|
Author
|
Topic: Correct Air/Fuel Ratio?
|
MidLifCrisis
Gearhead Posts: 540
From: Frederick County, MD
Registered: Oct 2001
|
posted 04-17-2005 09:23 PM
   
Other than reading plugs, which I find subjective due to color interpretation, I was wondering if anyone knows what the correct air/fuel ratio is? We have a dyno in town and it reads the mix from the tail pipes. Isn't it supposed to be something like 13 or 14 to one? Charlie
IP: Logged |
kid vishus
Gearhead Posts: 6405
From: middle of NC
Registered: Oct 2000
|
posted 04-17-2005 10:08 PM
With a wideband O2 reading from the tailpipes thru full exhuast, we like to see something around 13.2 to 13.5-1 and set where it makes most power. If reading from open headers, we usually shoot for 12.5 to 12.8-1.
IP: Logged |
indyphil
Gearhead Posts: 2690
From: Senoia, G.A. USA
Registered: Jul 2002
|
posted 04-18-2005 07:33 AM
Charlie it depends on the car - Let me explain what I mean. On Modern cars - with fuel injection and catalytic convertors they shoot for the stoichiometric air fuel ratio - which means the chemical equation for combustion shows just the right amount of oxygen (air) available to combust the fuel but no more. Too lean and the NOx emissions will be too high, and too rich and the Hydrocarbons and CO will be too high. The 3 way catalysts are designed to be run at "stoich" all the time. Stoich is around 14.3:1 I think. This is of course a variable since some fuels have alcohol in them and they are therefore slightly oxygenated and will be stoich at a lower ratio. The oxygen sensor in the exhaust helps the computer to adjust the mixture all the time so it always has the ideal stoich mixture. But of course thats only modern cars.If you disregard emissions and shoot for max power, then a richer (lower) air/fuel ratio like KV suggested will make a little more power - and probably reduce your cylinder temps and give you more margin against detonation - the evaporative effect of putting more fuel in helps cool the charge and reduce cylinder temps. Thats probably where you got your 14 number from, but most carburator guys shoot for a curve that is rich (12 ish) at idle and WOT but might be closer to 13-14 while cruising. with all the idle screws, pumps and jets on a carb you wont be getting the same mixture at all speeds and loads, I think KV is talking about Wide open throttle (like when you dyno the engine for Max Power) but you can tune to get that powerful full throttle curve and then have a leaner cruising condition and get better gas mileage too. ------------------
'68 coupe, '66 289 C code
engine, edel 600cfm carb, performer intake, dual exhaust http://www.geocities.com/ottouk_77/68mustang.htm
IP: Logged |
MidLifCrisis
Gearhead Posts: 540
From: Frederick County, MD
Registered: Oct 2001
|
posted 04-20-2005 04:51 PM
You guys are great. Thanks, Charlie
IP: Logged |
Mustangsandmore Forums
