Best ignition setup to run

[TurboBob]

.........
I'm still a little unclear about why 2 step rev limiting doesn't work with the stock setup. Where is the sync being lost and why?

think of it this way.

the coil pack is a sequencer and charges and fires the coils one after another in response to the EST signal from the ECM

When the EST signal goes from 0 volts to 5 volts, the ignition module begins charging a coil. When the signal drops from 5v to 0v it fires that coil. On the next pulse it does the same to the next one.

A 2 step prevents some pulses from getting from the ECM to the ignition module

When this pulse is not received, the ignition module does not generate that spark, but also does not know to advance a coil.

so when that pulse is dropped, the coil module is then one cylinder behind in the firing order...... until the next cam sensor pulse is received and the sync order is corrected.

is that any clearer?

Bob

 

[Alky V6]

think of it this way.

the coil pack is a sequencer and charges and fires the coils one after another in response to the EST signal from the ECM

When the EST signal goes from 0 volts to 5 volts, the ignition module begins charging a coil. When the signal drops from 5v to 0v it fires that coil. On the next pulse it does the same to the next one.

A 2 step prevents some pulses from getting from the ECM to the ignition module

When this pulse is not received, the ignition module does not generate that spark, but also does not know to advance a coil.

so when that pulse is dropped, the coil module is then one cylinder behind in the firing order...... until the next cam sensor pulse is received and the sync order is corrected.

is that any clearer?

Bob

Holy cow. If that's the case, I wouldn't dare try to 2 step with that system. That's just asking for a hole somewhere.

 

[THE WRAITH]

ok, so for a guy that has ams, xfi, and doesnt want to go to a distributor to run a two step without beating on the bottom end, they would buy what system and what is removed? links appreciated.... you guys have me really interested in this, of course we are talking about a car with air conditioning and hardly any room under the hood.

Car currently has stock coil pack and module! And I like the idea of the 2-step so I am curious!

Great Thread!!!!!!!!!!!!!

 

[TurboBob]

Holy cow. If that's the case, I wouldn't dare try to 2 step with that system. That's just asking for a hole somewhere.

It doesn't work very well, for sure.



Bob

 

[quickt]

ok, so for a guy that has ams, xfi, and doesnt want to go to a distributor to run a two step without beating on the bottom end, they would buy what system and what is removed? links appreciated.... you guys have me really interested in this, of course we are talking about a car with air conditioning and hardly any room under the hood.

Car currently has stock coil pack and module! And I like the idea of the 2-step so I am curious!

Great Thread!!!!!!!!!!!!!

MSD Dis4 would be the easiest. The Accel ICM would require individual coil or Coil on plug.

 

[Alky V6]

What is the reliability like with the MSD dis4?

 

[quickt]

What is the reliability like with the MSD dis4?

Worked good for me but others say they had issues.

 

[Alky V6]

Worked good for me but others say they had issues.

I thought I recalled some having problems with the unit.

 

[TurboTR]

If you have a FAST or DFI (or?) with delayed spark, it's not as bad as it sounds to say it has only 3 pulses per rev, vs say a 60-2 pulses per rev. If you set the crank position pulses to occur at say, 50 deg BTDC (as is commonly done), and you want a spark to occur at say, 30 deg BTDC, then there's only a 20 deg rotation delay between crank pulse in and spark pulse out. And at the point of spark, the current engine rpm data is only 20 deg old by then as well. Seems that's fundamentally reasonably accurate. A 60 tooth wheel gets 1 pulse every 6 deg. Ok, then the 60-2 has 2 extra pulses inserted vs the above scenario and could have a max angle between crank pulse in vs spark pulse out of 6 deg (rather than 20 deg per above), so it seems it would tend to be a bit more accurate. But maybe not radically so.

One reason mfgrs went to higher tooth crank wheels is, with OBD2 they were also then forced to detect engine misfires by law. They had to detect them because misfires affect emissions and catalysts. They generally do this by tracking and detecting (missing) crankshaft harmonics, and to do that you generally need more than 3 pulses per rev. And it's compute intensive.

The Tec manual says to run a small plug gap with boosted cars. On the order of < 0.025" if I recall. They want this small gap to help limit the amplitude of the secondary voltage under full load. Some see that spec as a sign of ignition "weakness" and are disappointed.

It'd be nice to have say, +/- 0.25 deg spark accuracy at all times (if you actually could). But also consider that there is a large amount of cycle to cycle variation in an engine (not related to spark timing), where each firing event is not the same as any other. One event makes higher pressure (it maybe needed less advance), the next event makes less pressure (it could have used more advance), etc. This can all be easily seen on a cylinder pressure trace machine. The variability at wot is generally hundreds of peak psi, cycle to cycle. A super spec ignition accuracy does not really help that situation. Of course a wildly innacurate ignition could contribute to it.

TurboTR

 

[Alky V6]

The Tec manual says to run a small plug gap with boosted cars. On the order of < 0.025" if I recall. They want this small gap to help limit the amplitude of the secondary voltage under full load. Some see that spec as a sign of ignition "weakness" and are disappointed.

TurboTR

You really need to explain this a little better to give the novice ignition person a correct sense for the plug gap suggestion given by Electromotive.

I must say that I feel ignition accuracy is very important in a very high output engine. And any V6 engine putting out over 500 hp is a very high output engine in my book.
Considering, many that run their tuneup on the edge will hopefully have their timing backed off 2 degrees as a safety margin, Isn't it entirely possible to see at least +/- 5 degrees of variance from target with the accuracy of a 3 pulse per revolution system?

 

[TurboTR]

Yes, totally agree on wanting an accurate ignition. Personally I'd be shocked to see the actual spark off by 5 deg from commanded during a full load acceleration pull, but have not looked into it much either. If it were in fact that bad, I'd want to fix it too. Don't think it is that bad, but we have programmable pattern and signal generators at work; maybe can hook up the 1st gen FAST box while it's out of the car and try to look into it and see what it actually does under acceleration.


From TEC's XDI-2 Users Guide.pdf:
...
-The load at which a spark plug fails is different for all spark plugs. With the XDI-2’s charging circuit, the more load you put on an engine, the more voltage will be applied to the plug. This is a beneficial situation: for a high compression engine, the voltage at the plug will be inherently higher (since there is more load). The detriment is that spark plugs and wires are only rated to a certain voltage (30-40,000 volts is typical), and can begin to “blow out” at around 40,000 volts. If that voltage is exceeded by a large amount for a long enough length of time, the spark plugs will either blow out, break down or arc to somewhere other than the electrode (often through the insulator directly to the engine block).

-The solution is to run smaller plug gaps on high-compression engines. This is perfectly acceptable with our ignition charging method, since the high load of the cylinder pressure will allow the voltage to be quite high at the electrode, but the small gap will keep the plug from seeing an over-voltage situation. Use the recommendations below as a guideline for spark plug gaps:
• Stock Street Engine 0.045”-0.060” (1.1mm-1.5mm)
• High Performance Street 0.030”-0.035” (.75mm-.9mm)
• Alcohol High Compression 0.025” (0.65mm)
• High Power 75 -115 HP per Cylinder 0.025” (0.65mm)
• Over 115 HP per Cylinder 0.022” (0.55mm)
• Over 12:1 CR or Over 14psi Boost 0.022” (0.55mm)


Basically they're saying, if you run a wide gap with a highly boosted engine you'll also be raising the voltage required to ionize that gap (start the arc). The secondary system (plug wires, plug, etc) can only take so much voltage before it breaks down somewhere. So control the output voltage somewhat by running a smaller gap to try and keep the voltage down below that secondary breakdown limit.

I'd been running a 0.022" gap with the stock CCCI with full boost (30+ psi) + nitrous. It worked ok as long as the plugs are pretty fresh. But didn't rev it to 8000 rpm either. It would start to pop some down the track when it was time to change plugs. Fresh plugs in and joila, back to smooth running. Not the best race ignition setup in the world by any stretch, but it can work.

It wasn't all CCCI fault either- running 160 lb inj on the street with C16 fuel, along with cooler plugs tends to be kinda hard on those plugs IME.

TurboTR

 

[Alky V6]

Very good post, Todd.

With the old plugs I was using, I also ran .022". I switched to a new plug with a radical cut back of the ground electrode. It's hard to get the gap below .033" and keep sharp edge to sharp edge, so I've pretty much settled on using .033". So far, everything is working good, even with my old set of 10mm Magnecors.

Lonnie has checked the timing scatter on various systems, and I can't remember the exact numbers but it would surprise you. It was more than I thought it would be. When we talked about it, I remember asking him who it was that was standing by the engine with the timing light at those rpms.

 

[charlief1]

I knew there was a reason I decided to watch this thread. Good info guys.

 

[SS/GN]

Msd?

The MSD type system part#62152 Dis 4 and part#8878interface module and harness.How does this compare to the accell or fast type systems.Thanks for the input,I am new to the Turbo buick and this is a great forum :biggrin:

 

[quickt]

Lonnie has checked the timing scatter on various systems, and I can't remember the exact numbers but it would surprise you. It was more than I thought it would be. When we talked about it, I remember asking him who it was that was standing by the engine with the timing light at those rpms.

It was 5-7 degrees on an average. You would see it go more than that. The crazy part is you only see number cyl.1 with a timing light. The scope shows other cylinders that would scatter when number 1 was on the money.

 

[quickt]

The MSD type system part#62152 Dis 4 and part#8878interface module and harness.How does this compare to the accell or fast type systems.Thanks for the input,I am new to the Turbo buick and this is a great forum :biggrin:

The C3I is a stand alone system. Scatter is a crank trigger function so it would be the same with stock ecu or aftermarket ecu. The DIS4 worked flawless on my car.

 

[SS/GN]

The C3I is a stand alone system. Scatter is a crank trigger function so it would be the same with stock ecu or aftermarket ecu. The DIS4 worked flawless on my car.

How fast did you take this system and why change?

 

[quickt]

10.0s 138 mph. I never changed my car. Sold the engine and put the car in storage.

 

[TurboTR]

Wish I had more details on the spark scatter issues you found. Is there a link to an old post?

Don't know any details, but I know that sometimes there are polarity issues with driving an external MSD box for example. Sometimes the external MSD spark box gets driven by the wrong polarity trigger signal from an aftermarket ECU, which could lead to alot of uncertainty/jitter as to where it actually triggers. It's possible, because EST and "points" triggers generally have opposite polarity. But either one could make an MSD box spark.

Again dunno, just wondering out loud on some possibilities. Maybe it is just that "broken", as quickt says. Really want to rig up some bench testing now And hopefully learn some useful things.

As Bob said earlier, running a distributor with no points (or crank trigger) in it eliminates the distributor as a source of spark scatter. It would spark in the same place as a CCCI module basically, that is, where the ECU tells the external MSD box to spark.

For grins, found an old vid clip of an early 4.5L S2 mill/GN1's test pass on the turbo. Just rolling it out and touring the countryside basically- no drama, typical Buick street car No loud car next to it, so can hear the engine pulling clean all the way through with the stock CCCI ignition (and clean plugs lol)

http://www.youtube.com/watch?v=ITR9J6GrR5A

(The Pacemaker intro storyboard is false).

TurboTR

 

[Rell87]

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