How much timing are you guys logging on a WOT pass? I am attempting to tune my 24X H/C/I project myself with HP Tuners. Just curious what seems to be the norm for timing with these Gen2 LT's and pretty much only find LS info when searching. I Know each car is a little different. I am only running 26* right now and working my way up.

 

26 is definitely low, the LS heads have very efficient chambers and don't need nearly as much timing. What are the heads, CR, and octane? You're probably going to want something in the mid 30's @ WOT. I was running 34-35 (logged) with my AFR's. Ported stockies will want a few degrees more.

If you look around on Karl Ellwein's site, you can sometimes find the timing printed on the engine dyno sheet.

 

Ive never messed with ignition timing on an LT1 (only Ford’s) but I would have to imagine that 26 isn’t to far off from stock? I’d probably start at 30 and go up NA.

 

The motor is a 12:1 static comp. 383 with ported stock heads and intake and XFI 468 running 93 pump fuel. I apreciate the replies.

 

I guess what fuel are you using? 93 Pump gas, a race fuel mix, or straight race fuel?
I have a NA 323 3V Mustang I run 30* with Shell V-Power 93, 33* with a 50-50 mix of Shell and MS-109, and I have run 36* with straight MS-109.

 

Stock LT1 timing is 33 in the table + 4 or 5 degrees from the PE adder, so 37 or 38 total. Like I said, shoot for mid 30's.

 

Is that for an OBDI or OBDII or both? Thats way more than I was expecting.

 

My car ran the best at 29 degrees total (B body). My opti may or may not have been clocked correctly (mystery cardone opti)
Kind of a PITA to flash the car between passes to find out what it liked...
The obd1 tunes do command a lot of advance, I wouldn't think the obd2 tunes are much different.

 

All of the tunes I've looked at are OBD1, but I doubt they're different. The original 33+5 comes from a 94 TA, but I checked a 95 Z28 and 95 Vette and they're all the same. The B-body LT1 is a little different because of a different head/CR and it's meant to run on 87 octane, so it runs 29+5. I also have a LT4 tune that someone copied a bunch of tables to a OBD1 tune, and that runs 35+5. Unsure if OBD2 has the same +5 spark adder though.

To be honest, the only way to know what your motor really wants is to put it on a dyno and play with the timing until you hit peak torque. But mid 30's total is far from radical. Most mail order tunes run a few degrees over the stock tables.

 

When datalogging will these (+ added degrees) show up in the final spark value or are they hidden?
Say for example above on the listed LT4 values of 35+5, will the datalog actually present a value of 40 or 35?

 

It will show up on the logger, the spark adder (EST system time lag) can be disabled if you prefer.

 

The datalog will show whatever the timing is, ie 40 in that example. The pcm has some sort of routine that adds extra degrees of spark depending on rpm in PE mode, probably due to limitations in the slow 90's processor to keep up at high rpm. You can disable it if you use Steveo's EEX XDF and set the "Unknown Spark Adder" to 0 (factory setting is 5) so the datalogs and spark tables match up.

 

Can anyone verify if this also occurs on the 92-93 LT1 ECU ?

 

PE or WOT timing advance adder goes clear back to CCC Q-Jets. The routines are in feedback carbs, TBI, LT1, black box vortecs and even LS stuff.

Its not because of slow processor speeds. Its there because a richer mixture can tolerate and requires more timing than a leaner mixture. You can be at full load and 14.7:1 air/fuel ratio and say 32° of timing. When the WOT or PE fuel enrichment hits and the air/fuel ratio drops into the 12s the engine will want 3-6° more timing. On heavy trucks and vans used for towing I have seen as much as 8° power enrichment spark added. My personal 11:1 383 sits at 24° at 100 kpa running at 14.1:1 air/fuel (stoichiometric for 10% Ethanol fuel) and I increase to 32° at 12.5:1 at WOT. Gives quite a torque bump. If you tried to run 32° of timing at 14.1:1 at full load the engine would knock the pistons apart or pound the rod bearings flat from detonation. I make peak power at 35° BTDC, but lose less than 3 hp at 32°. My MBT timing advance is therefore around 32°. I drop off 8-10 hp for each degree I retard less than 32°. Running high load at stoichiometric it gets spark knock retard around 26-27° timing. At 24° it is knock free. I programmed the PE TPS vs RPM table to bring on PE around 80 KPA. Its a very seamless transition vs stock where you open the throttle to 60% and the MAP is at atmospheric pressure and have a dead spot for 30% of the throttle before it finally enters PE at 90% throttle.

 

don’t go by numbers, read your plugs