An Alternative
Turbo Mini Forums

I've been costing up this Megasquirt kit, the four big injectors and a custom built intake to fit the four injectors and it seems to be getting very expensive.

As an alternative, has anyone considered using Megasquirt to improve the fuel metering capabilities of the HIF44.

As I see it, the problem with the SU is that the fuel metering is dependent on many uncontrolled variables. The amount of fuel delivered is dependant on the velocity of air over the bridge, the height of the piston, the needle size and the level of fuel in the float chamber. At the end of the day, it is a simple variable nozzle with a differential pressure across it. Fuel flows as a result but not accurately enough.

What if, instead of the fuel demand be dependant of the above, we could control the volume of fuel entering the float chamber? The system would self regulate by increasing the float chanber level to increase flow over normal and vice versa. Probably need to use a standard needle.

Is it as simple as manifolding a couple of injectors to supply fuel to the float chamber and removing the float valve. We would still need a 3 bar fuel system, else the injectors would have to be huge.

Anyway, I have all the bits to do this and hope to be testing it in a couple of months.

I will share anything I find.

Edited by Paul S on 8th May, 2006.

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."

I wont be pressurising the float chamber.

The closed loop of the megasquirt will ensure that the chamber gets as much fuel as the engine wants. The float chamber level will vary to provide fine control the mixture. The needle and jet will see whatever differential pressure is required to move the fuel into the air stream.

Presumably the costs above are based on building your own MS. I dont think I could do that. so £250 ish.

I dont like using scrap yard parts on something like this. You need everything in as new condition else if you get a problem you do not know where to look. Hence my cost estimates are a lot higher.

The cost for my solution is about £250 if you use a V2.2 MS, fabricate some fuel rails, MPi tank and pump and some bog standard injectors.

I'd be interested where you can get two 1600cc injector for £60?

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."

Axel,

The amount of fuel delivered by the carb is not dependent on the fuel level in the float chamber. It's dependent only on the pressure differential (dependant on air velocity and chamber pressure) and the size of the orifice (dependent on needle/jet size and piston position), as long as there is fuel in the chamber no matter what level.

So as Peter suggest, your best bet would be TBI but you could use your 2 injectors and the SU as the throttle body. Just remove the piston and needle and block off the holes left by the piston and jet and somehow put the injector close to the modded carb. You'll then have TBI that can be controlled by the current standard MS-1 with MSnS-extra code and has been done for different configurations both N/A and boosted.

What you save would be 2 injectors and the upgrade to MS-2. You would also not need to wait for my code to be done. But if you want to go to port injection then you could still use the SU as the throttle body and the SU manifold with injector pockets at the port (that might require some creative placement but could be done). Or you could do something like Peter and recoup some money by selling the SU, manifold and plenum (which are getting more expensive).

Regards,
Jean

http://www.jbperf.com/

Jean,

I disagree that the float chamber level is irrelevant to the amount of fuel delivered.

The actual negative pressure caused by the venturi affect of the bridge and piston is very small, hence, any slight change in the static lift will have an impact.

Ask anyone who has not set the float chamber level correctly!

If I use a standard needle, (thicker in diameter than normally required in a high performance application) then the tendency will be for the level to run higher than normal to overcome the smaller orifice.

I agree that there are simple ways of achieving fuel injection, but none other than your code will do it properly.

I can always use your system if this does not work. I have posted this idea because I want the views of you guys.

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."

Axel,

I won't argue about the fuel level effect because I'm not familiar enough with the SU's internals.

However, I think that what you're trying to do will be more difficult than TBI and not as effective. TBI will not be worse than an SU and this has been proven to work.

But I'm willing to be proven wrong and if you do go ahead with this let us know how it goes. That would be interesting.

Jean

http://www.jbperf.com/

I'm baffled as to why you would ever try such a thing ???

What would be the point ? Attempting to control the fuel level in the float bowl would be near on impossible.
And what benefits would it offer ??

Ultimately fuel is governed by the needle/jet and rate the dashpot rises anyway.

If you had suggested adding a couple of injectors, purely to supplement the carbs fuelling, then it would have made more sense.

I would think, that attempting ti "inject" fuel into the float bowl, is going to create a very unstable float level in the fuel blowl. Fuel wont exactly be entering it "smoothly" as it normally would.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Isnt the SPi an electronic carb that does what the carb does but electronicaly controlled??

Good point Mr. Sprocket, rather than going to the bother of trying to inject the float bowl, why not go along the route of trying to control the SPI throttle body (perhaps with a bigger or two injectors) with an aftermarket ecu?

What is actualy the issue with Megasquirt and the SPi. I know ed4ran tried it first with no idle control and well, that wouldnt work, i think he then tried a pwm valve but dont know how he got on with that, obviously not very well. The MSII hardware version 3 has built in facility for five wire stepper control. But then I think your going to reply that its the coding. Also noting that i presume yourself and ED were not using the injection cam. Just wondering as I intend to do some indepth reasearch and development and pointers on the stumbling blockswould be good to start