Could air cleaner upgrade make cruise very lean?

Greetings Ford Six Fans,

The Ranchero was very rich at idle, especially when cold (I have a wideband A/F gauge), and came up to operating temp very slowly. I suspected that either the power valve was opening at too high a vacuum (I have 11" at idle), or that the PV was leaking. I replaced the #65 PV with a #55 and now it idles well and comes up to operating temp more quickly. I tested the #65, but it seems to work.

I also replaced my typical 13" air cleaner with chrome top with a K&N air cleaner with a filter element top, advertised as a high flow air cleaner:





Since the PV and air cleaner replacement, the Ranchero idles at a reasonable air to fuel ratio, is at a reasonable A/F at part throttle and WOT, but is very lean (15.0 - 16.0) at steady cruise. I don't feel comfortable this lean, and plan to change the #70 jets to #71 to attempt to adjust.

Could the K&N air cleaner really flow so much more air as to cause the lean cruise?

Thanks
Bob the Builder

Yes. When you open the total area of the air supply to the carb, volumetric efficiency can go up. So you need more jet area.

K&N Filters are cotton and in the version you have, the whole air flow velocity is dropped around the air horn. The flow is not bent over a conical surface and feed axially or circumferencially ad before.

Due to space limits, I reduced my air cleaner size from a 3 inch tall by 13 air cleaner to a 1-3/4 tall version, and had to lean off my wide open throttle mixture on my propane Falcon. Even after going to a better flowing type of filter, air fuel mix wad still restricted at WOT. Bigger the filtration, better your Volumetric Efficency generally.

When cruising, is it surging or otherwise acting up?

15-16 AFR's at cruise aren't out of the ordinary, My Ford 200 cruises just over 15 AFR, and my Chevy 350 and Buick 455 both cruise right at 15.5 AFR.

I'd go for a 20-30 minute drive, listening for detonation and watching the temp gauge, then check a spark plug or two for overheating. I'm betting you'll find it's fine, and your fuel economy will be better as well.

Running lean while cruising is usually what you want. I can't get mine to cruise any higher than about 13.5. I've always heard cruising about 15 is great. As long as when you put the pedal down it richens up. But do try 1 size up and see what happens

Bob, i would like to see you in the 14.5-14.7 area cruising. WOT 12.7-13.1.

Hey Bob,
Why the rich recommendation for cruise? I'm at 15.5-16 cruise and doesnt seem to have any neg impact. WOT drops to 12-13.
On my drive from LA-Napa I did avg about 12 mpgs. Wont I see a big dent in that if I cruise lower?

As for the air efficiency, I put in the hi-po filter on my weber and i had the same nagging question. Seems tuned ok tho.

tks
DrC

DoctorC":1y6h980w said:

Hey Bob,
Why the rich recommendation for cruise? I'm at 15.5-16 cruise and doesnt seem to have any neg impact. WOT drops to 12-13.
On my drive from LA-Napa I did avg about 12 mpgs. Wont I see a big dent in that if I cruise lower?

As for the air efficiency, I put in the hi-po filter on my weber and i had the same nagging question. Seems tuned ok tho.

tks
DrC

Click to expand...

A couple of reasons - I don’t think a high performance engine has ever grenaded from being too rich, but plenty have from being too lean. My exhaust is so loud that I wouldn’t hear any detonation.

Also, I have a lot of faith in my tuner, and he advised me to cruise a bit richer.

Thanks
Bob