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Old 01-01-2005, 19:33   #1 (permalink)
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Question EA CPI vs MPI - What's the real difference?

First things aside, I'm well aware of the obvious differences between these setups - 2 injectors vs 6 and that neat'o intake manifold. Seriously, though, what did Ford tweak on the MPI to squeeze out those extra horses? 16% gains on power and around 8% more torque is nothing to be sneezed at, but surely that manifold alone doesn't make all the difference.

(For reference, the 3.9l CPI is a 120kw/311nm engine, while the 3.9l MPI is 139kw/338nm)

Basically, my understanding of it is as follows:
- The CPI allows better fuel/air mixing by having a longer intake pipe where the mixture is complete, rather than injecting the fuel at nearly the last minute allowing bugger all time for mixing.
- The CPI and MPI both share the same injectors and signal lines from the ECU, with the MPI firing 3 injectors at once (according to the wiring diagram I have, at least) instead of just 1. Seen as this isn't sequential injection, a higher pressure fuel system, nor different injectors, I figure the extra injectors wouldn't make any difference at all.
- The MPI setup has that kick-arse intake design, rather than an almost carby-style setup. This will surely make a difference, but 16%?
- The MPI engine is listed with a 1mm larger bore diameter. Could this be the part of it, or just a mis-print?

So what kind of trickery have Ford pulled here? I'm looking to squeeze more horses from this thing (will be going the full business later, but for now just little gains will do), and was wondering if I should source a high-flow filter assembly (either a complete after market "frying pan" replacement, or some wide plumbing over to a K&N pod where the MPI's filter normally is), or would I be better off getting myself an MPI manifold and plugging the injector openings while fitting my TBI instead of the normal throttle body assembly?

I do quite like the idea of the CPI setup, as this means better mixing and less injectors to replace if something goes wrong, or I feel like getting hi-po ones.

Any thoughts?

Cheers,
Jon.
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Old 01-01-2005, 23:58   #2 (permalink)
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Re: EA CPI vs MPI - What's the real difference?

It is easily possible to explain in my opinion.

16% difference isnt something to sneeze at, however, when you take the combination of differences between the engines, the extra power comes directly from the combinations of differences.

1. The tube length which allows proper mixing, no, thats incorrect. The air is moving at such a high velocity, and the fuel is injected at high enough pressure that suitable mixing occurs almost instantaneously.

2. I dont believe so. COnversions to MPI ive seen require new wiring looms and ECU which lends suggestion to there being a different system

3. I wouldnt call it kick arse, but it supports the first point in that, more air is supplied. this allows for a closer to stoich (spelling?) ration occur, this interns allows more power to be produced and whilst using potentially less petrol.

4. Not sure here, dont believe its a mis-print, because, Auto stores sell different gasket kits for MPI or CPI. That said, ive seen a few CPI engines that have been converted to MPI, so i cant imangine that there is to much difference, not at 1mm atleast.

The CPI setup has benefits, certainly over Carby, but the fact it has less injectors doesnt mean its cheaper. Orginally i believed that it might be the best setup to use for Gas research, but infact a snail setup from EF onwards is better. In the end, i suppose its horses for courses.
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Old 01-02-2005, 00:40   #3 (permalink)
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Re: EA CPI vs MPI - What's the real difference?

hi Thalyn

this has been a puzzling subject for me as well. now i dont really know a hell of a lot about mechanics and all, which is why i seek out help. but every mechanic i have ever talked to about doing an MPi conversion has told me its a waste of time! which confuses me becuase of all the different opinions, especially on this forum. the mechanics tell me there is no point for a few reasons:
- i would be loosing fuel efficiency due to there being 4 extra injectors
- the point you made as well, in that there are more components to go wrong, mainly injectors, and also more expencive to clean all of them or replace them
- the mechanics also tell me that, despite the numbers, there is no real world power increase to justify the conversion.

i was going to do the conversion myself, that is until i was told i would have to change over almost my entire LPG system to suit the MPi setup, and by the time it was all properly tuned, it would have parted with about $600! so the machanics i go to told me not even bother!
so this is now why i am interested in any not so over the top upgrades to the CFi system. i did like your pipe to a pod filter idea, sounds good! i was considering going a cam upgrade.
anyway, i dont know if that helps at all. but i also have nothing against the CFi accept the look of the "frying pan" (which the pod setup would probably fix!) and would love to hear of any other performance upgrades for CFi you or anyone else comes up with or has done!
good luck with your car
cheers
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Old 01-02-2005, 03:28   #4 (permalink)
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Re: EA CPI vs MPI - What's the real difference?

BargeEA - I'd be going to a different mechanic if thats the rubbish they tell you. Loosing fuel efficiency? Pfft thats crap. They don't just ram more fuel into the system, the fuel load is shared across the cylinders. So each injector is actually delivering less fuel.

I think that people on the Forum that have done the conversion will atest that there is a real world difference.

I've asked a few mechanics about the conversion. My opinion is that they generally have the "it's only an EA" mentality and make the conversion out to be this huge ordeal that makes a quad turbo look easy in comparison.

And if your chasing power then forget the CFI system, they don't allow any aggressive cams. I've heard of someone putting an ED XR cam in a CFI and got a power increase but don't know how much.

The only good thing about CFI is that it gives you plenty of room to access the oil filer.

And I know - I got a CFI.

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Old 01-02-2005, 03:45   #5 (permalink)
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Re: EA CPI vs MPI - What's the real difference?

BargeEA

If you have LPG why change to MPI anyway, since you aren't using it??? Why not change to straight gas instead and tune the car for that????
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Old 01-02-2005, 04:05   #6 (permalink)
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Re: EA CPI vs MPI - What's the real difference?

hi Dan
i do tend to agree the MPi would most likely have given me a performance increase, but like i said, i would have had to change the LPG setup, and i cant afford it. nor can i afford to just scrap it all together and run straight petrol as has been sugested either, i kinda like only having to pay $25 a week as aposed to $50 my mechanic would have done the MPi conversion for me if it wasnt for the LPG.
anyway, the cam i was thinking of putting in was a wade 1004 114, which from my understanding isnt very aggressive. but from what i read, there are a few problems with stalling after this cam is put in. (but it could have been a 112?) is the ED XR cam more or less aggressive? i'm not looking for much, just a bit sick of getting munched off the line by push bikes! i have to wait until almost 2nd gear till it even thinks about moving anywhere in a hurry! i have no initial throttle response at all! could this be my diff ratio though? i am almost 100% its a standard EB wagon diff, which if i'm not mistaken is a 3.08!
also, do u think the pipe from the carby thing to a pod filter in the air box area would work at all, or just a waste of time? it sounds interesting.
thanks mate
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Old 01-02-2005, 04:09   #7 (permalink)
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Re: EA CPI vs MPI - What's the real difference?

Quote:
Originally Posted by Epitome
BargeEA

If you have LPG why change to MPI anyway, since you aren't using it??? Why not change to straight gas instead and tune the car for that????
tune the CFi to straight gas, or convert to MPi and tune that? would tuning the CFi to straight gas make it run a bit better?
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Old 01-03-2005, 05:17   #8 (permalink)
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Re: EA CPI vs MPI - What's the real difference?

Thanks for your replies, folks. Just a few things spring to mind afterwards...

Re: the substitute computers and wiring looms, according to the Gergory's manual I have sitting right in front of me, the only differences to the engine management setup are the additional injectors (2 more on each line, making 2 groups of 3 instead of 1) and an ISC solenoid instead of an ISC motor. Now I realise that a Gregory's is hardly a substitue for a genuine Ford book, but if there were such substantial differences I figure they'd have shown them somehow (like the manual for my ZL and FE, which had extra bits all over the shop for MPI vs Carb). The fact they all run the same DAxx computers (DA89 in the case of my own) also suggests that there isn't really that many differences.

On the subject of LPG, my understand of that suggests that your mechanics are a bit daft (or just use LPG as a side-venture), as all you'd really need to update a Gen III system to accomodate MPI over CFI is a new component somewhere after the air filter element which allows the gas into the mix. Beyond that, there's an adjuster screw that can take care of just about everything else that'll need to be changed. Now if it were a Gen IV (liquid-phase injection) setup, I could understand - that'd require re-tuning the piggy-back computer, a new fuel rail, 4 more dual-fuel injectors and a few other odds and ends.

Now onto the bits I've picked up on and thought about from here...

SmokedEB mentioned the EF+ "Snail" intake manifold, which supposedly has superior design to the older manifolds. Now while I'm aware that the EF on all ran the EEC-V engine/transmission management system, would it be feasable to fit the EF intake manifold with the older injectors and ECU system? Would it be worth it? This is perhaps a bit beyond my scope at present (I imagine an EF manifold would cost more than I'm able to spend right now), but it would be interesting to know.

Also with cams, I don't think any engine much likes an aggressive cam without any kind of ECU mod. I can't figure why the CFI and MPI would be any different to each other in this situation, unless the MPI runs a higher-pressure fuel system to accompany its wider air intake. If this is the case, fitting an MPI fuel pump and/or regulator (together with a wider intake) could possibly recoup some of the power the CFI has lost to it's sibling.

Oh, and BargeEA, that pipe to pod idea came to me after seeing, time and time again, hi-po cars being fitted with mandrel piping leading into a pod at the end. Basically, my idea involves fitting an eliptical "hood" over the CFI setup into a single 3" (or larger) diameter pipe bent immediately through a right-angle, through a small length of mild-steel tubing of the same diameter into a pod filter mounted behind the passenger's headlight. While I don't know if it's a good idea, it certainly would open the intake right up. A similar setup could easily be adopted on an MPI model, and wouldn't be quite so akward as the throttle-body opening is already circular on these.


I really would be curious to hear from some of the folks here who have actually done the transition, particularly a list of what changes had to be made and, if possible, before and after dyno results and economy figures, as well as opinions on performance and drivability. My only real point of comparison really doesn't help me much, as I've only ever been in a higher output I6 with a 3-speed (and the S certainly hauls more arse than my Fairlane or LTD ever did).

Keep the thoughts coming, people. More the better, really.

Jon.
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Old 01-06-2005, 00:55   #9 (permalink)
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Re: EA CPI vs MPI - What's the real difference?

Wow. I wouldn't trust the Gregorys manual as far as I could throw it in this regard.
CFI and MPEFI are entirely different injection systems.
They run different injectors altogether.
CFI uses an injector that opens in stages. The ecu controls how much the injector opens which in turn changes the amount of fuel going into the manifold.
MPEFI uses a "normal" injector, which is just switched on or off, and the fuel pressure is controlled in a fuel rail.
Yes, CFI has runners to allow fuel/air to mix in the inlet manifold, but this is a disadvantage, not an advantage if you are talking about petrol. Fuel condensation is a major concern, which is why CFI is a heated manifold. MPEFI injects the fuel directly into the cylinder head, which allows the fuel mist to effectively go straight into the cylinder, allowing for a much more controlled mixture and therefore a much more controlled burn. That is primarily where your extra power comes from. Also, the fact that the manifold is not heated allows cooler air to enter the combustion chamber.
The way the idle is controlled is very different also. CFI uses a stepper motor which opens the actual throttle, and the ecu receives feedback on the throttle position. MPEFI uses an air-bypass solenoid mounted on top of the throttle body.
The ECUs are different because of the two above issues. A CFI ecu cannot work an MPEFI ISC solenoid, and an MPEFI ecu cannot work CFI injectors or ISC motor.
Fuel pressure is also different. CFI operates at 100 kPa, MPEFI at 200 kPa.

I did the conversion a few months ago and it is BY FAR the best thing I have ever done. Throttle response is so much better, power is really noticably better, fuel economy is about the same.

It is absolutely worth the effort to do it, there is a tutorial here: http://www.ford-tech.com/articles.php?articleId=46
Read that, and search around the forums. I don't think there is anyone that will say it's not worth it.
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