Anyone have the timing curve for a 71 401?

[rang-a-stang]

I don't see it on Tom Collins' site and Mr. Google is not helping me.

[PlasticBoob]

Here's from '74, hope that helps.

http://apicalnetworks.zapto.org/host/forum_hosted/ifsja/amc_timing1.jpg

http://apicalnetworks.zapto.org/host/forum_hosted/ifsja/amc_timing2.jpg

[rang-a-stang]

It does help some. In 71 401 had 9.5:1 compression (like mine) so I was going to start with that curve and go from there. By 74 401 was at 8.5:1.

[babywag]

Just remember you would need to plug it into something like excel and formulate the combined curves together("Hg vs. RPM)
I played with the factory curves way back when.
They didn't jive well with tbi MAP vs. RPM so I just modified the tbi tables.

[nograin]

If you can't find a '71 FSM, look for guys with a distributor tester and the tune up cards.
You can try Halifaxhops in Halifax Pa. He only rebuilds Chrysler distributors but may have and be willing to sell you the tune up cards your interested in.

It does help some. In 71 401 had 9.5:1 compression (like mine) so I was going to start with that curve and go from there. By 74 401 was at 8.5:1.

A lot of unknown differences but something is better than nothing.
If you can figure out additional engine differences (such as cam and heads) if any that will help further.

Some general guidance.
Higher compression ratio produces better combustion development so less timing advance is needed.
Cams with high valve overlap have more exhaust dilution at idle and need more advance at idle.
Early emissions reduction efforts (late 60s -mid 70s?) focused on CO & HC at idle (and decel). To do this Chrysler purposely set the initial timing later than ideal. This put more heat into the cylinder walls and better insured burning up all HC. They also ran the idle leaner to reduce NOx.
AMC probably addressed emissions in a similar manner. I think this is why we see initial timing of 2.5* & 5* BTC in the '74 FSM PB shared. ( Also is certainly why idle speed is 700 rpm.) It will probably run just as well or better with a little more initial timing and the rest of the timing about the same.
Just for comparison, the later timing specs after introduction of catylitic converters have initial timing around 10* and 12* for the 2V equiped 360s.

[rang-a-stang]

Thank you, gentlemen. This is, spot-on, exactly the info I am looking for.

This is what was in my BIN when I started. I let out a huge gasp the first time I saw it. 46 degrees?!?! Doesn't a cylinder fire every 45 degrees? When I drove it the other night it was backfiring as I got on the freeway, I am assuming that is because the spark was jumping from my rotor to the next cylinder post....


I trimmed all the values over 36 down to 36. That was all the brain power I put into it for now. I drove it like this and it is MUCH better (especially when it's cold). I intend to add a knock sensor next month when I get back from my next trips so I can tune more finely. I also posted up the same question over on theamcforum.com.

[babywag]

what kind of operating circumstances are you getting backfiring?
map/rpm/etc.?
backfire out TB or out tailpipe?

a gm tbi distributor is designed for better operation vs. duraspark.
this is why proper phasing should be done.

If you look @ timing map very limited operation in cells with 46*
if you playback a datalog and let it populate table you'll see what I mean.

[rang-a-stang]

I was merging onto the freeway, 3/4'ish throttle, higher RPM (maybe 3k?), and it popped 2 or 3 times but I didn't notice out the TBI or exhaust. I backed off the throttle, coasted off the freeway, and just drove around town for the rest of the time and had no other issues.

Today I drove it into work and had no issues. I hooked up my PCV this morning and that went fine, too.

I have some other issues to work on before I can tinker on my BIN more, anyway. My O2 sensor works great for a few minutes, then all the sudden starts going all over the place. I wonder if I torched it when I had it hooked up incorrectly. Look at this:

[wiley-moeracing]

is it a carb or fuel injected? a little confused. I see now you have tbi. never mind!

[rang-a-stang]

If you can't find a '71 FSM, look for guys with a distributor tester and the tune up cards.
You can try Halifaxhops in Halifax Pa. He only rebuilds Chrysler distributors but may have and be willing to sell you the tune up cards your interested in.

A lot of unknown differences but something is better than nothing.
If you can figure out additional engine differences (such as cam and heads) if any that will help further.

Some general guidance.
Higher compression ratio produces better combustion development so less timing advance is needed.
Cams with high valve overlap have more exhaust dilution at idle and need more advance at idle.
Early emissions reduction efforts (late 60s -mid 70s?) focused on CO & HC at idle (and decel). To do this Chrysler purposely set the initial timing later than ideal. This put more heat into the cylinder walls and better insured burning up all HC. They also ran the idle leaner to reduce NOx.
AMC probably addressed emissions in a similar manner. I think this is why we see initial timing of 2.5* & 5* BTC in the '74 FSM PB shared. ( Also is certainly why idle speed is 700 rpm.) It will probably run just as well or better with a little more initial timing and the rest of the timing about the same.
Just for comparison, the later timing specs after introduction of catylitic converters have initial timing around 10* and 12* for the 2V equiped 360s.

Copy that. I have 73 401 heads and my cam card so I can compare them. I think my engine is close enough that the 71 card gets me in the ball park, then go from there.

[babywag]

o2 sensor will swing pretty good that is normal especially if fueling is off some.