It really depends on the setup. I have seen LT1 builds want as much as 38* on pump gas at 12:1 compression.

I am sure my 383 would want more timing on pump gas if it were not pulling around a 7,000 lbs Express van with a 4L85E and only a 3.73 gear. 6L90E swap coming soon though. I bet it wants a little more timing when the engine is not under as much load.

 

Agreed. Mine sees between 38-40 on E85 with 12.7:1. Probably isn't gaining much at 40 compared to 38 but the plugs still look good.

 

I’ve NEVER seen an lt1 engine want less then 30 degrees at WOT even with 11.5 CR or more.. these old school design heads need timing

 

Typically 34-38 is where I see LT1s and LT4s make peak power. I have seen a couple that are knock limited to around 32-34, but that is not the normal. One of the knock limiteds was an iron headed LT1 in an 85 Suburban. The other was an aluminum head 383 in a heavy Fleetwood.