Originally Posted by jwscab

that's really only the case when using corvette BCC's right? other than the $32 in 85' in camaros and 'birds, they all used the small cap dist as far as I know for $32b and $6e

great detective work, BTW....

Originally Posted by RBob

Have some interesting information to add this this thread.

First item to note is that in the opening post of this thread, the table shown as for AUJP is not. It is the latency table used for AXCN & ANHT. Which are Corvette large cap distributors. The poster in the thread that liquidH8 linked switched the two tables in his post.

AUJP uses table 2 in the following:


I have been able to identify two different ignition modules for the small cap distributors. They are the 048 and the 369. Check out the picture of the modules. It is the first 3 digits.

I ran 2 each of the 048 & 369 along with a Holley module through some tests. This was done on a live engine using a marked balancer, timing light, and the What's Up Display to show the commanded SA timing and the engine RPM. The EBL Flash had 5 calibrations banks set up for testing.

Bank 0 was the stock calibration to start up the engine and let it settle in.

The other four banks all had the main & extended timing tables set to 20 BTDC. Temperature comp, PE, launch mode, and whatever else was zero'd out.

Then each of the four banks had different latency tables. Banks 1 & 2 had the two tables shown above. Then banks 3 & 4 had the same tables with the low RPM latency values of 0 filled in with the first value greater then 0 from above it.


The reason for this was that it was found that the at-crank timing dropped off with the stock table values of 0. The was still latency at the low RPM's that needed to be accounted for.

With this change running the RPM from 800 through 3200 had each module with the appropriate table holding a steady SA. Switch the table and the advance moved around as the RPM changed.

The Holley module (part # 891-103) matched table 2. This was from 800 through 3200 RPM. Did not test past this RPM.

You may be thinking that 3200 is a low RPM. However, look at the engines/vehicles the ignition modes are used in. None of these engines are high RPM. Trucks, Vans, TBI 3rd gens, Caprices, Wagons, even the TPI engines aren't high RPM engines. Note what happens in the following tests. . .



Another test: while checking the timing as the RPM was increased, both the 048 & 369 modules held steady until a particular RPM. This was with 048 & table 1, then 369 with table 2.

The 048 module, it held steady timing until about 3800 RPM where it retarded 4 degrees. Then by 5000 RPM the retard had increased to 6 degrees.

The 369 module, it held steady timing until about 3200 where it gained 2 degrees of advance. This held steady to 5000 RPM, which is the highest RPM it was checked at.


If we could get a sampling of the ignition module in various 3rd gen engines it would be helpful. Under the cap check the 3 digit number and post back. Along with whether it is TPI or TBI. If you know the stock BCC that too would be helpful.

Conjecture:

I know that the latest f-body TBI calibrations use table 2. This matches module 369. Same as the AUJP TPI calibration. I wonder if the 048 modules are for performance limiting, and are set up to limit the engine RPM. With the timing retarded, the power drops off, and most people either up-shift or lift.

Where the 369 modules (the ones I have are from 5.7l full size vans) are more performance oriented. What is interesting is that the 369 modules I have are newer then the 048's. Some even look to be replacements (too new for the age of the vehicle). Maybe a GM upgrade?

RBob.

Originally Posted by junkcltr

I was looking through the MAF $6E and the MAP $8D code the other day. I noticed that the coil dwell time appeared to be different. It looks like doing the MAF to MAP ECM swap using the stock MAF dizzy (large cap coil) will not charge (dwell) the coil long enough to saturate / charge it fully.

One more anomaly of doing a MAF to MAP ECM swap.

Originally Posted by junkcltr

anesthes,
I was refering to the AUJP code. People seem to mostly use the AUJP code when doing the 165 ECM to 730 ECM swap. Not sure about the $60 code. I was told that the $60 was an abandoned project and no one was working it.

Originally Posted by anesthes

It is. I'm on the fence. I don't want to buy another map sensor to try the $59 project, but at the same time I'm disgusted with $58/$60. And at even only 6psi boost, I'm afraid if I run $8D and try to add boost fuel with PE it may risk a failure.

But dwell time on the coil isn't really something I had considered in the past, and I wonder what the $58/$60 dwell stuff is like vs what a large cap dizzy code would be. I imagine a sy/ty would be a small cap remote coil..

-- Joe

Originally Posted by junkcltr

I am not sure how the $59 code maps the MAP sensor. In the BAUJP I made it so the MAP sensor conversion table is a table that is in the XDF and can be reprogrammable for any map sensor. The end user uses a vacuum gauge and small air compressor and plots out the MAP sensor vacuum/boost vs output volts. This goes into the table using the XDF. So, any MAP sensor can be used. Hopefully, the $59 code is like this.

Do not run the $8D with boost. You can fudge the fuel with PE, but there isn't anything that can be done with spark. HHhhmm, I never looked what would happen with the stock $8D and (small) negative PE spark values......do the two's comp. turn into big positive values?

Actually, with a supercharger at 6 PSI using PE fuel and the RPM spark tables wouldn't be "that bad" if starting out on the conservative side. My "don't run $8D with boost" probably comes from my last tuning project with a truck that would make 8PSI of boost (turbo) at 2800 RPM with 25% throttle. $8D would NEVER work with that setup.

Originally Posted by anesthes

Well I've never taken advantage of the extended spark tables on any of the 2-bar masks. I've always locked my advance in to the max I planned on running. Say for example, I could get away with 25 degrees at 10psi, but only 20 degrees at 15psi. I found the combos ran faster without hickups if I just locked in 20 degrees by 3k. When I tried retarding as boost went up it almost always lead to problems.

Originally Posted by anesthes

6psi is at like 6,000 RPM with my powerdyne. It really is a little blower. I was playing yesterday and only got the needle to dance a little into boost (1-2psi) at around 3k in 2nd gear. Same blower might get like 10psi on a small stock 302 but on my 358 with good heads and miniram it doesn't seem to make much boost.
-- Joe

Originally Posted by junkcltr

I was looking through the MAF $6E and the MAP $8D code the other day. I noticed that the coil dwell time appeared to be different. It looks like doing the MAF to MAP ECM swap using the stock MAF dizzy (large cap coil) will not charge (dwell) the coil long enough to saturate / charge it fully.

One more anomaly of doing a MAF to MAP ECM swap.

Originally Posted by junkcltr

I wish I new exactly. I would post the difference, but I am still investigating at this point. It looks like the small cap uses a shorter dwell time but I can't say for 100% right yet. I figure I would post it in case any one else was playing with $8D spark stuff.

If the small cap shorter dwell time is true then it would also lead to "nosing over" at higher RPM like the module spark latency thing you found with one dizzy module.

Originally Posted by anesthes

I think AXCN is a commented $8D corvette hac, I wonder what the numbers look like compared to AUJP and the earlier MAF code?

-- Joe

Originally Posted by RBob

I don't see any differences between ARAP [$6E], AUJP [$8D], AXCN [$8D], & ANLU [$61].

RBob.

Originally Posted by junkcltr

An interesting tidbit from the Megasquirt.info site

"For example, the older 7-pin HEI coil uses 3.5 milliseconds dwell, the newer 8-pin HEI external coil uses 2.5 milliseconds of dwell. Note that times longer than 4.0 milliseconds would mean the dwell is being reduced at as little as 2500 rpm, meaning longer dwell settings won't make the spark 'hotter'."

I can't find the source where they did the small cap external coil testing.

Originally Posted by junkcltr

Over the years the push has been to make coils that charge faster due to higher revving engines. A typical large cap wants 3.45msec to charge. A V8 at 6000 RPM only allows 2.5 msec charge time. The small cap coil at 2.5msec seems like a better fit. Aftermarket coils usually have a lower resistance to charge faster. Of course, more heat is made in the coil.

Originally Posted by RBob

Coil charge time is determined by the inductance, not the resistance. Or more accurately by the reactance of the coil windings. Which also defines how quickly the energy is delivered to the spark plug.

Note that the ECM calculation includes a dynamic dwell calculation. They just don't dwell the coil as long as possible all of the time.

For the higher rev'ing engines GM's answer is CnP setups.

RBob.

Originally Posted by junkcltr

We both know the charge time is from the inductance AND resistance of the coil. Yes, both the reactance of the winding (jwL) and the resistance of the wire itself. All trivial electronics. As for the energy delivered to the plug...we both know it is a lot more than the coil (rotor/cap spark gap, plug wire, plug, etc).

Originally Posted by junkcltr

I was looking at the dynamic calcs. It still looks like the small cap got 3.49 msec for a max. (desired) charge time for max. energy at higher rpms. When time ran out, the ECM reduces the dwell time because it has to..........but the small cap appears to need only 2.5 ms when the large cap appears to need 3.5ms. In other words, the small cap is inherently designed to work properly up to 6,000 RPM on a V8 with the ECM. The large cap is inherently designed to work properly up to 4,300 RPM on a V8 with the ECM.

Originally Posted by junkcltr

Oh yeah, one other thing is the current limiting of the module. That comes into play also for the energy delivered. Of the two small cap modules you tested.......did they both have the same current limiting?

Originally Posted by RBob

With the inductance being the major contributor to charge time.

Originally Posted by RBob

It appears that you still believe there is a difference between the small cap and large cap dwell calculations. $6E vs $8D, of which $8D is used on both small cap & large cap applications.

Originally Posted by RBob

What have you measured the coil charge times at? This is an important factor in when the current limiting comes into affect.
RBob.

Originally Posted by Blue1989RS

So would you guys say that the MAF setups ran the large caps with the 048 modules cause of the RPM limits they wanted to impose?

and that the MAP based stuff uses a small cap with a 369 to make it have more power up top?

Originally Posted by Blue1989RS

This is a very interesting thread for me. What if there was a way to make an external IM controller that you could adjust the charge time? It would be easy to make a circuit to intercept the ignition module pulse, add a fixed on (charge) time, and then send it down to the coil? If I'm correct, then the on time of the coil is independant of the rpm. It would again be easy to make the controller have a trim pot to adjust the on time. That way you could adjust it depending on what coil you are running. Similar to points adjustment.

Originally Posted by jwscab

these 2 modules are for the small cap only. It would be interesting to see how the large cap modules behave.

Originally Posted by jwscab

Hey Junk, I know it's a nitpick, and I brought this up already, but you've mentioned a couple times the 'MAF code' as a large cap, which isn't always the case. For instance, my '87 IROC is a MAF, yet uses the small cap. Just wanted to clarify for anyone not as closely familiar with this stuff that might be reading.

it may be from your investigation that ALL the maf code (32B, 6E) might well be using a 'large cap' value while using the small cap hardware in certain instances.