Vacuum/idle info

Free time and bored, so did some idle/vacuum readings now that I’ve adjusted everything by the book and the car is running excellent. For others reference?

I am running a USA 1988 HE V12 A/T with ignition timing at 22° BTDC (@3000 rpm) with 92 US octane fuel. (OEM is 18° with 87 US octane)

Cold - vacuum 14.5inHg at 900rpm
160F - vacuum 16.5 at 800rpm
Warm (180F) - vacuum 17 at 750RPM
PCV plugged - vacuum 17 at 600 rpm
Car in D or R (closed loop) - vacuum 15.5 at 700 rpm

Also, checked exhaust for misfire, slight intermittent both banks in open loop, perfect in closed loop. So surprisingly I get a smoother idle in closed loop, although I do have the ECU a tad rich (2.0V, 1.95V).

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The smoothness in D or R is probably due to the additional load rather than the switch from open to closed loop.

Don’t understand how load smooths out idle?

more rotational mass, so more inertia : less prone to small speed changes

My thought is that the torque converter also works kind of like a hydraulic dampener ?

With zero load, the fuel/air charge in the cylinder is very thin. With increased load comes increased density of charge, easier to ignite with a spark plug.

Kirby, off topic, I met a fellow Jaguar XJ-S owner in my neighborhood. I was showing him my engine, he saw the cold air intakes I had added through the headlights, and he said “Oh, you got that from Kirby’s book!”


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