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MG MGB GT V8 Factory Originals Technical - Use of Megasquirt - quite long

While this is not an engine conversion question as such, I have seen detailed Megasquirt comments on this section before so I thought it would be a good place to start.

I would like to use MegaSquirt to control ignition only as I want to retain the distributor and coil but not the points. The mechanical and vacuum advance retard of the distributor will be locked.

In the early days of MS you used to be able to convert it to MegaSpark. That does not seen to be what people do these days. Perhaps this is because they go for MegaJolt instead. So I am now considering using the current MegaSquirt II, but only its ignition features

The main megasquirt site, http://www.bgsoflex.com/megasquirt.html , says the following:-

“MegaSquirt-II, in conjunction with a V3 main board, can control a single coil directly (it still needs a distributor, unless you have a 1 cylinder engine). The high current circuit uses the VB921 dedicated coil driver IC, which limits coil current to about 7 Amps.”

The questions:-

1) Is there any reason why MegaSquirt II can’t be used for ignition only?
2) While their web site says the V3 board, can the V2.2 board be used with MegaSquirt II in the same way? If so des that mean that miniMegaSquirt, which I understand is V2.2 based can be used with MegaSquirt II in the same way?
3) Is the 7 amp limit a problem for 4 cylinder engine MGB using a traditional coil?
4) While I would not be using it to control fuelling, I assume I could still use its connection to a lambda sensor to observe the air fuel ratio?
5) I see reference to different types of ignition sensor. My current, rather old, electronic ignition uses a 2 wire sensor in the distributor where the points would be with a plastic collar over the cam. The plastic collar has 4 vertical metal bars equally spaced around it. Does any one know what the correct description of that type of sensor is? Will MegaSquirt II take that type of signal or will I have to change to 36-1?

Thanks in advance

David
David Witham

David, to answer your questions specifically:

1) Is there any reason why MegaSquirt II can’t be used for ignition only?

No reason other than price.

2) While their web site says the V3 board, can the V2.2 board be used with MegaSquirt II in the same way? If so des that mean that miniMegaSquirt, which I understand is V2.2 based can be used with MegaSquirt II in the same way?

Yes it can, I'm doing it. Haven't used the uS though so I can't say specifically.

3) Is the 7 amp limit a problem for 4 cylinder engine MGB using a traditional coil?

No problem there.

4) While I would not be using it to control fuelling, I assume I could still use its connection to a lambda sensor to observe the air fuel ratio?

You are quite correct, and more besides.

5) I see reference to different types of ignition sensor. My current, rather old, electronic ignition uses a 2 wire sensor in the distributor where the points would be with a plastic collar over the cam. The plastic collar has 4 vertical metal bars equally spaced around it. Does any one know what the correct description of that type of sensor is? Will MegaSquirt II take that type of signal or will I have to change to 36-1?

Your module sounds like a Pertronics Ignitor. It will work just fine.

Further recommendations, if there is any chance whatsoever of injectors in your future you should go to the v3.0 board. Current development work is centered around that board and will remain so until it is seen as having enough limitations to warrant a new revision. By contrast, development work for the v2.2 board has all but halted. There are still issues with that board which have never been worked out to everyone's (or at least my) satisfaction and they probably never will be. The probability is that your application will not be effected (the statistical liklihood is quite low, some would say impossible for what you have in mind) but the v3.0 has such greatly expanded capabilities that the choice should be an easy one. At some point in the future the UltraMegaSquirt board will be produced but the v3 board is so good that may not be for 2-3 years or even more.

It is the current state of the art in every way.

Jim
Jim Blackwood

Thanks Jim.

My existing sensor is from a Mobelec Magnum system rather than Pertronics and is 25 years old.

I assume UltraMegaSquirt will have sequential injection for a flat 16 engine!

I understand why you favour the V3 board. However, V2.2 ones come up on ebay at lower prices. From the point of view of what I want to do at the moment I think the main difference between them is that V3 will directly drive the coil but V2.2 will need an amplifier unit.
David Witham

David,

Sorry I am not addressing your specific questions but asking.

Why not use a pertronix Ignitor with a good distributor? For all the hassle your about to take on, the benifit is next to zero.

You do not address which motor you are running but that makes little difference. They all have the same problems generically.

One issue is timing chain slop/give/movement. Another is distributor shaft wear, gear wear, free play/back lash. Backlash in and of itself should be enough to say that using the stock distributor is not worth it if going through the hassle of manufacturing a wiring harness and programming a computer. A simple trigger device on the crank pulley eliminates these issues and will give you much higher precision. This is used with a set of coils- a DIS system. Over in the UK, there have been many plans for these kinds of retrofits as well as a company in the USA called Electromotive.

If only trying to control spark and get more precise timing with a computer, this does not give 100% compensation for all this normal wear and backlash. From my experience, you may be wasting time. At best, your only going to have something to change once or twice that could have been done with a pertronix and sending the distributor in to someone else or having it done on a dyno/rolling road.

-BMC.
BMC Brian McCullough

Brian makes a good point. With a fairly simple crank trigger, a readily available EDIS module and a coil pack or two your ignition is in business and only needs an advance signal from the MS. Not sure about prices there but here you can pick up a module and coil pack (or 2) for a hundred bucks or less. Sometimes much less, and junkyard parts are usually just fine. The VR pickup is about $15 new and a 36-1 trigger wheel is about the same. Denis (supercharger forum) had a novel mounting arrangement for the B series engine, and the MS can compensate for misalignment from TDC. That way you eliminate all the wear and stretch issues.

Jim
Jim Blackwood

Using the spark control of MegaSquirt will allow me to play with the advance curve which I could not do if I used petronix. I am not intending to use a worn out distributor.

I do a small amount of motor sport in the standard class. A change to wasted spark coil packs and no distributor would break the rules. Also retaining the distributor will provide an appearance of originality.
David Witham

I understand your reasoning but I think the time and money spent to do this is not worth the cost of having the distributor curved properly and if it needs to be changed later, you can add or subract advance and if you order a few differnt springs for it, you can change how fast the advance comes on. This is all done mechanically but it really goes pretty fast compared to computer programming and installation of the system your talking about. The only thing you will gain is removing the vacuum and mechanical advance which could possibly become a problem many years from now if its never maintained but this is minimal time spent. Also, you can remove the vacuum advance from the distributor, you can change the mechanical to take some of this function. If you go with a big cam and a vacuum sensor to wire into the MS system, you really will not have any benifits anyways. I am seeing minor benifits only from what your talking about, but the time and money spent are better on a recurved distributor and for you to learn how to drive a little better. Even if you picked up 2 BHP which I believe is doubtful over a good distributor system with a single coil compared to your MS controlled distributor system with a single coil- a better driver will be 1-2 seconds faster then you even on a small autocross or road race course.


I know we here on the conversions section are not quite the Nay sayers and I am breaking that among us but think its not worth it... That completly said, I think something like a pertronix in a distributor that has a controller on it such as the MS for only ignition and not FI would work fine. Why not? I have heard of other stock ECU's are used on motors that are converted to carb and the fuel system is just removed.

-BMC.
BMC Brian McCullough

This thread was discussed between 26/02/2007 and 27/02/2007

MG MGB GT V8 Factory Originals Technical index

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