ALFAGTV6.COM

This weekend I'm going to take the last step in converting my 86 GTV6 2.5L over to Megasquirt II.I'm running S cams and have removed my AFM.I've created an ignition curve table by interpreting what others have done and said on this forum and would appreciate your advice before I move forward.I'll be "locking down" my Hall effect distributor and Megasquirt will fire my Bosch coil directly.

Murray,If I may comment here??

Very coservative full throttle timing here..A good begin point..You wont hurt anything with your figures..

Remember rotor phasing..

Thanks Barry.So by conservative you mean I'm missing out on some fun I'm running "regular" low octane but you think I could push it up a bit ?

Rotor phasing ?? Educate me please.I'm going to be taking my signal off the stock Bosch Hall sensor.

24* BTDC at WOT quite conservative. I'm at 28 with 10.5:1 pistons, CB cams and 97 RON fuel.

here is the ignition table of the original distributor...may be you can use it...

Thanks guys.
Enzo you were kind enough to post that table already.problem is I can't understand it eg:@ 1500 rpm. "upper" 10deg./30 "lower" 8 deg.???

Murray,By rotor phasing I mean the rotor will be a lttle away from the No 1 wire when the MS recieves the referance trigger-30 to 50 or 70 deg before tdc.This tells MS that an event is coming up.while its calculating fuel and ign.,the rotor is moving towrds the no1 wire.
There is a window of a certain amount of cank degrees before it fires..If you left the dizzy as is,the rotor will have moved past and away from no1 wire and will have to jump a large gap "backwards" to the wire post.

If you need pics,shout..

As Zman says,the ignition map is conservative..Im running 32 deg wot above 4300rpm.Push your 24 deg up to 28 to start off with...

The uppers and lowers are tolerances in deg. max and min.If you go for the stock settings you cannot go wrong....wrong.....wrong....hehe..
Just remeber that Alfa`s spec from Enzo is in dizzy speed..not crank speed..

Murray,By rotor phasing I mean the rotor will be a lttle away from the No 1 wire when the MS recieves the referance trigger-30 to 50 or 70 deg before tdc.This tells MS that an event is coming up.while its calculating fuel and ign.,the rotor is moving towrds the no1 wire.
There is a window of a certain amount of cank degrees before it fires..If you left the dizzy as is,the rotor will have moved past and away from no1 wire and will have to jump a large gap "backwards" to the wire post.

OK Barry so this is what is referred to as "trigger offset" in Megasquirt.Is the value (30 -70 deg.btdc) easily determined or is it a matter of trial and error ?

As Zman says,the ignition map is conservative..Im running 32 deg wot above 4300rpm.Push your 24 deg up to 28 to start off with...

Will do and should it be maintained at 28 all the way up to 7000 rpm ?

The uppers and lowers are tolerances in deg. max and min.If you go for the stock settings you cannot go wrong....wrong.....wrong....hehe..
Just remeber that Alfa`s spec from Enzo is in dizzy speed..not crank speed..

Ok so the distributor rpm =1/2 crank rpm.
why the +%/! do the tables start at 100rpm =200 crank rpm ?
and how could a tolerance of ( upper -15 deg. - lower 45 deg.) work ?
Please excuse my bozo questions

Murray,Those are minutes of a degree..so that would be referenced to zero degree`s..

Id leave things at a conservative 28deg for now..If you want,drive on the road or dyno and push timing up for max krag..(power)

Yes,This is the trigger offset..I dont know what the adjustement range is for MS,maybe Steve can tell us..

To recap,rotor must be approaching no1 wire (about 1 cm away-10mm)when the trigger event takes place..Use an el cheapo plastic protractor to measure degrees on the dizzy..I made a pionter from an old rotor..

OK back to ignition 101

Ok I missed the ( ' ) and was reading it as deg.

So referring to the AR table they give electronic ignition advance values ranging from 0deg. (for simplicities sake forget the 1/60 th of a degree) @ 200 rpm (engine rpm.) up to 12 deg. (once again simplified) @ 6000 rpm. So how do we get from there to 28 deg?
Then we have the vacuum advance/retard tables which I assume are overlayed on the electronic values ?These range from 0 -300 mmHg (0 - 50kpa) but what determines if the values in the table are added or subtracted from the electronic values.I understand that increasing values of vacuum advance the timing but what condition retards it ?

So referring to my rudimentary drawing do I have the concept of ignition offset right ?

And all along I thought I knew something about internal combustion engines

Hi Murray,

Just picked up this thread and there's some interesting stuff here!

The trigger for MS can be any number from (I think) zero to 90 crank degrees before TDC. But bear in mind the dizzy rotates at 1/2 engine speed, then your drawing would be to far advanced. The drawing definately shows it going the correct way, but too far.

The sensor in the dizzy has 6 triggers which are each 120 crank degrees apart, you want the trigger to occour roughtly half way BEFORE cyl number 1. This doesn't have to be exact as the car will start and run (badly!) with the ignition 25+ degrees off and you can alter the MS settings on the fly to dial in the exact number. For example my ignition trigger is something like 78 degrees BTDC.

Although my trigger mechanism is a little different your trigger wheel is probably similarly located on the centre spindle with a tiny metal peg lock thingy thats an interferance fit. I hope we all agree "thingy" is the correct engineering term! I just placed the trigger wheel (minus locking peg) where I wanted the trigger in relation to the terminal for cyl 1, marked it then scored and filed a new locking slot in the inside of the trigger wheel. Then reusing the same locking peg - voila, trigger now at 78 rather than 9 deg BTDC.

Once the manual part is done and you've timed the dizzy by eye and input your best guess of trigger angle into MS...... set the MS to output fixed advance corresponding to your crank pulley idle marking (mine is 9) start it up and then just alter the trigger angle in the MS software until your strobe light shows the advance at 9 (or whatever yours is). Once that's set, point the fixed advance back to your table (input -10) and your done. Hope that helps.

Also agree with Barry, very conservative WOT settings, but you've quite agressive settings right off idle, so it will probably respond well from idle, but then feel noticeably flat higher up. But that's OK, it's definately the safe way to do it.

Steve

Hi Steve.Slowly but surely I'm getting there
Yes I believe "thingy" is technically correct.
Ok so because the dizzy is spinning at 1/2 crank speed the actual 60 deg between windows becomes 120 deg.Gotcha.
The illustration above shows pretty well the relationship between the Hall sensor and the no.1 cylinder mark - I estimate 135 deg.
I have a Hall "window" that comes into the sensor field when the rotor is about 15 deg.before the no.1 mark so if that is my signal to ignite shouldn't that work ?

Hiya Steve........

Murray,If I remember correctly here,the std. Alfa hall sensor setup triggers as the trailing edge comes through the gap.So when the edge is in the middle, it will trigger..Check it out by holding the coil wire in the left hand ...joking...but do check when it fires or triggers..Theres a lot of degrees in them thar windows..... Can MS be programmed for a falling trigger edge,or a rising trigger edge??Always go for a falling edge if possible..
I know Haltech works on rising,but setting the dizzy up for one wont work for the other..

Murray, this is quite a popular post you have started. I feel like I need to upgrade to a newer injection/ignition system just so I can join in the fun.

Yes Barry and I'll make sure I'm standing with bare feet in saltwater when I do it.
Yes the distributor appears to send its signal as the open "window"approaches the sensor,as you said about half of the vane still in the sensor.
MS can be set for either leading or falling edge so I'll take your advice.

Greg in a twisted fashion that only an Alfisti could understand this is fun .I'm learning how little I really know.Right now running fuel control only and with no AFM my car is starting to to be a little nastier - the way I like it.If I was smart I'd probably stop here,but somehow I just know that that EZ-L ignition system is stealing 1 or 2 HP that I've got to go after.
I recommend this experience to anybody who is patient and methodical so I guess you better get on board