6 is because i know its good, also i would be happy to see the back of the ignition sytem that is on there.

when i looked into having the 3.9 top hat linered and reconditioned it was going to cost a bit so i went for the 4.6

I spent a zillion hours chopping out rotten bits and replacing them last year before the repaint and now i just want the best out of it on petrol and gas, plus this seems a well proven avenue and recommeded by many on here.

As for the 3.9 i have got left i will be keeping it for another project some day.

All opinions and suggestions welcome

[Bull Bar Cowboy]

If you up the fuel pressure to compensate for the larger engine size then you will run into a serious issue ………….. you will exceed the injector pressure rating and it will drip fuel ……………. This will effectively lower the pressure and cause popping in the exhaust…………std 3.9 injectors start to drip at about the mid 40’s psi…………

LPG is about 10% less efficient than petroleum (look up the calorific values) ……… that is why you get less mpg when running on gas. To get the most out of gas you will need to significantly advance the ignition as it also burns a lot slower. I would guess that an overall increase of 10 – 14 degrees would be OK ……………..rarely will you get ‘knocking’ with LPG as it has a very high octane rating.

Don’t forget that when running on gas you will need to leave the efi fuel pump running to circulate fuel through the injectors to keep them cool………..

With an engine correctly set up on petrol, there is hardly any difference between the banks ……….. I have proved this with dual O2 sensors. Even on a plug chop there is probably more difference between cylinders on the same bank than between the banks !

Poor fuelling for OEM injection is a known issue …………… apparently (allegedly) done to give good urban combined figures at 56mph ………….. and also to appease the emissions laws of other markets………….. however any 94mm bore RV8 can give rise to liner / block issues regardless of fuelling…….. its more to do with a design weakness that have been well covered in other threads on here.

Ian

[ariane44]

I changed a 4.2 for the 4.6 - direct swap without problems. All well described on RPIs site.

At first I used the old settings which worked OK. Adding a Tornado chip (what I did - or, cheaper and more flexible, Megasquirt) improves things quite a bit though.

Cheers

Carsten ;-)

[Dr W]

Was thinking of sticking one of those RPi Voltage Amps on mine as it suggests you can improve mpg by 2-3 miles?

Has anyone any experience of them?

[Hybrid_From_Hell]

Having fiddled with more than a few V8s in my time Phnaaar I can say that there is a wide selection of nonsense spoken about tunning generally and V8s often

The good news is that you engines that do have a vast amount of interchangability - ir the 3.9 and 4.6 injectors are the same ERR722 s and the fitting therefore of a Hotwire Top end to a 4.6 bottom end is not difficult, there are some minor "Arrgh" moments but nothing that isn't easily sorted, esp if the 3.9 and 4.6s are both serpentine, again if 1 (say the 3.9) is non serp and the 4.6 serp then you have to make a choice etc, but this is not a tricky switch.

Then the getting it to ru bit

Again easy, few tweaks and your there, the rweal trick is getting it to run RIGHT.

This is then ECU country. The proper way (other than MS) would be to have a EPROM Chip from mark adams, he is clever enough that if you give the spec and intended usage and a breif chat he can alter your ECU so as to have the 3.9 chip replaced and reprogrammed with the Hedgehog chip he does with a MAP that will be close enough to make you smile and be safe for the engine.

The ECU is not interchangeable with the HW syste,. the 4.6s run GEMS systems, you could fir this but its trickier than the HW system and a chip. Also decide if you wnat LAmda sensors - best not unless you need them for MOT, if not then change the tune resistor (few quid) for a NON CAT one MArk A can advise around this, this bit is plug fitting in the loom

Fuel pressure - leave it ALONE, overfuelling via raising the rail pressure will cause nothing but problems, there is nothing wring with a std 3.9HW PRV system, IMHO even rising rates are a tad snake oil on all but either the highest tune motors, or for someone who will a- know what they are doing with it and b- can get the best out of them, even then I am unconvinced often that these add much at all. Yes, JED and other increased the fuel pressures on the race engines, and yes they cause problems, but for a race engine these are livavle, and this was more on the flapper 4.5+s where the fuelling was too low generally this and the Adjustable ECU tweak was a bit of a bodge, but was cutting edge in the mid 80s

The RPI Amp, well if you want to spend loads of money for a vaerage bit of kit, there are far cheaper and far better options - do a search been discussed loads.

The key difference you will have is Cubic capacity and fuelling requirements, the MAP in the ECU is fine for starting warm up, and spark, its just going to run too weak, the chip will resolve this, even a 4.2 ECU would be too lean so either MS it or Chip it, anything else is a nasty and frankly engine risky dangerous bodge

nige

[Pilley]

Alright Nige,

How much are we talking for an eprom chip? I mean that will sort the fueling but theres still the ignition to look at. I have had a few problems with ignition components over the years and would prefere a more reliable system.

Add to that the ability to switch ignition with MS and re-map to suit any changes made in the future, wouldnt i be better off with MS and Edis anyway.

Stu

[Bull Bar Cowboy]

Alright Nige,

How much are we talking for an eprom chip? I mean that will sort the fueling but theres still the ignition to look at. I have had a few problems with ignition components over the years and would prefere a more reliable system.

Add to that the ability to switch ignition with MS and re-map to suit any changes made in the future, wouldnt i be better off with MS and Edis anyway.

Stu

Use MS & EDIS and configure it for dual switchable spark maps.......................(IIRC pin 6 to earth to select second map)

you can then set the petrol fueling correctly for the 4.6 and also have the ability to switch off the injectors and select a second spark map for lpg. The only other modfwill be to override the fuel pump shutofff when on gas.................

As for price it depends on how you do it........................ if you build the ECU from a kit then I guess you are looking at £150ish ................ fully built is more, but not a lot more...............an EDIS8 module, 2 coil packs, VR sensor, and a trigger wheel will be about £100 or so..................

Once its all installed the AFM is redundant so you wont have to worry about LPG blow backs causing damage to the AFM................

Ian

[Hybrid_From_Hell]

I am prob out of touch ( Yeah ok but you know what I mean ) when I say Chip program fit around £350 ish +/-

Well into finished MS Territory

Nige