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So I was going through some things, and notice the ebl SA latency table isn't the same as say the AUJP bin, small cap dizzy. Is there a reason why?? I thought those valus were decided by the manufaturer of he dizzy, and can't be changed? Do these valuse affect you overall timing scheme, at all times? Or just limp home mode? And if the tables can be changed, how/why would one want to?
Here is a link to a post with a stock small cap and big cap dizzy latenecy table.
notice how the numbers are the same from 4400 and up, in the EBL.bin able, it goes to like 314 at 3600, then drops low again. where the stock tables, the latency continues to climb numerically as the RPM's increase.
Can someone please shed some light? I have found much in the search and on the web about this topic.
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__________________ A.S.E. Certified master mechanic Land Of The Free, Because Of The Brave http://www.cardomain.com/id/liquidh8 My rides: 81 Buick Century Wagon, 86 GN Turbo engine, 2004R, 3" DP, 3" Duals w/Magnaflows, CAI, Lots of porting, powdercoating, 18 lbs boost, more to come!! 79 Malibu Wagon-Vortec headed 350 w/tbi, 2004r, 2800 stall, n2o, 4 wheel discs, pro-touring suspension, killer PPI, J/L audio system 64 Chevelle Convertable SS-not done 302, w/muncie
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Ok, so I fired up my craptop and took a look at some stock tbi bins. the 5.0 and 5.7 bins share the EBL latency table, small cap dizzy. I see where RBob got it from, but, I open a 7.4 bin, 454, and the latency was way different. no the big block and small block chevys use the same dizzy, so why the different tables? And I had a 4.3 bin, and it to had a different table, but I can understand the v6 having a different table, it has a different module and only 6 cylinders. but the BBC uses the same dizzy and module, so why the change? I'm gonna keep searching the web in hopes of finding something more on this subject because it is bothering the crap out of me.
The purpose of the latency is to make up for lost time. The way the distributor operates causes a delay between when the reluctor passes the pole piece and the signal reaches the ECM. This delay changes according to the RPM of the distributor.
The code works by subtracting the latency value from the spark advance value. However, at this point in the code the SA has already been converted from an angle to time. Instead of 30 deg BTDC, it will be in micro-seconds BTDC (In actuality it is usec's ATDC as it will be firing the next cylinder is sequence. And because of that a subtraction of the latency value has the SA event occuring sooner, making up for lost time).
Now, if my math skills are still OK, here are some calc's that show by how much they adjust the timing. Plug firing or 90 deg crank rotation intervals:
26.67 * (4 CylPerRev) = 106.67 plug firings per second
1 / 106.67 = 0.009375, or 9.375 msec between plug firings
9.375 / 90 deg of crank throw = 0.104167 msec per degree, or 104.167 usec
8 cylinders at 6400 RPM:
2.34375 msec between plug firings
2.34375 / 90 deg of crank throw = .02604 msec per degree, or 26.04 usec
From AXKT the lastest '88 - '92 TBI Firebird/Camaro BIN the SA latency at 1600 RPM is 305.2 usec's (This is a small cap distributor).
At 104 usec per degree of crank rotation this is a little under 3 degrees of timing.
Oddly enough the latency value in AXKT at 4800 RPM is also 305.2 usec (there are different values at other RPMs). That value will be used from 4800 RPM through max RPM.
With that at 6400 RPM wiath a latency of 305.2 usec is 11.7 degrees of SA (substantial).
Ok, so if i went through and used this formula, i would get totally different values. And they are different in the EBL bin. Like @ 400 rpm it would be 208 usec. But in the bin it is 0. So is there some spark timing tuning going on here from the general? If the tbi engines used crappy swirl port heads, and the corvettes/camaro's with the tuned port motors used different heads, or the vettes using the aluminum heads, there seem to be different Sa latency tables for these engines. I guess what I am trying to get at, if the latency is to catch up for the delay in the rotation of the distributer sending the signal to the ECM, then I would think it would be the same for all the chevy's running the small cap distributer, v8's that is. Induction and head/cam combos shouldn't matter. But it appears this is the case.
Like if you are using a vortec head, or aftermarket head that has a better combustion chamber design. You could fool with these numbers a bit to get the timing to react different.
This is the ebl sa latency table, same a few 5.7/5.0 tbi tables I have. But the aujp table is different, the numbers are higher, and there isn't a dip at 3600 rpm. I wonder if that is from having an engine with a better cylinder head design, or camshaft or induction?
So if I am understaning this right, the latency value
Quote:
With that at 6400 RPM wiath a latency of 305.2 usec is 11.7 degrees of SA (substantial).
would have the total timing of say 30d, occuring 11.7 degree of crank rotation sooner?
Or is it the ecm making it's calcs to come up with the final timing number, the subtracting the 11.7 degrees from that number, i.e, right before the latancy adjustment, we have a 100kpa/64oo rpm timing of 32 degree, then subtract 11.7, so the total timing is really 20.3?
I think you mean this one.
Thanks for your reply in trying shed some light on the purpose of this table for me. I appreciate it!!!
Subtracting out the latency is done right before the hardware is programmed. In this case it is not reflected in the SA value we see. Put another way, what we see is SA in an angular measurement.
The latency adjustment to the SA is in time measurement. This is because as the RPM changes the time measurement changes for the same SA in degrees (angular measurement). The SA hardware in the ECM works on a time basis. It knows nothing about angular crank position.
The purpose of the table is to make the SA values we enter into the calibration match what is at the crankshaft. For an example take the table I posted above (from AXKT). At 6400 RPM there is a correction of 305.2 usec (11.7 deg).
Lets say that the timing in the ECM at 6400 RPM 90 KPa is 30 degees BTDC. This is also shown by the WUD as the ECMs current SA timing value.
We put a light on the damper and sure enough we see the light flashing at 30 BTDC. Cool.
Now zero out the latency table, all values set to zero.
At that same 6400 RPM 90 KPa, ECM timing of 30 BTDC, and now the timing light is showing 18.3 BTDC (30 - 11.7 latency). Not so cool.
Without the latency table the SA values in the calibration wouldn't mean much. To get 30 deg at 6400 RPM we would need to put 41.7 deg in the table. Not a good way to tune. And, with the latency varying by RPM, the SA table isn't going to look too good either.
Another aspect is the vehicle manufacturer. Engines are set up on a dyno fully instrumented. The SA is then mapped according to maximum best timing (peak pressure at 15 ATDC, no detonation, etc.).
This timing map is given to the driveability guys that do the final tunes. They use it as the maximum amount of timing allowed. In this case the value that is placed into the calibration needs to match what is found at the crank.
Without the latency table that can't be done.
Back to the 64 thousand dollar question: why does the small cap SBC distributor have different latency values then the small cap BBC distributor? Simply put there is something different in the distributors. Which piece is different, that I don't know. Could be the pickup coil, pole piece, reluctor, module, or the combination of them all.
So, what do you think would happen if I put the TPI SA latency table in my EBL-TBI bin? since the usec from 3600 rom on up are higher in a aujp bin, something like 216usec (not on my craptop)? And there also isn't that dip in usec @ 3600 rpm. I understand you are saying that something has to be different in the BBC distributer, but when I still worked in a shop, even now if I called the supply house, the P/N for the distributer, and even the replacement pick-up coil and shaft with relucter wheel, is the same part.
In an case, I appreciate all your replies to this subject thus far. Ithas helped me understand it a little better.
I know exactly what you are saying. A couple of years ago I beat my head on the wall over this. Then came to the conclusion that all of the small cap distributors I've been using have come from fully size Chevy vans. And using those latency values let my head heal.
But, I wonder the same as you on replacement distributor parts. The pick up coil for a V8 car is the same for a V6 car is the same for a truck. Don't know about modules, although I really have my doubts that there is a different one for different applications (within the same distributor family).
By changing the latency table values you will be changing the end spark timing. A larger latency will advance the timing and vice-versa.
On a closing note, I was going through a bunch of TBI BINs last night and found some patterns to the latency tables. I need to look at it again to track where they matched up.
RBob.
Last edited by RBob; 03-14-2008 at 04:30 PM.
Reason: removed an extra 'RBob' :)
Looked through the TBI BINs and noted the patterns between vehicles.
Code:
Matched set 1: The 3rd GEN cars match up with the 7.4l truck ECMs:
Truck 7.4l
Firebird/Camaro/Caprice/Roadmaster 5.0l/5.7l
BINs compared (9: 1 '6965, 2 '7747, 6 '8746 ECMs):
ANTZ AXKS
ANTY ANLU
AXKW APFN
AXKU AYKC
AXKT
Matched set 2: Then the 5.0l & 5.7l trucks have a matched set of latancy table:
BINs compared (7: all '7747 ECMs):
AMUN ASDU
ARPC AMUR
ACSC ARHT
ASDZ
Matched set 3: Then the 4.3l matched across 3 ECMs:
BINs compared (4: 1 '7747, 1 '8062, 2 '4288):
AMRW
AKDX
AULH
BARM
I figured I would have some advance timing. For the heck of it today on the way home from work, I tried a bing with higher latency values, advancing the timing. I didn't "feel" any noticable difference. This is from one drive. I couldn't pull over and get a dead stop WOT run, but I have a log from the last bin, everything being the same except the SA latency table to compare too. Most likely monday on the way to work, I'll try and get a run to compare the other one too. But if we are only talking 1/2 degree, or 1 degree here in different rpms, I don't think I'll notice too much while driving around you know?
I too an using a truck distributer. But in the future I am picking up an MSD for it, for the time being I am upgrading to a petronix module. So this in part is leading to this "want to know" deal about the SA latency, along with just wanting to understand it.
If you have a GM ignition module I would stay with that. As for the MSD distributor, try an email to them about the latency values. It would be interesting to see what they have to say about it.
As for the 1/2 to 1 degree difference, no, probably won't feel that. What you can do is to use a timing light and compare what the WUD reports for SA timing and what the light shows. Try this at different RPMs and see if the two continue to match up.
The higher the RPM the more critical the latency value becomes. Can do the timing light check at a standstill, no need for a high load, just RPM.
In the mean time I checked the TBI small cap latency values against the TPI small cap latency tables. The TPI tables match the 3rd gen cars and 7.4l BBC tables. So it seems that the SBC trucks are the ones with their own set of latency values. The pic's show the two sets of values used for the small cap. Note that this isn't all inclusive. There very well may be other small cap distributors with a different set of latency values.
The TPI BINS checked: AUJP, AXXC, AXXD (5.7l & 5.0l)
In the mean time I checked the TBI small cap latency values against the TPI small cap latency tables. The TPI tables match the 3rd gen cars and 7.4l BBC tables. So it seems that the SBC trucks are the ones with their own set of latency values. The pic's show the two sets of values used for the small cap. Note that this isn't all inclusive. There very well may be other small cap distributors with a different set of latency values.
The TPI BINS checked: AUJP, AXXC, AXXD (5.7l & 5.0l)
RBob.
Wow. I could understand a small difference, but that looks substantial.
__________________ 90 454SS; TBI 496. Best to date: 12.42 @107, 1.63 60 ft.
Wow. I could understand a small difference, but that looks substantial.
Yes, at 6,000 RPM it is 6 degrees of timing difference (between the two tables).
Makes me wonder if I did all of the calculations corrrectly. I've also been thinking of a way to bench test this. Will need a strobe to 'see' when the reluctor & pole piece line up. Then use that to trigger the scope.
Measure from then until the DRP signal activates for coil firing. Then also check for latency between the incoming EST signal and the C- signal. This will also leave all ECM latencies out of the picture.
I've also been thinking of a way to bench test this. Will need a strobe to 'see' when the reluctor & pole piece line up. Then use that to trigger the scope.
Measure from then until the DRP signal activates for coil firing. Then also check for latency between the incoming EST signal and the C- signal. This will also leave all ECM latencies out of the picture.
RBob.
Let me try and add a bit of help.....
An inductive timing light, if you eliminate the pick up and go directly to the trigger inputs, needs VERY little voltage to fire. They *will* fire on both rising, and falling edges at slow rates, so watch that. Polarity seems irrelevant.
The coil pickup leads are adequate for reliable firing.
You could take the pick-up coil leads directly to the inductive light trigger, and simply watch the reluctor vs pole piece relationship directly.
That will give you the mechanical/magnetic latency of that dissy. ( assuming your young eyes are better than mine, and you can plot the shift in rotational degrees, or you add a 12 inch diameter degree wheel in place of the rotor )
As speed increases, ( freq. increase, or time decrease ) the reactance of the pick-up coil will dominate. The field should ( if memory serves ) advance up to about 22 degrees or so relative to the real reluctor position at very high speeds. Either way, R and L are fixed by the windings of the pick up, so +j MUST increase with speed. How much depends on the L/R ratio, and thus the relative phase shift.
Once you've plotted that, you have your strobe against which you can calibrate all other latencies through and including spark plug wire, and plug gap by simply using the reluctor itself as your scope trigger "strobe."
Add a compressor and bottle, and you *could* even include latencies for in-cylinder compression effects.
At THAT point, latency of the timing light becomes dominant, and I think we're getting into splitting hairs.
May I also add that I'm grateful for this thread. Being able to log spark firings relative to DRP, I have noticed a discrepancy, but not worried much about it.
Methinks I'm about to compare the latency table for my dissy ( complete system, actually, which I have always had ) against what's in my EBL. Might reveal a thing or two.
I'll concede that the possibility my spark tables contain unknown compensations for wrong latencies doesn't exactly make my day, even though it's my own d&^% fault.
One or three degrees "off" should be pretty irrelevant, but 11 point anything is well beyond the window of acceptability, even considering the weather changing.
Being the adventurous type I decided to check out the latency table values & calculations on a live engine. The test unit: '85 Camaro LG4 converted to TBI with 350 truck parts (TBI, distributor, harness, etc).
BINs: used 2 BINs, both had the main, extended, SA set to 12 deg BTDC. Most other SA's set to 0.
BIN1 has above SA mod and stock latency tables (for SBC truck).
BIN2 has above SA mod and latency tables with +8 deg SA
The second bin (BIN2) latency table was increased in value that equaled 8 degrees of timing at that particular RPM. The calculations were done as posted ealier in this thread.
Results show that for the most part the latency values are correct. The low RPM area is where the timing lagged by about 1/2 degree. Instead of showing 12 BTDC it was around 11.5 degrees BTDC.
Switching to the second BIN the timing moved to 20 BTDC. Which matches up with the calculations.
A note about RPM. This being a tired LG4 with 200K miles or so on it, at 4500 RPM the timing went a little goofy. It retarded about 5 degrees and bounced between that and 20. Then by 4800 it smoothed out again, with 5200 the highest RPM checked (and briefly at that!).
In hindsight the events at 4500 RPM were probably due to the valves floating. This poor motor has a lot of miles on it. Makes a bench setup sound like a better idea.
Sounds like couple of 2x4, plywood and screws are in order. Since dizzy turns are 1/2 of the crank speed 0 to 4000 RPM variable speed motor (aka drill) is in order. An old tachometer, 12 volt supply, and ECM with harness pigtail should complement the setup. Oscilloscope tied to DRP line and tach
line.
This is an interesting thread i must admit, but I'm glad others are chiming in on the discussion. I wish I had the equipment to try out the test RF was talking about. I may make bin with the tbi car tables in it. Righ now I have a bin with values in between the two. I'll have to post ti and the xdf so it can be seen by all. So RBob, you are saying that there was an 8degree SA difference from bin 1 to bin 2, with nothing but the SA latency tables changed??
The latecy tables may just be there for the different pick-up coild used in the distributer. i know the is a green plug and a white plug, if I remember right. I'll have to look in my gargae, and at a few distributer I have to see the difference. I don't know if one was for the in cap hei, old style, or if it was a choile for the 7/8 pin moudule Fi distributor.
This is an interesting thread i must admit, but I'm glad others are chiming in on the discussion. I wish I had the equipment to try out the test RF was talking about. I may make bin with the tbi car tables in it. Righ now I have a bin with values in between the two. I'll have to post ti and the xdf so it can be seen by all. So RBob, you are saying that there was an 8degree SA difference from bin 1 to bin 2, with nothing but the SA latency tables changed??
The latecy tables may just be there for the different pick-up coild used in the distributer. i know the is a green plug and a white plug, if I remember right. I'll have to look in my gargae, and at a few distributer I have to see the difference. I don't know if one was for the in cap hei, old style, or if it was a choile for the 7/8 pin moudule Fi distributor.
With some masking tape on the damper and a timing light you can do the same as I did. That will verify if the latency values are correct or not.
Note that you shouldn't be posting an EBL BIN & XDF on any site. Copyrighted and proprietary information and all that.
So RBob, you are saying that there was an 8 degree SA difference from bin 1 to bin 2, with nothing but the SA latency tables changed??
Yes, the only change I made was to add enough latency at each RPM point of the table to equal 8 degrees of SA. This was done to verify that my calculations are correct (as posted above). And to verify how the latency table worked. Which it did both of.
Here is a copy & paste from Excel for the values used. Note that RPM of 0 is set to a 1 (can't divide by 0), and the BIN value was set to 255 (can't go higher).
The values in the 'usec for 8 degrees' column were added to the value already in the table. The result was a shift of 8 degrees more SA across the RPM range.
Yes, it is very interesting thread. I'll put together a block diagram and list of parts together. I have several other projects in the cue (sick parts getter that's occupying garage stall and must be finished first). I also have couple 7747 with a long harness pig tails and three different distributors. One standard small hat, one of the 91 B-body and full size CCC. This will take a bit of time, but it can be done.
For a bench setup I would leave the ECM out of the picture. It complicates things too much. The latency is the time delay between the pole piece & reluctor line up, and the REF+ signal to the ECM.
It would be interesting to see if there is an additional delay between the EST signal and C- going high. If so then that too should be included in the latency value.
For that matter, should be able to loop the REF+ back to the distributor EST signal. Then measure from the pole/reluctor alignment to the C- going high.
For the BYPASS signal just pull it to +5 volts for enabling the EST to control the module.
So, I think I'll do as you said, and make 0degree BTDC, with tape of a paint stick, take my timing light (i have a snap-on dial back) and sit the lap top on the fender there, the just rev it to the rpms in the latency table, and recond what i see and what the wud is displaying, if they are off, then I can adjust the table to make it match.
This could be a good test for those who use an other that stock distributer, i.e., MSD, accel, ect.
I wonder if the different tables were used in the trucks, just to keep a tap on the timing, figuring the truck would be under heavy loads some of the time? hmmmm, who knows. But I am gonna check just to make sure I am using the correct values. Maybe make a bin with less timing in it all over, like you did, and check it in park, again, as you did. Now the thing is, should it be kept as the general did it, flattening out the latency value at the upper rpms? I wonder what the latency tables look like in a later model engine, right before they got rid of the distributers?
Now the thing is, should it be kept as the general did it, flattening out the latency value at the upper rpms?
Need to have that RPM measured, otherwise I'd leave it just flatten. Gets sorta' hairy at the higher RPM range. I used some protective gear as the timing light had to be shot down behind the water pump. Straight down from above (from the fan, pully's, belts, etc.).
Quote:
Originally Posted by liquidh8
I wonder what the latency tables look like in a later model engine, right before they got rid of the distributers?
The LS1 CnP smart coils run a flat 22 usec latency at RPMs up to 8,000 on an eight cylinder. Not sure what the pickup has for latency times.
There is also masks out there that have a single value for latency. And both DIS & distributor equip'd vehicles are involved. Not too sure what to think of that. It may be that some ignition setups don't have much difference in latency vs RPM. And don't require correction for the entire RPM range.
OK, just been very busy here in the salt mines. I'll am trying to get Infinium scope on temporary loan once setup is debugged. My old Tectonics O-scope is still good but taking CRT pictures with a camera is so 20th century. I'll update a bit later this week.
Due to the weather, and time, I haven't went any further with this yet. Though I wil be renting the hobby shop on base Monday to fix my exhuast leaks (may be causing some erratic knock counts), change the oil, lube, clean the K&N, rotate the tires, and a few other small things. While I'm at it, I'll try and get this test done, and post my results.
So what I gather from this discussion is that many of us (especially ones doing retrofits) may have quite a discrepancy between indicated (aldl) and real world timing due to the latency tables.
Perhaps a database of latency curves for various common distributors would be handy.
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.
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?
Interesting.
For those of us interested, more study is certainly needed.
My original 1987 module failed some time ago, and was replaced ( cheap ) with an Autozone Duralast version.
Taking a timing light, and zeroing out all the advance stuff I can find, or know about, and setting a fixed timing of 20 advance, I buzzed the engine at each RPM in the latency table and recorded the difference. ( to 5200 )
Then, using Rbob's previously posted usec per degree at RPM, adjusted only the latency table, until the light showed substantial agreement throughout the range.
I'm not terribly fond of doing this too many times, as standing next to a screaming big block with a steel fan, timing light in hand isn't exactly comforting.
If it picked JUST the wrong moment to throw a fan blade, or a belt, well.....
Doing it this way includes *all* latency factors anywhere in the system, not just the dist and module, so there may be other factors at work, or I did something wrong.
The latency/RPM I found was...
I'm surprised at two things.
One, how much latency there appears to be.
Two, that it's SO high at *low* RPM.
Methinks my next step will be to rig up a photo-transistor thing and a known fixed reference on the damper, so I can do this NOT standing where I'm not real comfortable, or just motoring down the road.
Maybe I'll try and find an "original" GM module, and run that, too.
Stories about the reliability of the Autozone replacement make this sound like a good idea anyway.
That module is showing quite a bit of latency. And as you mentioned even low in the RPM range the latency is high. The must be a lot of filtering in that particular module.
Once I get a P/S together for the PM servo motor I'll be able to do this without leaning over a fender. At least with this car it has an electric fan (my original testing was on a different vehicle).
I also got a chance to test drive the car after some changes:
Used the 369 module
Used latency table 2 extended down to 0 RPM
Just in normal driving around the engine was smoother. It also pulled out from a stop better. With a stick the RPMs dip as the clutch is let out. By changing the 0 latency values to the ones shown helped in this regard.
For higher RPM, some spark table changes will need to be made. With the 048 module showing retard, the 369 module will be adding timing back in. So that 32-34 degrees of WOT SA will become 40 - 42 degrees of WOT SA.
Unfortunately I didn't test the Holley module at higher RPM (3200 max). Which are what the current SA tables are set up for. So I don't know what the SA did above that RPM. I think there's a can of worms here someplace
I was going to do as cflick did and massage the latency table to match through out the range (using the 369 module). But after the module swap-a-thon it wasn't in the plans for that day.
You guys have a much larger jump at this than I did. I don't even know what number module I have under the small cap dizzy. But I agree on the high RPM test being uncomfortable, lol. Anyway. I tried checking my latency tables with a light, but I have an old snap on dial back light, not sure I should use something like this. I also failed to make the timing the same all the way across the board. I was just trying to check to see if it was really what I had set in the bin.
Way to go guys on really diving into this. As RBob had noted, if we are using a latency table that is a little off, there very well could be some performance improvement in having a correct table.
Well, I pulled my cap and I have a standard brand replacement module in there. I figured since a few replacement seem to use the second table, 369, then I plugged those values in my bin to see where it gets me. I did notice that I keep creepiong up on the WOT timing and it gets better. I have vortec heads I was conservative on the timing, afraid to go over 36 total. I may have been getting 28 for all I know with the 048 module latency tables. hmmm. I'll have to check my spare parts and see if I have a 369 module laying around.
I guess the worst that would happemn is I would gain 2 degree or timing at WOT, who knows. I have to put the light on it and see where it gets me I guess.
Might be of some interested for users doing 165 ECM to 730 ECM small cap conversions. Using the tables from post one it would seem that the MAF (large cap) distr. module is slower than the MAP small cap distr.
Then, using a MAF dizzy (large numbers) with the stock AUJP / MAP dizzy (small dizzy) with the stock AUJP latency tables will add in MORE spark advance.
Example (tables from post #1):
stock AUJP at 4000 RPM: 198 usec
stock MAF at 4000 RPM: 290 usec (real module expected delay)
Want 30_degrees advance at the crank
3.75 msec/ign
41.7usec/degree of crank rotation
30 + (290/41.7usec) - (198/41.7usec) = 30 + 6.95 - 4.75 = 32.21 degrees at the crank
The user wanted 30* advance at the crank, but by using a stock AUJP with a stock large cap dizzy they got 32.2* at the crank without realizing it. Not a big deal for N/A, but things like that add up when using boost. It gets worse or better depending on the module used.
