James Drinkwater wrote:
> Got a quick query. How much effect does timing have on oxygen
content?
> I'm trying to dial in an engine and am using an O2 sensor. It's a small
> block Chevy V8 and the sensor reads rich, which is very much what I'd
> expected re: rich smell, fouled plugs, atrocious mileage. The engine's
new
> and the carb's used but in excellent (visual) condition.
> The carb's a 650cfm double pump Holley that's in very new condition
(used
> but still in original box) but got it from my machinist who drag races.
The
> jets indicate stock but who knows if somebody drilled them. The
> distributor's a Mallory Comp 9000 and at this point who knows what the
spark
> curve's set to.
> So, as I try to dial in the spark curve and fuel, I'm wondering, "Can
the
> timing curve significantly change O2? Am I trying to dial in the wrong
> system first?"
> Best Regards,
> Drink
>
>
Oxygen levels in combustion gases are as much a
function of combustion efficiency as they are applied
fuel mixture.
I use an LM-1 to tune my car. Lower numbers
indicate a richer mixture, and high numbers mean a lean
mixture. The magic 14.7:1 will provide a good balance
of power and economy for a near stock engine. If
you're using a radical cam, big heads, etc, you'll need
to run a little richer for smooth operation. Best
power production is generally 13-13.5:1 or so.
I've set mine up to have a mixture of about
13.8-14.0 at light throttle and cruise, and around
13.0-13.2 under power.
Here are two things I've noticed:
1. Yes, timing curve does affect sensor readings.
2. If the mixture is very rich, the reading
actually goes up - looking lean. If you add fuel, the
readings drop (as you would expect). If you add even
more fuel, the numbers start coming back up. Why does
that happen? I don't know, but it does.
If you're indicating a near normal reading (13:1
or higher), but it still smells rich and fouls the
plugs, use a smaller jet.
--
..boB
2006 FXDI hot rod
2001 Dodge Dakota QC 5.9/4x4/3.92
1966 Mustang Coupe - Daily Driver
1965 FFR Cobra - 427W EFI, Damn Fast.
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