1955 Pontiac (advice for setting efficient but driveable mixture?)

[iveyjh]

Originally Posted by KrautBurner

that seems aweful lean to me
but all my AFR tuning was done at WOT

thats why I mentioned a EGT (Pyrometer) could be a good safety gauge

I rarely go over 550 degree Celsius but that is under load and afr closer to
15 to 1.

[slownugly]

fuel injected lean burn cars go into the lower 20s but the neat thing about that is the exhaust temp actually drops once you cross a certain threshold.

they explain it a little in the article frank posted. the engine will run hotter closer up to about 18:1. but once you cross a threshold the exhaust temp drops, the downside is power loss. losing 20 horsepwer in a car on the ground while entering lean burn-not a big deal, many of us on this site drive lean burn cars many miles every day. losing horsepower in an airplane mid flight- not so fun. thats why he explains how to lean the engine out mid flight until the engine starts to sputter then richen it back up so it still has power but is at its leanest possible setting.

of course we are talking about carbureted cars and this is more difficult to achieve as compared to injection. with a carb you are going to be starting at the factory base point and dropping jet sizes, retarding timing, driving, repeat. would take a half a day to do or more where as with fuel injection and a laptop it could take just a couple hours. an even more involved route would be putting the distributor on a curve machine and custom weighting it. and/or installing the timing knob that msd makes.

i like this thread. got me thinking alot

[slowmover]

As to engine tuning stick to the GM recommendations of the period, IMO. "Best lean roll" is what I went for on my old Chryslers. The final carb adjustment was done in gear, at idle, and resting bumper against tree. (I wrote up an explanation an eon ago, here: Idle Speed Question")

I'd be more concerned with wheel bearing and brake adjustment all around. As well as looking for steering gear slop. Alignment needs be spot on.

If they can be found, articles on the old MOBIL Economy Runs of the era (one of the MoPar magazines; 1990's, IIRC) had quite a bit of info on how those drivers could achieve extraordinary FE.

A tach and a vacuum gauge on dashtop will provide enough info for consistency. Something this age undergoing a really long drive needs be more concerned with actually completing the trip versus a small fuel savings. FE is a measure of soundness, not savings, per se.

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