Timing curve for *my* 401

[FSJ Guy]

Several people have asked to see it, so here's the timing curve that I finally figured out for my 401. Don't try this at home!



The graph doesn't show it, but the Y axis (if you assume X is kPa) is RPM with low RPM at the bottom and higher RPM as you go right.

The little bump just before 2000 rpm isn't a whole lot, but it does seem to keep the engine happy. Who am I to say what it "should" be? I gave the engine the timing that it wanted, and this is how it ended up looking. <shrug>

[FSJ Guy]

And note that this curve is very simple. It basically simulates what the distributor does. The vacuum advance is simulated as if it were hooked up to manifold vacuum, high at idle and dropping off as load increases. The centripetal advance (obviously) advances with RPM but I found that I had to stop advancing it just after 2,000 rpm or it would knock.

At least that is what worked for my motor. Your motor will very most likely be different.

[BRUTUS]

Awesome! So many forums that i go to only talk about technical stuff like this but to have a 3-D graph... Awesome!

[letank]

Looks good, so what is the rpm range.... and the fractional units, 200 rpm.... is the red the highest advance?
thanks,

[FSJ Guy]

It starts at 400 rpm and goes up to around 3200 or so. I didn't add #'s because I don't want to encourage people to "copy" it. You should do your own experimenting. Every engine is different.

[Billygoat]

So other than spark knock (telling you it is to high) what indicates what your engine "likes"? for timing?

[FSJ Guy]

Originally Posted by Billygoat

So other than spark knock (telling you it is to high) what indicates what your engine "likes"? for timing?

Excellent question!

Stumbling or poor acceleration can sometime be the result of not enough timing. (Assuming that timing is the only thing changed!)

Also, backfiring on deceleration is a good indication that your timing is not correct.

Incidentally, today I had a chance to take the truck up a nice long steep road (1-2 miles). It pulled nicely all the way up and when I came back down, I was able to downshift and the engine compression held the speed back without any "burbling" or backfiring through the exhaust.

[JeepsAndGuns]

Do you have tuner pro version 5? From the looks of your picture the graphs display diffrently.
I have beel fooling around with timing in my cherokee 401 for a few weekends now. I REALLY like the emulation feature of my autoprom, its been invalueable in makeing my timing map. I am still not does yet but here is where I am at right now, just curious to see where everyone eles who tunes has their timing map set.

[srobertsfsj]

Ethan, sorry to bring up this old thread but is your graph final timing or do you have retard and warm bias turned on?

[Bill USN-1]

Scott,
I think you suffer from TMI.
You seem to look at lots of threads on lots of sites and try to believe everything said is correct and then you try to do everything to your bin all at once still thinking it's correct.

You really need to apply the KISS mentality.

The retard and bias have nothing to do with the timing table. Normally it's not even enabled until the tuning is done.
No retard is applied unless you have the retard enabled and there is actual ping present or possible false knock.
The bias only affects the timing table in setting the base.
Depending on the program used and for TP it depends on the actual XDF used, determines whether the bias is applied prior to displaying the main spark table.

There is a basic table provided on Binderplanet. There is another being passed around that is supposed to be for an AMC but if you look at it the idle timing is up around 40* and the 100map timing is actually higher then the 90 map timing. Both seem to not match any stock timing tables i have reviewed.

i would caution you to keep it simple and cautiously apply what you read as your engine may just not like it.

There are a lot of guys on all the sites that post like they are knowledable or an expert when in reality they have very little practicle experience tuning and only repeat what they read elsewhere...right or wrong.
Be careful.

[srobertsfsj]

Thats not really true, I only adjust one thing at a time and I only modify a couple of parameters. At first it was TMI but I have learned alot. I did take a 3 months break due to other issues so I only recently started back up and "refreshing" what I knew. I do alot more tuning than reading posts but I sometimes get results that I don't expect so I will do more research and try to figure out why the result was unexpected. I have a timing table that I feel is good and its not a copy of anyone else's, its just a bit more timing then some feel is needed.

[FSJ Guy]

Originally Posted by srobertsfsj

Ethan, sorry to bring up this old thread but is your graph final timing or do you have retard and warm bias turned on?

I don't use a knock sensor, so I zero'ed out the knock retard tables. They don't show up in the timing table, AFAIK, anyway.

I think that table showed the final values. Regardless, I have changed my timing and it doesn't look like that now anymore.

As everyone (including Bill, I believe) as said, give your engine what YOUR engine needs.

If it likes more timing in some places as compared to other peoples' motors, do it.

The "old" method of tuning the distributor timing was to advance it until it knocked and then turn it back a few degrees. I tried to do that with my electronic timing as well. I'd run it until I got knocking and then I'd pull the timing back in those areas.

[srobertsfsj]

Agreed and I am definitely finding that my engine likes more timing, maybe its the elevation, maybe its the Comp Cams 260H cam. Here are my numbers from this morning. I still need to bump up timing in the 70 to 85 kpa range

I guess my biggest fear was damaging the engine but I have my knock counter hooked up but knock retard disabled, seems even with the higher advance knock isnt that bad.

[grand_wag_85]

What are you guys running as far as a distributor goes, modified Duraspark?

[Bill USN-1]

There are several options but if you already have a duraspark then it works just as well as any of the other options.
To be modified correctly you lock out the mechanical adv and reset the reluctor phasing for computer controlled timing vice the mechanical timing.

Some guys get away with not doing it but it should be done so the rotor fires in the correct position in relation to the cap terminal.
If not phased the spark will need to jump a large gap.

The procedures are also in the FAQ's at binderplanet.