Does timing effect air fuel ratio?

[Paul G]

Might be a stupid question? But I dont know the answer. Is air fuel ratio strictly a jetting function? Or does timing play a part?

At our upcoming H.E.M.I. show next March we are having Personal Touch Dynomometer set up at the show again this year. Might be a great time to do a little performance fine tuning. 

[firefighter3931]

Yes....timing does impact A/F ratios. Increased timing requires more fuel & air. 


Ron

[BSB67]

Might be a stupid question? But I dont know the answer. Is air fuel ratio strictly a jetting function? Or does timing play a part?

At our upcoming H.E.M.I. show next March we are having Personal Touch Dynomometer set up at the show again this year. Might be a great time to do a little performance fine tuning.  

The actual air to fuel ratio does not change with timing.  However, the number you read on your wideband might move around with timing changes.  Optimum A/F will likely change with timing changes.

[XH29N0G]

Now you gave me something else to test!     And I'll have to do more test drives! 

[A383Wing]

You would need a 4 gas analyzer to see the change with timing. HC's and Nox will change with timing. The air/fuel will not change that much unless you do a jet or metering rod change

[Kern Dog]

The whole practice of tuning with these in car Air/Fuel guages is interesting. I found that I was running too rich even though I saw no smoke and it smelled as clean as a newer car.
Timing affects the ratio. If you tune it with the air cleaner off, it affects the ratio. A 200 rpm increase in idle speed affects the ratio. Only the wideband shows this. The car may "feel" the same but the guage tells the story.
Today I helped a buddy tune his car, a 71 Challenger with a worked 340/416. He had the timing set to 10 initial/25 total because anything more than that caused dieseling on shutdown. I told him that I've learned that the "run-on" is often incorrectly blamed on excessive timing. Many times the run-on is from the primary throttle blades being open too far at idle. Another contrubutor is using spark plugs with an incorrect heat range. The Air/Fuel ratio was in the high 16s at idle. I backed out the Idle Mixture Screws and the A/F numbers went to the mid 15s. I bumped the timing 5 degrees and the numbers went to the mid 14s. The car now runs faster and does not diesel upon shutdown.

[John_Kunkel]

I think it's more correct to say that timing affects "combustion efficiency" rather than air/fuel ratio.

[A383Wing]

yea..air fuel ratio stays the same no matter where timing is...which I said before...now if you change jets or rods, then A/F will change

[BSB67]

I think it's more correct to say that timing affects "combustion efficiency" rather than air/fuel ratio.

Well said.

[A383Wing]

Air-fuel ratio is going into the engine, combustion efficiency is what comes out