is this a normal-looking stock spark table for a swirl port iron head tbi?
pretty sure my table configuration is correct, just never seen one like it.
why is there 8-10 degrees less timing than makes sense, then they just throw it back in?
insight?
i have a california emissions spark table for the same engine and it's stranger still...
Quite frankly does not surprise me at all!!
These are actual CCC Q-Jet tables for the L69 in a Monte Carlo
And an 83 G20 Van, notice there is an 8* reduction between 2,400 and 3,000 @ 80 KPA.
Finally a LG4 in a GrandPrix
Last edited by Fast355; 07-03-2014 at 02:53 AM.
Based on the looks it seems like some kind of emissions maybe even mileage reason for less timing at part-throttle. I was shocked at how much cruise timing the fullsize G20 van had with the LF3 engine. I used a slightly tweaked version of that spark map with my TBI setup and later TPI setup with alot of sucess on my 83 G20 Van.
haha yeah, thanks, i guess compared to some other weird stock bins it doesn't look that odd
it's just kinda weird, it isnt even part throttle range, it's almost impossible to get there without being in power enrichment.. but then they throw a TON of timing in in higher map?
since i cant see any logic to it, i'll just roll my own..
Early calibrations were field developed and often don't look as nice or neat as the simulation based maps of today.
thinking of throwing something more traditional at it like this, bad idea?
doesn't look like a bad place to start.
1995 Chevrolet Monte Carlo LS 3100 + 4T60E
finally got logs going too, midrange is lean-ish (trims 138-145 in all cells with a decent sample count) and idle is a bit rich
not sure if that's just factory tune being lean, the cat delete and open element threw my VE off, or both...
Sounds like it may not have the peanut cam in it. Rich at idle from lower vacuum and lean under load from higher airflow.Originally Posted by steveo
yeah im thinking the same thing.
although the engine was "rebuilt" or "replaced" by previous owner, i have no idea what was used.
it still has swirlport lo3 heads on it, and stock-looking springs and retainers which i've verified are a reasonable distance from coil bind, so i assume whatever cam was used, if not the peanut cam, is not very large. vacuum at idle is 28kpa once its trimmed.
it has a very slight hint of lope at hot idle but that could just be that it's running a bit rough.
throws egr codes despite going through the entire system and egr operations seem normal, and that the exhaust is fairly unmodified.
total mystery engine, i guess i'll have to tune it as such.
............
Last edited by billygraves; 06-30-2019 at 06:23 PM.
If the dissasembly is complete the Code 32 test is also in there.
Since there were issues with dual exhaust on stock $42 trucks I added the Code 32 tests so they could be modified but still keep a workig EGR with CEL complete.
1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
-= =-
i might do that regardless.
i don't really care about the EGR test in this case anyway so i'll probably just delete it for the time being.
Funny you mention those. I had one, a Vin 9 HO in a 1988 Cadillac Fleetwood Brougham. It must have been the Vin Y cars with the limited timing advance. The larger cammed vin 9 had up to 60* advance at cruise and 34* at WOT with 24* practically off-idle at WOT. The whole WOT rpm advance curve was 8*.
Last edited by Fast355; 07-04-2014 at 08:05 PM.
someone with some experience with these limp output 305s verify im even in the right ballpark with that timing table? or should i back off a bit... im not a fan of running timing at the limit, i'd way rather less stress on the engine and cooler combustion..
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