Top end power loss after headers
14.7:1 is the stock stoich set in the PCM, once the car warms up and goes into closed loop the PCM will strive to stay at 14.7:1 at idle and part throttle operation. The PCM relies on the oxygen sensors for feedback on how the AFR is doing. The signal off a oxygen sensor is a sine wave, the sensors are always switching up and then down, which represents rich and lean. The average of the wave is the AFR. What happens is the sensor will pick up a lean conditon then the PCM will add some extra fuel, then it will read rich and then the PCM will pull some fuel. This is a continious operation that happens many times per second. The adding or pulling of extra fuels what is known as fuel trims, which are the PCM's fueling learning ability. As long as the O2 sensors are working properly the AFR will be 14.7:1. Cold start and WOT are different stories because in both of those conditions you are in open loop, which does not rely on any feedback for AFR correction.
Search around in the tuning forum for more information, there is a ton of it.
Search around in the tuning forum for more information, there is a ton of it.
Originally Posted by LSGunZ28
I do have an idea on how it operates. and I may not know as much as you maybe. But I have learned that 14.7:1 isnt really the A/f ratio cars generally operate at. That is just a ballpark number, just like how a 4 stroke cycle is: intake, compression, ignition, exhaust. But we all know it isnt that simple. a spark doesnt occur the whole time of the igntion cycle. just like overlap occurs and exhuast and intake cycle overlap with each other( just an example) and all those things. it isnt quite as simple. the A/f changes as TP changes as does load on the car, etc.
I am pretty certain of that.
But please put some input on my misinformation if you can, so that I can learn.
thanks.
I am pretty certain of that.
But please put some input on my misinformation if you can, so that I can learn.
thanks.
Originally Posted by brad8266
14.7:1 is the stock stoich set in the PCM, once the car warms up and goes into closed loop the PCM will strive to stay at 14.7:1 at idle and part throttle operation. The PCM relies on the oxygen sensors for feedback on how the AFR is doing. The signal off a oxygen sensor is a sine wave, the sensors are always switching up and then down, which represents rich and lean. The average of the wave is the AFR. What happens is the sensor will pick up a lean conditon then the PCM will add some extra fuel, then it will read rich and then the PCM will pull some fuel. This is a continious operation that happens many times per second. The adding or pulling of extra fuels what is known as fuel trims, which are the PCM's fueling learning ability. As long as the O2 sensors are working properly the AFR will be 14.7:1. Cold start and WOT are different stories because in both of those conditions you are in open loop, which does not rely on any feedback for AFR correction.
Search around in the tuning forum for more information, there is a ton of it.
Search around in the tuning forum for more information, there is a ton of it.
Originally Posted by LSGunZ28
I knew all that. But what I didnt know is that the stoich is set at 14.7 :1 even though that is the rating of AFR. However I am not entirely sure that when it goes to closed loop, it is doing precisely 14.7 : 1, what about higher elevations, less oxygen , but MAF cant tell that. so how will the AFR be 14.7:1? etc... That is why I dont hink it stays at 14.7 : 1 not even at 10% throttle.
Originally Posted by LSGunZ28
I knew all that. But what I didnt know is that the stoich is set at 14.7 :1 even though that is the rating of AFR. However I am not entirely sure that when it goes to closed loop, it is doing precisely 14.7 : 1, what about higher elevations, less oxygen , but MAF cant tell that. so how will the AFR be 14.7:1? etc... That is why I dont hink it stays at 14.7 : 1 not even at 10% throttle.
And yes it will always do precisely 14.7:1 even at high elevations because the oxygen sensors will always be able to read the AFR accurately and will report the status back to the PCM which will in turn adjust fueling to stay at 14.7:1. The MAF has nothing to do with it. The MAF provides the PCM wilth the baseline fueling and the oxygen sensors provide for realtime fueling adjustments on the fly, which are fuel trims. The elevation and other environmental factors dont matter because the oxygen sensors can always measure the amount of oxygen in the exhaust accurately and report it back to the PCM.
If you dont believe it go buy yourself a good wideband sensor and do some logging, you will see that on average it will stay at 14.7:1 at all times, it will fluctuate up and down for quick moments up to like 15.1 or down to like 14.2 but will stablize out at 14.7:1 everytime as long as you are in closed loop.
Originally Posted by brad8266
What do you mean by 14.7 is the rating of AFR, that doesnt make sense.
And yes it will always do precisely 14.7:1 even at high elevations because the oxygen sensors will always be able to read the AFR accurately and will report the status back to the PCM which will in turn adjust fueling to stay at 14.7:1. The MAF has nothing to do with it. The MAF provides the PCM wilth the baseline fueling and the oxygen sensors provide for realtime fueling adjustments on the fly, which are fuel trims. The elevation and other environmental factors dont matter because the oxygen sensors can always measure the amount of oxygen in the exhaust accurately and report it back to the PCM.
If you dont believe it go buy yourself a good wideband sensor and do some logging, you will see that on average it will stay at 14.7:1 at all times, it will fluctuate up and down for quick moments up to like 15.1 or down to like 14.2 but will stablize out at 14.7:1 everytime as long as you are in closed loop.
And yes it will always do precisely 14.7:1 even at high elevations because the oxygen sensors will always be able to read the AFR accurately and will report the status back to the PCM which will in turn adjust fueling to stay at 14.7:1. The MAF has nothing to do with it. The MAF provides the PCM wilth the baseline fueling and the oxygen sensors provide for realtime fueling adjustments on the fly, which are fuel trims. The elevation and other environmental factors dont matter because the oxygen sensors can always measure the amount of oxygen in the exhaust accurately and report it back to the PCM.
If you dont believe it go buy yourself a good wideband sensor and do some logging, you will see that on average it will stay at 14.7:1 at all times, it will fluctuate up and down for quick moments up to like 15.1 or down to like 14.2 but will stablize out at 14.7:1 everytime as long as you are in closed loop.
Originally Posted by LSGunZ28
I see. and by rating I mean that is the optimum AFR for a car, but not by performance standards.
Staging Lane
Joined: May 2006
Posts: 78
Likes: 0
From: IN
Brad definitely knows his ****! I always take the time to read a thread he has subscribed to. He knows more about fuel trims alone then I know about everything I think. I am definitely interested in what this dude has to say, I am trying to learn as much as I can from him while he is still on the board, hoping it will make me a better owner of the infamous FBod
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Originally Posted by Wheeler99WS6
Brad definitely knows his ****! I always take the time to read a thread he has subscribed to. He knows more about fuel trims alone then I know about everything I think. I am definitely interested in what this dude has to say, I am trying to learn as much as I can from him while he is still on the board, hoping it will make me a better owner of the infamous FBod
Believe me though there are plenty of instances here where I had to put my foot in my mouth after the fact.
not dry ya so i have nothing to do with the maf, my fuel get sprayed in at the same time the N2O does so its all good but i still have to get it tuned bad. when i get the tranny done im going to have it dynoed and tuned with my HPtuners.
i replaced my stock manifoldsand y-pipe with coated pacesetters and a TSP ORY pipe and i lost 1/2 MPH in the 1/4 mile and my E.T. was the same.
this seems odd to me because i feel a slight difference on the street.
regardless that i am running a flowmaster 80 i should have picked up a lil MPH at the track. i know i will pick up a lil if i ditch the flowmaster though.
any thoughts why this might be?
this seems odd to me because i feel a slight difference on the street.
regardless that i am running a flowmaster 80 i should have picked up a lil MPH at the track. i know i will pick up a lil if i ditch the flowmaster though.
any thoughts why this might be?
Originally Posted by multiplicityZ
i replaced my stock manifoldsand y-pipe with coated pacesetters and a TSP ORY pipe and i lost 1/2 MPH in the 1/4 mile and my E.T. was the same.
this seems odd to me because i feel a slight difference on the street.
regardless that i am running a flowmaster 80 i should have picked up a lil MPH at the track. i know i will pick up a lil if i ditch the flowmaster though.
any thoughts why this might be?
this seems odd to me because i feel a slight difference on the street.
regardless that i am running a flowmaster 80 i should have picked up a lil MPH at the track. i know i will pick up a lil if i ditch the flowmaster though.
any thoughts why this might be?
Originally Posted by multiplicityZ
i replaced my stock manifoldsand y-pipe with coated pacesetters and a TSP ORY pipe and i lost 1/2 MPH in the 1/4 mile and my E.T. was the same.
this seems odd to me because i feel a slight difference on the street.
regardless that i am running a flowmaster 80 i should have picked up a lil MPH at the track. i know i will pick up a lil if i ditch the flowmaster though.
any thoughts why this might be?
this seems odd to me because i feel a slight difference on the street.
regardless that i am running a flowmaster 80 i should have picked up a lil MPH at the track. i know i will pick up a lil if i ditch the flowmaster though.
any thoughts why this might be?
get a tune and the false knock will hopefully disappear?
and the weather was within 3 or 4* between the swap, a weekend apart.
but the car is not tuned, and i read earlier that having no egr/air and not getting it tuned out yet might have caused a problem too, besides the annoying SES light.
could an 02 sensor have taken a dump on me and be causing me some problems?
and the weather was within 3 or 4* between the swap, a weekend apart.
but the car is not tuned, and i read earlier that having no egr/air and not getting it tuned out yet might have caused a problem too, besides the annoying SES light.
could an 02 sensor have taken a dump on me and be causing me some problems?
Originally Posted by multiplicityZ
i replaced my stock manifoldsand y-pipe with coated pacesetters and a TSP ORY pipe and i lost 1/2 MPH in the 1/4 mile and my E.T. was the same.
this seems odd to me because i feel a slight difference on the street.
regardless that i am running a flowmaster 80 i should have picked up a lil MPH at the track. i know i will pick up a lil if i ditch the flowmaster though.
any thoughts why this might be?
this seems odd to me because i feel a slight difference on the street.
regardless that i am running a flowmaster 80 i should have picked up a lil MPH at the track. i know i will pick up a lil if i ditch the flowmaster though.
any thoughts why this might be?
8.33 @ 86.6 mph to 8.07 @ 89.25 mph with the same headers and Y pipe as you, the difference is I had a SLP Lm for a catback
Oh and I ran Nittos on both runs and launched it at 3700 RPM @ 12 psi Tire pressure vs 3100 RPM @ 15 psi tire pressure.
Originally Posted by BrandonDrecksage
13 to 1 is waht a car averages around when going WOT. Gas needs 14 to 1 to ignite, but when the engine is under load, you want to be runnign a little richer because of varibles in the air..ect. i.e. 13 to 1 in a n/a car and a lil below that in a f.i. car.