EGT and MPG

[NoDOHC]

I see this as two issues that you are addressing.

WOT lamda and WOT ignition timing is not the same as cruising lambda and cruising timing.

TTT, I am trying to use lambda, just for you.

I run lambda of 1.1 under cruise and 52 degrees BTDC at -45 kPA gauge (cruising vacuum). I get no lean surging at this lambda. I can safely touch the exhaust after cruising for 100 miles at 2,500 rpm (obviously it cools down between me stopping, opening the hood, getting out and feeling the headers). If I have been climbing a long hill (-20 kPA) for several miles, I can't safely touch the exhaust headers.

I run lambda of 0.9 under WOT and (after talking to RETed) about 25 degrees BTDC at 2,500 rpm.

I have actually found that lean surge kicks in about 17.4:1 (oops, I meant lambda of 1.18) and that I actually get better instantaneous fuel mileage at lambda of 1.1.

If you have a 0.72 Overdrive (and you are in 5th) and 550 cc/min injectors, instantaneous fuel economy is closely approximated by:

90/injector energize duration in ms

This is if you are only using the primary injectors (staged setup).

If I run 1.18 lambda, I see injector duration of 2.7 ms, at -37 kPA (averaged over several miles of flat road, steady state driving) = 33 mpg instantaneous.
If I run 1.1 lambda, I see injector duration of 2.5 ms at -45 kPA (averaged over several miles of flat road, steady state driving) = 36 mpg instantaneous.
If I run 1.0 lambda, I see injector duration of 2.7 ms at -48 kPA (averaged over several miles of flat road, steady state driving) = 33 mpg instantaneous.
If I run 0.9 lambda, I see injector duration of 3.0 ms at -51 kPA (averaged over several miles of flat road, steady state driving) = 30 mpg instantaneous.