What should I do about my main spark table?

[rang-a-stang]

@ rang-a-stang
hi, could you publish your new SA table?
mecanicus

Oh man, I have not logged in in a few months. For sure. I am at work right now but when I get home, I will post up my new table.

One of the best " makes sense " explanation I have seen for spark tuning.

Concur

I have a thought about this...

Have you verified timing to be correct? That what is being commanded is what is actually happening referencing crank angle, at RPM, I know without a dyno under load will be impossible to verify, but you can at least rev it in park and make sure that the actual timing follows commanded. I have seen a number of times where looking at commanded you'd think that the timing is far too advanced, but actual timing was not correct. There's a bunch of reasons for this, but starting with verifying correct timing is the place to start.

I have verified it a couple times. I had to rebuild my engine AGAIN and while it was apart, I verified the timing marks match the crank. Then when it was running, I pulled the timing plug and verified the dizzy was at 0. Plugged the timing plug back in, reset the computer, logged in my laptop and watched my timing bounce around, generally, where Tuner Pro said it should be.

Also of note, I had a rotor a few years back, that was manufactured incorrectly which made the phasing about 10 degrees off! Whenever my computer would command max timing, the spark would jump to the wrong distributor post and it would backfire like mad! SUUUUpper frustrating to find.

[rang-a-stang]

Ok, here are my tables. I would say they are about 90% complete. I am running it and I do not have much knock with 91 octane. Before i post it:
1) They way I created this is I went into Excel and created a two tables that had the same rows and colums as my main spark table in TunerPro.
2) I used one table and added the timing I would use if I only had a mechanical advance. So I started with about 10 degrees initial and went to 40 degrees total at WOT. Then I used the Excel average function to fill in the middle parts and create a smooth curve.
3) I used the other table to create a table that was ONLY what a vacuum can would do. So it added 12 degrees at max vacuum and 0 degrees at no vacuum. Then I used the Excel average function to fill in the middle.
4) I then combined the two tables and "adjusted" for common sense. For instance, when you add max RPM and max Vacuum above, you get 52 degrees in a few cells. I chopped that down to 46.
5) I have been driving on it and watching my knock counts. I had to make a few adjustments so far and will continue to do so but for now my truck runs pretty darn good.
Table.jpg
Graph.jpg

[Fast355]

40° is alot of WOT timing even for a low compression engine like a AMC Jeep V8. I would pull it back a few degrees on the top-end. Even without knocking it can actually hurt performance to have the timing over advanced. Was looking at an AMC 304 timing curve in a service manual the other day helping a Jeep TBI conversion guy with his rig. It had a factory spec of 35° @ WOT.

Edit..Said 30° but that was ignoring the 5°

This is what I ended up with on the 304 and it ran really well. The timing was set at 5° per the stock emissions label to prevent future confusion. I set the initial value in the ECM for 5°.

5* initial

Started the centrifical advance at 1,200 rpm, quick rise to 16° by 2,000, then on to 30° "mechanical" @ 4000 RPM

15° vacuum: start @ 6", fully advanced @ 13" in a straight linear line.

Gives the truck 35° total at WOT and 47° at cruise. ECM whacks the EST advance to 42°. 42° plus 5° is 47°.

Probably could have added a few degrees and run higher octane gas but what is the point? It runs great on 87 so why mess with it.

304 is stock save for a tiny RV cam, headers, duals and the TBI conversion. Probably could have dialed in more initial, kept the same idle timing and brought the advance curve in more quickly but as it was it would blaze the tires in the CJ at will in 1st gear.

[rang-a-stang]

That's good info, Fast355!

When I was first starting my timing table, I found this thread:
http://www.bulltear.com/forums/showt...Timing-Advance
I went to 40 since I have a knock sensor and figured I would watch knock counts and retard. My 401 is "Warmed over" (9.5:1 Forged pistons, port matched heads, Comp Cams 268H cam, Long tubes, 454 TBI on an Edelbroke Performer) but not really "built" per se. I also went a little soft on when it is all in because I would rather lose a little power than be knocking when I was tuning my fuel tables.

Honestly, I have been spending 90% of my tuning time in fueling and just barely touching my timing table. I also have spent the majority of my time working on 4K RPM and below because my TH400 shifts at WOT at 4k RPM. I am pretty super close to being done with my fueling table and will spend more time on my timing table in the next 4 months (4 months because I am about to go on a 2 month business trip). When I do start to dive in to timing again, I will revisit this thread, the bulltear thread, and some other tech manuals and such and get it going. Like I said above, my truck runs well; but I know I am not "done". I had to do a second rebuild between the time I started this thread and now (long story, debris, oil pressure, no muy bien) so that has set me back quite a bit.

[rang-a-stang]

I was working on some other things on my laptop and decided to take some of Fast355's advice and make some minor tweaks to my timing table. I backed my WOT timing down to 39 and brought in some more early to mid throttle timing in. I burned a chip with my new table and took it for a short test ride. Right away, the mid throttle power is markedly improved. Super stoked on that. This run did not go over 3500RPM so the 1 degree less timing at the top was not tested. I was about 3/4 of a mile into my run and broke a spider gear in my rear axle. I limped my truck home in FWD and parked it until Mid May (when I get home from my business trip). I did not have Tuner Pro running so I do not have any knock data. Here is the table I ran. Like I said a minute ago; this is MUCH better than the first one I posted.
table2.jpg
graph2.jpg