Whats a good air to fuel ratio
- Thread starter Trapper
- Start date
cloneman315
Active member
Re: Whats a good air to fuel ratio
still to lean at 15.1 it might stumble,its wot you need to watch
still to lean at 15.1 it might stumble,its wot you need to watch
JSM
Active member
Re: Whats a good air to fuel ratio
Good AFR is dependant on conditions.
First startup will be rich, your sensor/box may still be warming up also giving false #'s.
Once things are warm at idle in theory 14.7 is ideal. Now theory isn't always what works best but gives you a place to start.
0psi boost ~ 14.5
5psi boost ~ 13.0
10psi boost ~ 12.5
15psi boost ~ 12.0
These are just rough numbers to get you started.
When you are driving and go into deceleration you can see as much as 20 or max the sensor out. If the truck doesn't die, or run funny this is fine for DECEL.
Accell it will be richer.
No magic #, depends on a lot of things.
Good AFR is dependant on conditions.
First startup will be rich, your sensor/box may still be warming up also giving false #'s.
Once things are warm at idle in theory 14.7 is ideal. Now theory isn't always what works best but gives you a place to start.
0psi boost ~ 14.5
5psi boost ~ 13.0
10psi boost ~ 12.5
15psi boost ~ 12.0
These are just rough numbers to get you started.
When you are driving and go into deceleration you can see as much as 20 or max the sensor out. If the truck doesn't die, or run funny this is fine for DECEL.
Accell it will be richer.
No magic #, depends on a lot of things.
cloneman315
Active member
Re: Whats a good air to fuel ratio
i have not seen any of these trucks that idle good at 14.7 without stumbling,but thats just what i have seen.
i have not seen any of these trucks that idle good at 14.7 without stumbling,but thats just what i have seen.
sy#2921
BAMF
Re: Whats a good air to fuel ratio
I noticed on a stock tired motor is would not idle solid at anything greater than 13.6:1 however with a fresh motor and even ones that are built (cam seems to be the biggest influence) that with more idle timing you can get them to run just fine anywhere from 14.5-15:1 and idle solid.
This even carries over to the ls cars. The bigger the cam and the more idle spark the more they like to be leaned out. There does come a point like everything that too much is too much but interesting none the less.
I would love to test a stock motor cam only combo against this theory to see if that is really the cause or not.
I noticed on a stock tired motor is would not idle solid at anything greater than 13.6:1 however with a fresh motor and even ones that are built (cam seems to be the biggest influence) that with more idle timing you can get them to run just fine anywhere from 14.5-15:1 and idle solid.
This even carries over to the ls cars. The bigger the cam and the more idle spark the more they like to be leaned out. There does come a point like everything that too much is too much but interesting none the less.
I would love to test a stock motor cam only combo against this theory to see if that is really the cause or not.
the baPhoon
Active member
Re: Whats a good air to fuel ratio
Mine idles great bouncing from 14.5 to 14.9.
WOT im having trouble going real rich at 10.5ish.
Dont go lean that often.
I would shoot for an idle around 14 and a half and fine tune for a good idle from there.
Stay away from being rich at WOT heh, lots of knock.
Mine idles great bouncing from 14.5 to 14.9.
WOT im having trouble going real rich at 10.5ish.
Dont go lean that often.
I would shoot for an idle around 14 and a half and fine tune for a good idle from there.
Stay away from being rich at WOT heh, lots of knock.
gkrcr882
SyTyless......for now!
Re: Whats a good air to fuel ratio
Hook it up to a scantool and check. I had mine on a scanner, and at 195*, I was at 14.7 with the O2 switching like it should. Desired Idle was always about 20 RPM higher than actual, give or take. Ignition scope showed that everything was where it should be too. HC count (no cat) was about 4500ppm @ idle.
Hook it up to a scantool and check. I had mine on a scanner, and at 195*, I was at 14.7 with the O2 switching like it should. Desired Idle was always about 20 RPM higher than actual, give or take. Ignition scope showed that everything was where it should be too. HC count (no cat) was about 4500ppm @ idle.
Six-is-Enough
Use to do a little Boost
Re: Whats a good air to fuel ratio
If your not at wot or under boost, you will not hurt it being too lean. Might run like poo, but it won't burn up pistons or anything.
Just keep a eye on wide ban and adjust. :tup:
If your not at wot or under boost, you will not hurt it being too lean. Might run like poo, but it won't burn up pistons or anything.
Just keep a eye on wide ban and adjust. :tup:
Trapper
New member
Re: Whats a good air to fuel ratio
Well I think I got it, it gradually gets up to 14.7 or so at idle kinda bounces to 13 a little, I'm going to finnally take it for a short test drive tomorrow. Well se how it goes i will take the datamaster and run around with it a bit. But in the driveway during warm up it still spits a little mist out the exhast is that normal?
Well I think I got it, it gradually gets up to 14.7 or so at idle kinda bounces to 13 a little, I'm going to finnally take it for a short test drive tomorrow. Well se how it goes i will take the datamaster and run around with it a bit. But in the driveway during warm up it still spits a little mist out the exhast is that normal?
gkrcr882
SyTyless......for now!
Re: Whats a good air to fuel ratio
13 is right about where you want to be for a performance-oriented vehicle. The richer you are (to a point) the more power you will make, at the cost of fuel economy. The leaner you are, the more you sacrifice power for good enconomy. 14.7 is the ideal middle ground between the two, so if you aren't exactly there, don't sweat it. Rather see rich than lean for safety reasons, as I'm sure nobody bought these things for gas milage. I wouldn't worry about a little mist or carbon out the exhaust during warm up, since a very rich mixture is needed for cold start and warm up (like a choke). Mine spits a little when it first starts too, its very noticable if I'm parked on fresh snow. as long as it's not billowing black smoke, I wouldn't stress it. Could also be condensation forming in the exhaust system being vaporized.
13 is right about where you want to be for a performance-oriented vehicle. The richer you are (to a point) the more power you will make, at the cost of fuel economy. The leaner you are, the more you sacrifice power for good enconomy. 14.7 is the ideal middle ground between the two, so if you aren't exactly there, don't sweat it. Rather see rich than lean for safety reasons, as I'm sure nobody bought these things for gas milage. I wouldn't worry about a little mist or carbon out the exhaust during warm up, since a very rich mixture is needed for cold start and warm up (like a choke). Mine spits a little when it first starts too, its very noticable if I'm parked on fresh snow. as long as it's not billowing black smoke, I wouldn't stress it. Could also be condensation forming in the exhaust system being vaporized.