Turbo Mpi?
Turbo Mini Forums

The problem is getting the fuel evenly spread between each cylinder so that AFRs are equal.

This is very difficult with siamesed inlet ports.

The Rover MPi ECU was specially developed to overcome this problem and has a patent.

I have trialled Megasquirt with the Siamesed Code written by Jean Belinger.

This allows the point of injection to be mapped against RPM and MAP.

It works very well, better than a carb, but it has taken a lot of trials to find the injection timing that works.

I'm hoping that it will provide the solution. I'm sure it does, but will not make any claims to perfection until the testing is complete.

Read through the EFI section on this forum.

We may appear negative, but we do not want you to embark on a plan that appears unworkable.

Edited by Paul S on 17th Apr, 2008.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

OK,
Here's the way I understand it after 6-8 months on this forum and trying to understand a workable solution.

You can squirt the fuel in how you like, where you like, as the air gets sucked in (or blown in with a turbo) BUT, unless each cylinder gets the same (and correct) Air Fuel ratio then you will melt something on the lean ones.

If you have properly understood Marcel's link you should realise that even with a carburettor or single point injection (a long way back from the inlet valves so maximum time for fuel and air to mix) the difference in air and fuel densities in a dynamic situation along with the inlet valve overlap, means the outer cylinders run weak, by the laws of physics.
Squirt the fuel in nearer the valves (no time to mix) and you just made it worse.
Leyland/Rover's MPi appears to have got around this by staggering the timing for when the outer or inner cylinder's inlet valve was open on the siamesed port but, unless you know better, the Rover ECU is hard coded so it simply has an internal limit as to how much fuel it will squirt for the size injectors it was designed for - limit 80-90hp - so if you turbo the engine it can't put enough fuel in even if it gets the clever timing right.
None of the aftermarket systems allow different timing per cylinder, as they all assume 8 port engines...

I've probably missed a lot out there, over simplified it too much (maybe even some mistakes as I'm still relatively new to this) but, hopefully that will make you think a bit more.

Rod.

Schrödinger's cat - so which one am I ???

I agree with what you are saying, but it terms of getting the mix in there you don't really have a choice there are those two holes that spit into each cylinder so as long as the air is mixed by then it is kinda up to the head, does that make sense?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

http://www.turbominis.com/forums/index.php?p=vt&tid=171104

MPi Data link.

Wow there have been alot of good point to think about, and i think i have come up with a better plan now lol, i think at the begining when i thought this could all get done in a weekend was the wrong idea completely, so what i am going to do is buy a Mpi motor and build a test bed frame for it, build my manifold and install all the bits on it then fire it up on the bed and then i can run some tests, test a few different theory's and then if it does not work then i can just scrap the idea no harm done

Schrödinger's cat - so which one am I ???

In simple terms you could fuel your engine with an injector á la water pistol style, or even pour it in from a bucket. If you do this on a boosted engine sooner or later you will melt pistons. This is what people are trying to save you from doing, but if you don't believe us go melt some pistons for yourself and you'll see!

You know where to come if you need any help.

Glad that you took on board what we were trying to say.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

All the best with it, Paul S has done some fantastic research and you are well advised to have a good read of his threads to see what he has done and found.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Thanks alot guys!

In a nut shell this is how I see the issue:

With a carb you get a constant flow of fuel so fuel is always there when the desired inlet valve is open, however injection provides it in a short burst once (or in some cases twice) per revolution, and this won't (can't) always be when the desired inlet valve is open.

EDIT: I just realised that there was a second page after posting the above.

Edited by Rob H on 17th Apr, 2008.

You only need to look at all the aftermarket supercharger kits now available for the MPI, such as the vmax ona which i have. The injectors have to be put before the charger in order for the fuel and air to mix and prevent charge robbing. In an ideal scenario the injectors would be in the same position as in the standard manifold and the charger would run in a blow through configuration. This would open up endless tuning oppurtunities and a much easier means of intergrating an intercooler or chargecooler in to the system. The only reason this hasnt been done is down to the ECU and as already said no one has yet been able to replicate the MEMS ecu whilst allowing for more power. So that brings us back to putting the injectors before the charger and running a wet manifold set up.