JohnnyIroc

iTrader: (3)

I just looked at an old datalog and its obvious that from this table below that the motor is only seeing 30 deg of timing at full throttle under load. I have checked the timing with a timing light and it will go to 34 deg with the rpms over 3k but oviously thats not under load and low map kpa. I acquired this car recently and the previous owner obviously didnt do the best job tuning it. One of the tables was totally backwards and ive changed that already. The injector timing was way off and it stunk of unburnt fuel all the time which has been fixed too. Im sure this little cammed(230/236 583/585) 436ci sbc could use a little more timing up top and a little less down low. Does it really need 26-28 deg at idle and low load levels?! Any input would be greatly appreciated and id like to see if anyone can post a graph of a similar comboed timing advance table. Thanks

Tibo

iTrader: (15)

Ignition timing advice is hard to give because of things like Octane ratings, dynamic compression, combustion chamber design, quench height, etc,. I have a similar engine being that it is a 383 with AFR comp port 195s, a 236 cam and a pro ram. I started with the LT1 spark map and at the moment have tuned it for idle, cruise and brisk acceleration to 4000. I had to pull a few degrees of timing out in my cruise area, add some in the idle area and ramp down the advance curve on lower end acceleration but the LT1 map really is a great place to start. I think I'm at 34° WOT advance.
How much timing you need at idle is up to you and it will be a lot of testing. Within reason, you want whatever advance that gives the highest vacuum for a certain RPM. Then you'll have to play around with the air fuel ratio to see what pulls the most vacuum.


EDIT: The above table is a stock LT1 spark map, not the table I am using.

Orr89RocZ

iTrader: (20)

Idle doesn’t necessarily need 26-28 unless it helps vacuum and idle stability but it wont hurt you if you leave it that way to help transition into part throttle timing. In the 1000-3000 rpm and kpa up to 65-70, i would say 35-40 deg could be possible depending on compression heads etc like said above. 3000+ and 70 kpa up, taper down to wot timing.

wot timing 32-36 depending on heads, fuel etc lol. 30 seems low unless very efficient heads and high compression

JohnnyIroc

iTrader: (3)

forgot to add this engine is only about 9.7 compression and it has the old casting comp ported AFR 210 heads so its not very efficient

efiguy

iTrader: (2)

First of all you need to rescale your Kpa table. I'll bet it doesn't idle at 13 or even 19 kpa. Wherever it idles run two rows above that, then start from there.
Then as others have said, go for highest vacuum at all points except wot. There it's best to spend a few bucks and strap it to a chassis dyno to get a better baseline.
Make sure your air/fuels make sense in all areas as well before you start this process.