A/F at cruise and light load.

[No Quarter]

How lean or rich should I shoot for in light load around town situations. I know if I fatten it up the motor will run cooler but suck more gas. On the other hand a leaner mix should make the car feel peppier.

What a/f are you guy running between 1500-3000rpm while in vaccum?

 

[bobc455]

No,

As a point of reference, I cruise at about 15:1. The engine seems to run fine when I go leaner, but running too lean makes me nervous.

The only time you really need to add extra fuel to cool the engine is very heavy throttle / WOT. Otherwise, 14.7 is how virtually every other car (minivan, etc.) runs.

I could probably run a bit leaner since I run cold (160 deg. t-stat, cold spark plugs, etc.).

-Bob Cunningham

 

[norbs]

If your going to run lean, bump the timing to about 50 degrees, for very light cruise situations, I have run 15.9 on the highway at 2400 rpm, and the egt is 1250 constant, compared to about 15.1 where the egt is 1200 degree's, so theres not much difference there if your worried about melting things down.

 

[bruce]

Originally posted by norbs
If your going to run lean, bump the timing to about 50 degrees, for very light cruise situations, I have run 15.9 on the highway at 2400 rpm, and the egt is 1250 constant, compared to about 15.1 where the egt is 1200 degree's, so theres not much difference there if your worried about melting things down.

Running lean cruise mixtures, demands lots of timing, as you've said.
Lots of timing an lean mixtures raises EGTs as you've said.

Which also puts more heat into the oil. Which generates more oil vapor, which goes thru the PCV system and is condusive to detonation. The higher oil temp drops the oil pressure slightly. Also, puts more temp into the piston crown so that you need more Tip-In AE to not have any tip-in preignition.

While it might cost a couple MPG, 30d and 14:1 just might make for a happier engine, that'll last longer.

 

[No Quarter]

I've had to adjust some tables since the last dyno session. However prior the car cruised very rich. In the 11.9-10.1 area. Sometimes even richer. I was not responsible for that initial tune. That was with around 30* timing.

 

[norbs]

I have not seen any detontation, as this is only used for Very light cruising, and there is quite a bit of difference in fuel mileage from 15.9 to 14.1 a/f ratios. The motor does run hotter of course, but if your cooling system can handle it, (ive seen about a 10 degree increase in coolant temps max) why not try and maximize mpg. Just my point of view.